Saturday, May 18th, 1996 - The DC-XA single-stage rocket experimental vehicle flew this morning for the first time since its handover to NASA last year and major rebuild over the winter. The test took place at the same White Sands Missile Range, New Mexico site the original DC-X made its eight flights from. This first post-rebuild flight had originally been scheduled for Friday, but was delayed 24 hours by a faulty sensor on one of the vehicle's four RL-10-a5 rocket engines. This morning's flight was a minimal test-hop, 800 feet up from the launch stand, then 350 feet sideways to over the landing pad, then a vertical descent and landing, total flight time of about a minute.

The flight went as planned until the final landing phase, when the DC-XA descended the last few feet onto the concrete landing pad more slowly than expected. This final descent phase has been the object of ongoing tweaking dating back to the last several flights of the original DC-X. The target touchdown velocity is around four feet per second; previous touchdowns have varied from two feet per second to as high as fourteen feet per second - that last due to an invalid data problem with a radar altimeter rather than the landing control software, however.

The problem with slow landings is that the vehicle sits in the backwash from the rocket engines too long, and the base of the vehicle can suffer heat damage. There is some thought being given to landing the potential followon to DC-XA (if McDonnell-Douglas wins the X-33 competition) on an open grid of some sort to reduce backwash, but meanwhile DC-XA lands on a plain concrete slab, and slow landings can cause problems.

This morning's slow landing apparently started a small fire on the exterior of the vehicle. According to McDonnell-Douglas sources, the fire was promptly extinguished, and the vehicle has been de-fuelled and moved back to its launch stand in the normal manner. One of the vehicle's four body-flaps (hinged square control surfaces, one on each side of the conical vehicle near its base) was damaged and will have to be replaced. We're told there is no other obvious damage, but the structure around that body flap will be carefully inspected for possible heat damage. The DC-XA engineering/flight-test team will be looking into that and into why this landing was slow over the next few days, then implementing fixes.

There's no telling at this point whether this will push back the next planned flight dates of June 7th and 8th, but our first guess would be that those will slip by a week or two. We'll likely know more in a few days, though.

A quick bit of editorializing: Discovering and fixing this sort of problem is exactly why we test-fly experimental vehicles. Fly a little, see what breaks, figure out why, fix it, fly a little more. We look forward to the DC-XA crew discovering, and solving, more problems as this summer's test series continues.

A McDONNELL DOUGLAS NEWS RELEASE

The cone-shaped reusable launch vehicle, formerly known as the Delta Clipper-Experimental Advanced (DC-XA), made its first flight renamed as the Clipper Graham.

The Clipper Graham climbed vertically at 170 feet per second to an altitude of approximately 2,000 feet, then flew laterally for 550 feet up range before throttling back its engines and descending tail first onto the desert floor. Duration of the flight was 63.6 seconds.

Today's 10:15 a.m. MDT test flight was the second since advanced technology materials and components were integrated into the launch vehicle.

"The test flights are providing data to evaluate the performance of new lightweight components, which include a graphite composite liquid hydrogen tank, graphite composite intertank and aluminum-lithium liquid oxygen tank," said Dave Schweikle, McDonnell Douglas' DC-XA program manager.

"Each time the Clipper Graham flies, we are increasing our knowledge of the strength and durability of these lightweight materials, which have been exposed to cryogenic temperatures," he explained.

"The goal of the program is to demonstrate SSTO technology that will lead to the development of operational reusable launch vehicles," Schweikle said. "These launch vehicles will dramatically reduce the cost of placing payloads into space."

Today's flight provided the first test of a differential global positioning system (DGPS) which provides data to the Clipper Graham's navigational system. Signals from satellites of the Global Positioning System and a ground station were used to precisely determine the position of the reusable rocket.

Under a cooperative agreement with NASA, McDonnell Douglas extensively modified the launch vehicle by replacing original systems with a McDonnell Douglas-built graphite composite liquid hydrogen tank and intertank and a Russian-built aluminum-lithium liquid oxygen tank. The U.S. Air Force's Phillips Laboratory is providing flight management support to the flight test program.

In addition, Clipper Graham is flying with a graphite composite liquid hydrogen feedline and valve, a liquid-to-gas conversion system to fuel the reaction control thrusters, and a Russian auxiliary power unit to provide redundant hydraulic power for flight control.

Data from the DC-X and the DC-XA is being supplied to the reusable launch vehicle government-industry team. The X-33 is a large, reusable technology demonstration vehicle which is planned to fly in 1999. Success of the X-33 could lead to a national, industry-led decision to develop a commercial reusable launch vehicle early in the next century.

The McDonnell Douglas entry in the X-33 competition is a vertical takeoff/vertical landing rocket based on the configuration of the Clipper Graham. NASA is expected to announce a decision on the X-33 in July.

A McDonnell Douglas news release

The Clipper Graham began its 2-minute, 20-second test flight at 1:15 p.m. MDT. It was the fourth flight in a test series that began in May.

Program managers Dan Dumbacher of NASA and Dave Schweikle of McDonnell Douglas said the vehicle performed its flight maneuvers extremely well. It completed its planned test profile, which included an arc-like sweeping maneuver from a near upright position, before descending base-first from the 4,100-foot maximum altitude. All of the vehicle's components appeared to function normally.

However, approximately 200 feet above the landing pad one of four landing gear failed to deploy. The Clipper Graham touched down on the three deployed landing gear, shut off its engines, then fell on its side because it lacked the support of the fourth landing gear.

A committee will be established to investigate the cause of the incident. The committee will gather flight and landing data to determine what caused the problem. Engineers and technicians will not be able to examine the severely damaged vehicle for at least 24 hours because of safety considerations.

Dumbacher and Schweikle said the Clipper Graham is an experimental, high-risk technology program. The Clipper Graham is a follow-on of the Delta Clipper-Experimental vertical-takeoff, vertical-landing rocket that successfully completed a series of eight flight tests.

Dumbacher and Schweikle said each of the tests in the program has been more demanding, demonstrating the behavior of the experimental vehicle under a variety of dynamic flight conditions.