What happened with the Falcon 9’s second stage?

While the inaugural launch of the Falcon 9 v1.1 on Sunday appeared to be successful, placing the CASSIOPE satellite and several secondary payloads into low Earth orbit, there has been some chatter over the last two days about what happened to the rocket’s second stage after it released its payloads, including speculation—now refuted by the company—that the stage exploded.

SpaceX did not in the post-launch press conference that the company had planned to relight the second stage’s single Merlin engine after deployment, but encountered a problem. “We initiated a relight and the system encountered an anomaly and did not complete the relight,” SpaceX CEO Elon Musk said in a post-launch teleconference Sunday afternoon. “We believe we understand what that issue is and should have it addressed in time for the next flight of the Falcon 9.” He said he wanted to give the company more time to investigate the issue before discussing exactly what happened. “It’s nothing fundamental.”

However, early Monday veteran space analyst Robert Christy noted something unusual: there were 20 objects being tracked in orbit from the launch. The upper stage, the satellites, and some related items accounted for many, but not all, of those items. He concluded that there had been an explosion of the upper stage. “It seems to have suffered some kind of failure after the payloads departed,” he concluded in a blog post.

That claim soon made the rounds, and by yesterday SpaceX formally responded to some media inquiries about it. “Regarding the rumors you may have heard about the Falcon 9 second stage, in short, our data confirms there was no rupture of any kind on the second stage,” a SpaceX spokesperson told Space News. She said that there was a “controlled venting” of propellants to safe the stage after payload deployment (which produced a glowing, nebulous object to some observers in the Indian Ocean region thanks to being backlit by the Sun). That venting, SpaceX believes, may have knocked loose some insulation that accounts for the additional objects being tracked.

Musk offered a similar assessment to NBC News. “During venting to safe the stage, some foil insulation on the engine came loose,” he wrote in an email. “This is very lightweight, so will quickly re-enter and burn up, but it is reflective on radar.”

Dr. T.S. Kelso of CelesTrak has also analyzed the orbits objects being tracked. That analysis, he concluded in a message to the SeeSat-L mailing list, “doesn’t seem to suggest an explosion.” However, the distribution of the objects in the orbital plane is puzzling, he admits, and could be an artifact of the recent decision by the Air Force to close its “Space Fence” tracking system.