NASA has never been an exclamation-point outfit. The folks who work there may do extraordinary things, but they tend to talk about them in the dry and uninflected tones of the engineers they are.

So it was something of a departure last week when, after an unmanned version of what may well be the next spacecraft that will carry American astronauts into orbit took off from Cape Canaveral and returned home safely, the first official dispatch read simply: "SPLASHDOWN!!!" Unfamiliar too was how the announcement was made: it was a tweet. (See the top 10 scientific discoveries of 2010.)

That tonal change was by no means the most important thing that made the launch of the fancifully named Falcon 9 booster and Dragon space capsule different from all the granddaddy Saturns and Titans that have gone before it. Far more significant was that this ship was privately designed and privately built, the brainchild of the California-based rocketry start-up SpaceX, owned and operated by engineer Elon Musk, who also created PayPal.

"It's actually almost too good," the never reticent Musk said of his accomplishment at his postflight press conference. "There's a natural reaction that sort of blows my mind, and it's hard to be articulate with a blown mind."

If old NASA hands winced at this kind of giddy talk, they kept it to themselves - and wisely so. In the face of contracting federal budgets and an expanding private sector, the space agency of the golden years is being blown up and rethought - transformed from a government operation into a public-private partnership that, so its advocates say, will replace the politics, stodginess and glacial pace of Washington with the speed, nimbleness and accountability of the marketplace.