Some early space projects never get a lot of love. The two-man Gemini missions are one example. Were it not for a second project working at the same time in the pre-Apollo days, the manned landings on the moon would have been flown with problematic assumptions.

Project Apollo was in the midst of gathering important missing data required for a manned lunar landing by 1964. What were the best places to land? How can we test our precision of placing something in lunar orbit? How would radar work? How sturdy was the lunar surface? How would the automatic systems for lunar landing work?

To quickly answer that dilemma, NASA initiated three lunar reconnaissance unmanned projects in the early 1960s. The Ranger series came first. Its three probe variations were mostly unsuccessful either from launch or design, until the last three delivered useful close-ups (as in, right up into vaporizing on impact) photos of several lunar areas.

The five Lunar Orbiter missions all successfully launched in the mid-1960s, successfully orbiting and making extensive maps of virtually all of the lunar surface.

The third project was Surveyor. It’s goal: Soft-land on the moon, testing radar guidance along the way; verify the lunar surface was firm enough for supporting a Lunar Module; make photo reconnaissance of prospective landing sites.

Of the three unmanned lunar reconnaissance projects, Surveyor was clearly the risky one. While the Russians managed to soft-land a probe first in January 1966, gaining a new first (first soft-landing on any planetary body, first surface pictures from said body), the Americans held the clear momentum to a manned lunar landing with many, many other firsts through Gemini (first rendezvous of two manned vehicles, first docking, new records for space endurance), with no clear riposte by the Soviet manned mission project.

Not that Surveyor’s success or failure would’ve stopped Apollo landings, if Chris Kraft had his way.

November 22

Christopher C. Kraft, Jr., MSC’s Assistant Director for Flight Operations, outlined results of recent studies of the problems associated with lunar landing. The programs studied were Surveyor, Lunar Orbiter, deployment of probes on a simulated manned lunar landing mission, deployment of probes during lunar orbit on an unmanned mission, and deployment of landing aids during the manned lunar landing mission.
The studies supported the conclusion that it was still desirable to have an earth launch window of several days to give launch opportunity flexibility. For this purpose, it would be necessary to have a group of longitudinally spaced landing areas available. However, if there were a particular advantage, such as site certification, in being limited to one area and, consequently, one launch opportunity per month, this was considered to be acceptable. At least one launch opportunity per month would be required. Therefore, the certified area would have to be within the area available from performance consideration. This might mean a night launch, which was confirmed as feasible.

Although the manned lunar landing mission ought not to depend upon a successful Surveyor program, information for Apollo as well as general scientific information should be expected from the program. The concept was not supported that probes were a necessary prerequisite to a lunar landing nor was the idea of a separate probe mission approved. If the Surveyor program failed to provide evidence of the suitability of at least one area and if the consensus favored gathering additional information from probes, the feasibility of carrying probes on the actual lunar landing mission should be fully considered, together with the development of aids to real-time assessment.

Memorandum, Christopher C. Kraft, Jr., MSC, to Manager of Special Design Efforts, “Problems associated with lunar landing,” November 22, 1965.

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A Surveyor mockup. Note the retrorocket nozzle. The large rocket would be jettisoned prior to landing. (NASA)

Surveyor was a modestly simple and lightweight three-legged lander operated by the Jet Propulsion Laboratory and built by Hughes Aircraft. Surveyors were so comparably light, in fact, that all of them were hurled at the moon by translunar direct-ascent (no earth orbits), and by an Atlas rocket with the new and problematic Centaur upper stage.

Surveyor’s lightweight design was a compromise between objective and function. Atlas rockets were plentiful from Air Force surplus, as they were being taken off the American nuclear defense line in favor of other intercontinental ballistic missiles such as the Titan II. NASA had gotten a lot of practice in making the Atlas increasingly reliable by the time this probes flew, increasing their likelihood of survival to fulfill their mission. Nevertheless, the newer Atlas-Centaur combination didn’t have a superior payload capacity. The rocket would be called to push the very limits of its performance to get the landers into a lunar trajectory.

Surveyor was effectively a triangular frame with legs, with a few cameras, a robotic arm, two large solar panels with a couple of batteries and three small engines for final descent, all attached to a large retrorocket. It weighed only around 2,100 pounds (952.5 kg).

Terminal Descent (Emphasis on “terminal”)

The Atlas-Centaur of 1965 really wasn’t as refined as its modern counterpart. As noted before, the Atlas would launch the probe on a direct-ascent, with the Centaur pushing the probe as fast as it could, and on a lunar collision course.

Yep. Collision course. Surveyor would not orbit the moon, but use a Ranger spacecraft trajectory to their specific destination. The spacecraft could make a few course corrections along the way. Then, picking up speed as it enters lunar influence, the fun begins.

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Terminal descent is essentially a controlled free-fall to the moon’s surface. The spacecraft oriented its retrorocket motor around 40 minutes before impact. When radar senses that Surveyor is around 60 miles high, the retrorocket slows the spacecraft from a vaporizing 6100 miles per hour to about 240 MPH at an altitude of 4.8 miles high.

Surveyor’s landing radar kicked in after the retrorocket motor is jettisoned. Three vernier engines ignite to slow the spacecraft down to under 4 MPH, cutting off when about 14 feet high, letting the probe drop from there.

A few Surveyors bounced a bit after its verniers cut off a little too early, but generally the spacecraft were quite sturdy and set down where desired.

Surveyor’s central objective was to simply confirm that the moon’s surface was not composed of a sea of thick dust. The first to land, Surveyor 1, took a photo of one of its landing pads in the Ocean of Storms to confirm that lunar soil would be firm enough for a Lunar Module.

Of course, scientists were eager to study the photos, which revealed interesting soil that compacted like wet beach sand.

Surveyor_1_Foot_Pad

Surveyor 2 didn’t make it to its target of Sinus Medii. On its final descent, one of its three vernier engines didn’t light, and the probe tumbled to its doom.

Surveyor 3 landed in another area in the Ocean of Storms. This one was equipped with a small robotic arm and dug around a little bit to verify soil consistencies. While it lasted only a couple of weeks, from April 17 to May 3, 1967, this probe’s story was not quite over.

Surveyor 4‘s failure seemed to suggest that Sinus Medii was cursed, with a second attempt to land there after Surveyor 2. On entering terminal descent, all contact ceased with the probe. It’s believed the solid-fuel retrorocket blew up.

JPL moved on and successfully landed Surveyor 5 in the Sea of Tranquility. This probe carried an alpha-scattering surface analyzer to measure the type of elements found in lunar soil.

The curse of Sinus Medii was broken with Surveyor 6. Like Surveyor 5, it also carried that alpha-scattering doohickey for element measurements. For kicks and giggles, JPL reactivated the vernier engines for a short takeoff from the lunar surface. Number six kept working after the short jaunt.

Surveyor 7, the last of the series, was the most adventurous of all, landing on the rim of the crater Tycho.

None of the Surveyors had a lot of staying power. Their electrical power was maintained by solar panels and a few batteries. When the lunar night arrived, a period of 14 days, almost none of the probes could fully activate again.

Surveyor foretold the fate of later space landers. Electrical power is used to heat the electronics and battery. If power is constrained (by darkness or dust on the solar panels), insufficient heating in the extreme cold of night will cause the electronics to fail and/or the batteries to fail. Even as the probe’s solar panels returned to light, the electronics were too frozen to respond to ground commands or had no energy that would energize anything. Plenty of Mars probes in the later decades would meet similar ends, but JPL would make them remarkably more durable (one of the two Mars Expedition Rovers, built for 3 months, is still going after 12 years).

With the last Surveyor landing in January 1968 came a noticeable quiet in space missions. Apollo had suffered a blow with the Fire and everyone was rallying back to make the lunar landing goal. By Apollo 7’s launch in October, the role of the Surveyors were all but forgotten.

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Pete Conrad with Surveyor 3, working on removing the camera. Between the accidental damage to 12’s surface TV camera, forgetting some color film canisters on the surface, and Bean getting beaned by a camera on splashdown, it’s a wonder this camera made it home. (NASA)

But Surveyor would be granted an important cameo role with the second manned lunar landing, Apollo 12. The Lunar Module Intrepid, flown by astronaut Pete Conrad, demonstrated the first pinpoint lunar landing, placing itself about 600 feet away. Concerns about sandblasting the probe with the LM’s descent exhaust were justified enough. On inspection of the probe by Conrad and LM Pilot Alan Bean, the area facing the LM were actually cleaned a bit of lunar dust which had electrostatically deposited over the probe over the two years since it landed.

The crew took one of the probe’s cameras as a memento and for lunar exposure analysis. You can see the camera yourself at the National Air and Space Museum in Washington, DC.

Surveyor 3 became the first (and so far, only) space probe that rested on another world that has been visited by humans. (No, Mark Watney’s or Gallagher’s adventures don’t count.)

Sources:

ATLAS CENTAUR LV-3C DEVELOPMENT HISTORY by Ed Kyle, from Space Launch Report

Apollo Expeditions to the Moon (NASA)