section_path: Early U.S. uncrewed lunar missions (1958–1965)/Pioneer missions
section_name: Pioneer missions
paragraph_text: Pioneer missions
  
  Three different designs of Pioneer lunar probes were flown on three different modified ICBMs. Those flown on the Thor booster modified with an Able upper stage carried an infrared image scanning television system with a resolution of 1 milliradian to study the Moon's surface, an ionization chamber to measure radiation in space, a diaphragm/microphone assembly to detect micrometeorites, a magnetometer, and temperature-variable resistors to monitor spacecraft internal thermal conditions. The first, a mission managed by the United States Air Force, exploded during launch; all subsequent Pioneer lunar flights had NASA as the lead management organization. The next two returned to Earth and burned up upon reentry into the atmosphere after achieved maximum altitudes of around 114,000 kilometres (71,000 mi) and 1,530 kilometres (950 mi) respectively, far short of the roughly 400,000 kilometres (250,000 mi) required to reach the vicinity of the Moon.
  
  NASA then collaborated with the United States Army 's Ballistic Missile Agency to fly two extremely small cone-shaped probes on the Juno ICBM, carrying only photocells which would be triggered by the light of the Moon and a lunar radiation environment experiment using a Geiger-Müller tube detector. The first of these reached an altitude of only around 100,000 kilometres (62,000 mi), gathering data that established the presence of the Van Allen radiation belts before reentering Earth's atmosphere. The second passed by the Moon at a distance of more than 60,000 kilometres (37,000 mi), twice as far as planned and too far away to trigger either of the on-board scientific instruments, yet still becoming the first U.S. spacecraft to reach a solar orbit.
  
  The final Pioneer lunar probe design consisted of four " paddlewheel " solar panels extending from a one-meter diameter spherical spin-stabilized spacecraft body equipped to take images of the lunar surface with a television-like system, estimate the Moon's mass and topography of the poles, record the distribution and velocity of micrometeorites, study radiation, measure magnetic fields, detect low frequency electromagnetic waves in space and use a sophisticated integrated propulsion system for maneuvering and orbit insertion as well. None of the four spacecraft built in this series of probes survived launch on its Atlas ICBM outfitted with an Able upper stage.
  
  Following the unsuccessful Atlas-Able Pioneer probes, NASA's Jet Propulsion Laboratory embarked upon an uncrewed 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.