SpaceX Falcon 9 launch
SpaceX’s Falcon 9 rocket rises from its Florida launch pad. (NRO via Twitter)

SpaceX launched a top-secret satellite for the National Reconnaissance Office today, then brought its Falcon 9 booster back for a spectacular touchdown at its Florida landing zone.

The NROL-76 launch marks a milestone as the first SpaceX launch fully dedicated to a classified mission, and the first since the U.S. Air Force cleared the company to take on national security space projects in 2015. The only precedent came back in 2010, when SpaceX launched a couple of experimental nanosatellites for the NRO as secondary payloads on a NASA demonstration mission.

Today’s liftoff from the historic Launch Complex 39A at NASA’s Kennedy Space Center in Florida officially ended United Launch Alliance’s monopoly on spy satellite launches.

“Thanks to the SpaceX team for the great ride, and for the terrific teamwork and commitment they demonstrated throughout,” NRO Director Betty Sapp said in a post-launch statement. “They were an integral part of our government/industry team for this mission, and proved themselves to be a great partner.”

Blastoff had originally been scheduled for early Sunday, but the countdown had to be halted at literally the last minute due to concerns about anomalous readings from a sensor on the Falcon 9’s first stage. “Out of an abundance of caution, we opted to hold launch and replace that sensor in question,” said John Federspiel, a SpaceX engineer who served as launch commentator.

Today’s countdown, in contrast, proceeded smoothly all the way to launch into mostly sunny skies at 7:15 a.m. ET (4:15 a.m. PT).

Because the satellite mission is classified, neither SpaceX nor the NRO provided details about its mission, and SpaceX’s live video coverage had to cut away from the rocket’s ascent minutes after launch.

Experts have speculated that the payload is a spy satellite designed to collect data from low Earth orbit. In a posting to the SeeSat-L discussion forum, amateur satellite watcher Ted Molczan said the payload may be an “imagery intelligence satellite built by Ball Aerospace,” possibly with radar imaging capability.

Molczan and his colleagues plan to keep track of the satellite’s orbital parameters to find out if their speculation was correct.

Close-up of rocket stage separation, fast flip, boostback burn in a ring of fire and then landing burn

A post shared by Elon Musk (@elonmusk) on

After the Falcon 9’s second stage separated to push the mystery payload into orbit, the first stage relit three of its Merlin engines to brake its descent and fly back toward SpaceX’s Landing Zone 1, not far from the launch pad.

Video showed the booster zooming all the way down to its intended target, shining in the rays of the rising sun and setting off sonic booms.

“A beautiful sight to see,” Federspiel said during today’s webcast. As he spoke, SpaceX employees at the company’s California headquarters could be heard cheering in the background.

The feat marked the fourth touchdown at Landing Zone 1 for SpaceX’s Falcon 9 boosters, in addition to six at-sea landings. SpaceX plans to lower the cost of orbital launches by refurbishing and reusing the boosters. The first such reuse took place last month.

Although the day seemed to provide little drama, SpaceX’s billionaire founder, Elon Musk, tweeted that going ahead with the launch was a “tough call” due to high-altitude winds:

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