Takes Jolts in Stride
The Surveyor spacecraft, not yet ready to fly, already is learning to land – and under conditions equivalent to those expected to be found on the moon.
Since nobody has ever been on the moon’s surface, to man’s knowledge anyway, Surveyor is being given the worst of it in the tests designed to verify the design concept of the spacecraft’s landing gear. It is being dropped on to “moon rocks,” into “moon dust,” and slammed in to a simulated lunar surface on one, two and three legs with the impact down slope, up slope and on a side slope.
Significantly, Surveyor or rather a full-scale prototype space frame laden with dummy components, has passed a dozen tests to date with nothing more than aching “feet” for all its rough landings.
How do you create a lunar environment, particularly since no one has been there? It wasn’t easy, but available scientific knowledge and HAC’s engineering ingenuity were enough to provide a reasonable facsimile of what can be expected on the moon.
One of the greatest problems to overcome was that the moon’s gravitational pull is only one-sixth that on earth. To make the tests realistic, it was necessary to develop a device which would reduce the spacecraft’s weight by five-sixths, yet leave its total mass unchanged. That is, the device must be relatively massless, yet provide a lifting force which remains constant and vertical regardless of the vehicle’s horizontal or vertical motion.
In order to provide that part of the device which produces the constant lifting force independent of vertical motion, a technique used in aircraft drop testing to simulate wing lift was chosen. Two towering pneumatic cylinders provide just the right amount of weight reduction without changing the Surveyor’s mass. The device is then operated in conjunction with a special pulley system to simulate the moon’s gravity.
Irwin Baker, head of the Structures Section, Engineering Mechanics and Preliminary Design Department, Space Systems Division, designed the special pulley system which has a unique feature that maintains the constant vertical force even when the spacecraft is moved laterally.
Smooth or Rough
The simulated lunar surface can be made just as smooth or miserably rough as the need demands. For example, blocks of wood simulate “moon rocks.” The angle of the “lunar surface” can be varied to provide different angles for the spacecraft prototype to land on.
In addition, the horizontal and vertical velocity of impact can be controlled and varied so that almost every conceivable way of landing can be tested before Surveyor makes its actual landing on the real moon.
To obtain data on the rigid body behavior of the spacecraft and landing loads imposed on the spaceframe, the spacecraft is instrumented with a multitude of accelerometers and strain gauges. Oscillographs and tapes record the information from the instruments. Additional information is obtained from high-speed motion picture camera coverage.
Have the rugged tests proved anything? Most significantly they have proved that Ralph Dietrick, project engineer in charge of the landing gear design, was correct in his pre-test analysis.
Using a high-speed digital computer, Mr. Deitrick made an extensive study of the rigid body behavior of spacecraft under various lunar landing conditions. To date, the drop tests have shown good correlation with his original analysis.
Designed Test Site
Dick Harvuot, in charge of the High Temperature Structures Test Laboratory, at the Rodeo Rd. facility, where the Surveyor drop test facility also is located, designed and supervised construction of the entire test site.
It’s apparent he doesn’t think the moon’s surface is a bed of roses. But as is the case with most American space projects, realistic testing before launch has resulted in successful missions.
Regardless of what Surveyor finds on the moon, it’s unlikely that landing will be any more difficult that its prototype is now experiencing on Rodeo Rd.