Space travel can still be dramatic in 2016, but it's a cakewalk compared to half a century ago. Today marks 50 years since the unmanned Surveyor I probe lifted off from Cape Canaveral, and when it landed in the Oceanus Procellarum on June 2, 1966, it was more than the first US soft landing on the Moon, it was a leap into the unknown. Launched at the height of the Space Race and the depth of the Cold War, the stakes for the first of seven Surveyor missions were incredibly high, as NASA wrestled with untried technologies and questions about the basic nature of the Moon that could make or break any hope of a manned landing.

Surveyor I wasn't the first spacecraft to reach the Moon, nor was it the first to land. Locked in a rivalry to prove who had supremacy in space exploration, the United States and the Soviet Union had been shooting probes at our satellite since 1958 with dozens of failures and a handful of successes as unmanned explorers flew by the Moon, around it, or slammed into it.

The first "soft" landing on the Moon was made by the Soviet Luna 9 four months previous to Surveyor I. On February 3, 1966, Luna 9 used retrorockets to slow itself down over Oceanus Procellarum. Though the main spacecraft crashed into the lunar surface, it released an instrument package that used balloons to cushion itself on impact. The ball-like craft then opened and sent back images of the lunar surface.

The Space Race

Luna 9 is a prime example of the differences between the American and Soviet approaches to space exploration. The Kremlin was interested mainly in the military applications of space technology and its goal in the Space Race was essentially to rack up as many firsts as fast as possible for propaganda purposes, while the Americans were keen on developing full-blown space faring capabilities. This is one reason why Luna 9 only carried a simple camera system and ceased operation within three days of landing.

Landing sites of the Surveyor program(Credit: NASA)

Another factor in the Soviet approach was its emphasis on secrecy. Though it was called Luna "9," this was, in fact, the 12th Soviet landing attempt and the 21st Luna mission. The discrepancy is due to the policy of not acknowledging any Luna mission that failed to leave Earth orbit. In addition, where the Americans released images from its lunar missions live, the Soviets played things closer to the chest and the world's first glimpse of the Luna 9 images came from the Jodrell Bank radio observatory in Britain, which intercepted the translunar transmissions and deduced that the Soviets were using commercial fax technology.

Into the unknown

Though Surveyor I came in second in the race to land on the Moon, it was in many respects more significant. Its purpose was to act as a vanguard for the manned Apollo landings and the information that it sent back is credited as the reason why Apollo XI landed in 1969 instead of 1970 – and that it landed at all.

The ironic thing about Surveyor I is that no one thought it had any chance of succeeding. Of the seven Surveyor landers, NASA expected to lose the first four. This isn't surprising, since the previous Ranger project to take close-up pictures of the Moon by crashing camera-equipped impactor probes into it only succeeded on the seventh try.

It's easy to forget that many things we now know about about astronautics, space engineering, and the Moon itself were still major unknowns in 1966. We take it for granted that the craters and lava plains on the Moon are caused mainly by meteor impacts, but even in the early 1960s the question of whether they might be due to volcanoes had yet to answered.

In fact, scientists weren't even sure that the Moon had a surface. A major concern was that the Moon might be covered with a fine dust, like very light, powdery snow. The fear was that this dust might be so deep that astronauts would need to wear snowshoes or a spacecraft might vanish like a stone dropped in a pond. Sir Arthur C. Clarke actually wrote a Hugo Award-winning novel called A Fall of Moondust, which envisioned a future lunar colony where tourists are taken on boat excursions across seas of dust.

This problem was taken so seriously that NASA designed a series of lunar rovers that used Archimedean screws, snowcat treads, and even undulating, worm-like bodies with which to navigate lunar dust bowls. Even the Luna 9 landing left this issue in doubt, because it may have come down on a rock outcropping or simply floated on the surface like a buoy.

There were many other questions that Surveyor I had to answer. Could the Atlas/Centaur booster rocket handle a direct Earth-Moon launch? Could the on-board systems of Surveyor carry out the mid-course correction so it wouldn't just fly by the Moon? Could the new Deep Space Network track and communicate with the probe? What would the effects of space and the lunar environment be? Could the best technology available withstand the temperatures and radiation?

Of equal importance was the question of whether there was an area near the lunar equator where an Apollo Lunar Module could safely touch down. If there was a solid surface, how solid was it? What was its chemical composition? Was it strewn with boulders or smooth? Surveyor would provide the first direct answer to these questions. But the key objective was getting to the Moon. If that could be pulled off, the rest was money for old rope.

Surveyor I

Managed by the Jet Propulsion Laboratory (JPL) in Pasadena, California, Surveyor I was designed and built by the Hughes Aircraft Company in El Segundo. The 292 kg (644 lb) spacecraft stood about 3 m (10 ft) high. Since it wasn't expected to survive the first landing attempt, it was the simplest of the Surveyors, but all shared the tripod construction of thin-walled aluminum tubing and interconnecting braces that carried the power, communications, propulsion, flight controls, and payload.

Surveyor I preflight(Credit: NASA)

On top there was a mast with the solar panels to generate 85 watts of electricity during the day (around 14 Earth days) to charge the silver-zinc batteries, and below were three folding legs equipped with shock absorbers and special footpads made of crushable aluminum honeycombs. When extended, the legs reached out 4.3 m (14 ft). Communications were provided by a high-gain antenna and two omnidirectional conical antennae hooked to a pair of transceivers.

Of particular importance was shielding the spacecraft against the extreme lunar temperatures, which vary by hundreds of degrees between day and night. Therefore, Surveyor I was equipped with a coating of heat-reflecting white paint, and two insulated compartments with electric heaters for the electronics. Propulsion was provided by a solid-fuel retrorocket for braking, cold nitrogen gas thrusters for attitude control and throttleable vernier rocket engines running monomethyl hydrazine hydrate fuel and MON-10 oxidizer for touchdown, while navigation was based on a pair of sensors for sighting on the Sun and the star Canopus.

The very important eye of the spacecraft was the vidicon television camera, which was used to send back the first live color television images from the Moon. It's purpose was to show the structure of the lunar surface as well as the local topography. The vidicon tube was fixed to the top of the tripod while a mirror arrangement fed images to the lens and filter assembly. Photometric targets on the spacecraft provided calibration. The camera arrangement not only provided stability, but also allowed it to take stereo images for 3D analysis.

Flight to the Moon

Surveyor I lifted off from Launch Complex 36A at Cape Canaveral, Florida on May 30, 1966. Instead of going into Earth orbit and then lunar orbit as the Apollo missions did, this was a direct surface to surface flight taking around 65 hours. The landing zone in Oceanus Procellarum was chosen from images sent back by the Ranger impactor probes because they appeared to be typical of the lunar maria.

To the delight of mission control, the launch was successful and Surveyor deployed itself and carried out its midcourse correction without a hitch. Given that NASA didn't have much hope for a landing, the ability of the spacecraft to function, communicate, and stay on course already made the mission a success.

Rubble seen from Surveyor I(Credit: NASA)

On June 2, at an altitude of 75.3 km (47 mi) and a velocity of 9,403 km/h (5,843 mph), a radar altimeter ignited the solid-fuel retrorocket, which fired for 40 seconds. When this was jettisoned, Surveyor was 11 km (6.8 mi) above the surface and traveling at roughly 400 km/h (249 mph). Under radar control, the vernier engines fired and continued to guide the probe down under radar control. At a height of 3.4 m (11.1 ft), the engines cut off and Surveyor I fell the rest of the way under ⅙ Earth gravity.

The time was 11:17 am EST and the spot was about 100 km north of Flamsteed Crater and about 950 km from the Luna 9 landing site. Under live network television coverage, mission control cheered as Surveyor I touched down on target, on time, and continued to function. It didn't crash, wasn't swallowed by dust, didn't shut down, and didn't vanish into a ravine or tumble down a hill.

This was not only the first US lunar landing, but the first American landing on any extraterrestrial body, and the first fully-controlled powered landing on the Moon.

Live from the Moon

After 40 minutes of system checks, Surveyor sent back its first of 10,338 television pictures that it would take until night fell on June 14. At this point the solar panels no longer functioned and battery power was reserved for keeping the electronics warm. The first images showed one of the landing pads, which had scuffed the lunar regolith on landing to reveal the subsoil. Pebbles up to in inch in diameter could be seen, but none of the ultrafine dust that was feared. In addition, Surveyor took temperature readings and used its radar to study the bearing strength of the lunar surface. From all this, it was soon clear that Apollo was go to land.

Surveyor I television camera(Credit: NASA)

Surveyor achieved another first on July 6 when sunrise reactivated it. It continued taking images, reaching a total of 11,240, before battery failure brought the television transmissions to an end on July 13. However, the probe continued to return telemetry until January 7, 1967, when it went completely silent.

History's most successful technology demonstrator?

According to NASA, the success of Surveyor I put the Apollo program a year ahead of schedule. Over the next 18 months, the US would send six more Surveyor probes to the Moon – this time with scientific instruments to study the chemical composition of the satellite. Magnets would be used to seek out iron-bearing minerals, a robotic arm would scoop the soil, and an alpha backscatter instrument would identify the elements in the soil.

Surveyor III was visited by the crew of Apollo XII(Credit: NASA)

Surveyor III would be visited by the crew of Apollo XII, who would salvage some of its parts to take back to Earth for study. It also made the first unintentional lift off from the Moon when its landing engine failed to shut down. The first controlled lift off was conducted by Surveyor VI, which flew a total of 8 feet. Surveyor II crashed due to a landing engine malfunction and Surveyor IV went silent within three minutes of landing due to a possible explosion.

In the end, the Surveyor program was so successful that Surveyor VII was dedicated to pure science. When it set down near Tycho Crater on January 10, 1968, it carried out extensive surface tests to learn more about lunar geology. In addition, it carried a radar reflector, which was a precursor to the ones left behind by the Apollo mission and are still used to carefully plot the distance between the Earth and Moon by measuring the travel time of lasers fired from the Earth.

But it was Surveyor I that was the real pathfinder. A technology demonstrator that was never thought of as more than a way to try out the engineering before the "real" landing, it did more than surprise its builders by reaching the Moon safely. It also turned that Moon from a giant question mark into a real world where humans could set foot and where machines could work. The significant steps taken by Surveyor are what made Neil Armstrong's "giant leap for mankind" possible.

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