Hard Landings

When your assignment is to put a space probe on another planet, be prepared to sweat.

The first picture taken by Viking 1 on the surface of Mars, July 20, 1976. (NASA)
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Surveyor's braking rocket was so heavy because it had to deliver up to 10,000 pounds of thrust, the cost of counteracting energy rather than absorbing it, as Ranger did. To guarantee that the rocket's thrust travel as precisely through Surveyor's center of gravity as possible, engineers tried to make the rocket's nozzle perfectly symmetrical and aligned with the rocket's center of gravity. "It looked like it ought to be doable," Stoolman remembers, but there was no way to simulate accurately enough to be sure.

Then, at about 25,000 feet above the moon's surface, Surveyor would use small, liquid-fuel rockets to slow to about 8 mph in a vertical descent. The spacecraft would rely on these rockets, called vernier engines, for both control and descent the rest of the trip down. Their control system would use signals from a radar altimeter to measure distance from the surface and a Doppler radar to measure speed. The radars, which used new technology, also caused their share of headaches. And the verniers' development problems were so distressing that in 1964 JPL canceled its contract with Thiokol Chemical's Reaction Motors Division--only to re-award it a short time later, after the company continued working on the engines and made promising advances. With so many problems, says Stoolman, "we were running scared all the time. We didn't take anything for granted."

Technical burdens aside, one unknown loomed larger than any other: the nature of the moon's surface (see "A Smooth Spot in Tranquility," June/July 1989). Faced with uncertainty, the Surveyor teams designed the lander for a range of conditions. To absorb an impact on hard ground the three landing legs were fitted with shock absorbers, the footpads were made of crushable aluminum honeycomb, and three more honeycomb blocks were mounted underneath the craft's spindly frame. If, on the other hand, Surveyor encountered a dust layer several feet thick, as one scientist predicted, the engineers hoped its oversize footpads and wide body might act like snowshoes to keep it from sinking too far.

The Surveyor teams weren't the only ones grappling with unknowns. By this time NASA had been directed to put a man on the moon; Ranger and Surveyor were officially Apollo's advance team. But there were times when the NASA engineers working on Apollo seemed uninterested in Surveyor or even disdainful, a reflection of the rivalry between the space agency's manned and unmanned programs. Late in 1961 a Surveyor team visited NASA's Langley Research Center in Virginia to ask what their spacecraft could do to help Apollo. One Langley engineer responded, "Crash into the moon and smash all to hell." At least then, he added, they would know the surface was solid.

Surveyor engineers may have recalled that comment in April 1964, when a test version of the spacecraft, outfitted with working radars and vernier engines, was suspended from a balloon and lofted 1,500 feet above the New Mexico desert for a test of the landing system. Before the test could begin, a nearby electrical storm triggered the balloon's electronic release mechanism and the test Surveyor fell to the desert floor and broke into pieces.

For JPL, Surveyor's troubles worsened an already dire situation. Ranger 6 had failed that January. The bad news persisted even after Ranger 7 finally triumphed in July: A second Surveyor drop test failed in October because of a series of malfunctions. When engineer Robert Parks took over as project manager of the Surveyor effort, his colleagues at the lab offered condolences. "They thought I had taken on an impossible task," he says.

The delays cost the Surveyor team the moon race. On February 4, 1966, a Soviet soft-lander called Luna 9 alighted on the plains of the moon's Ocean of Storms and radioed back pictures. Luna didn't match Surveyor's technical sophistication, but that didn't lessen the sting at JPL. NASA's own attempt was only four months away.

On June 1, less than three days after a flawless launch, Surveyor 1 reached the vicinity of the moon. In Pasadena it was past 11 p.m., but JPL was alive with activity. Inside the lab's new mission control building, Parks and his team knew that everything in the landing sequence would happen automatically; all they could do was wait. Less than 50 miles above the moon, Surveyor 1's braking rocket fired a 40-second blast, then fell away. To everyone's relief, telemetry showed the lander wasn't tumbling. At 25,000 feet the verniers took over.

A mission commentator called out the diminishing altitude: 1,000 feet, then 500, then 50, then 12--and finally "Touchdown."

In mission control, no one could believe it--well, almost no one. "My feeling," says engineer Gene Giberson, "was, 'Yep, we did it, we did exactly what we said we were going to do.' " Geologist Gene Shoemaker, a Ranger veteran leading one of the Surveyor science teams, recalls having a different reaction: "My God! It landed!

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