SpaceX launched its Falcon 9 rocket for the first time in six months today, and then brought the first-stage booster back down for a first-ever Florida landing.

“The Falcon has landed!” SpaceX’s launch commentator announced.

Hundreds of SpaceX employees cheered the touchdown at the company’s headquarters in Hawthorne, Calif. “USA! USA! USA!” they chanted.

The flight’s main objective was to send 11 satellites into low Earth orbit to boost Orbcom’s OG2 network for machine-to-machine communications. The landing attempt was a bonus, aimed at furthering SpaceX’s goal of bringing down the cost of spaceflight dramatically.

Liftoff went off on time at 8:29 p.m. ET (5:29 p.m. PT). The Falcon 9’s second stage and payload separated from the first stage a little more than two minutes later, at an altitude of about 60 miles (100 kilometers). While the second stage fired up its engine, the first stage relit its engines to guide itself back toward land. Another engine burn slowed down the descent from supersonic speed.

As promised, a sonic boom was heard as the booster decelerated. (You can hear the boom at the 1:10 point in Ryan Kobrick’s video.)

“I actually thought at first that it had exploded,” SpaceX’s billionaire founder, Elon Musk, told reporters afterward. “But it turned out to be just that the sonic boom almost exactly coincided with the touchdown point, so that the sound reached me several seconds later.”

The engine firings set down the booster 10 minutes after liftoff on SpaceX’s Landing Zone 1, about 6 miles (10 kilometers) south of the launch pad on the Cape. Musk said the rocket touched down “almost dead center on the landing pad.”

SpaceX previously tried to land Falcon 9 boosters on an oceangoing platform, with mixed success, but this marks the first fully successful rocket landing for SpaceX, on land or sea.

The launch also marks SpaceX’s first space mission since a Falcon 9 broke up just after liftoff with a cargo shipment for the International Space Station. Musk said the failure was traced to a faulty support strut. That issue was addressed, and engineers made other upgrades as well.

Long exposure of launch, re-entry, and landing burns pic.twitter.com/Vw1ZJAtvhy — SpaceX (@SpaceX) December 22, 2015

Live video from LZ-1 pic.twitter.com/Ve6gEXfOdh — Elon Musk (@elonmusk) December 22, 2015

The landing procedure is part of Musk’s campaign to reduce the cost of orbital launches to as little as 1 percent of the current cost. Achieving that goal for rocket reusability could help open the way for Mars colonization – which is one of Musk’s long-range goals.

Musk said today’s success “dramatically improves my confidence that a city on Mars is possible.”

Last month, the Blue Origin space venture sent an uncrewed New Shepard suborbital rocket ship to the edge of outer space and then brought it back for a vertical landing. In the wake of that feat, Musk congratulated Blue Origin and its founder, Amazon billionaire Jeff Bezos. Musk pointed out, however, that bringing back a booster for a vertical landing after an orbital launch is more difficult and more significant than a suborbital there-and-back mission.

Bezos reciprocated today with his own double-edged congratulations to SpaceX via Twitter:

Congrats @SpaceX on landing Falcon's suborbital booster stage. Welcome to the club! — Jeff Bezos (@JeffBezos) December 22, 2015

The reference to “Falcon’s suborbital booster stage” runs the risk of revving up the rivalry between Bezos and Musk – or at least between Bezos and Musk’s fans.

Meanwhile, Musk said the booster would be checked out and potentially reused in ground-based tests of the rocket engines for NASA. “I think we’ll probably keep this one on the ground, just because it’s quite unique,” he said. “It’s the first one we brought back.”

Watch the full launch webcast from SpaceX: The liftoff comes at 32:00, and the landing comes at 42:00.