Rocketplane sets record

Feb. 23, 2006
The EZ-Rocket, a plane developed and built by Xcor Aerospace, Mojave, Calif., flew for 10 min this past December, setting a record for the longest flight ever for a rocket-powered plane.

The EZ-Rocket is Xcor's flying testbed for developing liquid-fuel rocket engines. It also set a record for longest rocket plane flight, about 10 min.

Xcor will take what it learns from the EZ-Rocket to build Xerus, a suborbital spacecraft that takes off and lands like an airplane.

One of the rocket plane's engines being tested at night shows the shock diamonds in the plume.

The EZ-Rocket, a plane developed and built by Xcor Aerospace, Mojave, Calif., flew for 10 min this past December, setting a record for the longest flight ever for a rocket-powered plane. It was also EZ-Rocket's last flight, according to Xcor. The company will now take the data gathered over EZ-Rocket's 25 flights and apply lessons learned about rocket engines to a suborbital vehicle, the Xerus, and try to make some money with it.

The EZ-Rocket is actually a highly modified Long-EZ, a kit plane designed by Burt Rutan. (Dick Rutan, Burt's brother, piloted most EZ-Rocket flights.) Xcor added dual-rocket engines, each with 400 lb of thrust and regeneratively cooled; liquid fuel cools the engines before being burned.

The engines burn isopropyl alcohol and liquid oxygen. To get fuel to the engine, Xcor engineers decided to pressurize the fuel tanks rather than adding pumps. So the team had to add a cylindrical fuel tank beneath the fuselage to carry the alcohol because the internal strake tanks, which normally carry aviation gas in most Long-EZ aircraft, have a complex shape that cannot be easily converted to a pressure vessel. Two tanks insulated with Styrofoam and stowed in the plane's back seat hold the liquid oxygen. The plane carries fuel for approximately 3.5 min of run time. This means the plane usually runs out of fuel in flight and the pilot must do a deadstick landing, which apparently is not a major problem.

With both engines running, it takes a 1,640-ft take-off roll to get up to 195 knots (top speed) and go airborne. The plane climbs at 10,000 fpm. The pilot has restarted the engines in midflight and completed several touch-and-go landings, another first for a rocket plane.

To keep the flight test safe, Xcor added an ultraviolet fire sensor in the engine bay, a large bottle of helium that can flood the engine bay to quench a fire, and separate Kevlar blast shields for each engine. If things go wrong, the pilot wears a parachute and can open the canopy quickly.

Xcor plans to scale up the rocket engines tested and proven by the EZ-Rocket and use them on Xerus, a reusable suborbital vehicle that will take off and land like an airplane. It should climb to approximately 40 miles high, accelerating to Mach 4, then glide or coast to an altitude of 62 miles. Outside the atmosphere at this point, it will maneuver using smaller 50-lb thrust rockets, also developed by Xcor.

The company plans on making a profit with Xerus in three markets: flying microgravity experiments, launching microsatellites into low-Earth orbits, and taking tourists for suborbital thrill rides. Researchers at other companies and government agencies pay up to $2 million/flight to carry experiments to low-Earth orbit and $12 million to orbit a small satellite. And some wealthy space tourists have spent millions to log a few days in the International Space Station. Xcor say it can make money at $500,000/flight by sending 22-lb satellites into low-inclination orbits or conducting experiments in near-zero gravity for short periods, or by charging tourists $98,000 (each) for a short space ride. Xerus would act as a reusable first stage for satellites, carrying the expendable second stage to launch height and speed. The company says it already has agreements with other firms to sell and lease vehicle services. Like the EZ-Long plane, Xerus will use liquid rocket fuel rather than a solid or hybrid fuel. But piston fuel pumps rather than turbopumps will move fuel through the craft. That's because most turbopumps are designed for larger rocket engines with higher fuel flows and don't scale easily to different sizes. Turbo-pumps also cannot start and stop rapidly, and Xcor plans on making several in-flight restarts during flight tests.

When the Xerus project goes into the black, profits will go into developing a follow-on spacecraft. It is too early to speculate on the design of this next spacecraft, but it will be bigger and faster, and go higher for longer, according to the company.

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