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

[325] While the Viking team calculated, planned, and debated where to land, the two spacecraft and their launch vehicles were delivered to the Kennedy Space Center. After completion of the prelaunch checkout, the countdown for Viking 1 began on 11 August 1975. At 115 minutes before the planned launch command, a thrust-vector-control valve-essential to launch- vehicle directional control-failed to respond properly when tested, and the countdown was halted while the valve was examined. Technicians found that a slight leak of propellant had caused corrosion. The valve probably would have worked, but the project management was not willing to take chances with a $500-million payload. The launch was rescheduled for 14 August.
Before the faulty valve could he replaced, another problem was discovered on the 13th. A check of the orbiter's batteries showed they were producing only 9 volts instead of the required 37, having been discharged by a rotary switch that had been turned on inadvertently after the first postponement. Even though the problem was quickly traced and the managers were convinced that it was the result of a failure outside the spacecraft, the batteries still required replacement, a process that would require much time. The entire spacecraft had to be removed from the Titan-Centaur launch vehicle and replaced by the second Viking. Jim Martin and Tom Young had been prepared for such a contingency-the second spacecraft had been tested and was also prepared for launch. This dual readiness for liftoff prevented a costly delay.
Countdown was resumed, and the launch was completed without further incident. Viking 1 was on its way at 5:22 pm EDT, 20 August 1975. 15 The shroud was jettisoned, the spacecraft separated from the launch vehicle, and the solar panels deployed. The star Canopus was acquired by the star tracker on the first try. Viking l was off to a good start.
Repairs were quickly made to pad 41, and the second launch vehicle was readied. Batteries replaced and tested, the first spacecraft was mated to the Titan-Centaur. But new troubles were discovered in the orbiter's S-hand radio system during precountdown checkout. When the difficulty could not he solved on the pad, the spacecraft was removed from the launch vehicle for [326] a second time. After replacing part of the S-band hardware, The Viking flight team was ready to try again.
The second launch was a cliff-hanger. The countdown was going smoothly as storm clouds began to gather near the Cape. Seven minutes before the scheduled liftoff, meteorologists at the launch site said that if Viking were not launched within ten minutes the flight would have to he scrubbed because of cloud cover, high winds, and possible lightning. Viking 2 left its pad at 2:39 p.m.. EDT 9 September, just three minutes before the order would have been given to cancel. About five minutes after the Titan and its cargo disappeared into the clouds, an intense rainstorm began and lasted for more than an hour. Eight minutes into the flight, all telemetry from Viking 2 was lost. Six minutes later, the stream of electronic data returned, and the craft went flawlessly on its way to Mars. Jim Martin may generally have discounted luck in the course of Project Viking, but on 9 September 1975 Viking 2 was a lucky spacecraft. 16
The Vikings had begun a journey half way around the sun. For the next 10 months, the landers would be kept in hibernation, with just enough activity to allow the flight team to monitor key systems. When the flight contollers tried to charge the second lander's batteries en route to Mars, the battery charger did not respond to the command. After several days of detailed analyses and tests on the "test lander" at Martin Marietta's Denver factory, the specialists concluded that something inside the battery charger had failed, and they used the backup charger to bring all batteries up to full charge. During November, a complete system checkout indicated that both landers were in excellent condition. Throughout the remainder of the....

The Titan III-Centaur launch vehicle thrusts Viking I upward on 20 August 1975 on its 800-million-kilometer journey from Cape Canaveral, Florida, to a 1976 landing on Mars. The spacecraft was to go into orbit of the planet in mid-1976 and after verification of the landing site, the lander would separate from the orbiter and descend through thin atmosphere to land gently with its scientific instruments and cameras.


[327]....cruise, lander and orbiter science instruments were prepared and calibrated for Mars operations. 17

Jim Martin and Tom Young noted in a postmission journal article that on paper the mission operations strategy appeared sound, but the "complexity of the mission made us duly cautious." NASA had never had to operate four spacecraft (two orbiters and two landers) at one time, and the Viking managers had sought to guarantee success by extensively testing the hardware and exhaustively training the flight team. Ground system tests verified the readiness of computer programs and all the interrelated equipment scattered across the United States. Compatibility tests between the ground system and the spacecraft led to many software modifications to facilitate command signals. A comprehensive simulation system trained the flight team and checked out the readiness of the entire system, while intentionally introduced emergencies tested the ability of men and hardware to adapt to unforeseen circumstances. Martin said time and time again that he did not believe in luck. In this highly complex business, one should rely only on hard work and brains. The Viking teams tested and retested their systems, and the results often meant personnel reassignment, schedule changes, and the modification of operational concepts. 18
Of all the tests conducted during the first half of 1976, the most important was the "A-1 Site Certification Timeline Validation." SAMPD-l, Science Analysis and Mission Planning Directorate test 1, was designed to evaluate the Viking 1 site certification decision process. Participants had agreed beforehand that this would not be a true simulation, since the data from the test would not be run through the computers. Some of the processing equipment was still not ready and, without better information about the landing sites, to simulate photos of those areas would have been difficult. SAMPD-1 would be an intensive review of exactly what data would be available at each step and how that information would be produced and distributed. From this drill, the Landing Site Staff hoped to identify any necessary procedural changes.
Conducted in early February, SAMPD-1 was judged by different parties as a success-or a failure. As mission director, Tom Young was satisfied because the exercise had allowed the flight team to evaluate the certification process and discover its weaknesses. But Gentry Lee, science analysis and mission planning director, looked back on the SAMPD-1 operation as a disaster. Flight team members had repeatedly arrived at certification meetings without knowing why they were there or else had attended them because they had had nothing else to do. After the test, Lee took steps to alleviate the confusion. He asked Norm Crabill, deputy chairman of the Landing Site Staff, to prepare a schedule for all regular meetings of the staff to be held during the actual certification process. Crabill was also called on to devise a procedure that would let all the participants know when Landing Site Staff decisions would cause changes in the flight team's plans. Updating documents, plans, and schedules was a major enterprise, matched only by the need to keep everyone working from the same revised materials.


Table 51 [whole page 328]

Major Training Tests for Planetary Operations


Uplink development exercise (demonstration test 4)
2-15 Dec. 1975
To design primary mission for, Viking 1 for 12 days following touchdown. Also to train for SAMPD and prepare for demonstration tests.
Science Analysis and Mission Planning Directorate (SAMPD)
test 1
8-12 Feb. 1976
To evaluate site certification process.
Continuation of demonstration test 4
22 Feb.-2 Mar. 1976
Simulated events of Viking 1 mission from 52 hrs before separation to 8 days after touchdown, to demonstrate capability to perform all necessary sequences and respond to data gathered.
Demonstration test 5
Demonstration test 4 success obviated test 5.
Demonstration test 6
31 Mar.-4 Apr. 1976
Simulated events on orbiter from 24 hrs before Mars orbit insertion to 4 days after insertion, to test downlink and uplink ptocesses.
Demonstration test 7
7-10 Apr. 1976
Simulated lander and orbiter operations from day 11, to test activities of active science mission following first sampling of Mars's soil.
Demonstralion test 4R
18-22 Apr. 1976
Detailed simulation of mission from 30 hrs before separation to shortly after touchdown, to retest sequences for separation, entry, and landing.
Training test 5
26-29 Apr. 1976
To test landed sequence for 8th Mars day and separation activities, with introduced anomalies.
Training test 3
2-4 May 1976
Simulation to test preseparation and separation activities, with introduced anomalies.
Training test 4
10-11 May 1976
To train for Mars orbit insertion, with introduced anomalies.
Operational readiness test
2-3 June 1976
Final dress rehearsal for MOI of Viking 1.

[329] In all, 40 "action items'' resulted from SAMPD-l, all requiring resolution before Viking 1 reached Mars, but once those actions were taken the actual certification process would proceed more smoothly. 19 Subsequent demonstration and training tests were more successful, with each exercise pointing the way toward readiness for the active science part of the mission. On 2 and 3 June, about two weeks before Viking 1 was to enter orbit of Mars, the last full-dress rehearsal was held without a hitch. The Viking flight team was finished with simulations. It was time for the real thing.