Feb. 9, 2000 The first major component of an experimental composite liquid oxygen tank for NASA's X-34 rocket plane has completed the curing process in an oversized oven at Marshall Space Flight Center in Huntsville, Ala.
The composite tank is one of 10 supplemental advanced technology experiments planned for the later stages of the X-34 program. It will be the largest composite liquid oxygen tank made and the first to fly on a launch vehicle.
By replacing structures usually made of metal with lightweight composite materials, combined with other technology advancements, NASA hopes to lower the weight of future launch vehicles and, as a result, cut the cost for launching payloads into orbit from $10,000 per pound today to $1,000.
Two tanks are being assembled and tested at the Marshall Center under a 50-50 cooperative agreement between Marshall and Lockheed Martin Michoud Space Systems in New Orleans. The first tank, now being built, will be used for ground tests. The second will be used for flight tests. Lockheed designed the tanks and will assemble and test them at Marshall with assistance from NASA engineers and technicians. NASA's share of the work is funded by the Advanced Space Transportation Program and managed by the Pathfinder Project Office, both part of the Marshall Center's Space Transportation Directorate.
The X-34 is a flying laboratory being developed to demonstrate technologies and operations aimed at making future reusable launch vehicles safer, more reliable and less expensive to build and operate. It is about 58 feet (17.7 meters) long with a wingspan of about 27 feet (8.4 meters).
Orbital Sciences Corp. of Dulles, Va., is building three of the experimental rocket planes under contract to the Marshall Center, NASA's Lead Center for Space Transportation Systems Development. The composite tank will be tested in the third X-34, while the first two X-34s to fly will use conventional aluminum tanks.
The procedure for curing the composite cylinder called for it to be heated at 350 degrees F for approximately 4 hours at a pressure of 92 pounds per square inch in a giant oven, known as an autoclave. The cylinder consists of layers ñ 18 plies of carbon cloth at its thinnest point and as many as 80 at its thickest. Each ply was saturated with epoxy resin that hardened in the autoclave.
Composites will be used for the tank's major structural components. The components include the main barrel section, two domed end pieces and internal domes designed to prevent liquid oxygen from abruptly shifting in flight and altering the flight characteristics of the X-34.
Composites are finding increasing use in the framework and skin of vehicles ranging from cars to jet fighters. But they have never been used outside the laboratory to contain supercold liquid oxygen.
"Composites usually become brittle and crack when exposed to liquid oxygen at minus 320 degrees," explained Mike Phipps, Future X Pathfinder flight experiments project manager at the Marshall Center. "Also the oxygen molecules are so small that it's difficult to keep them from leaking through the threads that make up the composite layers. If we can overcome those challenges, it will help make access to space more affordable."
"We believe this will be the largest composite liquid oxygen tank ever made and certainly the first to fly," Phipps noted. In addition to the composite tank, the other supplemental experiments planned are related to either thermal protection systems or on-board vehicle health monitoring systems.
The experimental tank passed a systems requirements review in November and its preliminary design review Dec. 10. The composite cylinder completed bakeout on Dec. 16. Manufacturing of the first barrel section began in early December. Dome fabrication will begin soon. The completed tank will be pressure- and temperature-tested between late May and early August. Ground tests for the X-34 flight tank are scheduled to begin in mid- to late-August.
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