Mars: History of Antacids
The milestone launch of NASA's latest Mars mission--called Spirit-- provides the impetus to revisit the remarkable journey of the earliest martian missions. Excerpts from the lively debates that took place prior to the 1976 Viking missions give immediacy and perspective on both the rewards and challenges that the Red Planet offers. In this and forthcoming issues, Astrobiology Magazine is pleased to commemorate the descriptions offered in the words of then mission contemporaries. NASA historians have compiled these notes in their five-hundred page edition of: On Mars: Exploration of the Red Planet. 1958-1978 (NASA HQ SP-4212).
The Problems List
Project Manager Jim Martin began the Viking Top Ten Problems list in the spring of 1970 to give visibility to problems that could possibly affect the launch dates.
|The robotic arm of the Viking 2 Lander extends to collect a sample of soil for analysis. Click to enlarge.
Viking project directive no. 7, issued 4 October 1971, codified the concept: "It is the policy of the Viking Project Office that major problems will be clearly identified and immediately receive special management attention by the establishment of Top Ten problems list."
To qualify for this dubious distinction, the problem had to be one that seriously affected "the successful attainment of established scientific and/or technical requirements, and/or the meeting of critical project milestones, and/or the compliance with project fiscal constraints."
Anyone associated with the Viking project could identify a potential priority problem by defining the exact nature of the difficulty and forming a plan and schedule for solving it. When Martin made an addition to his list, a person in the appropriate organization was charged with solving the problem, and someone in the Viking Project Office monitored his progress. Weekly status reports were datafaxed from the field to Langley.
At Martin Marietta, William G. Purdy, vice president and general manager of the Denver Division-through Albert J. Kullas and later Walter Lowrie, his project directors-sent weekly status bulletins on the lander's top problems, since that system seemed to have the greatest number of difficult components and subsystems.
In the spring of 1972, Martin told Cortright he hoped the supervisors of employees who had one of their tasks assigned to the top 10 list would not be penalized. Martin, not wanting a stigma attached to identification of a problem, was concerned that at Martin Marietta assignment of a problem might "automatically be considered as a mark of poor performance" when promotions or raises were given. Generally, the nature of the crucial problems was so complex that punishing one individual would not solve the problem.
As with the gas chromatograph-mass spectrometer and the biology instrument, the novelty of the technological task was often the source of the trouble. Some problems seemed to stay on the manager's worry list forever. Others made repeat performances.
The first flight-model computer was delivered to Martin Marietta in April 1974, nine months late according to the original schedule.
Faith, Testing Fate
Continuous monitoring of the subcontractor's troubles was rewarded, however, in late 1974 when the computers were finally ready for delivery. On 15 January, Jim Martin received the following message from Walt Lowrie at Martin Marietta:
"Oh ye of little faith-We gave birth to the last computer today, I don't know how you feel on the subject but it would appear to me that this top ten has now died of old age.
Seriously-although the path has been extremely tortuous I really feel we now have an excellent computer on Viking."
Martin removed the lander computer from his list of major problems. Thus it went, step by step-problems identified and then solved. At this stage in Viking's existence, there was very little glamor, just long hours, hard work, and an occasional antacid.
Deorbit-entry-landing thermal simulation tests, conducted on a component level, duplicated the effects of entering the Martian atmosphere-pressure increase, entry heating, and the post-landing cooldown.
Components were placed in the vacuum test chamber at 1/760 of an Earth atmosphere, heated to a temperature of 149°C, and held there for 530 seconds. Chamber pressure was then raised to 5/760 of an Earth atmosphere with cooled nitrogen gas, to provide an atmospheric temperature of -101°C. In this manner, the lander's passage through the Martian atmosphere with the attendant heating and cooling was duplicated. The change of 250°C represented the wide range of temperatures that the lander would be exposed to on Mars. Such extremes were part of the reason the engineering of the lander had been such a complicated task.
For all components, the most critical period would be the 15 to 20 minutes after landing, since by that time all equipment would be operating and the entry heat buildup would not have had time to dissipate.
Lightning Strikes Twice
In consultation with the Science Steering Group, the test engineers chose argon for the chamber atmosphere during the cold extreme, because preliminary data from the Soviet Mars probes had indicated that as much as 30 percent of the planet's atmosphere might be composed of this rare gas. Since argon promotes electrical corona and arcing in electronic components, the test teams were to determine whether there would be any adverse effects on lander subassemblies if the concentration of argon was that high.
|The guidance, control, and sequencing computer was the Viking lander's brain. Magnetic wires as fine as human hair are inserted into the computer at Honeywell Aerospace, Saint Petersbury, Florida. In testing, the HDC-402 computer, part of the lander's computer, looks like pages of a book. Credit: NASA History Office
Whereas the mass spectrometer went through the end-to-end functional and operational exercise, the biology instrument did not. The biology instruments were delivered too late for proper testing. By the time the hardware became available, limited time, money, and manpower argued against the thorough test.
Martin told Klein: "We have neither the dollars to extend the test nor the people to analyze the data." Other aspects of the biologists' plans for testing were likewise impossible.
"....your request for lander/biology tests with transmitters/antennae in real operational modes is also difficult to accommodate. As you know, this test would require use of an anechoic chamber (very expensive) or moving the entire lander to an outdoor location to avoid RF reflections (also expensive).
We made a fundamental decision in 1973/1974 that the lander [electromagnetic compatibility] test program had to proceed without a real biology instrument because such an instrument did not exist until much too late. Instead, we have relied upon the positive results of a rigorous EMC test on the instrument at TRW. In today's dollar limited environment, the dollars to plan, set up, and conduct another radiated EMC test for biology are prohibitive. We must rely on analysis and instrument level test experience."
To questions about the adequacy of the functional testing of the hardware on the proof-test capsule lander in Martin Marietta's thermal vacuum chamber and the biological operation of the experiments, Cal Broome told Martin on 30 June 1975, less than two months before liftoff. "The current planning assumes that the testing already accomplished is adequate, i.e., the combination of Biology [performance verification] at the lander level (instrument 103) and soil biology at the instrument level (instrument 102 and 103) is adequate to provide assurance of proper operation on Mars."
The minimum time required for an entire end-to-end electrical and pneumatic checkout of a biology instrument was one month on a round-the-clock schedule. Only abbreviated functional tests could be performed.
Viking lander capsule l arrived at the Cape on 4 January 1975, and engineers made a detailed inspection and subjected the capsule and lander to a series of verification tests, which included compatibility checks between the S-band radios and the Deep Space Network. Up to this point, the flight lander and orbiter had never been physically or electrically in direct contact, having been assembled over 1600 kilometers apart.
A lightning bolt that struck the Explosive Safe Area Building caused momentary excitement. Electrical charges from the strike induced currents that damaged two pressure transducers on the orbiter propulsion module S/N-005. After a quick review, the Viking managers decided not to fly this unit.
Viking orbiter l, and Viking lander capsule 1 were mated for the first time on 8 March.
Related Web Pages
Evidence for Snow on Mars - and Perhaps an Abode for Life?
Mars Odyssey web site (with new images)
Mars by Stories
Impact Crater Landing Sites for the 2003 Mars Exploration Rovers
Mars Exploration Rover Homepage
2003 Mars Exploration Rover Mission