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The Falcon 9 first stage detaches at about 70 km high and it descends in about 6 minutes. That means an average descending speed of 200 m/s

But what is the maximum speed it reaches on descent?

And what is the speed on touchdown?

uhoh
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Joe Jobs
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  • Some of old SpaceX videos 2-3 years ago have two velocity panels - for upper stage (as always) and for first stage after separation. Max velocity of first stage can be seen there. But I haven't time to find appropriate video now... – Heopps Oct 06 '20 at 09:35

2 Answers2

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FlightClub.io is a general purpose launch simulator, and has several Falcon 9 launches in its mission library.

But what is the maximum speed it reaches on descent?

It will vary from mission to mission. According to FlightClub, for the GPS III SV04 launch, the first stage reached a maximum of about 2300 m/s during descent, but that is largely horizontal velocity.

And what is the speed on touchdown?

FlightClub is suspect here, giving a speed of 84 m/s. That would be a very destructive landing.

This Cosmos Magazine article gives a figure of 20 km/h, or about 5.5 m/s.

Russell Borogove
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    5.5 m/s sounds quite plausible. If the legs touch and the rest of the rocket slows to zero over 1 meter (just for example), that would be 15 gees average. If it were 2 meters, only 7.5 gees. – uhoh Oct 06 '20 at 02:47
  • How about the vertical descent speed? I changed the question too. – Joe Jobs Oct 06 '20 at 09:32
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    @JoeJobs In Stack Exchange it's not considered appropriate to change the nature of the question after an answer has been posted, unless there is some mutual agreement with the answer authors. It's great to follow up on a detail in comments, but better wait for the author to respond to your comment before changing the question. I've rolled it back to the previous version. – uhoh Oct 06 '20 at 10:04
  • @uhoh I know the eye is easily fooled, but the soft-landings I've watched -- land-based ones, mostly -- sure look like the vertical speed in the last couple meters before touchdown is considerable less than that. I'm not arguing about the speed but more about the length of time of the final engine burn (deceleration). I'll try to find a video and count the number of frames with burn visible. – Carl Witthoft Oct 06 '20 at 11:44
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    Flight Club creator here - the landing burn in that GPS III sim is incomplete, clearly 84m/s is incorrect. However the real velocity at landing is something Flight Club would not be able to determine. Physically speaking, the velocity could be anything. Only way to figure it out with any confidence would be to analyse landing videos. – Declan Murphy Oct 07 '20 at 14:16
  • Technically everything in space flight is largely horizontal velocity, aside from a few seconds when the craft is close to the ground... – Peter Kionga-Kamau Dec 12 '22 at 23:27
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Here is SpaceX launch video of OTV-5 spaceplane for US Airforce.

Falcon 9 first stage returns to landing pad on Cape Canaveral, so it's not the most extreme reentry.

We can see the maximum velocity of the reentering rocket was about 4600 km/h (time mark 19:30 on the video). After that reentry burn starts to slow it down.

The information from second stage was not public in this launh. It's common practice for national sequrity payloads.

I remember there were others videos with translated data of first stage speed after separation, but at quick look I coldn't find. One can try on SpaceX Youtube channel.

Heopps
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  • Without any engine burns, what kind of speed would it reach? Assuming it is indestructibile and it can handle any amount of heating – Joe Jobs Nov 30 '20 at 15:39