Monday, April 30, 2012

The discarded extension of the Ranger program

Site of the guided impact of Ranger 9, March 24, 1965 (12.82°S, 357.61°E). LROC Narrow Angle Camera (NAC) observation M170579736R, LRO orbit 10272, September 13, 2012; resolution 49.6 cm, angle of incidence 16.1° from 44.64 kilometers. There are images of the impact showing more relief but this most recently released view, under a high sun, balances detail with contrast exposing more detail of the wispy ejecta albedo [NASA/GSFC/Arizona State University].
David S. F. Portree
WIRED/Beyond Apollo

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 December 13, 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 August 23, 1961, and burned up in the atmosphere a week later. NASA launched Ranger 2 on November 18, 1961; it burned up just two days later.

Ranger - Block III - spacecraft diagram [NASA].
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 January 26, 1962, missed the moon by 36,800 kilometers on January 28 and entered orbit around the Sun. Ranger 4, launched April 23, 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 April 26. Ranger 5 also suffered a power failure shortly after launch on October 18, 1962; it passed about 725 kilometers over the moon on October 21 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 January 30, 1964. It transmitted signals until it struck the moon’s Mare Tranquillitatis – the Sea of Tranquility – within a few kilometers of its target on February 2, 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.

Read the full article HERE.

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