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Move Over, Space Shuttle
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17908 |
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Section : |
NATURAL SCIENCE
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| Issue
Date : |
3 / 1990 |
2,495 Words |
| Author
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Walter B. Hendrickson, Jr.
Walter B. Hendrickson, Jr., is a veteran science writer with a
focus on space technology. |
On October 18, 1989, the inter-planetary spacecraft Galileo was launched from space shuttle Atlantis. Though its destination is Jupiter, its initial target was Venus. Accelerated by that planet's gravity, Galileo is now heading back to Earth before shooting off to Jupiter for arrival in December 1995.
The trip has some scientists worried that the Sun's intense radiation near Venus may damage Galileo's sensitive high-gain antenna. Others note that when the craft returns to orbit the Earth, there is a small but real risk that it could miss its orbital window and crash, spraying radioactive plutonium from its two power plants into our atmosphere.
Why such an odd trajectory? The reason for the interplanetary acrobatics is economy: the space shuttle's payload capacity was simply too small to hold a large enough booster to carry the 5,870-pound probe straight to Jupiter. Galileo was originally designed to be carried on a direct course in 1986 by a liquid-fueled Centaur booster, but after the space program safety evaluation following the Challenger accident, the Centaur was judged unsafe for shuttle applications; Galileo's new 32,500-pound booster uses lower-performance solid fuel, requiring the boost termed VEEGA - the Venus-Earth-Earth Gravity Assist - to makeup the difference.
Other projects in the works continue to push the limits of the shuttle's capability. The spacecraft Cassini, tentatively scheduled to launch in 1996, orbit Saturn, and drop probes into its atmosphere, weighs 11,500 pounds - 64,000 pounds with its upper-stage booster. Other projects are well underway that will weigh even more.
With a growing need for greater launch capability to accommodate increasingly demanding science missions, NASA is exploring other possibilities. One solution: Modify the developed and flight-proven shuttle hardware to assemble an unmanned launch system; or more simply, replace the crew-carrying orbiter with an unmanned cargo carrier.
The Shuttle-C Strategy
The current space shuttle places about 230,000 pounds into a low Earth orbit about 200 miles high. The trouble is that only 65,000 pounds of this is actual payload. The remainder includes the aerodynamic surfaces (wings and tail), life support system, heat-shield tiles, and other things needed to keep the crew alive and return them safely to
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