[249] The goal of obtaining the
greatest amount of scientific information possible from the
Martian surface was the major influence on the design and
structure of the lander. During 1975 and 1976, Mars and Earth
would be at their maximum separation distance, about 380 million
kilometers. Since the distance would vary during the mission and
since the length of relay opportunities would also vary, several
data transmission links were built into the lander equipment for
direct communications with Earth (1000, 500, and 250 bits per
second were available at a single transmitter output of 20 watts).
A second communications link, UHF through the orbiter, was
functionally redundant with the direct link. The orbiter relay had
three transmitter power levels (l, 10, and 30 watts) and two data
rates (4 and 16 kilobits). Since available communication time was
severely limited by the power available, typical communication
periods would be about 1 hour for the direct link transmitters and
20 minutes for the relay link transmitters. With these link times,
data rates, and power output, the rate of scientific data returned
to Earth would be about l million bits per day for the direct link
and 20 million for the relay link. Since the relay link was the
more efficient from an energy standpoint, the mission planners
would use the orbiter link for the majority of the mission's
activities.
Several electronic tricks could be played
with the data transmitted (telemetered) to Earth. Because of the
short transmission times, "housekeeping" engineering data would be
telemetered in real time. Much of the scientific data would be
sent on a delayed schedule, having been stored on the tape
recorder. Bits of immediate data and delayed data could be
electronically interleaved. Although this combination of
information cut in half the amount of data that could be returned,
it did guarantee the return of important scientific and
engineering data during the crucial communication periods.
Furthermore, each instrument was constructed to convert its
scientific information into a digital code. The imaging system
would produce large amounts of digital information, but the
biology instrument and the gas chromatograph-mass spectrometer
would send much lower volumes of data. With the exception of the
imaging system, the lander instruments could automatically
communicate with the guidance, control, and sequencing computer
when their storage capacities were full. At that time, the data
would be dumped into bulk storage. Imaging-data storage or
[250] direct transmission, however, had to be preplanned
because of the very large amounts of digital information.
Considerable technical sophistication was
required to execute the scientific experiments, digitize the
information collected, store the data, manipulate it, and transmit
it to Earth on cue. This technological complexity and
sophistication had a direct dollar equation: developing such a
complicated machine in a small package against a specific deadline
required a large budget. The world in which NASA operated,
however, was full of budget restrictions.
The stringent post-Apollo fiscal scene
forced the space agency's managers to work hard and be tough with
their personnel and their contractors. Legislators who favored
tighter federal budgets argued that such activity was a natural
part of NASA's job, but a decade earlier many of these same
senators and representatives had willingly appropriated extra
dollars when....
[251]....Apollo managers needed them to
solve the problems associated with winning the race to the moon.
Post-space race hardware was also expensive. and the Mars landing
was a complicated project. The Viking managers were committed to
accomplishing their mission in a scientifically valid manner and
within a reasonable budget, but more dollars-and the spirit of the
Apollo era-would have made it easier. Ingenuity and good
management would have to substitute for extra
appropriations.
Management's warnings about costs began to
sound like a broken record to many of the scientists in the Mars
venture; but, like it or not, scientists had to think about money
as much as about science. In the fall of 1973, the total project
cost had been estimated at $830 million. During the spring and
summer of 1974, that figure grew substantially, and despite
additional parings the estimated cost at completion reached $930
million by the fall of 1974. That amount, however, did not include
the extra dollars the biology instrument ($7 million) and the gas
chromatograph-mass spectrometer ($4 million) would demand from
fall 1974 to spring 1975. These two instruments long occupied
prominent places on Jim Martin's Top Ten Problems list.
Table 43
Cost History of Viking Lander
and Selected Subsystems (in millions)
