SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION

[Kabloona]

Re-entry burn?

Yes, good catch. Stage 1 appears to light up just as it's leaving the edge of the plume (at 0:55) and stays lit for about 17 seconds, consistent with a short entry burn.

I see no burn in that gif or the original that I viewed a few days back.  My version of events is that we see sun illuminating the stage because of its having launched at sunset, the camera being in darkness, and the two stages being in direct sunlight.  There is no burn because we see no gas coming from it.  We have a gas plume coming from one Merlin on S2 and if there were a burn on S1 (either boostback, re-entry, or (in the case of this flight) landing) it would have 3x the gas plume of S2.  Clearly not that.  So we're not witnessing a boostback as SpaceX indicated (didn't they?) would be the case and this video is too early in the flight for us to see the re-entry burn.  AFAIK, S1 is still going up during the period shown.

I've been rethinking the illumination source too as you describe and now I think you are correct that it's solar illumination and not the entry burn (there was no boostback burn at all). Oh well.

[iamlucky13]

In addition to OxCartMark's point:

Listening to the technical webcast again, the callout "Stage 1 entry burn has started" occurred at rough T+6:30. Stage separation was about 2:45, so there's about 3:45 between the two.

I don't know when the video starts, but when the camera first zooms in to where the first stage is visible, they appear fairly close together, so I suspect not very long after stage separation. It would have to be about 2 minutes or more after stage separation for the re-entry burn to be visible, so I do not think we see the re-entry burn plume.

Really cool video nonetheless.

[cambrianera]

Maybe it is flip of the stage. Until first stage is in front of the view reflection is small, when stage flips and side is visible, reflection increases. When flip ends and stage is engine first, reflection goes down again.

[Chris Bergin]

Standalone thread for the topic that followed as it became a standalone topic.
http://forum.nasaspaceflight.com/index.php?topic=39927.0

[PDZiemer]

We saw that a bit of a slow start on one of the 3 SpaceX engines left "a big impression"

Did I miss something, or does someone know more about the cause of the failed landing attempt than has been posted on the public forum?  Maybe I am overreacting and this is just speculation and not a known fact.  Any information that can be shared to clarify what is known about the cause of this particular outcome would be greatly appreciated!

I apologize because I do not know how to quote correctly.  The quote is from the Blue Origin Fourth Developmental Flight Thread post by Comga
http://forum.nasaspaceflight.com/index.php?topic=39953.msg1511546#msg1511546

---
Edit/Lar: Fixed your quote for you. Welcome to the forums..  If you want to quote from another thread, the easy way to do this is right mouse click on "quote" while viewing what you want to quote. Then open in a new window. Then copy the body of the new post to where you want to use it and edit it down to remove what you don't want. That's how I did the above.

[cscott]

We saw that a bit of a slow start on one of the 3 SpaceX engines left "a big impression"

Did I miss something, or does someone know more about the cause of the failed landing attempt than has been posted on the public forum?

While @comga could be referring to one of the ASDS landing failures (the one where Elon tweeted about "throttle valve stiction" (aka failure to throttle up promptly enough) as the proximate cause) his mention of "three engines" makes it clear that he is referring to the most recent landing attempt.  There is a little extra information in L2 about that.

[FutureSpaceTourist]

I made the mistake of posting this in the updates thread.

Still think it's worth recording the extent to which SpaceX were able to get SES-9 closer to its final orbit:

Stephen Clark ‏@StephenClark1 13h13 hours ago

Gwynne Shotwell, SpaceX: We delivered SES-9 satellite to better than expected orbit, saving 43 days orbit-raising time. #32SS

https://twitter.com/StephenClark1/status/720730575376547840

[Ben the Space Brit]

I made the mistake of posting this in the updates thread.

Still think it's worth recording the extent to which SpaceX were able to get SES-9 closer to its final orbit:

Stephen Clark ‏@StephenClark1 13h13 hours ago

Gwynne Shotwell, SpaceX: We delivered SES-9 satellite to better than expected orbit, saving 43 days orbit-raising time. #32SS

https://twitter.com/StephenClark1/status/720730575376547840

I would argue that this serves as an 'update', so don't be too hard on yourself.

Such an accurate orbital insertion is worth bragging rights, no doubt about that. It will also be a positive for attracting customers.

[Chris Bergin]

Yeah, I think it suffered from a trim that came before and after that post in the update thread, which was lots of off topic, but it's fine here.

[mn]

...

Stephen Clark ‏@StephenClark1 13h13 hours ago

Gwynne Shotwell, SpaceX: We delivered SES-9 satellite to better than expected orbit, saving 43 days orbit-raising time. #32SS

https://twitter.com/StephenClark1/status/720730575376547840

is that 43 days better than the original launch plan? or 43 days better than the new target after the mission profile change announced earlier?

Press release from SES via BusinessWire: http://www.businesswire.com/news/home/20160208005441/en/

Select Quotes:

In order to minimise the impact of moving the launch from late last year, SpaceX is supporting a mission modification. The changed mission will reduce the time needed for SES-9 to reach its orbital slot, keeping the Operational Service Date (OSD) in the third quarter of 2016, as previously foreseen.

[FutureSpaceTourist]

The SES briefing before the first launch attempt date (see http://forum.nasaspaceflight.com/index.php?topic=39348.msg1494946#msg1494946) said that the plan was to cut in half the time needed to reach final orbit.

On a quick search I can't find what that time was, but my vague recollection was that it was about 2 months and so the plan was to reduce it by about a month.

I'm sure the 43 days refers back to the original 2 months (or whatever it ways). You may find specifics in the briefing post linked to above.

[ZachS09]

Remind me if this question was answered already:

How many kilograms of fuel reserve did the first stage have at MECO-1?

[Kabloona]

We saw that a bit of a slow start on one of the 3 SpaceX engines left "a big impression"

Did I miss something, or does someone know more about the cause of the failed landing attempt than has been posted on the public forum?  Maybe I am overreacting and this is just speculation and not a known fact.  Any information that can be shared to clarify what is known about the cause of this particular outcome would be greatly appreciated!

For the record, it's now been publicly confirmed that the stage ran out of propellant.

Surprisingly enough, the first stage of the SES-9 mission did successfully make it to the ASDS barge at the end of its suicide plunge to begin slowing itself to a safe landing velocity.

However, the low propellant reserve became a crippling factor in the final seconds of landing, as the first stage ran out of enough propellant to successfully maintain the landing burn and slow itself to an acceptable landing velocity and orientation.

https://www.nasaspaceflight.com/2016/05/spacex-static-fire-jcsat-14-mission/

[Kabloona]

Remind me if this question was answered already:

How many kilograms of fuel reserve did the first stage have at MECO-1?

LouScheffer calculated that the stage would have needed about 16.7t of propellant to do the 17 second entry burn and the 3-engine landing burn. But since the stage ran out of propellant during the landing burn, it was likely a bit short of that amount, so maybe around 16,000 kg.

http://forum.nasaspaceflight.com/index.php?topic=40168.0

[baldusi]

(...)
For the record, it's now been publicly confirmed that the stage ran out of propellant.

Surprisingly enough, the first stage of the SES-9 mission did successfully make it to the ASDS barge at the end of its suicide plunge to begin slowing itself to a safe landing velocity.

However, the low propellant reserve became a crippling factor in the final seconds of landing, as the first stage ran out of enough propellant to successfully maintain the landing burn and slow itself to an acceptable landing velocity and orientation.

https://www.nasaspaceflight.com/2016/05/spacex-static-fire-jcsat-14-mission/

Please understand that lack of enough propellant to maintain the landing burn might also mean that reserves were so low that it generated cavitation issues.

[Kabloona]

(...)
For the record, it's now been publicly confirmed that the stage ran out of propellant.

Surprisingly enough, the first stage of the SES-9 mission did successfully make it to the ASDS barge at the end of its suicide plunge to begin slowing itself to a safe landing velocity.

However, the low propellant reserve became a crippling factor in the final seconds of landing, as the first stage ran out of enough propellant to successfully maintain the landing burn and slow itself to an acceptable landing velocity and orientation.

https://www.nasaspaceflight.com/2016/05/spacex-static-fire-jcsat-14-mission/

Please understand that lack of enough propellant to maintain the landing burn might also mean that reserves were so low that it generated cavitation issues.

Yes, I understand. IIRC, the "low thrust" was reported on one engine, so the other two were apparently running at full thrust. "Ran out of propellant" here is shorthand for "propellant level got so low that at least one engine was no longer able to run."

Similar to a car where "running out of gas" doesn't mean there is no gas at all left in the tank. Just not enough for the fuel delivery system to work properly.

So there was probably enough residual propellant left to make a nice fireball. ;-)

[TrueBlueWitt]

(...)
For the record, it's now been publicly confirmed that the stage ran out of propellant.

Surprisingly enough, the first stage of the SES-9 mission did successfully make it to the ASDS barge at the end of its suicide plunge to begin slowing itself to a safe landing velocity.

However, the low propellant reserve became a crippling factor in the final seconds of landing, as the first stage ran out of enough propellant to successfully maintain the landing burn and slow itself to an acceptable landing velocity and orientation.

https://www.nasaspaceflight.com/2016/05/spacex-static-fire-jcsat-14-mission/

Please understand that lack of enough propellant to maintain the landing burn might also mean that reserves were so low that it generated cavitation issues.

I would think the high Gs from 3 engine deceleration would help keep the head pressure up.. Or is that not enough to offset for the low volume and reducedstatic head pressure?

[mme]

(...)
For the record, it's now been publicly confirmed that the stage ran out of propellant.

Surprisingly enough, the first stage of the SES-9 mission did successfully make it to the ASDS barge at the end of its suicide plunge to begin slowing itself to a safe landing velocity.

However, the low propellant reserve became a crippling factor in the final seconds of landing, as the first stage ran out of enough propellant to successfully maintain the landing burn and slow itself to an acceptable landing velocity and orientation.

https://www.nasaspaceflight.com/2016/05/spacex-static-fire-jcsat-14-mission/

Please understand that lack of enough propellant to maintain the landing burn might also mean that reserves were so low that it generated cavitation issues.

I would think the high Gs from 3 engine deceleration would help keep the head pressure up.. Or is that not enough to offset for the low volume and reducedstatic head pressure?

If levels are super low, could the propellent line ingest helium pressurent via a vortex?  I'm thinking like a drain ingesting air in a sink.  Or would baffles prevent that from happening?  Apologies if that is a naive question.

[deruch]

(...)
For the record, it's now been publicly confirmed that the stage ran out of propellant.

Surprisingly enough, the first stage of the SES-9 mission did successfully make it to the ASDS barge at the end of its suicide plunge to begin slowing itself to a safe landing velocity.

However, the low propellant reserve became a crippling factor in the final seconds of landing, as the first stage ran out of enough propellant to successfully maintain the landing burn and slow itself to an acceptable landing velocity and orientation.

https://www.nasaspaceflight.com/2016/05/spacex-static-fire-jcsat-14-mission/

Please understand that lack of enough propellant to maintain the landing burn might also mean that reserves were so low that it generated cavitation issues.

I would think the high Gs from 3 engine deceleration would help keep the head pressure up.. Or is that not enough to offset for the low volume and reducedstatic head pressure?

If levels are super low, could the propellent line ingest helium pressurent via a vortex?  I'm thinking like a drain ingesting air in a sink.  Or would baffles prevent that from happening?  Apologies if that is a naive question.

One of the launch aborts from SES-9 was due to a low thrust warning because they "ingested" helium during start-up: 

C) 2016-02-28, Scrub at T-0, aborted on low thrust alarm. Rising oxygen temps due to hold for boat and helium bubble triggered alarm [65] (emphasis added)

So, at least under certain conditions it is possible.  Whether it is possible during the higher g-force landing burn or not, I couldn't say.