But it doesn't have to be so expensive, says Jay Penn of The Aerospace Corporation in El Segundo, California, which provides engineering research support for the US Department of Defense's space programme. "There is no fundamental technological reason why you can't achieve space tourism," he says. "We think we can get the price down to around $15,000 a passenger."
To gauge the potential market, Penn and his colleague Charles Lindley used a 1995 survey that asked people how much they would be willing to pay for a ticket into space. From this they estimated that a price tag of around $15,000 a ticket would pull in about a million passengers a year. They then worked out how to bring the price per flight down to this level.
Penn and Lindley found that the cheapest and quickest way to get lots of people into space and back would be to develop a two-stage shuttle system. The first stage resembles a short, fat rocket with wings. This takes a smaller winged rocket to the edge of space, where it fires up its own motors to push it into Earth orbit. The first stage glides back down to Earth to be refuelled for another launch. Meanwhile, the second stage docks with an orbiting space station, unloads its passengers, and collects previous passengers from the space station for the return trip.
In a forthcoming paper in the journal Acta Astronautica, Penn and Lindley say the reusable system will allow the number of flights to be stepped up dramatically to around 9500 a year, compared with the current 10 or so shuttle launches. The fleet and infrastructure would take about seven years to develop, and could start to turn in a profit after only six years of flights (see Chart).
To make this viable, the rockets would need to work reliably for hundreds of flights with very little maintenance. This means ensuring that they are kept well within their design limits- unlike the shuttle's engines, which are sometimes run at 109 per cent of the power they were designed to withstand. This would slash the number of ground engineers from the thousands needed by the shuttle, to a few dozen.
Another way to save money is to abandon liquid hydrogen as a fuel and use kerosene instead. Because the density of liquid hydrogen is very low, rockets need huge volumes of it to get them into orbit. This in turn means building vast tanks that are expensive to make and run because they have to be pressurised and operate at ultra-cold temperatures. Kerosene is much denser, so the tanks can be made a lot smaller. It can also be stored at room temperature and is far cheaper, at around 15 cents per kilogram instead of $6 per kilogram for hydrogen.
Written by IAN SAMPLE
New Scientist issue: 2nd November 2002
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