Space Shuttle: The Next Generation

A Leap Forward, then a Fall


To grasp what's wrong with the shuttle, it's important to understand how it works. The Space Transportation System, as the shuttle is officially known, is an orbiter—the winged crew- and payload-carrying vehicle—mounted to a large external fuel tank that has a solid rocket booster attached to each of its sides. At ignition, both solid rocket boosters, which provide most of the thrust to lift the shuttle off the launchpad, and the orbiter's three main engines fire; the rocket booster motors are powered by solid fuel, a mixture of ammonium perchlorate and aluminum, from their own canisters and the orbiter's engines are driven by hydrogen and oxygen from the external tank. About two minutes after launch, when the shuttle is about 28 miles high, just above the lip of space, the solid rocket boosters run out of fuel and separate from the external tank. They parachute into the ocean and are recovered for use on future missions. The orbiter and the external tank continue rising for another seven minutes, and then the external tank separates to disintegrate in the upper atmosphere. The orbiter's engines place the shuttle in orbit anywhere from 150 to 300 miles above Earth's surface. At the end of the mission, the shuttle lands like an airplane.




When it was designed in the early 1970s, the space shuttle was a gigantic leap forward. It was the first reusable spacecraft, a vast upgrade over the expendable small-vehicle-on-large-launcher system of the Apollo era. And with a payload of up to 50,000 pounds, it could carry more equipment, crew members and cargo than any other manned space vehicle.




But the shuttle also had significant flaws, which have become obvious over time. To start with, it is more inefficient and expensive to operate than NASA had originally envisioned. It takes thousands of people to run a shuttle flight, in part because some of the technology choices initially made by shuttle engineers proved problematic. Consider the huge array of computers: Each on-board system—electrical, engines, avionics, communications, to name just a few—is a separate component and must be monitored by an individual on the ground. What's more, hundreds of maintenance workers are needed during turnaround to inspect and repair everything from the old-fashioned solid rocket boosters—which because they use solid fuel cannot be shut off once they are ignited, and thus must be hardened before each flight against failure—to the fragile tile system that is supposed to keep the shuttle from burning up during reentry.




The excessive weight and size of the orbiter is also a drawback. When the system was built, the Pentagon insisted on the ability to snag disabled satellites and return them to Earth, which required a larger, sturdier orbiter. But the shuttle has hardly ever been used for that. And NASA's goal was to send the shuttle into space 30 to 50 times each year on science and satellite launch-and-recovery missions for the public and private sectors. The agency figured the cost of maintaining the big payload and oversize orbiters would be more than offset by a long line of customers who would keep the shuttle and its crew busy. But in reality, the shuttle has averaged only five launches a year, with few paying customers; the economies of scale NASA had hoped for never materialized. "Rarely do you see an instance where state-of-the-art technology enters service," says Keith Cowing, editor of Nasawatch.com. "You live with whatever moment in time you froze your design."