Will the Air Force Finally Get a Spaceplane?
If Boeing's X-37 can maneuver politically as well as in space.
- By Ben Iannotta
- Air & Space magazine, January 2003
(Page 3 of 5)
Son of Shuttle
When Boeing absorbed space shuttle builder Rockwell in 1986, it inherited Rockwell’s years of experience in studying the space shuttle’s landing profile. “We know the shuttle’s characteristics,” says X-37 program manager Al Santana, “and that helps us correlate our data and devise flight control algorithms.” Santana worked on the shuttle’s guidance, navigation, and control systems when the vehicle was being designed by Rockwell.
In the 21 years since the shuttle’s first flight, according to Santana, the important advances for reusable spaceplanes have taken place in composite structures, thermal protection systems, and avionics. Boeing engineers are experimenting, for example, with a new heatresistant composite material: carbon/silica carbide. Carbon/SiC, or C/SiC, can be used to form lightweight, thin control surfaces, Grantz says, that don’t require the additional external insulation of ceramic tiles. “You can get aerodynamic surfaces with smaller radiuses and thinner airfoil sections,” he adds.
Grantz expects the X-37 to withstand reentry temperatures even higher than those that the shuttle’s ceramic-tiled skin protects it against. The surface of the X-37 will heat to 2,700 to 2,800 degrees Fahrenheit, compared with shuttle temperatures of 2,400 to 2,600 degrees, he says.
The trailing edges of the X-40’s wings are an awkward-looking two inches thick because engineers assumed the X-37’s trailing edges would require ceramic tiles. Now that engineers plan to use C/SiC for the flaperons and control surfaces on the ruddervators, the wing and ruddervator trailing edges will be only one inch thick.
The slenderizing of the trailing edges is a rare instance in which the X-37 has slimmed down. Program managers decided to control costs by using more off-the-shelf hardware than originally planned, and as a result, the vehicle grew heavier. Then in the early spring of 2001, the management team determined that the goals of atmospheric and orbital testing weren’t as compatible as the team had first believed. The managers redefined the program’s goals, confining the X-37, like the X-40, to atmospheric tests.
In 2004, the X-37 will be dropped from a B-52 at 50,000 feet to demonstrate landing and descent. Boeing is still hoping to interest NASA in a second X-37 for orbital tests as part of the agency’s Space Launch Initiative, a program whose goal is to pave the way for new reusable launchers that would carry hardware and astronauts into orbit. SLI is being restructured, however, and NASA is studying a number of options.
Whether the X-37 will ever reach orbit has become more of a political question than a technological one. The X-37 program was helped into life by a Congressional maneuver. Congress, anticipating trouble with NASA’s X-33 single-stage-to-orbit program, added funding to the agency’s 1998 appropriations to study alternative approaches to reusable launchers. The following year, the House of Representatives earmarked $20 million for NASA’s participation in the Military Space Plane, reinvigorating a program that President Bill Clinton had killed with a line-item veto. The X-37 was the result of a Congressional effort to keep the Military Space Plane alive and its directive to explore alternatives to the roubled X-33. (NASA later canceled the X-33 program.)
Can This Marriage Be Saved?
The contract to develop the X-37 included Boeing’s agreement to pay approximately 50 percent of the cost. The government’s share included $16 million from the Air Force and the rest from NASA. The estimated cost of building and testing the vehicle ballooned from $173 million, which was to have paid for two orbital flights, to $234 million, which covers no orbital flights. But in August 2001, Air Force Secretary James Roche decided to hold the Air Force contribution at $16 million. “If it has no maneuverability because of weight growth, then you can’t demonstrate the concept of maneuverability,” says Colonel Mike Wolfert, a strategist in the programs and plans office at the Air Force Space Command in Colorado Springs.