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 for years been a siren song for rocket engineers. Back in the early 1970s George Mueller, the head of the Apollo moon-shot program, had high hopes for the space shuttle, but reaching orbit in one go never made it past the concept stage. Twenty years later private firms took a turn at beating the equation. It started when several communications firms laid ambitious plans to launch networks of dozens of satellites, each requiring a rocket ride to low-Earth orbit. Mueller came out of retirement to join Kistler Aerospace, where he developed a two-stage rocket in which the first stage, rather than being lost over the ocean, was to float down to Earth by parachute. Michael Kelly, head of Kelly Space and Technology, tested a ship that was to be dragged into the air by an airplane before scooting up to orbit on its own steam. Former NASA scientist and Mars enthusiast Bob Zubrin joined Pioneer Spaceplane and began designing a winged single-stage-to-orbit ship. Gary Hudson, head of Rotary Rocket, devised a peculiar rocket called the Roton that was to reach orbit without any auxiliary stages; on its way down, a helicopter propeller would unfold, and the rocket would float back down to Earth like a whirligig. Before any of these plans came to fruition, the grandiose satellite networks went belly up and demand for satellite launchers drooped. The private rocket ventures either disbanded or suffered indefinite delays.
NASA, however, still needed a replacement for its aging fleet of shuttles. It forged ahead with the X-33. The program had taken some big technological risks. For instance, one of the most difficult challenges is to design an engine that can work just as well at sea level as it can in the vacuum of space. The problem is, the nozzle needs to adjust its shape to the changing air pressure. One solution might be to use different engines for different altitudes; another might be to build a complicated mechanical nozzle that can change shape. The X-33 engineers opted for a bold approach. They designed the X-33’s “aerospike” engine so that the flow of air serves to shape the engine’s exhaust.
The aerospike engine turned out to be a big success. So did the X-33’s thermal shielding, a novel, skinlike coating that protects the fuselage from overheating upon entering the atmosphere. Unlike the space shuttle’s delicate ceramic tiles, the X-33’s shielding is virtually maintenance-free. Still, the project missed development deadlines and overran its budget. The fuel tank was the final straw. Made from an advanced composite material and tucked cleverly into the nooks and crannies of the ship’s sleek, wedge-shaped fuselage, it leaked chronically.
NASA still plans to spend $4.5 billion over the next four years on new single-stage-to-orbit technologies. The money, says program head Dan Dumbacher, will go not only to big contractors but to small, struggling rocket firms as well. The X-33, meanwhile, sits half built in a hangar in Palmdale, California. Unlike the Delta Clipper, it never got even a foot off the ground.
