In the summer and fall of 1962, NASA Headquarters planned at least 18 missions in the Ranger series. Some would have imaged the moon's surface to certify potential Apollo landing sites, while others would have had a more purely scientific intent. On 13 December 1963, however, the total shrank to nine, with science missions taking the brunt of the cuts. Ranger itself was partly to blame; all five Rangers flown up to that time had failed, undermining confidence in the program and building support for an early switch to Lunar Orbiter and Surveyor, Ranger's intended successor programs.
The Jet Propulsion Laboratory (JPL) in Pasadena, California, built the Rangers on contract to NASA Headquarters. The probes left Earth atop Atlas rockets with Agena B upper stages (image at top of post). Rangers 1 and 2, Block I spacecraft designed to test spacecraft systems and return data on conditions in space up to 1.1 million kilometers from Earth, weighed a little over 300 kilograms each. Both reached low-Earth orbit, where they became stranded by Agena B failures. Ranger 1 lifted off on 23 August 1961, and burned up in the atmosphere a week later. NASA launched Ranger 2 on 18 November 1961; it burned up just two days later.
Rangers 3 through 5 were Block II spacecraft designed to image the moon during approach and then rough-land a balsa wood-cushioned instrument capsule bearing a battery-powered seismometer. Rangers 3 and 4 weighed about 330 kilograms; Ranger 5 was somewhat heavier (342 kilograms). Ranger 3, launched on 26 January 1962, missed the moon by 36,800 kilometers on 28 January and entered orbit around the Sun. Ranger 4, launched 23 April 1962, lost power 10 hours after launch after its twin tapering solar arrays failed to open. It became the first Ranger to touch the moon, crashing inert on the lunar Farside (the hemisphere turned always away from Earth) on 26 April. Ranger 5 also suffered a power failure shortly after launch on 18 October 1962; it passed about 725 kilometers over the moon on 21 October and entered solar orbit. After the Ranger 5 failure, NASA tasked the RCA Astro Division with reworking the spacecraft's electronics.
Block III Rangers, the next in the series, were meant to radio to Earth images of the lunar surface as they plummeted toward destructive impact. All weighed about 365 kilograms. Ranger 6, the first of the Block III Rangers, left Earth on 30 January 1964. It transmitted signals until it struck the moon's Mare Tranquillitatis - the Sea of Tranquillity - within a few kilometers of its target on 2 February 1964, but its six cameras never switched on. The failure led to an independent review board, new program management, a Congressional investigation, and calls for the program's cancellation.
The first successful Ranger mission was Ranger 7 (launched 28 July 1964), which beamed to Earth 4,316 images of the Mare Nubium-Oceanus Procellarum (Sea of Clouds-Ocean of Storms) borderlands on 31 July 1964. Its last image, taken at an altitude of 519 meters, showed rocks and craters as small as 0.5 meters across. To commemorate Ranger 7's close-up examination of the region, it was named Mare Cognitum (the Known Sea). Ranger 7's success led to calls for the series to be extended beyond Ranger 9.
In December 1964, as part of the Apollo Contingency Planning Study for the NASA Headquarters Office of Manned Space Flight (OMSF) Advanced Manned Missions Office, R. C. Moore of RAND Corporation argued that to "discontinue the [Ranger] series [would be] to lose the opportunity of providing relatively inexpensive support for the far more expensive Surveyor and Apollo projects." He noted that the Surveyor lander was still under development and that the Centaur upper stage intended to launch it toward the moon had been tested three times with only a single success. Ranger and its Atlas-Agena B launcher were, by contrast, "fully developed and tested."
Moore then described possible missions for an extended Ranger program using Block III spacecraft. Examining the craters blasted by the Ranger 6 and 7 impacts might yield information about the moon's surface structure useful to engineers designing Apollo Lunar Module (LM) landing gear, he wrote, noting that the mission had been proposed for Ranger 8 by OMSF and the NASA's Manned Spacecraft Center in Houston. Moore added that rays (light-colored streaks of fine ejecta) from the large craters Tycho and Copernicus had made difficult the geological interpretation of Ranger 7 images of Mare Nubium. A second Ranger mission to the Ranger 7 site might aid geologists, he wrote.
Rangers might also be used to examine failed Surveyor and Apollo LM spacecraft on the lunar surface. "If our experience with other major spacecraft is any indication," Moore wrote, "not all. . .Surveyors and Apollos will be successful. . .It may be imperative to be able to determine what happened to a specific spacecraft after it landed." At $20 million per flight, he added, Ranger would be "a relatively inexpensive way to obtain answers to critical questions involving more expensive spacecraft systems." He acknowledged that this might also be achieved by a Lunar Orbiter, but pointed out that the first mission of that program would not occur for at least 18 months. (Lunar Orbiter 1 left Earth in August 1966, 20 months after Moore completed his report.)
Moore noted that the Lunar Orbiters would focus on the lunar Nearside equatorial region in which most piloted Apollo landings were meant to occur. Ranger missions to sites of interest both inside and outside this "Apollo Zone" would return images four times better than any expected from Lunar Orbiter, he estimated. Sites of interest might include heavily cratered lunar highlands terrain and the interiors of large craters - places too rugged for safe Apollo landings. In addition to providing valuable scientific data, Ranger images of specific sites would aid interpretation of Lunar Orbiter and orbital Apollo images.
Ranger might also be used to observe Earth in support of planetary missions. Moore expressed the hope that "more and more probes will be launched to the planets Venus and Mars," adding that observing Earth "as a planet. . . would provide valuable experience for the interpretation of data transmitted from another planet."
Ranger 8 (launched 17 February 1965) crashed within 15 miles of its target in Mare Tranquillitatis on 20 February 1965, after beaming 7,137 images to Earth. Moore's proposals notwithstanding, the spacecraft was not targeted to image a crater blasted in the moon's surface by a previous Ranger. Ranger 8 revealed that Mare Tranquillitatis closely resembled Ranger 7's Mare Nubium site. Apollo planners decided that Ranger 7 and 8 had confirmed that their Apollo LM design was capable of safe lunar landings, so gave the lunar scientists leave to select the Ranger 9 site. They chose the 70-mile-wide crater Alphonsus, a suspected site of lunar volcanism. The last Ranger left Earth on March 21, 1965, and impacted three days later within four miles of its target near the crater's 3500-foot-high central peak. It beamed 5,814 images to Earth.
Reference:
A Suggestion for Extension of the NASA Ranger Project In Support of Manned Space Flight, Memorandum RM-4353-NASA, R. C. Moore, The RAND Corporation, December 1964.
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