Word: verniers
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Dates: during 1960-1969
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...signal from earth it fired its three vernier engines, rose ten feet from the surface and then landed again, eight feet from its original site. It was the first rocket-powered takeoff from the face of the moon...
Testing a Duplicate. Immediately after the short corrective burst from Surveyor's three small vernier rockets, telemetry from the spacecraft showed that helium gas, used to pressurize both the vernier fuel and oxidizer, had begun leaking through a valve that had remained partially open. At the rate that helium was being lost, controllers feared there would not be enough pressure left to operate the engines during the final descent to the moon. The result would be a fatal crash landing...
Others kept working. Using computers, engineers calculated the rate at which the helium leak would decrease as pressure dropped. At Hughes Aircraft (Surveyor's designer and builder) and at a JPL test site, propulsion experts hurriedly put duplicate vernier engines through tests to determine their performance with low helium pressures. Feeding the results into computers, JPL scientists took less than 40 hours to work out a new and complex lunar landing sequence...
Then they put it to the crucial test of action. First they fired Surveyor's vernier engines for 33 seconds to consume more fuel and reduce the craft's landing weight. New instructions were radioed to Surveyor's memory bank and programmed into ground-based computers. As a result, the craft's main retrorocket began firing at a height of 26 miles above the lunar surface, instead of the originally planned 52 miles. It shut off at an altitude of only 4,400 ft., instead of 40,000 ft., after braking Surveyor...
Although Surveyor's mission was generally proceeding according to plan, analysis of its telemetry indicated that it had bounced three times (the first time 35 ft.) after its initial impact on the moon-lifted by its vernier rockets, which had failed to shut down. The unexpectedly rough landing occurred, scientists believed, when the approach radar that controls the rockets became confused by the difference in elevation between the crater bottom and its rim. But the rugged spacecraft quickly proved that it had not been unduly shaken up. Shortly after it landed, it looked down and coolly photographed a nearby...