Aerospace Technology Development

X-33 Metallic Heat Shield Ready for Flight

THE DEVELOPMENT OF A LOW-COST SPACE plane took a step forward last month when one of three technologies essential to its success was declared "ready for flight." Designed for NASA's X-33 technology demonstrator, the rugged, metallic thermal protection panels, developed and built by team member BFGoodrich Aerospace/Aerostructures Group in Chula Vista, California, are expected to dramatically cut maintenance time and costs associated with more fragile thermal tile systems.

Because the metallic panels on the lower surfaces of the X-33 make up the vehicle's windward, aerodynamic structural shell, the system also will obtain significant weight savings over traditional thermal systems, while being much more durable and waterproof. The metallic thermal protection panels passed an intensive test series that included sessions in high-speed, high-temperature wind tunnels. The panels also were strapped to the bottom of a NASA F-15 aircraft and flight-tested at nearly one and a half times the speed of sound.

 

The F-15 is used as a testbed aircraft to validate the durability of the X-33 thermal protection system materials.

Additional laboratory tests duplicated the environment that the X-33's outer skin will encounter while flying roughly 60 miles high at more than 13 times the speed of sound. Also, a thermal panel fit test successfully demonstrated the ease of panel installation and removal.

The thermal protection system combines aircraft and space plane design, using easy-to-maintain metallic panels placed over insulating material. As the X-33 flies through the upper atmosphere, the panels will protect the vehicle from aerodynamic stress and temperatures comparable to those a reusable launch vehicle would encounter while reentering Earth's atmosphere. Tests have verified that the metallic thermal protection system will protect vehicles from temperatures near 1,800 degrees Fahrenheit. Most thermal protection systems flying today consist of a fragile insulation material glued to the outside of the vehicle's shell. The X-33's protection panels do not require an aeroshell, resulting in a significant saving in weight over the Shuttle system. The more durable metallic panels and rigid blankets serve as the X-33 vehicle's aerodynamic structural shell, fastened to a composite standoff skeletal structure.

The Shuttle thermal system must be refurbished after each flight, using an estimated 17,000, or more, work-hours. The goal of the reusable launch vehicles, such as the X-33, is to reduce the refurbishment time so that the vehicle can fly within a few days. Mechanical attachments can allow thermal protection system panels to be quickly and easily removed and replaced to meet this goal. Also, metallic thermal panels last longer and do not require waterproofing, as does the Shuttle. The inherent ductility of metallic materials offers a potentially more robust outer surface. Its geometric parameters offer the opportunity to modify the design to accommodate different conditions.

"By developing and proving these systems, we're creating the ability to build space planes that eventually will fly to orbit, return for servicing and launch again as often as today's commercial airplanes make scheduled flights," said Dan Dumbacher, NASA X-33 deputy program manager, assigned to Marshall Space Flight Center in Huntsville, Alabama. Marshall is NASA's lead center for developing future space transportation systems.

Work continues on the two remaining technologies important for low-cost space access—an efficient propulsion system ideally suited to power a lifting body and, more importantly, lightweight-yet-strong composite cryogenic fuel tanks and structures to minimize vehicle weight. The X-33 program is now entering a phase of intense testing and qualification of the vehicle's components.

 

Closeup of F-15B Flight Test Fixture with X-33 thermal protection systems.

The X-33 is a half-scale technology demonstrator of a full-scale, commercially developed reusable launch vehicle that Lockheed Martin has named "VentureStar," planned for development after the turn of the century. Through airplane-like operations and a single-stage-to-orbit design, a full-scale reusable launch vehicle could dramatically reduce the cost of putting payloads into space.

Although suborbital, the X-33 will fly high enough and fast enough to encounter conditions similar to those experienced on an orbital flight path. This will help fully prove its systems and performance.

For more information, contact Dom Amatore at Marshall Space
Flight Center.
Call: 256/544-0031.
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