The design also included a pyrotechnically-isolated external high pressure tank with additional helium that could be connected to the main tank prior to the critical Venus orbit insertion burn to ensure maximum thrust from the 445 N thrusters during the SRM firing. The tank contained 133 kg (293 lbm) of purified hydrazine. The actual propulsion system design consisted of a total of 24 monopropellant hydrazine thrusters fed from a single 71 cm (28 in) diameter titanium tank. Final conservative estimates of worst-case side forces resulted in the need for eight 445 N thrusters, two in each quadrant, located out on booms at the maximum radius that the Space Shuttle Orbiter Payload Bay would accommodate (4.4-m or 14.5-ft diameter). The Star 48B, containing 2,014 kg of solid propellant, developed a thrust of ~89,000 Newton (20,000 lbf) shortly after firing therefore, even a 0.5% SRM alignment error could generate side forces of 445 N (100 lbf). In the case of Magellan, the spacecraft design did not lend itself to spinning, so the resulting propulsion system design had to accommodate the challenging control issues with the large Star 48B SRM. In a typical spin mode, any unwanted forces related to SRM or nozzle mis-alignments are cancelled out. Prior to Magellan, all spacecraft SRM firings had involved spinning spacecraft, which made control of the SRM a much easier task. The spacecraft was designed to be three-axis stabilized, including during the firing of the Star 48B solid rocket motor (SRM) used to place it into orbit around Venus. Develop an understanding of the geological structure of the planet, including its density distribution and dynamics.Obtain near-global gravity field data with 700 km resolution and two to three milligals of accuracy.
Obtain a near-global topographic map with 50 km spatial and 100 m vertical resolution.Obtain near-global radar images of the Venusian surface with a resolution equivalent to optical imaging of 1.0 km per line pair.In 1985, the mission was renamed Magellan, in honor of the sixteenth-century Portuguese explorer Ferdinand Magellan, known for his exploration, mapping, and circumnavigation of the Earth. The proposal included a limited focus and a single primary scientific instrument. The VOIR mission was canceled in 1982.Ī simplified radar mission proposal was recommended by the Solar System Exploration Committee, and this one was submitted and accepted as the Venus Radar Mapper program in 1983. They first sought to construct a spacecraft named the Venus Orbiting Imaging Radar (VOIR), but it became clear that the mission would be beyond the budget constraints during the ensuing years. Beginning in the late 1970s, scientists pushed for a radar mapping mission to Venus.
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