The Space Siren.(X-33)(Brief Article)

The Delta Clipper was a squat little rocket shaped like an inverted ice-cream cone. It never did much. One day in June 1995, out on the White Sands missile range in New Mexico, it rose slowly on a plume of exhaust to a modest height of 2,800 feet, hovered for a moment and settled itself gently back down on the desert floor. Although McDonnell Douglas engineers had cobbled the rocket together for a few tens of millions of dollars, NASA rejected it the following year in favor of the X-33, a far more technologically ambitious project. By the time NASA gave up on the X-33--the project was canceled earlier this month-- it had cost NASA and its contractor, Lockheed Martin, more than a billion dollars.

The failure of the X-33 underscores just how difficult it is to do what Flash Gordon did years ago on television: get from the ground to outer space and back again without a fuss. How cool would Flash have been if he had had to strap on a fuel tank the size of an office building before takeoff? That's what NASA does with the space shuttle. For the first 60 miles it rides piggyback on a 500,000-gallon tank, which is then jettisoned into the ocean. The practice of using expendable parts is more than uncool, it's expensive: it's partly why each shuttle flight costs several hundred million dollars.

The exorbitant cost of reaching Earth's orbit has much to do with why space exploration is currently so unfashionable. The one big manned space project, the International Space Station, is derided for costing so much and accomplishing so little. But much of its $100 billion price tag goes to ferrying parts and people to orbit. (When finished, the station will weigh about 1 million pounds; each pound costs about $8,000 to put into orbit.) The same goes for the estimated $400 billion it would cost to send astronauts to Mars. The Red Planet may be a quarter-billion miles away, but the toughest and most expensive part of the trip is the first 250 miles.

Gravity is the culprit. A spaceship zipping around the solar system is always being pulled this way by the sun and that way by planets nearby. But as long as it doesn't get too close to any one heavenly body, it can fire its rocket engines briefly and coast the rest of the way. A ship on Earth has no such luxury. The force of gravity pulls it too strongly downward. As the rocket climbs, however, gravity loosens its grip. Once the rocket gets a few hundred miles high, it doesn't take much more oomph to escape Earth's orbit altogether.

Sounds easy, until you try to do it in a single bound. The obstacle here is the rocket equation: the bigger the payload, the more fuel you need to fling a rocket into orbit. Fuel, of course, weighs quite a bit itself, and it requires a heavy tank to hold it. That adds even more weight, which in turn requires more fuel and so on. By the time you reach the end of this calculation, you're facing two choices: you can strap on a huge fuel tank, or you can build a ship that is so light and efficient that it beats the rocket equation.

Beating the equation has ...