Ranger program

• 1. Introduction

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  The Ranger program was a series of uncrewed United States space missions in the 1960s, built for one purpose. Its goal was to take the first close-up pictures of the surface of the Moon. Each Ranger spacecraft was designed for a one-way trip. It would photograph the lunar surface as it approached and transmit every frame back to Earth. The pictures would keep coming until the spacecraft hit the Moon and was destroyed. That design leaves a spacecraft with no second chance and no return journey. It also leaves engineers with a brutal question. What happens when the mission depends on everything working perfectly in the final minutes, and almost nothing works at all? This documentary follows the program from its first launches to its last. It asks why the early flights went so badly, how the cameras were built to work until the very end, and what the pictures finally revealed.

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• 2. Shoot and Hope

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  At one point, the program carried a blunt nickname: "shoot and hope". The label was earned. The first six flights in the series all failed, one after another, each in its own way. Pressure followed the failures. Congress opened an investigation into what it called "problems of management" at two places, NASA Headquarters and the Jet Propulsion Laboratory, usually shortened to JPL. The agencies were reorganized twice. James D. Burke had served as program manager for the first five spacecraft. When all five missions had failed, Harris Schurmeier was assigned as project manager. Ranger 6 then failed as well. The turnaround came in July 1964, when Ranger 7 successfully returned images. Two more successful missions followed it. Yet the program had never been meant to be a gamble, because its designers had planned it carefully from the start, in stages.

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• 3. Three Blocks

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  Planning began in 1959, and the plan split Ranger into three distinct phases that engineers called blocks. Each block had its own mission objectives and a more advanced spacecraft than the one before. JPL's mission designers scheduled several launches within every block. The idea was to gain as much engineering experience and scientific value as possible, and to make sure at least one flight succeeded. Block 1 held two spacecraft, launched into Earth orbit in 1961. Ranger 1 left the ground on the 23rd of August 1961, and Ranger 2 followed on the 18th of November 1961. Neither was meant to reach the Moon. They were tests of the Atlas-Agena launch vehicle and the spacecraft equipment. Problems with an early version of the rocket left both craft in short-lived, low orbits. There they could not stabilize themselves, collect solar power, or last for long. The design did not go to waste. In 1962, JPL reused the Ranger 1 and 2 design for two probes bound for Venus. Mariner 1 failed, and Mariner 2 succeeded.

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• 4. Misses and Mysteries

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  Three spacecraft headed for the Moon in 1962 as Block 2, and none of them delivered science. Ranger 3 launched on the 26th of January 1962, Ranger 4 on the 23rd of April 1962, and Ranger 5 on the 18th of October 1962. Each carried a TV camera and a radiation detector. Each also carried a seismometer in a separate capsule, slowed by a rocket motor and packed to survive a gentle landing. The whole craft weighed 331 kg. The three flights proved that the Atlas/Agena B rocket could perform well and that the spacecraft design was sound. Unfortunately, they never proved both on the same attempt. Ranger 3 had trouble with the rocket and the spacecraft, missed the Moon by about 36,800 km, and has orbited the Sun ever since. Ranger 4 had a perfect launch, yet the spacecraft was completely disabled. Even so, the team tracked its seismometer capsule to an impact just out of sight on the lunar far side, which validated the communications and navigation system. Ranger 5 also missed the Moon and was disabled. Near the end of this block, investigators found a possible culprit for some failures. A type of diode flown on earlier missions produced problematic flakes of gold plating in the conditions of space.

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• 5. Six Cameras

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  The Block 3 spacecraft each carried six cameras, split into two self-contained channels. The F channel, for full, had two cameras: a wide-angle A-camera and a narrow-angle B-camera. The P channel, for partial, had four cameras. P1 and P2 were narrow-angle, and P3 and P4 were wide-angle. The cameras were basically the same design, differing in exposure times, fields of view, lenses, and scan rates. Each channel had its own power supplies, timers, and transmitters, so one channel could keep working if the other did not. The timing of the last frames shows how close to the ground the cameras kept shooting. The final F-channel picture was taken 2.5 to 5 seconds before impact, from an altitude of about 5 km. The last P-channel picture came 0.2 to 0.4 seconds before impact, from about 600 m up. The resulting images beat the best Earth-based views by a factor of 1000. Leonard R Malling led the design and construction of the cameras. Their preamplifiers relied on a small vacuum-tube device called a nuvistor.

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• 6. Seven Reaches the Moon

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  On the 30th of January 1964, Ranger 6 flew a flawless course to the Moon. Then an accident in flight disabled its television system, and it could take no pictures. The next three Rangers carried a redesigned television system and were completely successful. Ranger 7 launched on the 28th of July 1964 and hit the Moon on the 31st of July 1964 at 13:25:49 UT. It photographed its way down to a lunar plain south of the crater Copernicus, soon named Mare Cognitum. More than 4,300 pictures from six cameras reached waiting scientists and engineers. The images showed that impact craters dominate the Moon's surface, even on plains that look smooth and empty from Earth. Great craters were marked by smaller ones, and those by tinier pockmarks, down to the smallest size anyone could make out, about 50 cm. The light-colored streaks that radiate from Copernicus and a few other large craters were also explained. They turned out to be chains and nets of small craters and blasted debris from the original impacts.

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• 7. Eight and Nine

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  Ranger 8 launched on the 17th of February 1965 and swept an oblique course over the south of Oceanus Procellarum and Mare Nubium. It crashed on the 20th of February 1965 at 09:57:37 UT in Mare Tranquillitatis, the Sea of Tranquility. That spot lies about 70 km from where Apollo 11 would land 4½ years later. Ranger 8 took more than 7,000 images. They covered a wider area than Ranger 7's pictures and reinforced its conclusions. Ranger 9 launched on the 21st of March 1965 and came down on the 24th of March 1965 at 14:08:20 UT. Its target was Alphonsus, a crater 90 km across. Its 5,800 images were nested concentrically and made use of very low-angle sunlight. They strongly confirmed the picture of craters upon craters across gently rolling terrain. Block 3 had four launches in 1964-65, and Ranger 9 was the last. Research, development, launch, and support for Rangers 1 through 9 together cost approximately $170 million.

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