Home Table of Contents What's New Image Index Copyright ScienceViews Search


On Mars: Exploration of the Red Planet. 1958-1978

 
 
SCIENCE DATA RETURN
 
 
 
[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)

Date

Estimated Cost at Completion

Total Lander Actual Cost

Biology

GCMS

Lander Camera

GCSC

Total Lander

3 June 1970

-

17.8

-

-

360

19

Sept. 1970

13.7

20.6

9.8

3.4

-

-

Aug. 1971

17.0

25.0

12.9

-

401

62

Feb. 1972

34.5

35.0

17.4

-

381

107

July 1972

32.3

35.0

18.1

10.2

420

149

Apr. 1973

29.2

35.4

22.9

10.2

430

286

Mar. 1974

44.2

38.7

23.1

24.1

512

411

July 1974

50.3

39.9

27.4

24.7

543

451

Sept. 1974

55.0

-

23.5

28.1

559

473

Mar. 1975

59.0

41.0

27.5

-

545

545

June 1976

59.5 a

41.2 a

27.3 a

28.1

-

553.2 a

a Actual cost incurred.
GCMS = gas chromatograph-mass spectrometer.
GCSC = guidance, comrol, and sequencing computer