I. The Unthinkable

Commercial passenger service to space is a difficult proposition. To succeed, it has to contend with the pull of gravity, violent rocket-propelled accelerations, heavy vibrations, supersonic speeds and shock waves, vertical climbs, the lethality of the outside environment, and the problems of deceleration and heating during re-entry into the atmosphere. It has to do this safely, reliably, repeatedly, and perhaps profitably, while carrying ordinary passengers in ordinary clothes, who, if they are traveling point-to-point, will want to bring along ordinary luggage as well.

We are far from that now. But by last fall, Virgin Galactic, a self-described “spaceline” founded by the flamboyant British entrepreneur Richard Branson and based in Mojave, California, was nearing the moment when it could offer rides to as many as six passengers at a time. In terms of space travel, these rides were to be baby steps—at best, a brief, straight-up excursion above the so-called Kármán line (100 kilometers high, in near-vacuum conditions, where space is somewhat arbitrarily said to begin), followed by a straight-down re-entry into Earth’s atmosphere and a gliding return to the airport of origin. There had been technical setbacks, impossible promises, and all too much hype. Nonetheless, more than 700 people had bought tickets, most recently at $250,000 apiece, and after a decade of development and $500 million of investment, the machines were impressive and real.

There were two of them, constructed of carbon composites, and each for the moment was one-of-a-kind. The first, known as WhiteKnightTwo, was a strange-looking, twin-fuselage mother ship with a 140-foot wingspan and four turbofan engines—a heavy lifter designed to suspend a rocket ship between its fuselages, take off with it from a runway, and fly it into the thin air at 47,000 feet for a horizontal launch. The rocket ship itself, known as SpaceShipTwo, was a twin-tailed, stubby-winged aircraft the size of a business jet, built around a hybrid rocket engine containing enough fuel for a one-minute burn—sufficient to thrust the aircraft to a speed of Mach 3.5 (about 2,500 miles per hour) in a vertical climb and project it into space, from which it would return without power, as a glider. It had a two-pilot cockpit and a cabin large enough for six reclinable passenger seats, as yet to be installed.

At the core of the design was an unusual twin-boom tail that straddled the rocket motor. The tail had vertical stabilizers and various movable control surfaces, and operated more or less conventionally in regular flight. What made the tail unusual—highly unusual—was that the entire twin-boom apparatus was hinged. In regular flight it was held in position by mechanical locks, but it could be unlocked and then raised to a 60-degree angle overhead—nearly perpendicular to the fuselage. This raising of the tail was meant to be done in the thin air of near space, where aerodynamic loads are small. The purpose was to control the subsequent atmospheric re-entry by forcing the fuselage and wings into a flat attitude, like a pancake or belly-flop in relation to the fall. The resulting drag would tame the descent speeds and distribute the re-entry heat across large surface areas, rather than concentrating it on narrow leading edges. In short, raising the tail would keep the ship safe during re-entry. New terms for the invention had been coined: once raised into the upright configuration, the tail was said to be “feathered,” and descents from space were said to be “feathered re-entries.” Preliminary low-altitude test-flying had shown it to work well. The spaceship had not yet flown into space, but there was good reason to believe that, once it did, it would safely negotiate the dangers of coming back down.