SpaceX's largest launch

Photo: SpaceX

SpaceX launched its heftiest rocket with 24 research satellites Tuesday, a middle-of-the-night rideshare featuring a deep space atomic clock, solar sail, a clean and green rocket fuel testbed, and even human ashes.

It was the third flight of a Falcon Heavy rocket, but the first ordered by the military.

The Defence Department mission is expected to provide data to certify the Falcon Heavy — and reused boosters — for future national security launches. It marked the military's first ride on a recycled rocket.

Both side boosters landed back at Cape Canaveral several minutes after liftoff, just as they did after launching in April. But the new core booster missed an ocean platform, not unexpected for this especially difficult mission, SpaceX noted.

"It was a long shot," tweeted SpaceX founder and chief executive Elon Musk.

SpaceX did manage for the first time to catch the fairing, or nose cone, in a giant net on an offshore boat. The California-based company is trying to recover and reuse as many rocket parts as possible — rather than letting the pieces sink in the ocean — to drive down launch costs.

NASA signed up for a spot on this Falcon Heavy, along with the National Oceanic and Atmospheric Administration, the Air Force Research Laboratory, the Planetary Society and Celestis Inc., which offers memorial flights into space.

An astronaut who flew on NASA's first space station back in the 1970s, Skylab's Bill Pogue, had a bit of his ashes on board, along with more than 150 other deceased people. Pogue died in 2014.

Musk said it was "our toughest rocket launch ever." The satellites needed to be placed in three different orbits, requiring multiple upper-stage engine firings. It took several hours to release them all.

The Deep Space Atomic Clock by NASA's Jet Propulsion Laboratory is a technology demo aimed at self-flying spacecraft. Barely the size of a toaster oven, the clock is meant to help spacecraft navigate by themselves when far from Earth. NASA also was testing a clean and green alternative to toxic rocket and satellite fuel.

The Planetary Society's LightSail crowd-funded spacecraft will attempt to become the first orbiting spacecraft to be propelled solely by sunlight. It will be released next week from its temporary perch on a spacecraft and opened a week later.