SpaceX F9 : Bangabandhu-1 : KSC 39A : May 11, 2018 : Discussion

[Kaputnik]

Late abort brings back memories of early F9 launches! When was the last one?

[ZachS09]

Late abort brings back memories of early F9 launches! When was the last one?

NROL-76 was aborted at T-52 seconds due to a first stage LOX sensor issue.

Intelsat 35e was aborted at T-9 seconds twice in a row due to GNC and ground computer problems.

SpaceX CRS-10 was aborted at T-13 seconds due to a Stage 2 TVC actuator issue.

[LouScheffer]

Very interesting - constant thrust of 190klb all the way up rather than constant chamber pressure.

Commentator says first stage Merlins will be throttled to maintain 190,000 lbs of thrust as the atmospheric pressure decreases with altitude.
This seems like half an explanation.  Why would that help? 

My guess - to reduce the g-loads on the vehicle. The acceleration will be already increasing due to all the fuel that has been burnt no longer weighting the rocket down and engines increasing thrust will only add to that. I guess on some missions it might not be a problem but on some (crewed missions, more sensitive satellites) it could be useful.

I wonder if this is some side effect of human rating?  To meet NASA specs, they need 40% margin on all parts at all times.   Perhaps the rocket has this margin at sea level, but margins would drop to less than 40% if they allowed the natural thrust growth with higher altitude.  So they use constant thrust to stay at 40% margin.

The reason I suggest this is that constant thrust should have more gravity loss, and hence would normally be avoided.

This also explains why the first stage burn times are just a little shorter, rather than a lot shorter as you would expect, given higher thrust and the same tanks.

[deruch]

If I remember right, when SpaceX went to subcooled LOX, temperature issues meant they were basically committed to a window of a few seconds (basically, no chance for a hold, so a hold would be a scrubd). But that does not appear to be the case today - they appear to at least have the capability to hold.

And I too am intrigued by the lack of frost. There should be plenty over the LOX tank. My guess is Clayjar's guess is right, some sort of coating. 

And dang, a scrub!

SES-9 was the first with subcooled LOX and they had multiple holds after loading including a potential second attempt after an abort post engine ignition.  I do believe that might also have been the case in the early launches with subcooling.  They might have gone later to "once we load LOX, we go or we scrub", but that wasn't the initial procedure.

[ZachS09]

SES-9 was the first with subcooled LOX and they had multiple holds after loading including a potential second attempt after an abort post engine ignition.  I do believe that might also have been the case in the early launches with subcooling.  They might have gone later to "once we load LOX, we go or we scrub", but that wasn't the initial procedure.

Actually, Orbcomm-OG2 F2 (the first ever landing of a Falcon 9 booster) was the first with subcooled LOX.

[whitelancer64]

So, the SpaceX down the side of the first stage is not iced over.  Is there a coating or something they could use to keep it from frosting over?  (I don't know what a superhydrophobic coating would do on the outside of a subcooled LOX tank.)

No, it's much simpler - the SpaceX logo is now entirely on the RP-1 tank. So the LOX tank can, and still does, frost over and not obscure the logo.

[ClayJar]

I didn't notice this maybe because my screen and resolution is too small. Could you grab a screen of what you're referring to and share it here?

I've attached an unaltered screenshot from a couple minutes before launch.  The area of the SpaceX logo is clearly different than the surrounding area.  If you use Photoshop to alter the exposure curve, you can easily bring up the contrast there, but I figured it would be better to leave it as is so that I wasn't piling compression on enhancement on compression, ad nauseum.

So, the SpaceX down the side of the first stage is not iced over.  Is there a coating or something they could use to keep it from frosting over?  (I don't know what a superhydrophobic coating would do on the outside of a subcooled LOX tank.)

No, it's much simpler - the SpaceX logo is now entirely on the RP-1 tank. So the LOX tank can, and still does, frost over and not obscure the logo.

The LOX is on top, is it not?  They moved the SpaceX, but they moved it from the part of the first stage that is RP-1 up to the middle, so naturally, it should frost over more.  (Post-landing visibility being one assumption for why it was moved -- the LOX section being less sooty once you've landed once.)  Also, you can clearly see that the area around the SpaceX is different than the surrounding area at the same level.

Of course, since I don't have up-close detail of the Falcon 9 Block 5 as it's icing over, I can't eliminate the null hypothesis, i.e. that the SpaceX logo may ice over just as much as its surroundings but just look a bit different due to how they put the SpaceX logo on there or something they did to it pre-launch (e.g. after static fire cleaning, or whatever).

[rickl]

NROL-76 was aborted at T-52 seconds due to a first stage LOX sensor issue.

Intelsat 35e was aborted at T-9 seconds twice in a row due to GNC and ground computer problems.

SpaceX CRS-10 was aborted at T-13 seconds due to a Stage 2 TVC actuator issue.

How about aborts after ignition?  There was F9 Flight 1* and COTS-2, and I seem to recall at least one other time.

(*I hadn't paid attention to SpaceX before that.  They had an ignition abort and turned around and launched successfully the same day.  I had never heard of that ever happening before.  That was when I started taking SpaceX seriously.

I watched the Gemini 6 ignition abort live, and I know it happened a few times with the Shuttle, but in none of those cases was there another launch attempt the same day.

I realize I'm veering off-topic, but has that ever happened with any other rocket?  Feel free to point me to the proper thread.)

[envy887]

Just to confirm, both stages are indeed block 5.

So will this include a thrust increase of M1D Vac to some 1000kN?

The thrust of M1DVac currently available on SpaceX's website seems not matching the sea-level version. In v1.1 era it is 11% more powerful (720kN vs. 800kN), but now only a 2% increase.

No, the MVac doesn't have a thrust increase with Block 5 AFAIK.

Ok, I take that back. Musk said today that the MVac increased to 220 klbf (979 kN).

[IanThePineapple]

NROL-76 was aborted at T-52 seconds due to a first stage LOX sensor issue.

Intelsat 35e was aborted at T-9 seconds twice in a row due to GNC and ground computer problems.

SpaceX CRS-10 was aborted at T-13 seconds due to a Stage 2 TVC actuator issue.

How about aborts after ignition?  There was F9 Flight 1* and COTS-2, and I seem to recall at least one other time.

(*I hadn't paid attention to SpaceX before that.  They had an ignition abort and turned around and launched successfully the same day.  I had never heard of that ever happening before.  That was when I started taking SpaceX seriously.

I watched the Gemini 6 ignition abort live, and I know it happened a few times with the Shuttle, but in none of those cases was there another launch attempt the same day.

I realize I'm veering off-topic, but has that ever happened with any other rocket?  Feel free to point me to the proper thread.)

SES-9 aborted after ignition at least once

[ZachS09]

SES-8 aborted after engine start on Thanksgiving 2013.

[Norm38]

On the conference call, I heard Musk say that thrust is reduced because of increasing vibration.

[Comga]

SES-8 aborted after engine start on Thanksgiving 2013.

All of this is available in cartman's terrific SpaceX Launch Log

[mn]

How about aborts after ignition?  There was F9 Flight 1* and COTS-2, and I seem to recall at least one other time.
...
I watched the Gemini 6 ignition abort live, and I know it happened a few times with the Shuttle, but in none of those cases was there another launch attempt the same day.

I realize I'm veering off-topic, but has that ever happened with any other rocket?  Feel free to point me to the proper thread.)

If I remember correctly the SSMEs required inspection/maintenance if there was an abort after ignition. (Or maybe even if the clock stopped within the last 30 seconds).

[Wolfram66]

Why did they wait so late in the window to attempt the launch?

[ZachS09]

Why did they wait so late in the window to attempt the launch?

My complete and utter guess is technical gremlins that SpaceX never told us publicly, or they might have monitored upper-level winds since they could've been RED at the start of the window.

[lonestriker]

Why did they wait so late in the window to attempt the launch?

My complete and utter guess is technical gremlins that SpaceX never told us publicly, or they might have monitored upper-level winds since they could've been RED at the start of the window.

On the webcast, they said they were looking at the telemetry logs to determine the cause of the abort.  ULW would not be telemetry.  I seem to recall two consecutive aborts due to some GSE sensor being out of whack; so maybe it's just the wind again, swaying the rocket just past the threshold to trigger an abort.

[OnWithTheShow]

Why did they wait so late in the window to attempt the launch?

My complete and utter guess is technical gremlins that SpaceX never told us publicly, or they might have monitored upper-level winds since they could've been RED at the start of the window.

On the webcast, they said they were looking at the telemetry logs to determine the cause of the abort.  ULW would not be telemetry.  I seem to recall two consecutive aborts due to some GSE sensor being out of whack; so maybe it's just the wind again, swaying the rocket just past the threshold to trigger an abort.

He wasn't referring to the abort. He was referring to the decisions during the course of the day to push later into the window.

[Jim]

I wonder if this is some side effect of human rating?  To meet NASA specs, they need 40% margin on all parts at all times.   

That is not a requirement.

[ChrisC]

Elon’s press call earlier:

Transcript of the call:
https://gist.github.com/theinternetftw/5ba82bd5f4099934fa0556b9d09c123e

I just wanted to call out theinternetftw with extra thanks for providing this transcript.  I listened to the telecon audio, AND then read the transcript, and really got a lot of detail out of the latter that I'd missed the first time through.  And reading it, even with the finer detail, goes a little faster than listening to it.  I'm sure you're using some speech-to-text software there but there's still a lot of human effort involved and I wanted to thank you for it, more than just clicking the little "like" button.