The X-33, the half-scale model of the first true space plane, originally was to land seven times at Dugway Proving Ground when experimental flights started in 1999. But now planners say that number probably will be upped to 10.
The addition of three flights, starting in 1999, is the biggest surprise in the project's final environmental impact statement, released by NASA last week. It is a result of the proposed elimination of a landing zone for short-range flights."We had been looking at three ranges" where the unmanned plane could land after blasting off from Edwards Air Force Base, Calif., said Rebecca McCaleb, director of environmental engineering and management at NASA's Marshall Space Flight Center, Huntsville, Ala., and the head of the team that analyzed the proposal.
However, she added, "at this point the program's preferred test plan is to only use two of those."
Eliminated from the recommendation were the three landings that had been considered for Silurian Lake, Calif., the closest landing zones.
Since the goal of 15 test flights remains in effect, the three remaining landings were added to Dugway, a desert base about 180 miles west of Salt Lake City. The plan does not recommend changing the five landings planned for Malmstrom Air Force Base, Mont., for longer distance flights.
The final EIS was released last week, but a formal decision on the plan will not be issued for another month while it is examined by officials.
Both take-off and landing zones will be on bases run by the Army and Air Force. "We must be sure that they are comfortable with whatever the test plan is," she said, referring to military officers.
The X-33 will be wedge-shaped, about 67 feet long and 68 feet wide. It will weigh 273,000 pounds when loaded with liquid hydrogen and liquid oxygen. Although it won't be capable of going into orbit, it will reach speeds of 11,000 miles per hour - more than 15 times the speed of sound.
The aircraft is being built under a cooperative agreement between NASA and Lockheed Martin Skunk Works of Palmdale, Calif., with NASA investing $941 million and Lockheed Martin at least $212.
If X-33 succeeds, the full-scale project, a vehicle named Venture Star, should be built by Lockheed Martin early in the next millennium. Venture Star, the "Reusable Launch Vehicle," could replace the space shuttle, slashing the cost of lifting cargo into space from the present $10,000 per pound to $1,000 a pound.
Asked if X-33 is still on schedule, McCaleb said, "It may be a little bit later. The first flight may be in July instead of March" 1999.
The 14-month program of X-33 flights, according to the statement, will try to verify engine performance, control surfaces, temperature protection and navigation. Other goals are to:
- Demonstrate a reusable system of super-cold tanks of liquid hydrogen and liquid oxygen, including insulation systems.
- Verify the durability of the integrated thermal protection system.
- Achieve flights of up to 11,000 mph.
- Show that the composite material of which the vehicle is made is thermally protected.
- "Demonstrate ability to perform seven-day turnarounds between three consecutive flights." A turnaround is the time needed between landing and the time the vehicle is serviced, refueled and ready to fly again.
- "Demonstrate ability to perform a two-day turnaround between two consecutive flights."
- Show that a maximum of 50 workers performing hands-on maintenance, refueling and other operations can get the plane ready to fly again.