Today's Starliner launch kept the boosters attached for an additional 48 seconds after they burned out. Keeping the dead weight and additional drag is pretty obviously suboptimal.

During the live broadcast Tim Dodd (The Everyday Astronaut) already got the answer by someone in his Discord channel: "They hold the boosters to control where they fall". Certainly that makes a lot of sense if there's something they certainly do not want to hit.

Is that true, and if it is what exactly were they trying to avoid hitting?


1 Answer 1


Scott Manley speculates they were trying to avoid hitting themselves.

Because the launch trajectory was so low the altitude at burn out was still inside the atmosphere. He speculates the engineers were concerned aerodynamic forces might cause the boosters to "recontact" the spacecraft. So they held on to them until they were at a higher altitude where separation would be safer.

Scott Manley - Boeing's Starliner Recovers And Makes Bullseye Landing @ 11:15

An example of a booster recontacting after separation on an Ares 1X launch.

  • $\begingroup$ If there was still some aerodynamic drag the extra mass without much additional drag would reduce the loss of velocity. $\endgroup$ Commented Dec 24, 2019 at 21:49
  • $\begingroup$ That might actually make sense! It would be great if we could find some data on the height while separation occurs for the one engine centaur and the used two engine centaur with the lower flight profile. Or even better the dynamic pressure at booster separation. $\endgroup$
    – Christoph
    Commented Dec 24, 2019 at 22:41
  • 1
    $\begingroup$ @RichardSilvera: Only true if they were coasting. But in this case the main engine was still running, so the boosters were dead weight and drag. $\endgroup$
    – Michael
    Commented Dec 25, 2019 at 11:45

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