ablation - the process of absorbing heat and vaporizing

ablative material - material used as TPS that absorbed heat and when it got too hot it would vaporize

absorption - the conversion of radiant energy into energy of a different form

alloy - a combination of metals

conduction - heat energy traveling from substance to substance or through substances

conductors - substances that conduct or transfer heat well

convection - transfer of heat by currents in fluids or gases

disposable - not used over and over; used only once

Inconel - an alloy in the TPS on the X-33

insulators - substances that conduct heat poorly

micrometeoroids - very small meteoroids that are danger to space vehicles while in space

payload - people, experiments and other cargo on a spacecraft

radiation - the method of heat transfer by waves in space

Reinforced Carbon - Carbon (RCC), silica tiles, felt blankets - four materials used as TPS on Columbia, the original Space Shuttle

reusable - able to be used over and over

reusable launch vehicle - spacecraft that can be used over and over with little repair; that works like a rocket but lands like a plane.  For example: the spacecraft Columbia, Challenger and Discovery.

structural shell - the skin of a spacecraft, which, on the X-33 will serve as skin and TPS

VentureStar - a proposed replacement space vehicle for the Space Shuttle that would cost less to operate and be ready to launch faster

X-33 - a “technology demonstrator”  half the size of VentureStar used to test the many technologies that will be used on VentureStar. It will not reach orbit nor carry a payload but will launch from an upright, position and, like a plane, be ready to launch again in a few days.