The Jupiter IRBM was combined with an upper-stage assembly (a solid-rocket cluster similar to that used on Redstone-Explorer series) for lunar flights. This launching vehicle, called Juno II, can send a Pioneer payload weighing about 13 pounds to the vicinity of the Moon. The Juno II was also used to launch Earth satellites, including a 100-foot inflatable sphere.
A growing interest in space exploration in the late 1950's led to the desire for launch vehicles able to lift increasingly larger scientific payloads. The four stage Jupiter C (sometimes called Juno I) used to launch Explorer I had minimum payload lifting capabilities.In fact, Explorer I weighed slightly less than 31 pounds.
Juno II was a modified Jupiter IRBM with the same upper stages as Juno I. Huntsville's Juno II was part of America 's effor to increase payload lifting capabilities. It was developed by Dr. Wernher von Braun and the rocket team at Redstone Arsenal in Huntsville, Alabama. Between December 1958 and April 1961, the Juno II launched space probes Pioneer III and IV, as well as Explorer satellites VII, VIII and XI.
In the early years of space flight development, the carryover from weapon system programs was the Nation's chief set of assets in astronautics. Generally, a large amount of money was saved by taking space flight hardware from advanced points on the production lines of ballistic missile hardware wherever possible. The Explorer, Thor-Able, and Juno II programs have made substantial use of existing missile hardware.
The first "National Space Vehicle Program" was presented to the National Aeronautics and Space Council on 28 January 1959. The report was critical of the current launch vehicles -- Vanguard, Jupiter C, Juno II, and Thor-Able -- calling them hurriedly assembled, not very reliable, and lacking growth potential to meet future needs.
Among other achievements, a Juno II successfully launched a Pioneer IV satellite on March 3,1959, and an Explorer VII satellite on October 13, 1959. Pioneer IV was a joint project of the Army Ballistic Missile Agency in Huntsville and the Jet Propulsion Laboratory in California. It passed within 37,000 miles of the Moon before going into permanent solar orbit. Explorer VII, with a total weight of 91.5 pounds, carried a scientific package for detecting micro-meteors, measuring the Earth 's radiation balance, and conducting other experiments.
Responsibility for Juno II passed from the Army to the Marshall Center when the Center was activated on July 1, 1960. On November 3, 1960, a Juno II sent Explorer VIII into a 1,000-mile deep orbit within the ionosphere.
Explorer VIII was significant in Marshall's history since the Center was involved in the mission in at least three different ways. First, the Center had responsibility for the Juno stage of the vehicle. Second, it had responsibility for conducting the launch from the Launch Operations Directorate at Cape Canaveral. Finally, Marshall shared responsibility with Goddard Space Flight Center for designing, preparing, and testing the satellite.
Juno II had not proved particularly useful. Other launch vehicles later replaced the Juno II as the primary launcher for the Explorer satellite series. On April 27 the Explorer Xl satellite, containing a unique gamma ray telescope, was launched by a Juno II rocket. The spacecraft was referred to as the S-15 astronomy satellite and was developed by the Massachusetts Institute of Technology. This was the last successful firing of the Juno II, which was "retired" following a 2 1/2 year period of service.
In Juno III, the solid propellant rockets in the upper stages were slightly larger. Juno III was not built.
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