SpaceX FH: STP-2 : LC-39A : June 25, 2019 - DISCUSSION

[cscott]

Did they bring home just the one side, or both sides of the fairing?  Haven't really been able to tell from the pictures...

The GO sister ships haven't made port yet.  They would be the ones carrying the other fairing half.

https://twitter.com/SpaceXFleet/status/1144681621162987523

[Paul_G]

During the booster boostback burn there was something "flying around" with a gaseous "tail" in the plume interactions. It can be seen in the IR view from T+02:45 to 02:50 (from 27:43 in the Youtube video). Does anyone know what it was?
I'm not suggesting that anything went wrong, I'm just curious.

I noticed that - it definitely looked (to the untrained eye) like something spinning around and gassing out - in my snapshot it doesn't look much, but for the second or so that it is visible in the video stream, it looked significant. Perhaps it was something from the side booster ejection mechanism - during the pre launch chat on the video stream, the separation mechanism was described as using high pressure gas.

[gongora]

Are you sure you're not just looking at the exhaust from the center engine on the core that's still burning?

[Paul_G]

Are you sure you're not just looking at the exhaust from the center engine on the core that's still burning?

It doesn't look like the exhaust - in the video stream it definitely looks an object spinning, rather than the core engine thrust impinging on the boosters. Perhaps its just the result of the Infra Red video.

[Robotbeat]

Are you sure you're not just looking at the exhaust from the center engine on the core that's still burning?

It doesn't look like the exhaust - in the video stream it definitely looks an object spinning, rather than the core engine thrust impinging on the boosters. Perhaps its just the result of the Infra Red video.

it’s a phenomenon in the exhaust itself.

[OneSpeed]

Are you sure you're not just looking at the exhaust from the center engine on the core that's still burning?

It doesn't look like the exhaust - in the video stream it definitely looks an object spinning, rather than the core engine thrust impinging on the boosters. Perhaps its just the result of the Infra Red video.

gongora is correct, it is a downstream Mach disk formed by the interaction of the exhaust plumes  from the core stage. There is an excellent explanation of this phenomenon in the video 'The flames of the rockets, part 2 of 2' by 'French Space Guy' starting at:

[intrepidpursuit]

During the booster boostback burn there was something "flying around" with a gaseous "tail" in the plume interactions. It can be seen in the IR view from T+02:45 to 02:50 (from 27:43 in the Youtube video). Does anyone know what it was?
I'm not suggesting that anything went wrong, I'm just curious.

It's basically the high altitude version of a Mach diamond. It's normal and can be seen with many kerolox rockets, here's an example on a Saturn V

Recent F9 launch seen pretty much from sideways, starting at around 30 seconds in:

This guy must be from LA. If the boosters landed in Vandenberg now THAT would be impressive.

[ugordan]

[mlindner]

Here is a plot of the second stage telemetry. It took a while to process the 350,000 odd frames from the webcast, but it is interesting to note the low acceleration implied by the raw data, less than 1g for all burns. This distortion would have been caused by the high yaw angle used for the plane changes, which resulted in a much lower measured ΔV than actually occurred.

Correction for those reading the plot here, 980 cm/s^2 is 1g so all the burns were all over 1g.

[mark_m]

Here is a plot of the second stage telemetry. It took a while to process the 350,000 odd frames from the webcast, but it is interesting to note the low acceleration implied by the raw data, less than 1g for all burns. This distortion would have been caused by the high yaw angle used for the plane changes, which resulted in a much lower measured ΔV than actually occurred.

Correction for those reading the plot here, 980 cm/s^2 is 1g so all the burns were all over 1g.

I took it to mean the raw data implied a (misleading) less-than-1g set of burns, which became the final greater-than-1g values after accounting for the high yaw angle.

[Alexphysics]

23 objects tracked now, including Falcon upper stage. LightSail should still be inside Prox-1, and Tepce may not have split yet, so this could be all.

DSX and PSat-2 are identified.

NORAD  Name      NSSC ID    Type  Country Period Incl.   Apo  Peri

44339  OBJECT A  2019-036A  TBA     TBD   99.13  24.00   725   709
44340  OBJECT B  2019-036B  TBA     TBD   99.12  24.00   725   708
44341  OBJECT C  2019-036C  TBA     TBD   99.12  24.00   725   708
44342  OBJECT D  2019-036D  TBA     TBD   99.11  24.00   725   707
44343  OBJECT E  2019-036E  TBA     TBD   99.10  24.00   725   707
44344  DSX       2019-036F  PAYLOAD US   316.92  42.21 12035  6005
44345  FH R/B    2019-036G  R/B     US   306.86  42.24 11936  5449
44346  OBJECT H  2019-036H  TBA     US    96.27  28.52   853   307
44347  OBJECT J  2019-036J  TBA     US    96.24  28.53   850   307
44348  OBJECT K  2019-036K  TBA     US    96.23  28.52   852   304
44349  OBJECT L  2019-036L  TBA     TBD   99.10  24.00   724   707
44350  OBJECT M  2019-036M  TBA     TBD   99.10  24.00   724   707
44351  OBJECT N  2019-036N  TBA     TBD   99.09  24.00   724   706
44352  OBJECT P  2019-036P  TBA     TBD   96.23  28.53   849   307
44353  OBJECT Q  2019-036Q  TBA     TBD   99.09  24.00   724   706
44354  OBJECT R  2019-036R  TBA     US    96.19  28.53   847   305
44355  OBJECT S  2019-036S  TBA     US    96.19  28.53   847   305
44356  OBJECT T  2019-036T  TBA     US    96.15  28.52   847   301
44357  PSAT2     2019-036U  PAYLOAD US    96.17  28.53   845   306
44358  OBJECT V  2019-036V  TBA     US    99.09  24.00   725   705
44359  OBJECT W  2019-036W  TBA     US    96.14  28.52   847   300
44360  OBJECT X  2019-036X  TBA     US    96.12  28.53   848   297
44361  OBJECT Y  2019-036Y  TBA     US    96.12  28.52   848   297

Now it seems the FH second stage ended up in a bit different orbit than the DSX after all so it could probably be that the earlier orbit estimate was not very good and now with a better estimate it really shows some difference between both orbits. If that's the case, maybe there was a propulsive passivation after all.

[OneSpeed]

Here is a plot of the second stage telemetry. It took a while to process the 350,000 odd frames from the webcast, but it is interesting to note the low acceleration implied by the raw data, less than 1g for all burns. This distortion would have been caused by the high yaw angle used for the plane changes, which resulted in a much lower measured ΔV than actually occurred.

Correction for those reading the plot here, 980 cm/s^2 is 1g so all the burns were all over 1g.

My mistake. I should have said 'for all of the first burn' (SES2). From the telemetry, the ΔV was 7022 - 6963 = 59m/s, over a 23 second burn. That's an average of 2.6 m/s², or 0.26g, much less than the Merlin engine could deliver with that gross mass. E.g. if the engine was actually producing a 4g burn, then the yaw angle must have been cos-1(0.26/4) = 86.27°.

[ThatOldJanxSpirit]

23 objects tracked now, including Falcon upper stage. LightSail should still be inside Prox-1, and Tepce may not have split yet, so this could be all.

Now it seems the FH second stage ended up in a bit different orbit than the DSX after all so it could probably be that the earlier orbit estimate was not very good and now with a better estimate it really shows some difference between both orbits. If that's the case, maybe there was a propulsive passivation after all.

I’m estimating that to be a 145 m/s manoeuvre at around apogee. If they lit the engine it would have consumed about 200kg of propellant which would seem to be a very tight margin. Most likely they just dumped everything through the nozzle as shown in the animation. Assuming the same Isp as an N2 CGT (70s) then a tonne of propellant would have been vented, so this seems quite credible.

Likely that cruising for an extra two and a half hours then demonstrating that the vehicle was still controllable and fluids could still flow was an adequate demonstration to the USAF that it was capable of relighting for GEO insertion.

[Comga]

https://twitter.com/spacex/status/1146546495241371649

View from the fairing during the STP-2 mission; when the fairing returns to Earth, friction heats up particles in the atmosphere, which appear bright blue in the video

Super cool
The reentry seems remarkably stable
The fairing looks almost empty in the distorted view of the fisheye lens.
What’s that ring that appears faintly around 0:15 and strongly at the end?
The video is under one minute.
Is it sped up, edited?
The chute just appears. Any deployment action is hard to see.

[Vettedrmr]

The video is under one minute.
Is it sped up, edited?
The chute just appears. Any deployment action is hard to see.

Edited, yes.  But it doesn't look like it runs at anything other than normal speed.

Have a good one,
Mike

[ThatOldJanxSpirit]

https://twitter.com/spacex/status/1146546495241371649

View from the fairing during the STP-2 mission; when the fairing returns to Earth, friction heats up particles in the atmosphere, which appear bright blue in the video

Super cool
The reentry seems remarkably stable
The fairing looks almost empty in the distorted view of the fisheye lens.
What’s that ring that appears faintly around 0:15 and strongly at the end?
The video is under one minute.
Is it sped up, edited?
The chute just appears. Any deployment action is hard to see.

I also note there is a lot of thruster activity during entry.

Is it me, or have they mounted the fairing sideways. Both the entry and Ms Tree videos seem to show it flying sideways on. Iirc in all previous videos it has flown pointy end first.

[cscott]

I also note there is a lot of thruster activity during entry.

Is it me, or have they mounted the fairing sideways. Both the entry and Ms Tree videos seem to show it flying sideways on. Iirc in all previous videos it has flown pointy end first.

There's further discussion in the fairing reuse thread: https://forum.nasaspaceflight.com/index.php?topic=37727.msg1962801.msg#1962801

I agree the landing is "sideways" but the re-entry video seems to be looking aft from a nose-mounted camera re-entering nose first. To me, at least.

[matthewkantar]

Rewatching the fairing reentry video, this time on a desktop instead of my phone. Definitely one of the best space vids I have ever seen.

I have a question, not sure if it has been answered here: Is the little bit of thermal protection we have seen on the tip of the fairing protection for the ascent, or for the descent?

[Alvian@IDN]

I have a question, not sure if it has been answered here: Is the little bit of thermal protection we have seen on the tip of the fairing protection for the ascent, or for the descent?

The former. Although the fairing reenter even faster than the center core, it's (relatively) lightweight, the air pushes the fairing like a piece of paper falling down instead of like a pencil (okay, maybe not that light, because it still need parafoil)

[codav]

I have a question, not sure if it has been answered here: Is the little bit of thermal protection we have seen on the tip of the fairing protection for the ascent, or for the descent?

The former. Although the fairing reenter even faster than the center core, it's (relatively) lightweight, the air pushes the fairing like a piece of paper falling down instead of like a pencil (okay, maybe not that light, because it still need parafoil)

I strongly disagree and say it's the latter, for two reasons.

First, rocket speeds through ascent aren't high enough to really heat up the fairing tip so much that it needs any additional protection. No other rocket using expendable fairings have this extra protection.

Second, SpaceX only recently added this extra metal protection to the tip to fairings which were planned to be recovered. The recent RADARSAT launch, for example, didn't sport the thermal protection cap. And in the reentry video, you can clearly see sparks coming from the tip, which is the area where air compression is highest as the fairing is moving very fast horizontally as it hits the upper atmosphere tip-first. The camera has a large field of view, it's a fisheye lens, so it is not clearly visible.