COLD WAR DRONES MAY HELP TEST ROCKET ENGINE NASA MAY TEST ROCKETS WITH DRONES.

Byline: Jim Skeen Staff Writer

EDWARDS AIR FORCE BASE - A Mach 3 Air Force spy drone that flew secret Cold War missions might be coming out of retirement to test a new engine system that could power future spaceships.

NASA's Marshall Space Flight Center is considering using the remaining D-21 drones, built in great secrecy by what is now Lockheed Martin Skunk Works, to test a combination rocket-ramjet engine intended to fly faster than six times the speed of sound - about 4,200 mph.

``We would like to put an engine on an existing airframe,'' said Garry Lyles, manager of Advanced Space Transportation Program at Marshall. ``We're looking at the D-21 and a follow-on to the Hyper-X (experimental aircraft).''

The new engine system is termed a rocket-based combined-cycle, or RBCC, engine.

The idea is to develop a spacecraft engine that would not need to carry its own oxygen. Saving the weight of an oxidizer could allow future spaceships to take more cargo into space, lowering the cost of getting commercial goods into orbit.

A ramjet is a type of jet engine without traditional jets' whirling turbines to compress air to oxidize fuel. Ramjets are capable of extremely high speeds, but because they have no compressor turbine, they only function when air is being rammed into their intake by the high velocity of the aircraft.

Rocket motors can gain thrust at takeoff, when a ramjet is ineffective. Once the aircraft has gained some speed, about 2,000 mph, the ramjet can be turned on to gain velocity.

``Hopefully, the RBCC combines the best of two worlds,'' Lyles said.

After climbing to a high speed and altitude, the engine would switch back to a rocket motor to carry the aircraft into space.

NASA has tested large-scale models in wind tunnels with favorable results.

``What's left to be done is to prove it can be built and be lightweight enough to be a flight engine,'' Lyles said.

NASA's Marshall is looking to conduct the flight test under the Pathfinder program, an effort aimed at testing future space technologies in a relatively low-cost manner. The program has a limit of spending $100 million to $150 million per flight.

Using an existing airframe could help reduce the costs, which is one reason why NASA is considering using the D-21.

Black and stubby, just a huge engine sprouting modified delta wings, the D-21 was built during the 1960s and kept secret during its entire service life. Its existence was not made public until an aviation enthusiast found one in 1977 in an Air Force aircraft storage yard in Arizona.

The D-21 drones were capable of flying at speeds of about 2,200 mph and at altitudes of 80,000 to 95,000 feet. Former Skunk Works President Ben Rich, in a 1995 book he wrote after his retirement, said they spied on China's nuclear missile test facilities.

One D-21 crashed in the Soviet Union, Rich said, recounting a story of how a CIA official told him that he got a piece of one from a KGB official, who said it had been found by a Siberian shepherd. The D-21 drones, each about 43 feet long with a 19-foot wingspan, were air-launched aircraft. Versions of the SR-71 Blackbird spy planes and later B-52s were used as mother ships for the launches.

The D-21 drones flew from 1966 to 1971, when the program was canceled. At least 38 drones were built.

In 1994, NASA's Dryden Flight Research Center acquired four D-21 drones as part of the SR-71 Blackbird assets loaned to the agency by the Air Force.

Another possible candidate for the rocket-ramjet engine tests is an enlarged version of the Hyper-X, a high-speed experimental aircraft that NASA plans to fly this year.

The Hyper-X design would require more work than just lengthening its 12-foot-long airframe, because NASA wants an aircraft that can be recovered after a flight. The Hyper-X is designed to end its missions by plummeting into the ocean.

It is also possible that a new airframe could be designed and built to house the engine, Lyles said.

For flight tests, whatever aircraft is used to carry the RBCC would be attached to a modified B-52 bomber and taken aloft. The test aircraft would be dropped and then powered up to speeds of about Mach 4, about 2,800 mph.

Flight tests could be done in 2005 at Edwards.

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Photo: D-21 drones, which flew spy missions during the Cold War, may be used to test a new engine system that could power spaceships.

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