Spacecraft of the future could consume themselves to make extra fuel, say researchers in the US. Scientists from three companies-including aerospace firm Lockheed Martin and Thiokol Propulsion, the company that makes boosters for the space shuttle-are studying ways to turn spacecraft parts into a usable fuel. The first to be considered are communications satellites, which are useless once their fuel runs out because they can no longer make the minor positional adjustments-called station keeping-that keep them in their orbital slots. A satellite that uses parts of its own structure as fuel would be lighter at launch, as it would not have to carry so much onboard propellant. This would mean that rocket-launching companies could carry larger payloads into orbit and allow satellites to burn their own body parts to boost themselves into higher orbits.
The research, which is funded by the US Air Force, is being managed by Physical Sciences Incorporated, a technological consultancy based in Andover, Massachusetts. Project leader Prakash Joshi confirms that studies are under way to develop what he calls "dual function structural propellant materials"-but the company declines to elaborate on the nature of the substances under investigation.
However, New Scientist understands that the researchers are studying novel kinds of thermoplastic composite materials which can offer a combination of structural strength during launch and then be chemically converted or burnt off in orbit.
At present, spacecraft like the space shuttle use materials such as aluminium and graphite for their major body parts-for example, boosters and external fuel tanks. But these are, in effect, "dead weight" that requires fuel to be carried aloft. Although the shuttle's solid rocket boosters parachute back to Earth for retrieval and re-use, the huge external tank is simply jettisoned when the craft reaches orbit.
Says Joshi: "The idea is to look at new materials which you could use to build a spacecraft and which could be consumed in orbit when their strength is no longer needed. Most of the strength of the spacecraft is needed during launch because of the G-forces, but once it gets up there you don't need a massive structure to hold the spacecraft together."
If suitable materials can be identified, Joshi's team will develop a prototype component to demonstrate that auto-cannibalism is viable. The next step will be to decide how to incorporate the new materials into a spacecraft.
"It may be that in order to take advantage of this material you will have to design spacecraft a lot differently from the way you do now," Joshi says. Possibilities might include burning off body parts in situ to create thrust in a particular direction. Another method might be to use a central "recycling plant" with mechanical, chemical or solar systems to convert the structures into fuel-although this would carry a weight penalty.
Author: Carl Franklin
New Scientist magazine issue 14 August 1999
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