The most elusive initials in the business of space flight are SSTO — or single stage to orbit — the business of flying a reusable spacecraft that takes off in one piece, goes to space in one piece and lands in one piece. Every airplane that has ever been built works that way. But spacecraft? Not so much.
Rockets shed stages as they go because each piece of hardware you cut loose and drop in the ocean makes you lighter — and thus faster. But getting to space in one piece requires huge engines with lots of fuel to lift and land a single, solid machine. Huge engines and lots of fuel, however, add weight, which requires even bigger engines and more fuel—and on and on.
The next best thing is to launch rockets that shed stages, but don’t dump them all in the ocean. Instead, the first stage lands in one piece to be used again, sending the upper stages to space. There’s still a lot of waste in that system, and not everything comes home to be used again. But the first stage does live to fight (and fly) another day, and that cuts costs dramatically.
The Delta Clipper, built by McDonnell Douglas, tried something like that in the 1990s: flying just one stage up and back — and failed. The shuttle kind of tried it, except the external tank was not reusable and the shuttle itself was an expensive, dangerous, finicky ship that lost two crews.
Today’s news out of SpaceX, that after multiple tries it has succeeded in launching a rocket and landing a first stage back on the ground while the payload went on to orbit, was thus a milestone in space. It’s not the whole SSTO loaf, but an important half.
Jeff Bezos — celebrated bookseller and aspiring rocketeer — made his own kind of history in November when his Blue Origin rocket company successfully fired a single stage rocket to an altitude of 62 miles (100 km) and brought it back for a similar upright landing. But puncturing the atmosphere to touch space is different from launching multiple orbital vehicles as SpaceX has, and while Bezos recovered the entirety of his rocket, he has a long way to go before he puts real space flight points on the board.
The private space game remains a wide open contest, and Blue Origin or SpaceX or any one of multiple other competitors may ultimately come out on top. But for today at least, SpaceX has scored a very big win.