<P> Following the unsuccessful Atlas - Able Pioneer probes, NASA's Jet Propulsion Laboratory embarked upon an unmanned spacecraft development program whose modular design could be used to support both lunar and interplanetary exploration missions . The interplanetary versions were known as Mariners; lunar versions were Rangers . JPL envisioned three versions of the Ranger lunar probes: Block I prototypes, which would carry various radiation detectors in test flights to a very high Earth orbit that came nowhere near the Moon; Block II, which would try to accomplish the first Moon landing by hard landing a seismometer package; and Block III, which would crash onto the lunar surface without any braking rockets while taking very high resolution wide - area photographs of the Moon during their descent . </P> <P> The Ranger 1 and 2 Block I missions were virtually identical . Spacecraft experiments included a Lyman - alpha telescope, a rubidium - vapor magnetometer, electrostatic analyzers, medium - energy - range particle detectors, two triple coincidence telescopes, a cosmic - ray integrating ionization chamber, cosmic dust detectors, and scintillation counters . The goal was to place these Block I spacecraft in a very high Earth orbit with an apogee of 110,000 kilometres (68,000 mi) and a perigee of 60,000 kilometres (37,000 mi). </P> <P> From that vantage point, scientists could make direct measurements of the magnetosphere over a period of many months while engineers perfected new methods to routinely track and communicate with spacecraft over such large distances . Such practice was deemed vital to be assured of capturing high - bandwidth television transmissions from the Moon during a one - shot fifteen - minute time window in subsequent Block II and Block III lunar descents . Both Block I missions suffered failures of the new Agena upper stage and never left low Earth parking orbit after launch; both burned up upon reentry after only a few days . </P> <P> The first attempts to perform a Moon landing took place in 1962 during the Rangers 3, 4 and 5 missions flown by the United States . All three Block II missions basic vehicles were 3.1 m high and consisted of a lunar capsule covered with a balsa wood impact - limiter, 650 mm in diameter, a mono - propellant mid-course motor, a retrorocket with a thrust of 5,050 pounds - force (22.5 kN), and a gold - and chrome - plated hexagonal base 1.5 m in diameter . This lander (code - named Tonto) was designed to provide impact cushioning using an exterior blanket of crushable balsa wood and an interior filled with incompressible liquid freon . A 42 kg (56 pounds) 30 - centimetre - diameter (0.98 ft) metal payload sphere floated and was free to rotate in a liquid freon reservoir contained in the landing sphere . </P>

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