Its designation suggests that the Boeing-NASA X-37 is the X-38's predecessor, but the craft actually came into being only last August. Both it and the X-40A, which has already been dropped from a helicopter to glide to a successful autonomous runway landing, resemble scaled-down space shuttles. The two craft are aimed at developing technologies for an unpiloted orbiter that would be able to fly in space and return to land on its own. But the X-37, larger and more complex than the unpowered X-40A, has a rocket engine that uses jet fuel and hydrogen peroxide. Boeing says the X-37 could lead to a commercial launch vehicle that provides cheaper access to orbit.
The X-31, a delta-wing airplane with thrust-deflecting paddles and the ability to fly at extreme attitudes with its wings fully stalled (see "Stall Tactics," Apr./May 1991), was the last active member of the previous wave of test aircraft. If it gets further funding from the three partners backing it-Germany, Sweden, and the United States-it will embark on a second career. With most of its vertical fin and rudder removed, it will be used in a program called VECTOR, for Vectoring Extremely short takeoff and landing Control, and Tailless Operations Research, which will focus on aircraft using vectored thrust aboard carriers.
Expect the surge of new designs to continue. Other numbered slots for X-craft are reportedly allocated, and there's even a conceptual drawing of an X-44 in circulation (it's said to resemble a tail-less F-22).
The first generation of research craft were designed solely to conduct research in aerodynamics. The latest generation are combining high-speed research in aerodynamics and spaceflight with exploration of a realm that research aircraft have never probed before: economics. Reduced size and weight, smart avionics that replace the pilot, new low-cost materials that resist high-Mach heat-all signs point to a future in which performance remains the foremost goal, but affordability runs a close second.