phi (totient) wrote,
phi
totient

did spacex relight the first stage yesterday?

Some years ago, SpaceX came up with an audacious plan to return the first stage of their launcher to the launch site for reuse. They made an amazing looking video featuring, at 0:40-0:50, a first stage turnaround and relight. This was widely dismissed as science fiction and even when they did it on the Cassiope mission in September the belief was that it was only possible because Cassiope was a lightweight mission to an easy orbit. And publicly, SpaceX has been saying they were not going to try this on the SES mission that launched yesterday.

But I don't think they'd be working on this unless it could work for real missions too. And with that in mind I took another look at yesterday's launch video. The first thing I noticed is that all nine first stage engines shut off at once, at 3:10 in that video (or about 2:57 after liftoff). This is a departure from past launches (and common practice on other multi-engined rockets) where they've shut two engines down earlier than the others to prevent acceleration from going too high as the tanks empty. The payload is certainly heavier than last time, but this makes me think there was still fuel in the first stage tanks at separation. The first stage goes out of frame briefly but from 3:29 to 3:34 it can be seen firing turnaround thrusters. Then the ground telescope video cuts out and from there all we get is onboard video from the second stage.

So, did it relight?

It sure looks like they tried.

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