It's a long road from the inception of a thing
to its realization.
-- Moliere
In addition to its special contributions to science, the Magellan mission has a distinctive place in the current U.S. space program. It is the first planetary spacecraft to be launched by the shuttle, and it is the first of a series of missions resuming planetary exploration since the launch of the Pioneer Venus craft 12 years ago.
Magellan is named after the Portuguese explorer Ferdinand Magellan (see Chapter 6), whose expedition circumnavigated the world in the early 1500s. His journey revealed the vast nature of Earth and the distribution of broad oceans and continents. Similarly, the spacecraft Magellan is expected to provide a global understanding of the poorly known surface of Venus.
Concept studies of a radar-imaging mission to map the Venusian surface were begun by NASA in the early 1970s at JPL. The project was named Venus Orbiting Imaging Radar (VOIR), and science investigators were selected in 1979. However, VOIR was deemed too costly and was canceled in 1982. In October 1983, the Venus mission was reinstated as a NASA budgetary new start and named the Venus Radar Mapper (VRM), a reduced undertaking that eliminated all experiments except the gravity-field experiment and those involving the radar (which included imaging, altimetry, and radiometry). Also, to accommodate a reinstatement proviso that the spacecraft be built for about half the originally estimated cost, VRM used mission-proven technologies and spare components from other flight programs such as Voyager, Galileo, and Ulysses. The major contractors selected for this JPL-managed mission were the Martin Marietta Astronautics Group in Denver, Colorado, for the spacecraft and the Hughes Aircraft Company of El Segundo, California, for the radar sensor. VRM was officially renamed Magellan in 1986.
Thus, with a scaled-down experiment package and with other compromises, such as the use of an elliptical orbit compared with VOIR's circular one, the Venus mission was on track again with a launch planned for May 1988.
The Challenger disaster in 1986 caused another delay. The explosion led to the reevaluation and subsequent cancellation of the Centaur G-Prime booster as cargo on the shuttle. The most powerful upper stage ever designed, Centaur was to have propelled Magellan to Venus. Its explosive liquid-oxygen and liquid-hydrogen propellants, however, were deemed too dangerous to be carried in a manned space vehicle.
The U.S. Air Force's less-powerful Inertial Upper Stage (IUS) replaced Centaur as the booster for Magellan; this required some modification of the spacecraft designs and mission plans. The aluminum Centaur-adapter structure was replaced with a lighter, graphite-epoxy frame for the IUS. A lighter spring mechanism was also used to separate the less-massive IUS from the spacecraft after burnout.
The launch procedure was changed to deploy the solar arrays before ignition of the IUS because the booster's roll-control thrusters were too close to the ends of the solar panels while in their stowed (folded) position. Lastly, rather than subject the entire spacecraft to a repetition of full static tests in the new IUS configuration, a mockup Magellan structure was used. Fidelity was assured by using real components borrowed from a Voyager spacecraft on public display at the National Air and Space Museum in Washington, D.C.
The loss of the Challenger and the 32-month suspension of shuttle missions delayed and reshuffled many planned space activities. The Galileo mission to Jupiter, for one, would have to launch in October 1989, the date initially set for Magellan, or wait another two years for the necessary alignment of planets. The result for Magellan was an early May 1989 launch and the use of a Type-IV trajectory. This meant that the spacecraft would spend 15 months traveling one and a half times around the Sun before arriving at Venus. The original May 1988 launch date would have allowed Magellan to reach Venus in 4 months by traveling less than 180 degrees around the Sun via a Type-I trajectory.
Thus, the $551 million mission (see Table 2-1) and the spacecraft that will soon arrive at Venus are much different than NASA had planned a decade earlier, yet the basic scientific mapping objectives remain unchanged.
Table 2-1. Magellan Costs
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Item $ M
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Spacecraft (without radar) 287
Radar 120
Project cost through launch + 30 days 49
Mission operations/data analysis through 95
end of the Project on 10/29/91
Total 551
Extened mission cycles though 1996 218*
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* Not yet funded.
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Chapter 3 - The Geology of Venus
The Magellan Venus Explorer's Guide
