When returning the side boosters of the latest Falcon Heavy launch to their landing site, their trajectories keep them right next to each other, and I noticed that a "wall" of vapor is visible midway between them. This made me wonder whether flying two boosters near each other has any performance effects in terms of fuel savings or waste. Does anyone know?

  • $\begingroup$ I'm thinking that landing near launch site may make the booster fly into the turbulence the rocket produces at take off. This may also affect descent performances. $\endgroup$
    – Manu H
    Jun 26, 2019 at 13:20
  • $\begingroup$ Do we have any evidence for the actual distance between the two during the reentry phase? $\endgroup$
    – asdfex
    Jul 1, 2019 at 9:29
  • $\begingroup$ @asdfex, I don't, but I would be interested to know. $\endgroup$ Jul 2, 2019 at 1:21

1 Answer 1


There is likely minimal effect.

At rocket speeds, there is very little effect of shear stress, the only significant effect is particles hitting the leading surface of the rocket.

Also due to how fast hey are going, the effect of the rocket of "pushing air out of the way" does not have time to get far ahead of the rocket, and this drops further behind as you move radially away from the rocket.

In fact the 'wall' in your question is the boundary of this region of influence.

As the leading bit of neither rocket is inside the volume effected by the other, neither is significantly effected (at least in terms of net force, vibration/temperature etc is a different game as these don't just effect the leading bits).

  • 3
    $\begingroup$ I like this answer but I wonder if it's all still true even when the rockets are descending / travelling in the direction their exhaust is going? $\endgroup$ Jun 26, 2019 at 1:46
  • $\begingroup$ @foobarbecue interesting question. The same observation that if it was outside of the cone around the end of the exhaust plume then little effect would occur for the same reason. It didn't look to me like this was happening, but its hard to be sure. If it did happen, it would hinder the performance. It would cause less drag and therefore need more active deceleration. As there is no reason for them to be so close on decent, i doubt it would come up. However, if they started trying to land two cores on one drone ship, this could well be an issue. $\endgroup$
    – ANone
    Jun 27, 2019 at 16:13
  • $\begingroup$ @ANone This answer lacks sources, can you provide some evidence for your claims? $\endgroup$ Jul 1, 2019 at 9:00
  • $\begingroup$ Since ANone has not been with us this year, I have locked this post since it still provides no evidence. I don't want to delete since it appears to be helpful. If ANone returns to provide sources or if someone else would like to edit sources in, then I can unlock the answer. $\endgroup$
    – called2voyage
    Sep 21, 2020 at 16:55

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

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