MACH 10, BUT NOW WHAT?

A number of hypersonic-related programs are drawing confidence from the back-to-back successful flights of NASA's X-43A research craft that show scramjet operation at Mach 7 and Mach 10.

Last week's free flight at Mach 10 was especially important because it's difficult to test on the ground at that high speed. An early look at the data suggests that a series of 0.005-sec.-duration reflected shock tunnel runs did a very good job of predicting the flight, says Robert Bakos, vice president of ATK GASL in Ronkonkoma, N.Y.

Those two results--that the engine/ airframe combinations produced usable thrust, and that their behavior was close to analytical and wind tunnel predictions--should give a boost to other programs that haven't flown yet by increasing confidence in the validity of their designs, says Anthony Castrogiovanni, ATK GASL president. "Hopefully today's flight, showing it can be done twice, will trigger Defense Dept. interest," he said after the Nov. 16 test. ATK GASL, along with NASA Langley Research Center, was responsible for the X-43A "Hyper-X" design, and the company built the 12-ft.-long craft at its facility in Tennessee.

By having an integrated engine and airframe in free flight at operational conditions, Hyper-X has gone "orders" beyond what has been accomplished previously with scramjets, he says. Other tests have been mostly on the ground or, if in flight, fixed solidly to the front end of a booster rocket or were not an integrated vehicle.

Despite the apparent X-43A success, NASA has no funded scramjet follow-on program to capitalize on the new knowledge and retain the expertise. The three-flight Hyper-X program cost $230 million, and that would increase if it were all under the current "full cost" accounting system.

A team of officials from the Langley, Dryden, Glenn and Ames research centers are proposing a "modest but aggressive spiral development approach" of scramjet activities working with the Defense Dept. and universities, says Vincent L. Rausch, the Hyper-X program manager at Langley. Individuals working the final test showed frustration at having many years of work come to a halt as they finally obtained promising flight data. Rausch and others have proposed working toward a scramjet first stage for space launch (AW&ST Nov. 1, p. 56).

The Nov. 16 launch had been delayed several times, most recently on Nov. 15 when malfunctions required rebooting the X-43A computer twice. Each reboot took 40 min., pushing the flight beyond available range time and daytime landing requirements for the B-52B carrier aircraft of NASA Dryden Flight Research Center here. Dryden conducted the flight test, and it was the last research flight for the venerable "008" B-52B, which has been dropping test aircraft since 1959. Boeing Phantom Works did systems engineering, thermal protection, guidance, navigation and control design, flight control software and internal layout and structural design.

The X-43A was mounted on the front of a modified Orbital Sciences Pegasus launcher first stage. The stack, weighing 43,000 lb., was carried under the right wing of the B-52B and dropped westbound at 2:34 p.m. PST over the Pacific Ocean at 40,000 ft. from a point about 50 mi. off the southern California coast. The solid rocket motor took the stack up to the Mach 10 starting condition at 110,000 ft.

At 7-8 sec. after motor burnout, pistons pushed the X-43A forward away from the booster at Mach 9.8, and the X-43A's higher density made it pull ahead. Very little tipoff was observed at separation, unlike the Mach 7 flight on Mar. 27 that had noticeable tipoff, and drag and lift higher than expected (AW&ST Apr. 5, p. 28). Engineers learned from that and were able to correctly adjust for the faster condition.