ICARUS 12, 10-45 (1970) 1This work was performed for the Jet Pro- Television Experiment for Mariner Mars 1971! D. MILTON, R. WILDEY, axon D. WILHIEELMS US. Geological Survey, Flagstaff, Arizona, and Menlo Park, California B, MURRAY, N. HOROWITZ, R. LEIGHTON, ann R. SHARP California Institute of Technology, Pasadena, California Bellcomm, Inc., Washington, D.C. C. SAGAN anp J. POLLACK Cornell University, fthaca, New York J. LEDERBERG ano Jc. LEVINTHAL Stanford University, Stanford, California W. HARTMANN University of Arizona, Tucson, -trizona ¥ ’ , T. McCORD Massachusetts Institute of Technology, Cambridge, Mussuchusetts B. SMITH New Mexico State University, Las Cruces, New Mexico M. DAVIES Rand Corporation, Santa Monica, California G. pe VAUCOULETURS University of Texas, Austin, Texas ‘ C. LEOVY University of Washington, Seattle, Washington - Received December 11, 1969; Revised January 14, 1970 The Television Experiment objectives are to provide imaging data which will complement previously gathered data and extend our knowledge of Mars. The two types of investigations will be fixed-feature (for mapping) and variable- feature (for surface and atmospheric changes). Two cameras with a factor-of-ten difference in resolution will be used on each spacecraft for medium- and high- resolution imayery. Mapping of 70° of the planct’s surface will be provided by medium-resolution imagery. Spot coverage of about 5% of the surface will be possible with the high-resolution imagery. The experiment’s 5 Principal Investigators and 21 Co-Investigators are organizcd into w team. Scientific disciplines and technical task groups have been formed to provide the formulation ofexperiment requirements for mission planning and instrument development. It is expected that the team coneept will continue through the operational and reporting phases of the Mariner Mars 1971 Project. Laboratory, California Institute of Contract No. NAS 7-100. Technology, sponsored by the National Aero- 10 H. MASURSKY, R. BATSON, W. BORGESON, M. CARR, J. McCAULEY, W. THOMPSON, G. BRIGGS, P. CHANDEYSSON, ano IK. SHIPLIEY Y nauties and Space Administration, under ET NH ote Tea ME gn te ayes Mmmm ts Ge aac ake mee a Re ce nt dn emer e eet en te emcee Ra CA ee AT Me ae on St in or l¢ or M be en oh ins Tes ph orl COt Che ue per ibd en SE ia UR RT og LS ALAM et EE ee ASR RON rebar oe bent IRL OUTS Mr ed toms Pinna fae fa, na PEON i ee MP apa 1 Oe fe te ae PE WE ee etre Pe Ns Wm MARINER MARS | I. Intropuction The primary objective of the television experiment on Mariner Mars 197) is to provide imaging data that will increase scientific know ledge of Mars and the solar system. This objective ean be defined further: (1) To investigate various Martian phenomena in order to achieve a more complete understanding of the dynaimies, history, environment, and surface physio- graphy of the planet. (2) To obtain imagery suitable for development of better geologic, dynamic, and topographic maps of the planct in anticipation of choosing areas for more intensive investigations, which will, in later planetary programs, culminate in landings on the surface. Although the experiment is not expected 1o provide direct information regarding the possibility of life, it is expected that it will provide indirect evidence on the suitability of Mars as a habitat for life. 1. Preinsertion Sequence Mariners VJ and VII (Mariner Mars 1969) took 50 and 93 pictures, respectively, of the full planetary disk during approach start- ing at distances of about 1.2 and 1.8 million km, respectively. A similar pre- insertion sequence is planned for the two spacecraft of Mariner Mars 1971. Not only will this allow geologic and topographic surveillance of the whole planct. but, more important, will provide new information on the changed appearance of Mars in 1971, allowing better planning of the orbital picture-taking sequences. The Martian season during the mission will be different from that during the 1969 encounters; it will be more like that observed telescopically in 1958. The pre- insertion sequence will provide higher- resolution images than do the Earth- hased photographs, and will help to optimize the orbital photographie sequences. When compared with Mariner VI and VIL pre- encounter pictures, this preinsertion se- quence also will provide carly scientific data pertaining to changes of Martian features. 971 TV EXPERIMENT ll 2. Orbital Scientific Objectives The television studies in orbit consist of two types of scientific investigations: fixed-features and variable-features. In the fixed-features investigation, the sur- face features will be seen at greater re- solution than possible from observations by telescope from Earth and more com- pletely than by Mariners 1V, VI, and VII. The objectives of the fixed-features investigation are as follows: (1) To obtain a broad range of image information to be used for regional strati- graphic studies of tectonic featur es, crater configuration and distribution, and local surface environments. (2) To measure, by photometric and photograminetric analysis, surface slopes and elevations; to ‘determine surface brightness and albedo differences: and to per form analyses related to improving the accuracy of the photometric runction for various regions on Mars. (3) To obtain improved values for the figure of the planct and thereby investigate possible departures from hydrostatic equilibrium. (4) To study the surface characteristics of Phobos and Deimos. The variable-features investigation will study time-variable phenomena on the surface and in the atmosphere of Mars in order to obtain information on atmospheric structure and circulation, details of diurnal and seasonal changes, and clues regarding the possibility of life on Mars. The specific phenomena to be studied are the following: (1) The “wave of darkening.” (2) Polar caps and cap-edge phenomena. (3) Nightside atmospheric and surface fluorescence. {4) Haze in the atmosphere. (5) White “clouds” in nonpolar regions. (6) Dust clouds and dust storms. (7) Phenomena of possible exobiological significance, Details of these investigations and a description of the Mariner Mars 1971 television subsystem are presented in the following sections of this paper. one ce neem nee me ro y 12 H. MASURSKY, ET AL. TABLE I Contract NUMBERS ror INVESTIGATORS Investigator Affiliation JPL Contract J. Lederberg, Proposal? Stanford University 952489 E. Levinthal Stanford University 952489 C. Sagan Cornell University 952487 J. Pollack Cornell University 952487 H. Masursky, Proposal¢ US. Geological Survey Defense Purchase Request (DPR) WO-8122 J. McCauley U.S. Geological Survey Defense Purchase Request * (DPR) WO-8122 D. Wilhelms U.S. Geological Survey Defense Purchase Request . (DPR) WO-8122 M. Carr U.S. Geological Survey Defense Purchase Request (DPR) WO-8122 D. Milton U.S. Geological Survey Defense Purchase Request (DPR) WO-8122 R. Wildey US. Geological Survey Defense Purchase Request (DPR) WO-8122 W. Borgeson U.S. Geological Survey Defense Purchase Request , (DPR) WO-8122 R. Batson U.S. Geological Survey Defense Purchase Request (DPR) WO-8122 B. Smith,® P. I. Appointment New Mexico State 952488 7/1/69 University B. Murray, Proposal California Institute JPI/Campus Contract 69829, of Technology California Institute of Technology M. Davies Rand Corporation 500974 W. Hartmann University of Arizona 952486 N. Horowitz California Institute JPL/Campus Contract 69829, ; of Technology California Institute of Technology R. Leighton California Institute JPL/Campus Contract 69829, of Technology California Institute of Technology C. Leovy University of Washington 952491 T. McCord Massachusetts Institute 952499 of Technology R. Sharp California Institute JPL/Campus Contract 69829, of Technology California Institute of Technology W. Thompson, Proposal Belleomm, Inc. Supported by Office of Manned Space Flight, NASA; NASW-417 G. Briggs Bellcomm, Inc. Supported by Office of Manned Space Flight, NASA; NASW-417 P. Chandeysson Belicomm, Inc. Supported by Office of Manned Space Flight, NASA; NASW-417 E. Shipley Bellcomm, Inc. Supported by Office of Manned Space Flight, NASA; NASW-417 G. de Vaucoulcurs, Proposal University of Texas 952490 @ Principal Investigators are under Jet Propulsion Laboratory subcontracts, originally sponsored by the National Aeronautics and Spaee Administration, under Contract NAS 7-100. > Because of the pressure of other commitments, B. Murray was replaced by B. Smith on July 1, 1969. "ANA nt Reale Ae teeter meme see pene eee getter ae = MN a be we ot, ow MARINER MARS 197] TV EXPERIMENT 13 3. Extended Mission The nominal mission is designed for a duration of 90 days. However, various hardware modifications may make it possible to extend the lifetime of the space- craft to a year or more. Increasing distance of the spacecraft and Mars from the Earth will then reduce the rate of data flow to the equivalent of only 50 to 100 pictures per month. II. ORGANIZATION Operating relationships for the television experiment, showing the organization of the proposed investigators into a team effort, are discussed in the following paragraphs. The Principal Investigators and Co- Investigators who submitted experiment proposals to use television imagery (see Table 1) were regrouped to function col- lectively as the Mariner Mars 1971 tele- vision team. The television team matrix is shown in Fig. 1. The team discipline or task group members were chosen from the investigators associated with the selected proposals, Coordination of the television team efforts is performed by the team leader, who was named by NASA in consultation with the Principal Investigators in the area of television imagery. The team leader furnishes Project Management with re- commendations concerning — television equipment fabrication and modification, testing, calibration, mission operations eee ay i wae aorears eed, TEAM LEADER H. MASURSKY DEPUTY 8. SMITH DISCIPLINE GROUPS VARIABLE SURFACE ATMOSPHERIC GEODESY/ FEATURES GEOLOGY EXOBIOLOGY PHE NOMENA CARTOGRAPHY C, SAGAN J. MeCAULEY J. LEDERBERG W. THOMPSON G. deVAUCOULEURS T. MeCORD M. CARR N. HOROWITZ G. BRIGGS . R. BATSON J. POLLACK W. HARTMANN C. SAGAN? Cc. LEOVY W. BORGESON R. WILDEY D. MILTON W. HARTMANN? E. SHIPLEY M. DAVIES G. deVAUCOULEURS?® R. SHARP &. LEVINTHAL? J. POLLACK? B. SMITH® B, MURRAY® D. WILHELMS , 8. SMITH H. MASURSKY? N. HOROWITZ TASK GROUPS HARDWARE MISSION ANALYSIS DATA PROCESSING B. SMITH W. THOMPSON E. LEVINTHAL . P. CHANDEYSSON D. MILTON T. McCORD R. LEIGHTON J. POLLACK P. CHANDEYSSON W. BORGESON C. SAGAN R. WILDEY E. LEVINTHAL B. SMITH B. MURRAY T. McCORD W. BORGESON R. BATSON G. BRIGGS Note: The photointerpretation teom matrix illustrotes the current assignment of functions. structure will be reviewed by the Investigctors periodically for adequacy to meet science and Project requirements. The organizotional structure will be reviewed before receipt of the First Mors picture. a = . Iindicotes second ossignment. TS eae ren nee patience eye ome Fie. t. Photointerpretation team matrix. Dep al ere This organizational Se a te ne at ee loo eer \ Neocraens 14 H. MASURSKY, ET AL, (including orbital trajectory parameter Propulsion Laboratory, but was changed selection), and image processing. later to Bruce Murray. After Murray’s The team organization has been reviewed appointment to the Venus-Mercury Pro- and altered several times since its original gram, he was replaced as chairman of state. As new problems have arisen, new the hardware group by Bradford Smith, task groups have been formed to solve who also replaced him as a Principat In- them. The hardware group was directed vestigator (on July 1, 1969). David Norris initially by Howard Friedman of the Jet replaced Friedman in mid-1969 as the (s) LENS HOLDER ASSEMBLY s | - MECHANISM . ~ MECHANISM DUST COVER oe ——-—- -—— INFRARED OPTICAL SOURCE og oo LIMIT SWITCH Cb FILTER WHEEL : StS : HOUSING 25 PIN e €&. TT * CONNECTOR —_==“E25 "p]— heater! FILTER WHEEL pei. i SHAFT ASSEMBLY “te ~ SOLENOID MOUNTING ea BRACKET LIGHT 7 SHIELD é = -——-~-- HOUSING SUPPORT PLATE ~_ ™ — PLATE SS ee PS _- 7 >> SHUTTER 37 PIN CONNECTOR ~ rant Se | iE BASE PLATE ASSEMBLY INFRARED et AY ~~ MAGNETIC OPTICAL SENSOR———#= =), 5 eRe et Ee SHIELD SN as y aa eee m ms oN CIRCUIT b oS age “a BOARD SPACER ‘VIDICON FACE-—— MAGNETIC SHIELD MOUNTING SURFACE CAMERA HEAD Fic. 2(a). Mariner Mars 1971 television subsystem: wide-angle camera, (b) SH iy " “n n~ cor grec the me wh pla cle Meccs erp whe me CEB MARINER MARS 1971 ¥V EXPERIMENTS . 15 () SHUTTER VIDICON CHASSIS BASE TUBE ADJUSTMENT MOLE SCREWS 9 MIRROR JL - SPACER RODS FRO NT SUPPORT 4 AW CAMERA MOUNTING SURFACE EXTENDER SPIDER AND SECONDARY MIRROR Fic. 2(b). Mariner Mars 1971 television subsystem: narrow-angle camera. contact at the Laboratory for the hardware group, JIT. Instrument DEscuirrion The television subsystem to be used in the Mariner Mars 1971 television experi- ment consists of two cameras (Fig. 2), which are mounted on the spacecraft planetary sean platform, with supporting clectronics housed in the bus portion of the spacecraft. The wide- and narrow-angle optics and some portions of the electronics are identical to the equipment developed for the Mariner VI and VII television sub- system. (A simplified block diagram of one of the cameras is shown in Fig. 3.) * The wide-angle camera (50-mm_ focal length), which has a field of view of 11 by 14 deg, utilizes a six-element lens and is equipped with a filter wheel that can be commanded to place any one of eight ANALOG-TO- AMPLIFIER be DIGITAL CONVERTER DIGITAL . DEFLECTION bieaies outeu FOCUS UTPUT ALIGNMENT FILTER orcs (ie Whee, (H] SHUTTER VIDICON LIGHT INPUT cols FILTER SHUTTER VIpIeON VIDICON CONTROL CONTROL ORIvERS SUPPORT ¥ia. 3. Block diagram of slow-scan television subsystem. r te, os) ered “44s H. MASURSKY, ET AL. TELEVISION CAMERA PERFORMAN TABLE II CE CHAR ACTERISTICS Characteristic Wide-angle camera Narrow-angle camera Focal length (mm) Focal length ratio Shutter speed range (msec) Angular field of view (deg) Active vidicon target raster (mm) Number of vidicon reseau marks Sean lines per frame Frame time (sec) Picture clements per line Bits per picture clement Video carrier frequency (k Hz) Video baseband (kHz) Video sampling frequency (kHz) Video passband (kHz) Resolution at 1800 km Brightness range in automatic sequence (ft-Lamborts) High Medium Low 50 500 f/4.0 f/2.35 3 to 6144 3 to 6144 Il by 14 Ll by 14 9.6 by 12.5 9.6 by 12.5 111 oe 700 700 42 42 . 832 832 9 9 28.8 28.8 7.35 7.35 14.7 14,7 21.45 to 36.15 1 km per picture element pair 21.45 to 36.15 0.L km per picture element pair 2200 to 44 2200 to 44 1100 to 22 1100 to 22 550 to 11 550 to Il spectral and/or polarizing filters in the optical path. The wheel can be advanced zero, one, or two steps between consecutive wide-angle pictures by ground command, or will take two steps between cach picture, cycling continuously through a four-filter sequence when in the automatic mode, The narrow-angle camera (500-mm focal length), which has a field of view of 1.1 by 1.4 deg, utilizes a 200-mm-diameter Schmidt-Cassegrain telescope and the same type of video design as the wide-angle camera; it has a single fixed filter. The spectral range of the narrow-angle camera, therefore, must be established before Jaunch. Both cameras have focal-plane shutters, similar to the type used on the Surveyor and Mariner Mars 1969 television cameras, After passing through the filter and shutter, the optical image is focused onto a slow- scan vidicon, which is operated with a cathode-modulated electron beam. Vidicon electron beam focus, alignment, and verti- cal and horizontal deflection are performed magnetically. (See Table 11 for some of the significant instrument parameters.) The video signal is processed by a video amplificr, as shown in Vig. 4. The modulat- ed baseband video from the vidicon photocathode is current-amplified by a preamplifier (the maximum photocathode current is about 5 Namp), then bandpass- filtered, amplified, and refiltered. The signal is then demodulated, synchronous with the vidicon cathode chopping input. The demodulated video signal is amplified and low-pass-filtered to produce baseband video reconstruction, which is converted to a digital signal that forms $32 nine-bit words for each of the 700 television lines. The digital signal is transmitted to the data automation subsystem (DAS), where it is rate-buffered and formatted for input to the spacecraft’s digital tape recorder. There it is stored until it can be played back, at a Jower bit rate, to the Deep Space Stations and relayed to the Space Ilight Operations Facility to be recorded and reconstructed into a picture. The 85-ft MARINER MARS 197] VV EXPERIMENT 17 BANDPASS BANDPASS SYNCHRONOUS VIDICON FILTER FILTER *) DEMODULATOR , oC AMPLIFIER 7 PREAMPLIFIER POST ] sEFER CARRIER FREQUENCY GENERATOR q 9-bit RATE SPACECRAFT LOW-PASS ANALOG-I0- : DIGITAL FILTER DIGITAL » (DAS) wr] TAPE CONVERTER RECORDER Fic. 4, Video signal processing. antennas of the Deep Space Network are capable of receiving picture data, but at a much lower bit rate than the 210-ft antenna at Goldstone, California. There- fore, most picture playbacks must use the 210-1t antenna. In addition to buffering the television data, the DAS supplies the various timing control functions for the television sweep circuits, and computes the average video levels of each wide- (or narrow-) angle picture to set the vidicon exposure time for the next wide- (or narrow-) angle picture. The resolution of surface features and of the area in the field of view of each camera is dependent on the slant range from the cameras to the planetary surface. With the cameras pointed in the nadir direction and the spacecraft at an altitude of 1500 km, surface resolution in the wide- and narrow-angle cameras corresponds to about 1 and 0.1 km, respectively. The definition of resolution used here is described below. It is possible, by ground command, to take one single wide- or narrow-angle picture, fo take pictures in wide- and narrow-angle pairs at selected points on the surface, or to take a mixed sequence (wide, narrow, narrow, wide, cte.) of pictures until the tape recorder is filled (about 32 pictures). In the automatic- exposure-control mode (no use of an over- riding ground command), the television pictures will be recorded in a continuous alternating camera sequence. In this mode, there are three brightness ranges, which are the same for both cameras, giving a total brightness range of from 1] to 2200 ft-Lamberts. IV. Ixvesricgations The television experiment on Mariner Mars 1971 consists of two distinetly different, but complementary, types of investigations, one of which will be assigned to each of the two spacecraft. The first, which is called the fixed-features investigation, serves a wide range of basic data needs and is designed principally to define the geology and topography of Mars at resolutions consistent with broad, contiguous coverage. This investigation can be conducted most efficiently by a 12-hr Goldstonc-synchronous orbit of high inclination (50 to 80 deg) with periapsis initially about 15 deg from the terminator (see Fig. 5). The second and more complex mission, caHed the variable-features in- vestigation, is concerned primarily with the detailed study of diurnal, scasonal, and secular variations, including surface and atmospheric phenomena. The variable- features investigation can be conducted most efficiently by an orbital period of 32.8 hr, a 4/3 harmonic of the planet’s rotational period-—with periapsis chosen to lic either near the terminator or the co 18 H. MASURSKY, ET AL. GOLDSTONE 25 deg SET (0 days) EVERY OTHER REVOLUTION MOTION LIMB IN VIEW (0 days) GOLDSTONE 25 deg RISE G+ (0 days) EVERY OTHER REVOLUTION CENTER IN VIEW (0 days) Fic. 5. Mariner Mars (971 12-he mapping orbit. subsolar longitude, depending upon a further weighting of mission objectives (sce Fig. 6). The inclination is to be as low as possible, while still avoiding Sun occultation (probably 40 to 50 deg). Although primary responsibility for the fixed-feature and variable-feature inves- tigations will be assigned to Missions . A and B, respectively, it is reasonable to assume that both spacecraft will contribute to both types of studies. Contingency plans, in the event of failure of one space- craft before or after insertion, have yet to be developed ; there is general agreement that both types of data are essential to GOLOSTONE 25 deg SET {0 days) MAPPING MODE LIMB IN NODE LINE VIEW (0 days) CENTER IN VIEW (0 doys) 3? GOLDSTONE 25 deg RISE 0 doys} MAPPING MODE DIRECTION OF LIMB OUT OF VIEW (99 days) CENTER OUT OF VIEW (90 days) EXIT EARTH OCCULTATION (0 doys) LIMB OUT OF View (0 doys) ENTER EARTH OCCULTATION (0 days) CENTER OUT CF VIEW (0 days) PTO SUN (90 days) TO SUN (0 days) CENTER IN VIEW (90 days) LIMB IN VIEW (90 days) NOTE: 5 = DIRECTION OF ARRIVAL ASYMPTOTE obtain the maximum potential of the 1971 missions, l. Fived Features Scientific Objectives A requirement for systematic scientific exploration of a solid heterogencous planet is the detailed knowledge of its surface. Therefore, the principal objective of this mission is to acquire the maximum amount of geologic, geodetic, topographic, and cartographic data at the most useful resolutions. These data will permit study of surface distribution of bright and dark regions, fine structure of minor topographie Bae ot LIM& OUT OF VIEW (50 days) Ee tes at EXIT EARTH OCCULTATION (0 days} AeA ee ne ~— CENTER OUT OF VIEW (90 days) : BL U8 OUT OF VIEW (0 doys) : 97 er Reo ENTER EARTH OCCULTATICN (0 doys} 2 . CENTER OUT OF VIEW (0 doys) : TO. SUN (90 days) TO SUN {0 days) h CENTER tN VIEW (90 days} LIMB IN VIEW (70 days} NOTE: $, = DIRECTION OF ARRIVAL ASYMPTOTE Fig. 6. Mariner Mars 1971 32.8-hr variable features orbit, tomer cee dc as Wi, in pl in, th -— ow See yam een Tae ee MARINER MARS 1971 TY EXPERIMENT 19 details, and analyses of processes such as volcanism, tectonism, impact, mass wasting, and acolian activity, thus greatly improving knowledge concerning the structure and evolution of Mars as a planct. Geometric and photometric optical imagery of the surface of Mars will permit the following: (1) A determination of the shape or figure of the planet, i.c., the ellipticity of the mean surface reference level which may differ from the dynamic ellipticity (as suggested by Earth-based data); this, in turn, will provide information on possible departures of the planct from hydrostatic equilibrium, which may be supported by stresses in the upper crust. (2) The derivation of high-precision geodetic coordinates of a large number of well-defined topographic features neces- sary to construct greatly improved maps of the planet, i.e., charts of the surface distributions of albedo and elevations in a rigorously defined geodetic network; it already is evident from Karth-based radar data that albedo and elevation differences on Mars do not. have a clase correlation. Detailed studies of this correlation (or Jack of it) may have great significance for an interpretation of observed albedo variations. (3) A synoptic geologic and topographic map of Mars at the Jargest practical scale, based on interpretations of low and high Sun angle imagery, will be compiled. (4) Enhancement of the interpretability of the variable-features investigation. The degree of topographic dependence js one of the most important questions regarding the wave of darkening. ‘This can be determined only by pairing the high Sun albedo vari- ation data of the variable-features in- vestigation with the low Sun topographic data of the fixed-features investigation. (5) Construction of a framework to interpret the data from the other experi- ments concerned with surface properties or bulk characteristics (infrared radiometry, infrared spectroscopy, S-band occultation, and celestial mechanics experiments are obvious examples). Lunar mascons suggest that there may be gravity variations relatable to the surface structure. (6G) Effective planning for high-resolu- tion orbiters and Janders throughout the 1970s. The Mariner Mars 1971 fixed- features investigation will provide broad, contiguous photographic coverage at uni- form resolution that wil] be similar to the Jarth-based Innar telescopic photo- graphy, along with nested spot samples at 10 times greater resolution. It will, like the lunar photography, provide a com- prehensive, and thercfore flexible, decision- making base for future exploration efforts. Visual Resolution and Its Operational JImoplications The Mariner Mars 1971 television sub- system was inherited without substantial modification from earlier flyby missions. lts maximum resolution capability is somewhat Iess than that considered opti- mum for planet wide reconnaissance, prim- arily because of limitations in the optical system, the lack of image motion com- pensation, and the necessity to keep a high periapsis in order to maintain planetary quarantine restrictions. If, how- ever, the system operates at or near its resolution Jimits, a very meaningful regional reconnaissance can be conducted. To achicve this goal, the photographic coverage must be obtained within a narrow range of illumination conditions, ie., at low Sun angles, in arder to increase target contrast and thus maximize photo- graphic resolution. The term resolution, as it is applicd to television experiments, often leads to confusion about truc system capability. To avoid this difficulty with regard to the Mariner Mars 1971 flights, a brief dis- cussion of resolution as it applies to television experiments is presented in the following paragraphs. Photographic resolution is usually stated in terms of separable white-on-black line pairs per millimeter in the image. In spacecraft vidicon systems, the scale width of a single television line at a particular altitude is often given as the index to system resolution. The value for the width of a television line of the wide-angle Meet te Nene ORE Peroni ne dime 20 Il, MASURSKY, ET 41, (a) (b) -4 [~ TD pr pn ng - RANGER VII RANGER VII 199 =5}- 4 O- Bonpland E n wee € > so 7 9 199-Fe 5 ee e 194 2.7 4 Bonpland H~O 3 3 at Yo -8b 4 = a ——-—_..-. -F ja 4 170 Ta _ -10 ao 2 3 4 5 6 7 Fic. 7. (a) Areal coverage of selected, nested R plots from frames indicated, camera for Mariner Mars 1971, from a periapsis altitude of 1500 km, is 4 km. This does not mean, however, that one can actually recognize 1-km objects on the surface, For any given spacecraft television subsystem, the size of the smallest re- cognizable object is a function of overall target contrast, which is highly dependent on Sun elevation, shape, sharpness of outline, and other factors. For example, - high-contrast objects such as fresh, young craters are more detectable than subdued, older craters. The more numerous small, subdued craters of an impact population cannot be seen near the resolution limit; however, small, sharp craters of the same size are readily detectable. The observed size-frequeney distribution is thus cen- sored as it approaches the resolution limit of the system; cumulative crater counts usually show a “roll-over,” or flattening, at about 4 to 6 times the size of the smallest identifiable crater. This effect can be seen in Fig. 7 from the unpublished terrain analysis work by Edgar Bailey, U.S. Geological Survey, who prepared cumu- lative crater counts from single, nested, progressively higher resolution Ranger VI frames. The cumulative plot for each (Im) (Ikm) bogig diameter, cm anger VII frames. (b) Cumulative crater frequency individual frame shows this roll-over at a point about 5 times the size of the smallest detectable crater. The widely cited roll-over of the Mariner LV crater frequency curve below 20 km and the “genuinely lower abundance and/or systematic change to smoother craters on Mars” (Sharp e¢ al., 1967), at a point about 5 times the size of the smallest detectable crater, can be looked upon with some suspicion (Chapman ef a., 1969). This roll-over may, in fact, not reflect any fundamental change in surface charactoristies in the vicinity of 20 km, but simply may reflect an over- estimate of the real identification resolution of the Mariner LY television subsystem. Extrapolation of the Mariner IV curve to 1 km produces a crater deficiency almost an order of magnitude below the number actually measured in the Mariner VI high- resolution narrow-angle pictures (Leighton ef al., 1969). Similar effects produced by resolution falloff in the small size ranges can be anticipated for the Mariner Mars 1971 cameras so that the real resolution will be mach less than the figure given for the scalu width of a single television line. The effect of lighting angle on resolution has important operational implications. ate me Pe ae Tee ee ew AH SF at AME AEE ae Cae e aE st MARINER MARS 1971 Vv EXPERIMENT 21 64 T T T I I T 32+ 7 CLASSIFICATION (GEOLOGIC MAPPING) we 4 IDENTIFICATION £ (TOPOGRAPHIC MAPPING) Zab 4 : a ~ Zz 4F 7 x 5 DETECTION THRESHOLD 2 4 ol 4 0 ! 1 { { i i ! 1 0 10 20 30 40 50, 60 70 £0 90 SUN ELEVATION ANGLE, deg Fic. 8. Relationship between types of resolution and Sun clevations. (After Keene, 1965.) Keene (1965), in an empirical study before the first Lunar Orbiter flight, was able to determine quantitatively” the effect of variation of Jighting angle on the resolution of a photographic subsystem. Objects of varying size and shape, with reflectance properties similar to those of the Moon, were photographed at varying Sun eleva- fions; the response by vicwers was categorized into zones of no detection, detection, and identification as a function of object sizc and Sun elevation. Figure 8 is an adaptation of Keene’s general results which, in spite of limited knowledge of the Martian photometric function and large- scale topography, are parametrically ap- plicable to photography of Mars. Three positively sloping curves define the different types of resolution important in a television experiment. The first is detection resolution, which is the zone in which the presence of an object can be established in the image, but the object cannot be classified. H, for a given system, the detection resolution at a Sun elevation of 10 deg is taken as about 1 km (at a height of 1500 km, the detection resolution of the Mariner Mars 1971 wide-angle camera will be about 1.5 km), then the effects of increasing lighting angle can be assessed. Ata Sun elevation of 50 deg, the detection resolution falls off by about a factor of 2. Thus, detectability iS at a maximum near the terminator because of the enhanced contrast produced by shadows, and it decreases with higher iWumination. The seeond curve defines the zone of identification resolution in which one can discriminate between topo- graphic forms such as hills, peaks, craters, ete., but in which thor ough photogeologic analysis i is not practical. The classification, or geologic mapping curve, has been added to Keene’s plot by comparison of the smallest: objects mapped by the U.S. Geological Survey to the detection re- solutions of the Ranger and Lunar Orbiter spacecraft, In general, there is almost an order of magnitude difference between the standard detection resolution and the size of the smallest geologically classified feature, irrespective of variation in Sun co 22 Wf. MASURSKY, EY AL, angle. Thus, a 1-km feature may be detectable at a Sun elevation of 10 deg, but a feature must be about 4 km across to be truly recognizable, and at least 8 to 10 km before it ean be classified in a geologic sense. ligure 8 shows the importance of near- terminator periapsis photography for the fixed-features investigation. If the tele- vision experiment is to yield topographic data to the limit of its restricted cap- abilities, most of the imagery should be acquired at Sun elevations no greater than 30 deg because of resolution falloff. Preliminary evaluation of the Mariner VI and VII pictures indicates that the near- terminator region is photographable. No obvious veiling atmospheric haze or ob- securing cloud cover were detected in the semi-vertical — near-encounter pictures (Leighton et at., 1969). The information content of the pictures, except for the very bland terrain in the floor of Hellas, is good up to illumination angles of 30 deg. Topo- graphic details can be discerned at angles of 60 to 70 deg in the case of “chaotic” terrains. Thus, most of the Mariner Mars 1971 fixed-feature coverage can be pro- grammed for Sun elevations between 10 and 30 deg, but the capability will exist to acquire higher Sun angle data in the event of temporary atmospheric problems or for special purposes such as the acquisition of albedo data, Mission Profile The nominal 12-hr mapping orbit is shown to scale in Fig. 5; viewing conditions at the beginning and end of the 90 days in orbit are indicated. A mapping sequence begins with Goldstone rise about 5 hr before periapsis passage (1). When the Goldstone elevation angle reaches 20 to 25 deg, the spacecraft will empty the tape recorder of the television data taken dur- ing the previous periapsis passage when Goldstone was at the antipode (2). The readout takes about 3 he when the 16,2- kbps data rate is used with the 210-ft Goldstone antenna. When the recorder is playing back, no other science data can be transmitted. About 20 min before periapsis (3), the television camera beving to take pictures which are sent to the now-empty tape recorder for storage. The other instruments send their data stnul- tancously to the tape recorder while transmitting it back to Goldstone in real time. The picture-taking sequence ends a few minutes after periapsis passage, when the tape recorder is full and the spacecra lt is Approaching the dark side of the planet (+). Occasional observations of Phobos and Deimos (and Saturn for calibration purposes) may be obtained between (+) and (1), and at other orbital positions. Because the orbital period is 12 hr and the rotation rate of Mars is about 24 hr 37 min, the planct will rotate slightly less than 180 deg per orbital revolution, Thus, mapping coverage of alternate sides of the planet will be coupled with a small (about 9 to 10 dey) daily shift in longitude of the subperiapsis point (Mig. 5). A complete mapping circuit in an eastward direction around the planet will be completed in about 20 days. After 90 days, the area between —60 and +40 deg latitude will have been covered by the wide- and narrow- angle cameras: the wide-angle camera, with contiguous, low-resolution (} km/television line) pictures, and the narrow-angle camera with uniformly interspersed spot covcrage at higher resolution (50 m/tclevision line). The area covered during each 20 days, and typical “footprints” for the wide- angle camera coverage are shown in Fig. 9, Regions of special interest. can be re- examined every 20 days with a full array of sensors. Thus. during the mapping phase. there will be opportunity for adaptive operations, making use of previously recorded data, Barring severe equipment. problems, however, the fixed- features investigation should proceed in a nore systematic and less adaptive fashion than the variable-features investigation, After 20 to 54 days in orbit, depending on the actual performance of the high-rate channel, the sequence will be modified because increasing Karth-Mars distance will cause the tape playback rate to be dropped to 8.1 kbps, even with the use of the 210-ft antenna. At that time, cither a full tape recorder of data will be taken at AA VA te RP cee eV Ta oe Ny cote 23 “UOISSTUL ALP-OG JO PGI UY Toy spud oOo Btourvoy opsur-aptm yoaid.éy puv o8vs0aod PRAY °6 OTT SAV O48 ~ UG cssessensessesnrssssneonss SAYS O8 — 1G ee ee SAV OF 7 LY coceceereeee SAV OF — UL mews e ences SAW OZ - 0 t y ! ¥ “ aeeademmudinaeedintcme ee nrimpnaeceewensaumness aan ak a erat re vee wn Gem wand mea te jena oduaweg quem ahem nee Og ne . . , _ 1 t . 1 7 XPE | ‘ : ! . ' ' 2 + i. | ! \ a 7 R MARS 1971 TV § Bap ‘JqQNLILY1 te cee tee DHOE Ba ; PENS -09 ; Bap 99 = NOILVNITONI .. 44 @t = GOIwad iZ6L YIGWSAON 61 = ALVG TVAISYV | . wy OOP L = JGALLIV SiSdvidad : . . LL AVW 6 = 3LVd HONNAVI MOA = memset fenton, aaa hg vie wept “ seh ct Prana * 4. pS J s 2 i nd < cnn en bene eet : ek en . eee _~ Sepeoneaaociarag nares pose N, Meee teas neg ens eter rete se ds es -O ms nat? i Sra ( > ; : : _— ae ~ Bn eemeyotY ; wa - . re SOOT ce eaeemee -OY yo t + a . a i : : i i soo : ‘ 4 OS aie It : se i 4 rt n we ‘ iN iA 7 ‘ 2K. ; ¥INCGAD ' | ; oo YIVRONN woe Sree een vane te Ae eran cee eee nie ae pee) eng MRR siete aethliae ena tit peemanenareammmmmmentsincmn me am = emo" pte ne “ft hr 24 H. MASURSKY, ET AL, -10 ns Rees pees pee T T — t T THIRD ORBIT ESy aah FIRST ORBIT 2 WIDE-ANGLE CAMERA ¥ -1a}- 4 wr a =~ ba = -22b 4 s -26 4 NARROW- ANGLE CAMERA -30 f I 1 i { 1 L 1 70 74 78 82 86 70 94 98 $02 108 LONGITUDE, deg \ Fic. 10. Relationship of narrow-angle camera coverage to wide-angle camera footprints. RESOLUTION Timm Tem 10 cm lim 10m 100 m l km 10 km 100 km 1000 km oo a oo __ CIRCULAR BASINS: DISTRIBUTION OF MARIA AND TERRAE i oo IMPACT CRATERS: SIZE AND AGE CONTINUUM Po CIRCUM-BASIN, ELANKETS AND STRUCTURES TERRA BASINS ANDO LIGHT PLAINS pO CHAIN CRATERS AND RILLES PT DARK BLANKETING UNITS Pe ees, RIDGES i oo - ~_ CONES AND I2SEGULAR CRATERS CALDERAS AND VOLCANO-TECTONIC DEPRESSIONS HYBRID CRATERS, IRREGULAR CRATERS HYBZID TERRA UNITS BASE SURGE PATTERNS Poe REGOLITH DEPTH VARIATIONS - BLOCK DISTRIBUTIONS AND MOVEMENTS ' - eee ae SOIL AND BLOCK FABRICS SOIL SIZE AND SORTING "EQUILIBRATION FEATURES" "ENDOGENETIC FEATURES” "EXOGENETIC FEATURES" aq _ TELESCOPIC STUDIES RANGERS VII, VIIL EX ~~? —> ° ° 3 LUNAR ORBITERS 1, Ul, Hl LUNAR ORBITER IV (MAPPING MISSION) oa ~~ SURVEYORS 1, UH, Vv, Vi, Vil LUNAR ORBITER V (SCIENCE MISSION) te ne APOLLO FIELD GEGLOGY EXPERIMENT e * MARINER MARS 1971 Fic. LL. Resolution thresholds and points of diminishing information returns for sclected Junar features. ST Tr ne semen eg a Soe na ee a cree pea ew ee eres tee seamen RO Lue Meee SHWRS LEE OMe yay 2 hme mow cere nme ete | AR anette, Lm Aiea Sate bs Rae WN ae os NN pitiaae ey Mee 7 ave, nT 9 9 athe Mere Abo ety Dow weirs ote Litt AN bq tee Wo Se eetia se OI ge ntl keer TO eon mt a ee ny a ne alee SPA me ate cect Lee Se oe atten ces Sey AMR one A tem Et ete 7 ce Lol r ay > 7 MARINER MARS 197] TV EXPERIMENT 25 ! RESOLUTION i Lem 10 em Ym * 10 m 100 m tke 10 km 100 ken 1900 ka or T T T |! tod T Ty! t v 3 DISTRISUTION AND GENERAL © PROPERTIES OF CONTINENTS ¢ AND BASINS, MARIA-TERRAE : : PLANETARY STRATIGRAPHY L : “ PLANETARY GEODETICS 7 : : : : : PLANETARY TECTON / E- , ~ ° MAJOR VOLCANIC : . PROVINCES - CRUSTAL : / ASSIMILATION : : . wm LUNAR ORBITER IV # ‘ 3 : / —————_ RANGERS Vil, Vili, AND IX 40 MAJOR PHYSIOGRAPHIC. . . ~ < PROVINCES CIRCUK- ASIN fo eeeee MARINER MARS 1971 g BLANKETS anf FIXED-FEATUSES MISSION 8 STRUCTURES (WIDE-ANGLE CAMERA) 8 : g _. : moe mee MARINER MARS ISTT 2 DOMES, CONES, FLOWS . VARIASLE FEATURES MISSION - Pr AND MARE RIDGES : (WIDE-ANGLE CAMERA? g e : v . ° * MARINER MARS 197t ERAS AND HYSR CAL! preenie ERID y (NARROWI-ANGLE CAMERA) : : 20-- LARGE PAPACT FEATURES MARINER MARS 1969 FREQUENCY DISTFISUTIONS (BOTH SPACECRAFT) F ‘| me mm ARINER MARS 1769 SMALL CRATER OISTRIBUTION :. FAR ENCOUNTER ALLISTIC EROSION tok BALLISTIC EROSION Pf were MARINER IV : PATTERNED GROUND — MASS WASTING : EROSION - DEPOSITION : BLOCK DISTRIBUTIONS : * © CRUSTAL STYLE-STATISTICAL : SOIL AND BLOCK TEXTURES | : vee ae — ee 2 Fig. 12, Comparison of Mariner Mars 1971 fixed-features investigation with performances from other spacecraft. every other periapsis or half the amount of data will be taken at each periapsis passage. ‘The rest of the sequence stays the same. There is considcrable overlap in the coverage from each 20-day Jongi- tudinal cycle. This characteristic is particularly advantageous in the fixed- features investigation because it gives the capability of acquiring, in these zones of overlap, cither pictures taken with high Sun angles, convergent stereo (explained later), or special-purpose color and polari- metric data without sacrificing contiguous coverage. Figure 10 shows the area covered by the narrow-angle camera in the “foot- print” of the wide-angle camera. Although almost, 70°24 of the planet will be cover- ed by the 1.0-km-resolution wide-angle camera, about. 5°, will be covered by the 0.1-km-resolution narrow-angle camera. This small fraction of the surface sampled ata tenfold gain in resolution, however, will allow observation of many features of fundamental geologic, geophysical, and geochemical importance (Figs. 1J and 12). If features of exceptional interest are observed, narrow-angle pictures can scan the region of these features in Jater passes, and convergent high-resolution — stereo coverage can be obtained at the sacrifice of systematic wide-angle coverage. Anticipated Results Geodesy. The basie element for the exploration and mapping of the surface of a planet is the three-dimensional shape of this surface, ie., the “figure” of the planet. In a fast-rotating planet such as Mars, the normal expectation is that the surface is very nearly in approximate hydrostatic equilibrium under the com- bined effects of centrifugal force and 26 H. MASURSKY, ET Ar. gravity, allowing for the internal mass distribution, A persistent discrepancy between the dynamic ellipticity. derived from perturbations of the satellite orbits (and more recently the earlier Mariner flights) (f, =: 0.00525) and the optical ellipticity of the disk derived from many consistent visual and photographie ob- servations (f, = 0.0105: de Vaucouleurs, 1964) has been frequently discussed in the past and remains unexplained. A combined analysis of the limb contour from pre- insertion and apoapsis photography and anew geodetic control network should lead to a definitive solution for the average Shape of the Martian surface. Such a study is also needed to define the Martian equivalent of the geoid, ie., a standard reference surface for mapping. Departures of the actual surface from the reference spheroid will give information onelevations and, in conjunction with gravity studies, on departures from hydrostatic equilibrium and isostasy, A refinement of the direc- tion of the rotation axis of Mars, cur- rently known to a precision of about 0.1 deg, will also follow from an analysis of the apparent motion of the control points on the surface due to planetary rotation. Cartography, X primary objective of the Mariner Mars 1971 missions is an accurate mapping of albedo and a new geodetic control network to determine the physical size and shape of the planet and to solve for the dircetion of its spin axis. This network of points on the surface of Mars also is used to orient the planetwide coordinate system for the preparation of cartographic materials. Tho control points are identified on a series of different pictures and their positions measured; then, by analytical triangulation, their coordinates on Mars ean be computed using the spacecraft’s known locations on its trajectory. Once the locations of the control points ave known, it is possible to solve for spacecraft positions at which additional pictures have been taken by these same photogrammetric techniques, In this way, the Mariner VE and VI pie- tures will be used to define a control network for positioning the topographic detail and markings on the new charts of Mars. It will be possible, for several reasons, to use the Mariner Mars 1971 pictures to improve the aecuracy of the Martian geodetic network. The most important reason is the flexibility of picture-taking with regard to altitude and coverage permitted with the long-duration orbital flight in contrast to the flyby missions. Thus, it will be possible to obtain high- resolution pictures of most of the planet for detailed identification of the control points as well as at a more optimum altitude for making measurements. Wide- angle pictares taken between 7000- and 14000-km altitude collectively covering the entire surface of Mars should bea good compromise of resolution and area covered for locating and measuring the positions of control points. The camera positions on orbit in 1971 should be known with greater precision than could he determined after the 1969 Hyby when uncertain outgassing shortly before encounter artificially modi- fied the trajectory. Improved camera calibration and the increased number of reseau marks should also improve the L971 measurements over those obtained in 1969, Discrepancies of 5 to 10 dev in latitudes and longitudes (300 to 6ou km at the surface) are not uncommon between various published maps (de Vaucouleurs, 1963): a recently completed 10-year Mars Map Project (de Vaucouleurs, 1970) in which all Barth-based visual and photo- graphie data from L877 to 1958 were rigorously reanalyzed and reduced to a couimon system of geodetic coordinates may have reduced errors to about 1 deg or a little better (~5u km). at least in regions where sulliciently well defined and stable surface “markings” (i.e, albedo Variations) are available at ground re- solutions varying from » to lL deg ~ 30 to 60 km in high-contrast regions to perhaps 2 to 3 deg~ 150 kin in low-contrast regions. One of the major mapping applica- tions of the high- and low-San wide-angle camera photography will be to locate precisely, in a well-defined geodetic Co- ordinate system, the surface distribution s en” ote, ara meets MARINER MARS 197] £TV EXPERIMENT 27 of albedo differences and to compare it with surface clevation differences to a resolution limit of 1 or 2 lan. Jopography. The major initial product from the fixed-features investigation will he contiguous (forward and side lapping) jow-Sun-angle imagery of about 70°% of the planct. In these pictures, surface textural detail will be emphasized at the expense of detailed albedo variation data. However, high-Sun-angle pietures of selected arcas will be acquired in the zones of overlap shown in Fig. 10 and also from the variable-features investigation. If the first spacecraft performs nominally for 90 days, the wide-angle camera should pro- vide about 2500 individual pictures at a detection resolution on the order of 1 km. The narrow-angle camera will provide the same number of nested, noncontiguous pictures with detection resolution of alout yagm. Hypsometric control for cartographic purposes will be weak because of the limited stereometrie capability of narraw- angle, small-format, high-altitude orbiters (Borgeson, 1966). In the nominal stereo mode (50%, forward lap), the Jif or height-measuring capability of the wide- angle camera will be on the order of 3 km, If operated in a convergent stereo mode,” Alf can be improved to better than J km. Because this operation will create un- desirable gaps in the mapping coverage, it will be used only in’ special-interest situations, probably in the zones of overlap between 20-day longitudinal cycles (sec Vig. 9). Most. of the relative height. data from this mission will be derived, as in the lunar telescopic case, from shadow-length measurements with an estimated precision on the order of 200 to 1000 m. This relief measurement technique requires low-Sun, near-terminator conditions in order to have an acceptable percentage of the total area of each picture in shadow. This represents a second justification for near- terminator opcrations. Keene (1965) gives a plot that is useful in estimating the percentage of area in 2 Principal point at center of successive frames by incans of fore and aft or sideways tilt along the orbital path. shadow for surfaces of varying roughness under different lighting conditions. If the i-km seale, depth-to-diameter ratios on Mars are on the order of 0.05 (5.7 deg), as suggested by Mariner IV photometric data, the shadowed area should be less than 1% of each picture at a Sun angle of 25 deg. At 15 deg from the terminator, however, the shadowed area increases to about 70%, an acceptable figure for shadow measuring. Although this tech- nique can provide an abundance of high- quality, relative relicf data, it will not be useful for the production of contoured maps. The main products from the visual imagery probably will consist of ortho- photographic mosaics and semiquantita- tive airbrush renditions of the surface, with Jocal spot elevations from the shad- ow-length measurements similar to the 1:1000000-scale Junar charts prepared from telescopic data by the Acronautical Chart and Juformation Center. An additional monoscopic slope-measur- ing technigue called “photoclinometry” can be used for supplemental relief in- formation. However, the technique is dependent on low-Sun and near-full-phase pictures of the same area at similar resolutions to control albedo effects, and on an accurate photometric function. In the lunar telescopic case, even with a well- described photometric function, a small error in albedo correction can lead to as much as a 100° error in slope determina- tion (Rowan ef al., in press), Where the albedo is not constant, as on Mars, the problem of extracting truly meaningful slope measurements becomes almost. in- surmountable. Another aspect still under investigation for the Moon, is that photo- clnometric profiles at comparable scales generally give lower roughness values than those derived photogrammetrically. It is theoretically possible. however, to tie together the photogrammetric and photo- clinometric profiles to achieve better results than can be obtained singly by either method, but the methods are time- consuming and expensive (Wu, 1969). Although considerable emphasis has been placed on this technique in past and present unmanned flight. programs, SAEED orion sone 28 H. MASURSKY, ET AL. particularly for Apollo site evaluation, it should be considered as a supplemental method of extracting relief data. The primary value, when used by itself, is in the statistical evaluation of the relative roughness characteristics of terrain units for geologic classification and for enginecr- ing purposes (Rowan ef al., in press) and in estimating the shapes of objects such as boulders and their tracks near the limiting resolution of an imaging system. Geology. One principal geologic result of the fixed-features investigation will be a synoptic map of Mars at the largest practical scale, with emphasis on regional structure and stratigraphy. At the present time, 1:5000000 scems to be the most practical scale for the planned coverage; in this case, the map should resemble, in degree of detail, Earth-based hinar geologic maps (Wilhelms, 1969). This type of classification work has extensive terrestrial and lunar precedent and has proved to be an effective and reproducible analytical method. It docs require, however, qualita- tive experience-based judgements with re- gard to the relative importance of various textural criteria for classification purposes. A unique characteristic of the geologic mapping approach is the use of observable Superposition, intersection, and entbay- ment relations in the reconstruction of surface history, thereby introducing time into the analysis. A further assct is that geologic mapping forces treatment of the visual and other data from the entire electromagnetic spectrum in an internally consistent manner. Observation is separ- ated from interpretation; thus, special genetic pleas based on previous theory and partial treatment of the available data are, for the most. part. avoided. A rock-strati- graphie approach will be used, based on that long applied terrestrially, and intro- duced in systematic geologic mapping of the Moon in 196¢ (Shoemaker and Hackman, 1962; McCauley, 1967), and more recently adopted in the Soviet Union by Sukhanov, ‘Trifonov, and Blorensky, and in Great Britain by Guest and Murray. Reduction of remote sensing data to the form of meaningful planctwide geologic maps requires that there be an effective tradeoff between the resolution that the system is capable of delivering and the amount of coverage obtained to be sure that major landforms are properly sampled and that they can be spatially related to one another. The solution of the traceotf lies in the nature of the planetary surface in question and the scales at which various phenomena ean be studied. The importance of object scale in attempting to understand or to model terrestrial geotectonic phenomena has been described by Carey (1962). The seale dependence of observation, experiment, and theory is implicit in most work in terrestrial geology; but this fact is often overlooked. Studies of the Moon by tele- scope and by unmanned probes (Ranger, Lunar Orbiter, and Surveyor) that spanned some six orders of magnitude in resolution capability. revealed a scale dependence ov hierarchy of surface forms like that deseribed for the Earth by Carey (sce Fig. 11), Selected examples of the types of features recognized are plotted; the begin- ning of the bar at the right indicates the detection resolution or scale at which one begins to acquire useful visual information for the particular feature. The dashed segments of the bar at the left indicate the scale range in whieh high-resolution data are, for the most part, unnecessary. The beginning of the dashed line could be considered as the point of diminishing returns or the point at which it is no long: er reasonable to attempt high-resolution photography at the expense of coverage that could be used more profitably else- where, A point of maximum efliciency ina given experiment, i.e., where the most effective tradeoff between resolution and coverage is achieved, ean be defined and lies near the center of each solid bar. Figure 11 also indicates that there are certain critical-resolation thresholds for the Moon, marked by the beginning points of each bar, to the wight of which (low: resolutions) the data are insufficient for effective geologic analysis, the amount ¢! coverage obtained notwithstanding, As av example, at I-km resolution in the tele- rn Wrenn SA Ae ARENT AI MARINER MARS 197] TV EXPERIMENT , 29 scopic range, one can do a respectable job with gross lunar exogenetic features, ¢.g., the circular basins and large impact craters. High-resolution data from the rarious Imaging probes were necessary, however, to deal effectively with the naturally smaller-scale features of internal origin, e.g., volcanic, tectonic, and mass- wasting phenomena (endogenetic and equilibration features), A similar set of critical-resolution thresholds for Martian landforms can be expected, and several examples can be secn in the data from Mariners VI and VII. Most of the Mariner VI wide-angle camera coverage in near- encounter sequence (Frames 17, 19, 21, 23) with resolutions on the order of J km per television line shows only flat-floored, almost rimless craters surrounded by what appears to be featureless terrain (Fig. 13). The nested narrow-angle pictures (Frames 18, 20, 22) with resolutions of about 0.1 km per television line, on the other hand, show that gentle Jinear ridges and patches of blocky terrain are present locally, indicating that the inter-rater arcas at higher resolution are actually more complex than they appear in the wide-angle camera. Another resolution threshold crossed by the narrow-angle camera is evidenced by the change in frequency of sharp appearing craters in narrow-angle pictures, as opposed to those observed by the wide-angle camera (Leighton cf ail., 1969), Jn additian to imagery well below the threshold necessary for assessment of the relative roles of internal and extemal processes, the other specia] requirement for elective geologic analysis is that the coverage be contiguous and at uniform resolution. ‘This stems from the require- ment for a regional setting for each ecologically classified feature. The ad- Vantage of recognizing a field of small, irregular craters is doubtful unless it is known whether they are part of a field of similar craters that surround a slugle, much larger crater. If one has the coverage to establish this fact, the small, irregular craters may be identified from their Spatial distribution as secondaries. Uniform resolution demands that the pictures be taken at about the same place in the orbit (near periapsis) and with approximately the same lighting. The need for reasonably uniform resolution is derived from the internal consistency requirement — in geologic mapping. If a unit is defined and outlined on the basis of fine textural properties, cumulative crater frequency or any other morphologic characteristic, the resolution must remain reasonably constant throughout the study area if the boundaries and relations to other units are to be effectively defined. Crater Studies. With detailed photo- graphy of a substantial portion of Mars, we can make advances in several areas that bear on the ancient meteoroid envivon- ment of Mars and on surface processes during its history: (1) Detailed structure of the Jargest Martian basins and their similarity to the multiring lunar basins may shed light on both Martian and lunar features. Arc the linar basins low-velocity impact sites involving cireumtcrrestrial bolides unique to the Earth-Moon system? (2) If uneroded, preserved cratered areas can be identified on Mars, are the densities and sizes of craters compatible with the numbers and lifetimes of Aars-crossing asteroids? (3) Are there ancient regions saturated with craters, or are the oldest regions unsaturated? (4) Do small-scale structures systematically show features indicative of crosion processes? Jlow have eraters been crased in the craterless arcas such as lcllas? Relation of Fived-Features Investigation to Karlier Television Experinents igure 12 is an attempt to relate the mapping phase of the fixed-features in- vestigation to the results of other unmanned probes and to a nominal variable-features investigation in order to contrast the operational stvles of the two types of investigations and to show, in terms of a better geologic understanding of Mars, what isexpected from the mapping phase of the investigation, Fifteen types of planctary investigations, identified from available literature concerning the Moon and Mars, are positioned approximately in terms of the resolution required and "CENQ omngord of8ur “MOLUT UE Ueto? 049 Jo Aqxetdutoo oy} o1ON "WT 0098 qnoqu st dias wow opSue- wore OYA JO VOISUOUETp Jrom—qsua oy, ‘do, oyy a st YOU i} a . . o . wf- = . “IYSL ALY OY} 7B SE IOPVUIULIO] OPT, woIVN Oy sTUOTRoNa ota Jo orn so aT (OUT A T/UL_ TQ iR0Eqe PUOTIUNPOSAT VIOUVD OPFUR-MOLIVU “OUT AL/UUL T qnoqe tuoynyosat vazourre o]suUC-OpL) srround ofue-wo.en PUR -oplM Woap soungord Py TOUNRTL POPs JO OVSOTY "ET “DIET ; - @lare : ‘ ’ : , ; ’ H i a : Lito ‘ : = : oe : ! : ~ ae : mw : Le E . ” : ~ att ane gall SING wd . wo ag Ma : i mre . ‘ . ' z : ‘ a ! . . : L . z cune . re . o i 5 . x, mea ‘ Ra : wat ar! 4 ©? Nay eG : a eo . . ? ‘ , : i : i. . . wo i . ww bo * ' oe " t 1 = i ‘ : oo eed . vias d fy fy in rao F ar , 2 t : : ' i. ae i vote : . 4 fe, Do Det lia, i 4 io . - ® JE zl o . oF me . ie etre d < awe Ho aX 4 AR Me Nam face ROA BR EN le a AL Ob Anita Poneto A AA CrP R CAIN ME SIO AIO Ake hot hapa MARINER MARS 197] TV EXPERIMENT 31 + estimates of the amount of contiguous coverage necessary to study the particular phenomenon and to place it in a regional context. ‘The Jines shown for each mission define a zone (to the right of cach line) in which the studies identified can he con- ducted meaningfully. Studies that are shown to the Ieft of the Ines are not possible, because resolution is below the required threshold. 1t can be scen that the Mariner IVY, VI, and VIT missions permit only generalized studies of the surface structure of Mars and, perhaps, some preliminary work on large crater frequency distributions hampcred both by resolution and coverage limitations. The Mariner VI and VII far-cncounter sequences and the polar cap coverage represent advances over Mariner IV. The coverage of the mapping mission by the wide-angle camera on Mariner Mars 1971 should be better by a factor of 2 than the coverage by the wide-angle camera on Mariners VI and VIF and similar in information content to the hinar telescopic¢ data, thus permitting the same type of regional, structural, and stratigraphic analyses performed before Ranger and Lunar Orbiter. The narrow-angle camera enhances overall mission potential with its spot-sampling capability and may permit study, on a statistical basis, of some phenomena that fall in the Lunar Orbiter IV range-—secondary craters and internal features, An additional asset is the ability to point the narrow-anyle camera, without sacrificing contiguous coverage, at areas previously determined to be of special interest in the zones of redundaney. The Mariner VI and VII television results support the current plan for two complementary missions in 1971. Although apparently smoother and less cratered at comparable photographic scales (1 km and 0.1 km per television line) than some parts of the Moon, Mars presents, with the exception of the floor of Hellas, a moderate- ly variegated surface on which at least four major types of terrain can now be recognized. ‘The data from Mariners 1V, VI, and VII suggest that it is a primitive body more like the Moon than the Earth, but that it probably is of comparable 2 geologic complexity. In the case of the Moon, some 44 major rock-stratigraphie units and 10 different geologic provinces are now recognized on the near-side (Wilhetms and MeCauley, 1969). The distributional patterns of these units are the key to unraveling surface history. With the improved resolution expected from the Mariner Mars 1971 television subsystem, the recognition of additional terrain units can be anticipated and the distribution patterns of these will be delincated by means of the contiguous Mission A coverage. This then will be the framework within which to interpret data on variable features and to plan subsequent. investigations, particularly surface sampl- ing by landers such as those envisioned for 1975. 2. Variable Features Mariner Mars 197] will provide the first opportunity to study features of the surface and characteristics of the atmosphere of the planet with good spatial and temporal resolution—a. significant advantage, since diurnal, seasonal, and secular variations are widespread on Mars, and since fine topographic structure has been detected, The phenomena of interest are of con- siderable meteorological, geophysical. and exobiological importance. They juclude the seasonal and secular contrast and reflectiv- itv changes of dark areas: possible seasonal changes in the opposite sense in bright areas; secular changes in the boundaries of dark areas; recession of the polar cap, the vertical structure, together with spatial and temporal variations, of the gaseous atmosphere and any hazes associated with it; yellow and white clouds; and surface frost patches. These phenomena are dis- cussed in the following paragraphs. In addition, it is important to determine locales where significant seasonal or other variations occur to aid Janding site selection for future missions. Contrast Changes Wave of Darkening. During the Martian spring, the contrast between dark areas and bright areas increases progressively; a 32 Hi. MASURSKY, ET AL, maximum darkening is achieved in late spring or early Martian summer. The contrast. decreases in a manner analogous to the first half of the cycle. In addition to an enhancement in contrast between bright and dark areas, there is some evidence that changes in color also occur. Changes in the polarization of sunlight seattcred from the dark areas also accom- pany the changes in reflectivity. Secular changes in the borders of bright and dark areas probably are related: sometimes these erratic variations change large areas over a period of 2 years, but smaller secular changes over periods of months are possible. Under the best Earth-based resolution, the dark areas resolve into a leopard-skin pattern of small, dark spots, which have characteristic dimensions of a few hundred kilometers and characteristic time scales of about a week for seasonal albedo variations. The integrated albedo change in these spots is responsible for the darkening cycle, In the biological explanation of these seasonal changes, Martian organisms in- habit the dark spots: their Springtinic growth, in response to increased tem- peratures and humidities, causes the darkening events. To test this particular hypothesis, data from the {elevision, infrared radiometry. and infrared spec- troscopy experiments will be compared and cross-correlated. Several nonbiological hypotheses have been proposed as alter- natives, including one in which seasonal changes in wind patterns (caused by meridional circulation or dust. devils) redistribute the particle sizes in the bright and dark areas and produce the albedo changes (Sagan and Pollack, 1969), Here, detailed correlation of dust storms with the darkening cycle is important. In any study of the darkening cycle, it is essential that the lighting conditions be kept constant, or variations due to the scattering phase funetion may be mis- interpreted as intrinsic athedo variations. In studying the scasonal changes, the contrast changes and changes in the reflectivity ofa given area will be measured. (These two parameters are not equivalent because bright areas also may undergo albedo variations.) It is obvious that determinations of reflectivity variations require constant lighting conditions. Even for contrast measurements, there is no guarantee that the two areas in question will have the same phase function; thus, again, constant lighting conditions are desirable. A tentative statement. of this requirement is the constraint that the phase angle, the illumination angle, and the reflection angle be constant within 10 deg over a 90-day period of observation. At the time of arrival of the Mariner Mars 1971 spacecraft, a variety of dark areas between +5 and —-30 deg latitude will be just before, near, or after the maximum in the local darkening eyele (Pocas, 1962), Primarily the second half of the darkenin eyele will be viewed. Low-resolution, Earth-based — studies indicate that absolute contrast and con- trast. changes are greatest in the orange spectral range. Thus, an orange filter on the television camera will be used for such purposes, The amplitude of the contrast changes observed from Barth varies greatly fron dark area to dark area, but some 10 to 30°) is a representative figure. Ft is important to determine the chanye in contrast (with respect, say, to the larve equatorial bright areas) and the change in absolute reflectivity. The intensity levels in pictures taken at different times will be compared and determined, within a few percent. Also, changes in polavization of the reflected light must be determined at least to this accuracy. To accomplish this, the way in which the vidieon char- acteristics change with time must be known to reasonable accuracy. The seasonal darkening is a wave only in the statistical sense, aud some areas deviate markedly from a progressive pattern (Pollack ef af., 1987). The 1971 arrival date will not permit close studies of such deviations, but some useful information may be obtained from the timing of the second half of the darkening cycle, which must be viewed on a global seale, rather than in a few specific regions. Global surveillance also is required to study the apparent brightening of bright areas, especially bright areas in the south- cor o ext fey » o™ at a- ee ee oe MARINER. MANS 197] TV EXPERIMENT 33 ern hemisphere near 40 deg latitude. These areas brighten at the same time that adjacent dark arcas darken. While there are occasional frost or cloud events that also occur over these bright areas during the Martian summer, the changes in question appear to be intriusic to the surface. The use of a blue filter may help to distinguish between these twa pos- sibilities; intrinsic changes in the surface may not show much contrast with a blue filter, but frost or clouds can be expected {to show such contrast. Finally, with global coverage, data derived from the Mariner Mars J971 variable-features in- vestigation can be readily related to the lower-resolution, Farth-based — photo- graphs. Secular changes, particularly variations in the boundaries between bright and dark areas, may be observable for more than the 90 days provided for the mission. Soordinate control points on a small scale will be useful in detecting such nonperiodic events. In general, the smaller dark areas that are Jargely surrounded by bright areas, such as Solis Lacus, exhibit the secular changes. Good spatial and temporal resolution should provide a better under- standing of the relationship between the mechanisms involved in the seasonal and secular variations. Polar Cap and Polar Can Edge. The edge of the southern polar cap, which will have receded considerably by the time of arrival, is of great interest. Observations from earth indicate that islands of frost are left behind during the general recessions of the cap. This has been attriluted to tem- perature or pressure differences in the terrain, or to differences in the prevailing wind velocities with terrain. Local slopes may also play a role as noted in Mariner VIL pictures. The infrared radiometry experiment on Mariner Mars 197] may help to resolve this issue. Also, the tem- peratures of two adjaccut frost-covered areas, one of which loses its covering significantly before the other, will be compared. The albedo of the frost-free areas (i.c., whether they are bright or dark areas) and their altitudes (i.e., whether they are clevations, depressions, or some intermediate category) will be investigated. The Jatter parameter may be obtained from measurements from the ultraviolet spectroscopy, S-band occultation, and infrared spectroscopy experiments. From many biological points of view, the receding polar cap is the most intcrest- ing Martian locale known. Hopefully. the edges of both the northern and the southern polar caps will be photographed. Almospheric Phenomena There are two gencral classes of atimo- spherie phenomena: (1) the gaseous atmo- sphere, and (2) hazes or clouds in the atmosphere. These phenomena are ob- served and measured by the scattering and absorption that they produce on the incident solar radiation. A great deal of interest has been centered on the vertical structure of the atmosphere and haze, which, when observed at different latitudes and as a function of season, will provide important data on the Martian atmospheric processes, perhaps including atmospheric dynamies in the polar regions. Knowledyc of the vertical structure also is important jn determining the physical processes involved in the formation of any haze. Data on the vertical structure ean be derived by viewing the area above the limb of the planet when the atmosphere is viewed against a dark background (sce Young, 1969), Pictures of the terminator can be used to assist in the determination of the structure of any thick hazes that may be observed. As one moves away from the terminator, increasingly higher altitudes are shadowed. so that the bright - ness distribution bevond the terminator can be a sensitive indicator of the structure of the atmosphere. Gaseous Atmosphere. The scattering pro- pertics of the gaseous atmosphere are known, and the absolute wumber densities of molectles can be determined from the brightness profiles. The conversion depends on the composition of the atmosphere ; however, it is expected that the measure- ments from the ultraviolet spectroscopy. S-band occultation. and infrared spectro- scopy experiments will provide some of the needed information. 34 H. MASURSKY, ET AL, Hazes. The limb pictures acquired by Mariner VIL revealed the presence of a haze in the atmosphere a few tens of kilometers above the surface. This haze exhibits spatial variations. in intensity and in altitude, and, reasonably, it also may be expected to be subject to temporal variations. The optical thickness of the observed haze in the vertical direction is estimated to be only a few hundredths (Leovy, 1969) and as such would not be detectable in surface photography except at viewing angles greater than about 60 deg. There also is some evidence for the localized presence of a thicker haze that would impair surface photography. The far-encounter pictures of Mariners VE and VII showed an extensive region of obseura- tion over part of the southern polar cap, and the neav-encounter pictures show an area of diminished contrast at the western edge of the cap. These effects could be the result ofa haze with an appreciable optical thickness. The presence of any haze with a significant optical thickness would. be an important factor to the variable- features investigation of temporal varia- tions, because variations in the haze can simulate or mask changes in both the albedo and the contrast. Seattering from the haze can be separ- ated from that of the gaseous atmosphere because of the unique spectral dependence exhibited hy Rayleigh scattering in the gascous atmosphere, By using successive pictures taken with filters transmitting different spectral passbands, it is possible to distinguish amorg those regions where Rayleigh scattering is predominant, and todetermine the spectral dependence of the haze in the region in which the haze is predominant, The scattering law for any haze is not. known a priori, and it may not be possible to make divect quantitative measurements of the dust ov acrosol densities. Clouds. Although the recent data acquired by Mariners VI and VIL failed toidentify positively any clouds. numerous Karth-based observations have recorded phenomena which seem to possess cloud- like characteristics. Such obscryations indicate that clouds tend to form near the morning terminator and to disappear during the day. By combining measure- ments from the infrared radiometry, ullraviolet: spectroscopy, S-band occulta- tion, and infrared spectroscopy experi- ments, a reasonable understanding of the meteorology of a local point will be pro- vided, and various alternatives for physical processes on Mars will be determined. T'wo-color observations will allow a preliminary separation of clouds into the two basie types observed from Earth: (1) yellow clouds, which are presumably dust stirred up from the surface; and (2) white clouds, which are either water or carbon dioxide condensation products. Both white ant yellow clouds can be expected to have lifetimes ou the order of a day, and the study of their motion will provide informa- tion on circulation of the Martian atmo- sphere, Observations from the infrared spectro- scopy experiment may help to distinguish between water and carbon dioxide clouds, From temperature structure information, obtained from investigations of the carbon dioxide bands, occultation experiments, and determinations of the atmospheric Water-vapor content, saturation conditions near the cloud can be studied. The spectra from this experiment may indicate the presence or absence of such characteristic ive features as the 12-p absorption maxima, Yellow dust clouds are of interest. from a_ strictly meteorological viewpoint, in order to study the mechanism responsible for placing surface particles into sus- pension in the atmosphere. The global wind patterns may be responsible; in this case, dust raising will occur over an extended area. Allernatively, dust devils may be the principal mechanism. Dust raising ata given time may take place in very localized regions, perhaps 0.b to L km across, and the highest resolution would be required to observe them. There is also a special interest in yellow clouds because they represent a possible agent for effecting surface variations, One quantitative model of the seasonal changes invokes the exchange of dust particles by global circulation or by dust devils, ~~ w Om me ~ eo ° ace gag gee ab atten woos a anes, cera ae ee RYE Ea A ete nm RN ee ene ants at 4 MARINER MARS 197] ‘TV EXPERIMENT 35 between dark and bright areas (Sagan removal and deposition of small dust and Pollack, 1969). Phus, darkening and particles, as indicated by the presence of brightening events will be correlated with — dust clouds. eerie. ur > TAO ATE, FO LTE TS ET GS OE TINE STREET . . 3 q 4 * « . > ® a 3 3 3 Y 7F73 y 4 Tce ee fg op geneat torn ramones toc og “a 4 . . - * . “ 4 noe 4 a coe mate ok . pisik | . . . . wee ny BL CU ln mes ak ae Bn I BY sient inion a tin wicks dla a wench bit la tak lee tia Ae ree nee hide ne le areata Re ete ae Ee HG. V4. Par-encounter pictures showing atmospheric and atmosphere-surface effects, Picture shutter times wore: GP34. duly 30. 1969, 07:32 UP: 7F73, August 4.1969. 31:15 UT; 7P76, August 4, 1969, 13:36 UT. Marked changes seem to have oceurred, between the Mariner Vi and VIL fivbys, in the appearance of high northem latitudes. Some of these changes are revealed by & comparison of Frames 634 and 773. which correspond to approximately the same central meridian and distance from Mars. The widespread. diffuse brightening covering much of the nurth polar cap region (point 3) apparently corresponds to the “polar cap hood”? which has been observed from Karth at this Martian season (northern carly autainn). The extent of this hood is smaller in pictures from Mariner Vib than in pictures from Mariner VI. Particularly stuiking are several long light streaks near Nix Olympica (point 6 in Frame 773) and numerous circular features resembling craters, which have bright centers and dark edges. Several of the circular features exhibit one or more concentric circles similar to. but Jess striking than, those near Nix Olympica. Two features of this type forin two of the westernmost points of the classical “W-eloud” (paints and 5). ae f 4- 36 H, MASURSKY, ET AL. ; ; v - . + ; one + ~- + rx : Poa ea, : ze {> Ne ? £ . i 2 : N _} i a] a : t aa i on i : Re : fail j an i Ne. f Tee 5 ~ . [ e i ee en eee 4. . . Fig. 15(a). Composite of polar cap Frames 7N1O to TN20. Effects of automatic gain control are evident near the terminator (right) and at cap edge, Rm NM ee une eA ear fat meg eae me ge vtrol are | MARINER MARS J97] gv EXPERIMENT Fore rarer eerie or gage pte os oe } aay fo poe , fs ag i ; oe, i ‘ a g : se ; ee a, . : ( Me, . t : i 1 i e i 3 i : 7 i f ‘ 7 ? i : i ? : i i 7 i e | j ! x i f ? * 2 | r f fl | : 7 "9 2 j ; fF t 7 é ae s vy r / x f > é i i j f a / / ! y } 5 3 / j ! 3 bx ; ea ? ea Mca, ? : te : ‘ Bereta atin ede 5 37 . 4k . hes aye guia Wh, mA ay . Fic. 15(b). Composite of polar cap Frames TNE) to 7NIY from the wide-angle camera. The effeets of automatic gain control have been partially corrected, but contrast is enhanced. The south pole lies near the paralicl streaks in the lower-right corner of frame TN17. ; ' t ! 1 ' b hoe. t ae = - } ) t 38 IL, MASURSKY, ET AL. Some Implications of Mariners Vl and VIL Because Mariners VI and VII spent a relatively short period of time (especially if we exclude from consideration the far- encounter sequence) in the vicinity of Mars, it was not expected that much new information on time-variable features would be acquired by these missions. Nevertheless, a number of new and relevant phenomena were uncovered (Leighton ef a@l., 1969). Pictures of the details of the forming polar hood (lig. 14) suggest that detailed synoptic observations of these clouds will be of cousiderable interest. Similarly, observations in the W-cloud area of Tharsus-Candor (Fig. 14), combined with the history of past Earth- based observations of the region, mark it as a prime candidate for detailed time- sequence photography. The irregular and serrated nature of the edge of the retreating ERAT SELES IOR TETRA TRA RE ECE, REET IAS 5 ae ‘ : ke, poisise. a Be eae eee ao ii ad Ped > polar cap, as shown by Mariner VI and VIE photography (Fig. 15), promises to reveal in 1971 a high-resolution history of the retreat of the cap toward the pole. Direct evidence of the existence of a high-altitude aerosol haze laver (fig. U6) points to the advantage of observing this phenomenon over a significant time interval. The remarkable absence of craters both large and small in Hellas (lig. 17) suggests some erosion process of major magnitude present there and not in other parts of the Martian surface. Regardless of the nature of the Hellas erosion mechanism, detailed observations of Hellas as a function of time are clearly indicated. The unusual geometry of Nix Olympica (Fig. 14) and its Karth-based record of time raviability make it a candidate for time- sequence photography. It is possible that further reduction and analyses of Mariner ALR re sree pap ay civ DEE EEN ET . en seine ae a neti ak i thes ; a fe Poy Eso ead Bie. 16. Mariner VII limb Frames 7N1, 2, 3, and 5. Note the sharp haze layer adjacent to the limb in Frames 7N1, 3, and 5, and the magnified view (tenfold magnification) in Frame 7N2. The prominent, cratered dark feature in Frame 7N5 is Meridiani Sinus. North is approximately toward the right. me Bruit, s a Lai . neon nee ecu Rrepentans ceceana ge me . — . _. — ee cece mene, meee Hoe nt emer pi nt es me we : pe Pag a . ; i 7 ” To \ Z TT ne ce - / “ i % K } : . Po ae / S ee : me / a f : m 0, / i x : ; : . \ ; a ( ‘ \ = . po yo 7 f \ ‘ o é \ . ~ . of \ a ’ f: \. -= / \ & : . ; _ . * 45 : , =! : — k : 4 : , ” j ~ 7 “ 5 . ! ! = 7 f ; = : i é = . : 3 a“ - a 5 5B ; FR22 Re a, . N30 : . a ha oe Map Fie. 17. Composite of seven Mariner VII pictures showing the cratered dark arca, Hellespontus; the ridged, broken boundary between Hellespontus and Hellas; and tho featureless terrain of the bright. circular ‘“desert.”’ Hellas. Large-scale variations in contrast are suppressed x + . . . woe . : ~ ~ eArTA +. ~ . + by automatic gain control, Lighting conditions are similar to those of Fig. 13. Frames 7N17 to 7N2]. North is approximately toward the top. 3 & E § S } 3 I os i) 4 Lory mo F r red r ae 4 af 4- 40 H. MASURSKY, ET AL. Vi and VII pictures will point to additional time-variable phenomena to he intensively studied during the Mariner Mars 1971 missions. Exobiology: Search for Evidence of Life or of Biologic Habitats What is known of the Martian environ- ment, thus far, has suggested to some that life, if any, operates on a bare subsistence level in a marginally possible habitat, at least as measured by earthly standards. Because the low-resolution (~1 km) tele- vision camera does not reach the scale of biologically characteristic structures on Earth that might be found in the most favorable habitats, it is unlikely that orbital photography can give direct evidence of life on Mars. High-resolu- tion photography, however, could provide evidence of anomalies such as tupheaviness of tree trunks (oriented in the gravity field) or Sun following by leafy forms. The isolated oasis is one of the possible models for a habitat (Lederberg and Sagan, 1962). The subsurface and inte- gvated-disk temperatures of Mars are far below freezing, and most of whatever moisture has been retained by the planct must be in the form of water of hydration and deep permafrost. An oasis would be a locale of thermal activity where the crust is broken and the subsurface warmed sufficiently to release the moisture to the surface. There it is not only available to organisms, but also must dissipate into an arid atmosphere. Ef such oasis sites exist, they are obvious major targets for infrared hydrothermal mapping; they also could contain photographic manifestations such as clouds, volcanos, macro-relief, and related colorations. Another possibility is that Martian tife has evolved a specific adaptation to separate its water acquisition mechanism from the solar flux at the surface and to filter the photochemically destructive ultraviolet. On this model, a Martian “Sant”? would have leaves, encrusted with an ultraviolet filter material (iron oxide or carbonate would serve) and a tough barrier to evaporation. These plants would be joined to the bound-water or ice- harvesting mechanisms below by a deep tap root. A community of different organisms that collectively serve the same functions is also imaginable. Chemically bound water may be tappable by Martian organisms. There is no systematic way of enumerat- ing all possibilities; many other models are conceivable. At most, one of them is likely to survive criticism when Mari- ner Mars 1971 provides ftrther indirect evidence regarding life on Mars. Orbital Constraints To avoid solar occultation (a present constraint on the mission), high-inclination orbits must be used. The maximum southern latitude of the subspaceeraft point occurs in that part of the orbit where the spacecraft nears the longitude of the subsolar point. High Sun is desirable for measuring surface albedo, because prob- loms associated with photometric slope effects can be avoided. Thus, basic observa- tions of ground phenomena will be made when the spacecraft is near the subsolar point (small phase angle). The constraint that a given area be viewed under essentially constant lighting conditions throughout the mission, when combined with the requirement for good temporal resolution (ie. observations of the same avca with successive samplings separated by no more than a few days). severely Lrnits the number of possible orbits. To first order, only harmonic orbital periods P equal to simple fractions of the Martian rotation period, P,, ave acceptable: P= (w/n) Ps, where m and ware small iutegers. A given locale is thus viewed under similar lighting couditions once every mPssm Martian days. ‘To satisfy the time requirements, <4. If P were made equal to Ps, only slightly more than one-half of the planet could be observed throughout the entire mission. By choosing P= (mfr) P;, m 4x, a rota- tion of subspacecraft longitudes in sueces- sive orbits is obtained. For example, if Gain) = 2, we see, in two suceessive orbits, longitudes displaced by 180 deg. However, in this case, some regions would CONOR EE A ARE coer, LN EE RIAA OE Rete mG iN age MARINER MARS 1971 TV EXPERIMENT 4] be viewed very obliquely. An orbital period of P ~ (4/3) P;, which successively views longitudes displaced by 120 deg, overcomes this difficulty and yet is con- sistent with requirements for good temporal coverage of a given area (~ 4 days). Periods of less than 24 hr could entail a complete orbit without passing over Goldstone; therefore, the tape re- corder could not be emptied before the next data acquisition opportunity would gceur, Thus, a period «4/3 P; appears optimal, with the caveat that the period be slightly different so as to compensate for the apparent solar motion. Mission Profile A nominal 32.8-hr orbit for the variable- features mission is shown in Fig. 6; viewing conditions at the beginning and at the end of the nominal 90-day lifetime are indicated. A typical sequence begins a few hours after apoapsis, carly in the mission. After the morning terminator of Mars enters the scan platforim’s field of view, five or six full-disk pictures of the planet are taken by the wide-angle camera at intervals of about L hr. Experiments of opportunity with the narrow-angle camera also may be performed. If possible, these near-apoapsis pictures will be played back before the near-periapsis photo- graphy; this can be accomplished in Jess than 1 hr per frame using a 2-kbps rate and the 85-ft antennas of the Deep Space Network. At the beginning of the mission, the spacecraft. passes local Martian noon (high Sun elevation angle) approximately 1 hr before periapsis passage at an altitude of 5000 to 7000 km. Because the orbit is a * harmonic of the Martian rotation period, the spacecraft will pass over this same region at high Sun every three orbits. By slewi ing the scan platform and taking w ide- angle pictures every 84 see, it is possible to build up overlapping coverage of a large part of each 120-deg region. Experiments of opportunity with the narrow-angle camera would also be performed at this time. The pictures must be stored and subsequently played back. Ifthe spacecraft is over the 2)0-ft antenna (which occurs approximately each third orbit), at least some of the data could he played hack at 16.2 kbps during the 20 to 30 min before periapsis photogray sav. Ordinarily, play- back will occur after periapsis passage. Three or four pictures of the evening terminator and limb will he obtained beginning about 30 min before periapsis passage. About 18 min before periapsis passage, terminator pictures af selected areas previously recorded near Jugh Sun will be obtained by the wide- or narrow- angle cameras. At periapsis passage, three or four vertical wide-angle pictures of the terminator will be taken. It is desirable to play back all stored pictures before the next near-apoapsis photographic se- quence begins, Photography of Phobos and Deimos also will take place at appropriate times during the mission. Because of the apparent solar motion, the above sample photographic sequence will vary into the mission (sec Fig. 6). e.g., the time of taking high-Sun pictures. Typical photographic sequencing “footprints” for this mission are displayed in Fig. 18. Beeause high jwiority is placed on global coverage to observe the seasonal changes, a small sacrifice in resolution is made to achieve this coal. For exiunple, with orbital periapsis at the evening terminator and a posigrade orbit, observa- tions could be made when the spacecraft is nearest the subsolar point with a Hnear resolution degradation of only about a factor of 3 (see Fig. 6). Under these circumstances, the Alartian semidiameter, as seen from the spacecraft, is abont 22 deg, and with the wide-angle camera’s field of view (11 by J4 deg), about 10 overlapping pictures will provide complete coverage of the iuminated disk. Because the maximum number of pictures that can be stored on tape is about 32, a complete set. of pictures from much lower altitudes cannot. be obtained. The remaining pictures could be used for other purposes, ¢.g., complete coverage with a second filter, or concomitant narrow-angle pictures interspersed among the wide-angle pic- tures. ‘To obtain a set of overlapping pictures, the platform must be properly slewed betaveen frames. Ratan eae ERENT IY ES 4 Lees “VERIO LAOQUIND OFFUL-MOILU PIE ODEN pue ssene) punoay WAG TPES TE Fur ous Utd Sunny SSE So ioy Sep ‘2A MON sok Feet me ae TEA terae. 2 if : vi Uae vk i “PARI vi ' t ~ i € g = - : \ ms = > = . gf | a ge 7 a = a ° a 2 be oe ‘ae O%7 EG a a _ QE o eta Q. ' CO ee RE ee ape EMT re iNOCAD VIOKINOS LON 6l aya TWAS am | AVY 6 aLVG HONOY1 Hh ~ 3 grocer oo Tn nnn STII ITE TPA. A ltt yn he ogy. Ny tte vf af % atten ee eect depart meet ig ee tee ae penn yen MARINER MARS 197] pv EXPERIMENT 43 3. Alartian Satellites: Phobos and Deimos An important byproduct of both the fixed- and variable-feature missions is the opportunity to photograph, in fair detail, the satcllites of Mars. Phere are three general views as to their nature—--all speculative: they may be debris left over from the formation of Mars, objects captured from the asteroid belt or else- where in the solar system (they are about the size of the Apollo objects), or, least likely, artificial satcHites of an extinct Martian civilization, as proposed hy Shklovskii. Whichever one of these pos- sibilities is correct, the satellites are of major scientific interest. Apart from their orbital properties, virtually nothing is known about Phobos and Deimos-—the radii are estimated by assuming, rather arbitrarily, an albedo and by deducing radii from their apparent magnitudes. The satceHites are so small that they are well below the limiting size at which hydrostatic equilibrium forms spherical figures for natural objects in the solar system. As a result, they should have asymmetrical shapes, as is known to be the case even for some asteroids con- siderably Jarger in size, Rough calculations show that the pro- posed 12- and 32.8-hy orbits will approach within 6000 to 7000 km of the orbit of Phobos; the 12-hr orbit will approach equally near the orbit of Deimos (although Viewing may involve rotation off sun/ Canopus lock). Such close approaches will occur once each orbit. This gives a line-pair spacing of about 150 m for the narrow- angle camera, or about 75 to 150 lines across the satellites. It would then be possible to compile a photographic atlas of Phobos and of Deimos with more resolution clements in each than the best contemporary Harth-based photographie maps of Mars. For a 12-msee shutter specd, there is no motion smearing due to rotation, even if Phobos and Deimos have rotation periods as short as that of the fastest rotating asteroid, Icarus. In most cases, about 30 narrow-angle pictures near closest approach are adequate for a complete map. lor a rotation period of 2 hr, this corresponds toa picture every few minutes for only 1 hr. The shapes of the range curves, computed by John Freeman of the Jet Propulsion Laboratory, show the minima to be relatively flat over time intervals of } or 2 hr. Continuing observations of these satel- lites could be useful in calibrating the television subsystem (which is particularly Important in order tu accomplish the variable-features investigation), if exten- sive observations of Phohos and Deimos are performed over the entire rotation cycle of these satellites and over 180 deg in phase angles. Very close approaches are not required for calibration, In addition to photographic recon- naissance of Phobos and Deimos. the non- television experiments on Mariner Mars 1971 will be directed at these satellites, As a result, it may be possible to obtain the following information about Phohos and Deimos: their topography. ecometrical figures, periods of rotation. obliquitics. albedos as a function of wavelength and position, polarizations at large phase angles as a function of position. surface temperature distributions. thermal jn- ertias, surface powder packing fractions, and ultraviolet and infrared spectra, Iselipses of the Sun by Mars, as scen from Phobos and Deimos. should be fainly common during the mission. and infrared radiometric observations of the satellites during such eclipses should give additional information on thermal inertias. as well as on surface thermal anomalies. If the range is sufficiently small, perturbations of the orbiters by Phobos and Deimos May five a rehable estimate of the masses of the Martian satellites and therefore of their densities——a possible clue to their origins, Tn a varicty of fundamental respects, observations of Phobos and Deimos pro- vide important contrals for observations of Mars. For example. a serious question in the study of cratering statistics of Mars is the extent to which crosion processes have obliterated craters formed during earlier cratering epochs. One erosion mechanism that has been discussed is 44 If, MASURSKY, ET AL. wind-blown dust. Since Phobos and Deimos very likely have no atmospheres at all, they can have no wind-blown dust. If their ages are comparable to those of Mars, they provide a control impact counter in the absence of wind-blown dust. Another possibility worth investigating is whether the scattered light from Mars is low enough to permit probing the Martian atmosphere by observing occultation by Mars of Phobos and Deimos. Tt is conceivable that the Mariner Mars 1971 missions can convert Phobos and Deimos from objects about which we know virtually nothing into objects about which we know a great deal. V. RELATIONSHIP WITH OTHER JSXPERIMENTS Results from the television experiment will be compared with the results from the other experiments aboard Mariner Mars 1971, with a productive exchange of data, Some of the most interesting interfaces are discussed in the following paragraphs. Some hypotheses of the seasonal darken- ing invoke a relationship with high temperatures and humidities. Two-dimen- sional maps obtained from the infrared radiometry and infrared spectroscopy ex- periments, at the same time and of the same area as the set of overlapping tcle- vision frames, will permit a close examina- tion of biological models of the wave of darkening. Measurements of white clouds obtained from the infrared spectroscopy experiment nay help to distinguish carbon dioxide clouds from water clouds. Observations of clouds by the infrared spectroscopy, S- band occultation, and ultraviolet spectro- scopy experiments may permit determina- tions of their altitudes. Altitude mapping from the infrared spectroscopy, ultraviolet spectroscopy, and the S-band occultation experiments will indicate how albedo is correlated with elevation, over a wide range of latitudes, Temperature maps of the polar cap areas will help to indicate whether areas that become frost-free are cooler or warmer than adjacent regions that retain their frost deposits longer. Determinations of the altitude of the frost-free regions by the ultraviolet spectroscopy, S-band oeculta- tion, and infrared spectroscopy experi- ments also will be made. Studies of the collar near the polar cap edge by the infrared radiometry and infrared spectroscopy experiments will provide data regarding its reality and composition, To check wind-blown dust models of seasonal changes, the meridional tem- perature gradient as determined by the infrared radiometer will be correlated with seasonal changes. ACKNOWLEDGMENTS Although all team members contributed to and reviewed the text of this artiele, (he principal contributors were Jd. MeCauley, fixed features (geology); W. Hartinann (craters); G. de Vaucouleurs and MM. Davies (geadesy/enrto- graphs); OC. Sagan, J, Pollack. anid W. Thompson, “Sagan, Phobos and Deimos; variable features ; and 1. Norris, hardware. 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