The X-43A was a tiny unmanned test aircraft designed by NASA to do one thing: go absurdly fast. It was part of the Hyper-X program, built to prove that a scramjet could work in real flight rather than just in a wind tunnel. To get it into the thin upper atmosphere, the X-43A wasn’t launched from a runway. A B-52 carried it to altitude, then a Pegasus booster rocket fired and pushed it to several thousand miles per hour. Only after the booster fell away did the X-43A ignite its own engine. That e