3
$\begingroup$

Will separating a stage(first) immediately after its burnout cause damage to the upcoming stage (2nd stage).?

Also,do the first stage separation and second stage ignition happen at the
same instant ??

Please share some flight events of a rocket launch.

$\endgroup$
  • $\begingroup$ Do mean why the events are sequenced burn out → wait → separation → wait → start next stage engine ? What other sequence do you expect? $\endgroup$ – DarkDust Sep 24 '18 at 11:12
  • 1
    $\begingroup$ So one part of your questions is "Do stage separation and next stage ignition typically take place in parallel or one after another? Why is it done one way or the other?" Did I get that right? But I still don't get the first part of your question regarding the burn out of the previous stage? $\endgroup$ – DarkDust Sep 24 '18 at 11:42
  • 3
    $\begingroup$ engine shutdown ins't an instantaneous event, and lower stages tend to be higher thrust than upperstages, especially when empty. $\endgroup$ – JCRM Sep 24 '18 at 12:42
  • 2
    $\begingroup$ Not all launch vehicles do this. Both the Soyuz launch vehicle and the Titan II perform(ed) "fire in the hole" staging, in which the upper stage lights before separation. See this video for Titan II staging: youtube.com/watch?v=PBkZNMM_IUg $\endgroup$ – Tristan Sep 24 '18 at 14:40
  • 1
    $\begingroup$ @uhoh I believe they called them "blowout panels" $\endgroup$ – Tristan Sep 24 '18 at 19:36
3
$\begingroup$

One reason for a brief pause between burnout of a lower stage and ignition of the next stage is to facilitate a gravity turn. If the rocket is still in substantial atmosphere, there is significant aerodynamic drag acting on the upper part of the vehicle. Keeping the lower stage attached can help offset the drag because of its mass and kinetic energy.

$\endgroup$
4
$\begingroup$

First question:

Will separating a stage(first) immediately after its burnout cause damage to the upcoming stage (2nd stage).?

While there are some exceptions such as the Soyuz 2-1v which is specifically designed to start the 3rd stage while the 2nd is still burning, there is almost always a delay between one stage burning out and one stage igniting. Stages do not burn out all at once; there is a residual amount of thrust that tapers off over a few seconds. This is usually accounted for by the delay between stages, but this was the exact mode of failure for a Falcon I launch in 2008. It seems they miscalculated the delay needed between MECO and staging.

"If there had been one extra second, this wouldn't have happened"

Here is a very dramatic video of the Titan II performing a similar type of staging (Thanks @Tristan)

Next question:

Also,do the first stage separation and second stage ignition happen at the same instant ??

No, there are usually at least a few seconds between stage separation and ignition. This timeline of the Falcon Heavy maiden flight shows an 8 second delay (from T+0:03:07 to T+0:03:15) between the two events. This is especially critical for reusable rockets such as the Falcons because the first stage must not be damaged.

$\endgroup$
  • $\begingroup$ Yep, the key is a "controlled separation" to prevent damage to the unburned stages which almost always results in a few second delay between burn-out, separation, and ignition of the next stage. The basic goal being to not damage the engine bells on the unburned stage during separation. $\endgroup$ – David C. Rankin Sep 26 '18 at 5:44

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.