April 7, 1961

TENTATIVE MARINER B DESIGN CONCEPTS
FOR USE IN EXPERIMENT PROPOSAL PREPARATION

The following specifications for this mission are the result of a
study conducted a JPL. These specifications are to be used for planning
purposes and do not necessarily represent a final design of the spacecraft.
Two possibilities have been considered. The first consists of a space-
craft with a planetary entry capsule to be separated near Mars. The
design distance of closest approach of the spacecraft is 8,000 kilometers,
at which time the velocity will be 5 kilometers per second in Martian
coordinates. The capsule will land slightly north of the Mars equator,
with descent to be accomplished by ablating materials until approximately
Mach one velocity is reached, and subsequently by parachute. The parachute
descent time is estimated at 10 to 15 minutes. Planetary experiments
can be conducted from the capsule or bus. Data from the capsule will be
relayed to the bus for retransmission to earth. During capsule descent,
and for approximately 30 minutes after landing, the capsule-bus transmission
rate is estimated at 2,000 bits/sec. Following a 23-hour eclipse, com
munications will be reestablished at 20-200 bits/sec for 10 hours. Data
automation storage in the bus is estimated at 2x10! bits with an acceptance
rate into the storage wit of 2.4x10 bits/sec from all experiments. In
the Martian vicinity, communication to earth is estimated at 100-200
bits/sec. This necessitates 10 days of subsequent transmission to empty
the data automation system.

Weight. allocation for experiments on the bus is estimated at 140-180
pounds, exclusive of, power and data handling. Forty to fifty pounds is
estimated for the capsule. Power estimate for irtterplanetary cruising
is 15 watts for all experiments. During planetary encounter, the power
estimate for the bus experiments is 25 watts. Capsule instrumentation
power is estimated at 10 watts for 12 hours subsequent to parachute opening.

The above figures represent the most crucial design parameters. Aban-
donment of the capsule concept, if necessitated by design considerations,
would modify the experimental arrangements. An increase of bus experiment
instrumentation from 140-180 pounds to 240-280 pounds may occur if the
capsule is not feasible. The trajectory would be approximately the same
as in the capsule-bus configuration.

The above information has been included to give the experiment proposer
some idea of the need on his part to seriously consider minimal weight,
power, and communication so that these factors do not unduly influence
the final selection of experiments.