X-42 is the designation of a still-classified United States military, space-related program. Specifications, or photos, of the program have not been released to the public. As a result, not much is known about its goals. Not much is known about the program itself, either. It is believed to be a liquid-fueled rocket, upper stage capable of boosting a payload of up to 4,000 lb (1,800 kg) into orbit.

External links
X-42, globalsecurity.org

Space launch vehicles of the United States