Space: Surveyor 5 Is Alive And on the Moon

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Back came new moon-surface pictures. In came data that would reveal the composition of the lunar soil. Ad mirable scientific achievements but, for scientific drama, the most exciting accomplishment of Surveyor 5 last week was making it to the moon at all.

The spacecraft's 65-hour trip began well. Blasting off from Cape Kennedy, Surveyor was aimed so precisely that without correction it could have hit the moon within 26 miles of its intended landing site—one of the most accurate launches achieved by the U.S. space program. But controllers at Pasadena's Jet Propulsion Laboratory, aiming for perfection, ordered a delicate midcourse maneuver to place Surveyor directly on target. It was then that the entire mission came close to disaster.

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.

Three times the JPL controllers ordered Surveyor's verniers to fire, hoping to jar the sticky valve shut. The leakage slowed but did not stop. Within an hour, helium pressure had dropped from 5,000 lbs. to 3,000 lbs. per sq. in. Dejectedly, some JPL scientists suggested that it would be best to fire Surveyor's retrorocket immediately, placing the craft in high earth orbit. It would be preferable to have a live spacecraft in orbit, they argued, than a dead one on the surface of the moon.

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's 6,000-m.p.h. approach speed to only 67 m.p.h., instead of 350 m.p.h.

This strategy reduced the burden on the verniers, which then had to fire only 106 sees, to stabilize the craft and slow it to a safe 8.1-m.p.h. landing. The margin was perilously close. Data analyzed after the touchdown showed that helium pressure was down to 556 lbs. per sq. in.—just 6 lbs. more than the minimum pressure required to operate the engines.