SPEEDY X-43A RIDES AGAIN NASA PREPARING NEW SCRAMJET TEST.

Byline: Jim Skeen Staff Writer

EDWARDS AIR FORCE BASE - NASA is gearing up for next month's flight test of a small unmanned aircraft designed to fly faster than 4,900 mph, with a dress rehearsal scheduled today for the experimental craft's mission.

Today, the National Aeronautics and Space Administration will conduct what it calls a captive carry flight in which the ultra-high-speed X-43A, mounted on a Pegasus winged space booster rocket, will be carried aloft by a modified B-52. The captive carry flight will simulate the X-43A's free-flight test.

Today's mission will originate at NASA Dryden Flight Research Center at Edwards Air Force Base but actually be conducted at the Naval Air Warfare Center Weapons Division Sea Range over the Pacific Ocean, off the central California coast.

The X-43A's free-flight test is tentatively scheduled for Feb. 21, said Dryden spokeswoman Leslie Williams.

The X-43 program is testing an ultra-high-speed, ultra-high-altitude jet engine called a scramjet - supersonic combustion ramjet - which could be used in future space launch vehicles and for high-speed military and civilian aircraft.

Scramjets pull oxygen for combustion from the atmosphere rather than carry the extra weight of its own oxygen as a rocket does. By not having to carry oxygen, a spacecraft can save fuel weight and carry more equipment.

The first attempt at flying an X-43, in June 2001, ended with researchers intentionally destroying the craft when the Pegasus booster rocket carrying it went out of control after the rocket's control fins broke off.

A number of factors apparently contributed to that incident, including the launching of the booster rocket-mounted X-43 at 23,000-foot altitude, where the atmosphere is much denser than the 40,000 feet at which Pegasus rockets are launched when they go into space.

For the testing today the booster's fin actuator system was beefed up, and the rocket will be let go by the B-52 at a higher altitude, 40,000 feet.

For the free-flight test on Feb. 21, the booster-mounted X-43 stack will be released over the ocean by the B-52. After a brief free-fall, the Pegasus booster engine will ignite and push the X-43 to an altitude of 95,000 feet and a speed of Mach 7, roughly 4,900 mph.

As the booster engine burns out, the X-43 will separate and fire its scramjet engine for about 10 seconds. The engine will then shut down and the craft will perform a set of preprogrammed maneuvers before crashing into the ocean.

The X-43 will not be recovered.

Plans call for flying one other X-43A vehicle, which will hit a top speed of about 7,000 mph.

Counting the X-43 that was destroyed, NASA is spending $230 million on the research program.

The X-43 is NASA's first test program dedicated to hypersonic research since the last X-15 rocket plane flight at Edwards Air Force Base in 1968.

The X-15's fastest flight was Mach 6.7, or about 4,520 mph, with W.J. ``Pete'' Knight - now the Antelope Valley's state senator - at the controls.

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(1 -- 2 -- ran in AV edition only) Above, today's test of NASA's supersonic X-43A unmanned aircraft will originate from Edwards Air Force Base but be conducted over the Pacific Ocean. Below, the X-43A is mounted on a Pegasus winged space booster rocket for the test.

Jeff Goldwater/Staff Photographer