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Water Rockets Are Go

by Duncan Graham-Rowe
London - Dec 4, 2000
There's a new way to fire spacecraft into orbit -- a giant spurt of air and water. Amateur rocketeer Scott Taylor's Hydro Pneumatic Accelerator (Hypacc) should be capable of launching objects as big as the space shuttle into orbit without using huge amounts of rocket fuel. Hypacc will instead use the immense pressure of water at depth to provide the necessary initial lift, says Taylor.

"I'm not a rocket scientist and I know there must be thousands of wackos out there all pushing their ideas," Taylor told New Scientist. "But I'm just trying to establish if there's anything to this idea." So far, the reaction has been fairly positive, he says.

In Taylor's scheme, the spacecraft (see Diagram,) sits at the bottom of a very long silo that is almost entirely submerged in the sea and acts like the barrel of the gun. Beneath this, separated by a valve, is a chamber filled with compressed air.

Opening a vent equalises the pressure above and below the valve, allowing it to be released. The chamber is open-bottomed so water rushes in from below and discharges up the barrel. "The rising volume of water provides a constant force and pressure onto the compressed air, which propels the shuttle capsule," explains Taylor.

The air expands rapidly as it tries to equalise with atmospheric pressure, pushing the rocket ahead of it. Water rushing up the barrel increases the thrust.

The final exit speed at the mouth of the barrel depends upon the diameter and length. A 10-metre-wide barrel 1 kilometre long would be capable of launching a mass of 10,000 tonnes, the equivalent of five space shuttles. The force of the air, says Taylor, would enable the vehicle to exit the barrel at speeds in excess of 1000 kilometres an hour.

But Barry Moss, a space launch expert at Cranfield University has his doubts. "Besides being a major civil engineering project, this could only ever launch very small payloads," he says. When factors like friction and air resistance are taken into account, he doesn't believe there will be enough thrust.

Taylor says that although the speed is nowhere near the 29,000 kilometres per hour escape velocity required, it does mean that the craft would be travelling at immense speeds when it reaches sea level -- at which point the on-board rockets are fired.

This would be a considerable advantage over an entirely rocket-based launch. For example, only 1 per cent of an Ariane 5 rocket's mass is its payload. Most of the rest is fuel and 60 per cent of this is in the boosters, which are jettisoned anyway.

This article appeared in the December 2 issue of New Scientist New Scientist. Copyright 2000 - All rights reserved. The material on this page is provided by New Scientist and may not be published, broadcast, rewritten or redistributed without written authorization from New Scientist.

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