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New Scientist
Later this year, American millionaire Dennis Tito hopes to fly to the International Space Station on a Soyuz rocket, becoming the world’s first space tourist on a $20 million package holiday. But a revolutionary new way of fuelling a space shuttle could one day make such space tourism far cheaper-and even safe enough to fly from civilian airports.
The trick is to harvest liquid oxygen from the atmosphere. The proposed new fuelling system, called Alchemist, would allow a plane the size of a Boeing 777 to take off from a runway with an orbiter on its back. It would fly around in the atmosphere for a few hours, storing away oxygen in liquid form. The oxygen would then be combined with liquid hydrogen and used to blast the space-shuttle-sized orbiter into space.
“Normally, you carry six pounds of liquid oxygen for every pound of hydrogen. When you take off with only hydrogen, you carry only one seventh of the propellant weight,” explains Dana Andrews, chief technology officer at aerospace company Andrews Space & Technology of Segundo, California. Since 90 per cent of a conventional rocket’s take-off weight is fuel, he says, cutting that figure leads to a huge saving.
The company has proposed its novel oxygen-harvesting scheme as part of NASA’s Space Launch Initiative, a program that’s studying emerging technologies for a reusable launch vehicle that is safer and cheaper than the space shuttle.
By doing without liquid oxygen at take-off, the plane’s total weight would be cut almost in half. Better still, because there would be no chance of liquid oxygen coming into contact with liquid hydrogen, the likelihood of an explosion during launch would be considerably reduced. This means the carrier plane and orbiter would be able to take off from a commercial airport-and passengers could sit in comfortable, airliner-style chairs, rather than enduring the rigours of a vertical take-off.
“We feel that this will bring the cost down low enough for space tourism to be common in 15 to 20 years,” predicts Chris Hoeft, a spokesman for Andrews.
The carrier plane would take off from a runway using conventional jet engines powered by standard aviation fuel. At an altitude of about 8000 metres, the combined aircraft and orbiter would cruise around for about three hours, collecting and liquefying air. To do this, air would be diverted from the carrier plane’s jet engines and passed through two heat exchangers-one in the skin of the wing, and another in the plane’s fuselage. The second exchanger would use some liquid hydrogen fuel to further cool the air, which would then be centrifuged to separate out the oxygen (see Diagram).
After the carrier plane had stashed away about 340 tonnes of liquid oxygen-more than doubling the plane’s overall weight-it would switch to rocket mode, using the liquid oxygen and liquid hydrogen to blast toward the edge of the atmosphere. Close to that point, the orbiter would separate and zip into orbit, while the plane would glide Earthwards, later reigniting its standard jet engines before landing. After its mission is complete, the orbiter would re-enter the atmosphere and land like the space shuttle.
NASA has awarded Andrews Space $70,000 to draw up a more detailed plan-but the firm needs about $7 million to develop the idea fully. James Hill of Cerulean Freight, which is designing an alternative launch vehicle, is sceptical. “I’m afraid they’ll probably end up with a net loss,” he says, reasoning that Alchemist’s complicated machinery and long flight time might cancel any energy advantages.
Author: Kurt Kleiner, Toronto
New Scientist issue: 17th February 2001
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