Where Next, NASA?

NASA's Space Launch Initiative has yielded concepts for an orbital space plane from Lockheed Martin (above, left) and a shuttle-type launch vehicle from Boeing (above, right). The proposed space plane will be a small crew transporter lofted atop an expendable rocket. The space shuttle successor will be a larger, cargo-carrying craft. Current plans call for it to incorporate air-breathing hypersonic engines and reusable, kerosene-fueled rockets. | Photograph courtesy of Space Launch Initiative/NASA.