Author Topic: SpaceX F9 / Crew Dragon : Crew-7 : KSC LC-39A : 26 August 2023 (07:27 UTC) (Read 163607 times)

Perchlorate · « **Reply #420 on:** 08/26/2023 02:33 pm »

Is there a video of the launch that has the 1st stage altitude and velocity displayed continuously?

On droneship landing missions, it seems that entry burn starts at a velocity of about 8,000 km/hr and sheds about 2,000 km/hr. After entry burn shutdown, velocity sometimes sneaks back up a little before the quickly-thickening atmosphere reduces velocity rapidly.

I don't recall how RTLS missions differ in this regard. But I'd love to watch the velocity numbers around this (apparently) abbreviated entry burn.

[ edit: slowed down the speeds from 2.6% of the speed of light to 8,000 km/hr. Thanks, ChrisC! ]

Ghoti · « **Reply #421 on:** 08/26/2023 02:41 pm »

Was it a 3 engine landing burn?

abaddon · « **Reply #422 on:** 08/26/2023 02:59 pm »

It’s too bad this was a NASA launch broadcast missing 1st stage telemetry, would have been fascinating to see its entry speed and what kind of g load the stage saw due to atmospheric deceleration.

ZachS09 · « **Reply #423 on:** 08/26/2023 04:40 pm »

Quote from: Ghoti on 08/26/2023 02:41 pm

Was it a 3 engine landing burn?

Yes. The engine plume during the landing burn grew brighter two seconds into the burn, indicating the ignition of two more engines in addition to the center engine.

Those two outer engines fire for four seconds before leaving the center engine to slow the booster down to a soft landing.

ChrisC · « **Reply #424 on:** 08/26/2023 05:23 pm »

Quote from: Perchlorate on 08/26/2023 02:33 pm

On droneship landing missions, it seems that entry burn starts at a velocity of about 8,000 km/sec and sheds about 2,000 km/sec. After entry burn shutdown, velocity sometimes sneaks back up a little before the quickly-thickening atmosphere reduces velocity rapidly.

On ASDS returns, from my memory, typical entry burns start at 7900-8100 km/h (not km/sec

) and end at 5900-6400. It's something I check for every launch, watching to see if SpaceX is trying out a more aggressive entry. Sometimes I see a 8400 start and wonder ...

Quote

I don't recall how RTLS missions differ in this regard.

And if you are used to ASDS returns, the RTLS numbers are jarring, because they are MUCH lower, on the order of 4500 -> 3000. The boostback burn nulls out most of the horizontal component. Of course you can check the previous coverage for details.

Certainly an "out of family" entry -- I hope we learn more.

EDIT 1: Here is the entry burn for the Tranche 0 RTLS launch earlier this year, about 20 seconds long: https://youtube.com/watch?v=vnnUoZ66ihg&t=19m40s

EDIT 2: I finally finished watching the entirety of the launch coverage, and noted that the SpaceX commentator said that the entry burn would be ""just about 10 seconds" in length. The actual burn was more like 2-3 seconds, and at the time NSF's own commentators were clearly surprised and concerned at that short duration. IMO it was absolutely not normal, but I'll wait until it's confirmed somehow weeks from now

EDIT 3: It finally occurred to me to go check the other CCP launches. Every one prior to this one (all the way back to Demo-2) was an ASDS landing! I didn't hear them mention the milestone of a first-time RTLS during the coverage. So then I checked the non-CCP launches, specifically Axiom-2 which was RTLS. On that one it's clear that the entry burn was about 12 seconds long. During that burn, the speed reduced from ~4640 km/h to ~4380 km/h, a rather small amount, and it was only a single engine burn. But again I say, the Crew-7 behavior was definitely different and notable

EDIT 4: Veteran forum member OneSpeed analyzed this launch in comparison with AX-2 in this post in the Falcon simulation thread. See that post for timing data, graphs and a simulation video, but here's their conclusion:

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So, to summarise, the maximum dynamic pressure on re-entry is similar for AX-2 and a generic Starlink launch, but was 16% higher for Crew-7, and would be 25% higher if the re-entry burn was deleted. The maximum heating was least for AX-2, but both Crew-7 and Crew-8? would still have less heating than a Starlink launch.

There is a small saving in propellant, 480kg for Crew-7, 860kg deleting re-entry entirely. Deleting re-entry might enable an additional 80kg of payload to orbit. It depends whether the Crew-7 short burn resulted in damage to the booster. If Crew-7 was undamaged by the higher than usual dynamic pressure, then perhaps the re-entry burn could be deleted for some future RTLS missions?

edkyle99 · « **Reply #425 on:** 08/26/2023 06:09 pm »

To me, it looked different, that entry burn, but not out of sorts. The stage landed normally, the landing burn seemed normal. If there was a problem I think the stage would not have diverted to its LZ-1 landing. A benefit of the short entry burn is a cleaner stage after landing!

- Ed Kyle

FutureSpaceTourist · « **Reply #426 on:** 08/26/2023 06:15 pm »

LouScheffer · « **Reply #427 on:** 08/26/2023 07:36 pm »

Quote from: ChrisC on 08/26/2023 05:23 pm

Quote from: Perchlorate on 08/26/2023 02:33 pm
On droneship landing missions, it seems that entry burn starts at a velocity of about 8,000 km/sec and sheds about 2,000 km/sec. After entry burn shutdown, velocity sometimes sneaks back up a little before the quickly-thickening atmosphere reduces velocity rapidly.
On ASDS returns, from my memory, typical entry burns start at 7900-8100 km/h (not km/sec ) and end at 5900-6400. It's something I check for every launch, watching to see if SpaceX is trying out a more aggressive entry. Sometimes I see a 8400 start and wonder ...
Quote
I don't recall how RTLS missions differ in this regard.
And if you are used to ASDS returns, the RTLS numbers are jarring, because they are MUCH lower, on the order of 4500 -> 3000. The boostback burn nulls out most of the horizontal component. Of course you can check the previous coverage for details.

Certainly an "out of family" entry -- I hope we learn more.

I don't think it's out of family - RTLS just does not require a long entry burn. This has been mentioned before, and is even more apparent on FH side booster returns. They start their entry burns with a speed much lower than ASDS missions have at the end of their entry burns. My guess is that they still need the burn for steering, even if they do not need it for heating. So it can be *much* shorter.

DigitalMan · « **Reply #428 on:** 08/26/2023 08:40 pm »

On the webcast there was a mention that 1st stage shuts down a little early and 2nd stage burns longer compared to previous crew missions. So, less velocity for the 1st stage to shed on entry.

Yellowstone10 · « **Reply #429 on:** 08/26/2023 09:23 pm »

Quote from: DigitalMan on 08/26/2023 08:40 pm

On the webcast there was a mention that 1st stage shuts down a little early and 2nd stage burns longer compared to previous crew missions. So, less velocity for the 1st stage to shed on entry.

Axiom-2 also used an RTLS profile, and its entry burn lasted 8 to 10 seconds, starting around T+6:25:

Crew-7's entry burn began maybe a couple seconds sooner (probably within the margin of error of the timecode), and the commentator (SpaceX's Jessie Anderson, I think) mentioned the center engine lighting for "just about 10 seconds". As for the landing burn, Crew-7's began at T+7:22 with landing at 7:38 (judging by the camera on the booster). For Axiom-2, it looks like it began at T+7:28 with landing at about 7:45. So that would be consistent with it carrying more speed after the entry burn.

Targeteer · « **Reply #430 on:** 08/26/2023 09:25 pm »

Caught the end of a conversation between Dragon and Hawthorne about flight patches not being on board-guessing Increment 70. Jaws added they did scrounge Crew 7 patches from their personal items and velcro provided by SpaceX to attach them to flight suits. Hawthorne apologized for the error and stated the patches will be on CRS-28

Yellowstone10 · « **Reply #431 on:** 08/26/2023 09:51 pm »

Re: patches - apparently they forgot to attach the patches to the blue flight suits that were launched on board Crew Dragon.

The other off-nominal item - GPS 2 has dropped out, which they believe is due to off-nominal performance of one of its two antennas. They're go on the other two GPSes, and they think they may be able to resolve the fault by power-cycling the antenna, but since it's not urgent they're going to take more time to research the fault.

hektor · « **Reply #432 on:** 08/26/2023 10:05 pm »

Targeteer · « **Reply #433 on:** 08/26/2023 10:08 pm »

Dragon has a do not disturb sign

zubenelgenubi · « **Reply #434 on:** 08/26/2023 10:21 pm »

Quote from: catdlr on 08/26/2023 08:04 am

Thanks to Steven and FST for the great coverage.

Also, thank you to our NSF webcasters!

Targeteer · « **Reply #435 on:** 08/26/2023 10:54 pm »

no joy with GPS 2 power cycle. Phase burn go on 2 remaining units

Targeteer · « **Reply #436 on:** 08/26/2023 11:16 pm »

nominal phase burn

Yellowstone10 · « **Reply #437 on:** 08/26/2023 11:25 pm »

Another slightly off-nominal situation they just took care of:

https://twitter.com/Ian_Benecken/status/1695575977580011794
https://twitter.com/Ian_Benecken/status/1695576534617145784
https://twitter.com/Ian_Benecken/status/1695576938604032415

Quote

Another craziness on the #Crew7 mission: earlier @AstroJaws reported to #CORE that by looking out of the window they realized the blinking landing LEDs outside the #Dragon are constantly on. #SpaceX analyzed the situation and found out that pre-launch they were turned on as part of a functioning test and were forgot to put back off before launch. Since SpaceX has no telemetry on that system after liftoff they asked the #Crew7 crew to manually punch in the command to turn off the functioning test. That did the trick and the landing LEDs turned off outside #Dragon #Endurance.

penguin44 · « **Reply #438 on:** 08/27/2023 02:46 am »

Is it me or does this launch seem rushed? Landing LEDs not off, nosecone debris, forgot the patches. Until now it seemed well oiled.

FutureSpaceTourist · « **Reply #439 on:** 08/27/2023 05:17 am »

Quote from: penguin44 on 08/27/2023 02:46 am

Is it me or does this launch seem rushed? Landing LEDs not off, nosecone debris, forgot the patches. Until now it seemed well oiled.

I suspect every Dragon launch has its (minor) issues, but we may not always pick up on them?