SpaceX Falcon 9 FT - ORBCOMM-2 - Dec. 21, 2015 (Return To Flight) DISCUSSION

[bstrong]

I wonder why the returned stage has a white band in the middle with less soot than above and below.

Start of ignition with green tinge from ignition fluid. The first stage is still pretty close.

From this angle, it looks to me like the discoloration at the top could have come from scorching/soot from the S2 engine. But that doesn't quite explain the clean line visible from the other side.

I wonder if they paused after loading half the LOX, giving more time for ice to form on the lower half of the tank.

[cscott]

The soot would have been deposited during the boostback, reentry, and landing burns---most likely the latter two since there would have been little atmosphere to "blow" the exhaust back onto the stage during the boostback burn.

The LOX tank would still be partially full during those burns, so consensus seems to be that the cold LOX somehow prevented soot deposition.  There was a great deal of debate (in one of the other threads) about the exact mechanism, how full the LOX tank would be at the time, etc etc.

Edit: having relayed what seemed to be the common opinion, I wonder myself if there's a different explanation.  Perhaps the lower soot is from *launch* (remember the "muddy water" of a previous launch), with the sharp line due to lox-induced ice, which would have been covering the entire top at the time.  Then the top soot is from S2, as proposed above.  And little/no soot from boostback, reentry, or landing.

[Dudely]

Photo of booster with crane:

Most of it is covered in soot except for a wide white band in the middle, why is that? I've seen some speculation that this was due to ice covering the LOX tonk but all the fuel should have been drained by now. Maybe a layer of ice prevented soot deposition earlier?

The soot gets there only during flight. During flight, the tanks are very, very cold, even when mostly empty, so they always have at least some frost. Soot doesn't stick to ice or frost very well, and is removed when it melts.

I find it hilarious that the CGI renderings and videos of landing show it as black because they knew about the soot. I saw so many people asking "why don't they paint the legs black like in the promo video". Because that wasn't paint. . .

The clean white lines through the lighter soot at the top is where the LOX vents are.

[Rocket Science]

Historic article William, thank you and to NSF coverage of the event, well done all!!

[Lee Jay]

Photo of booster with crane:

Most of it is covered in soot except for a wide white band in the middle, why is that? I've seen some speculation that this was due to ice covering the LOX tonk but all the fuel should have been drained by now. Maybe a layer of ice prevented soot deposition earlier?

Why would they assemale a lattice boom crane for this lift?  If any lift called for a hydraulic crane this is it.

[Ben the Space Brit]

I wonder why the returned stage has a white band in the middle with less soot than above and below.

This is only a guess on my part but I wonder whether the answer lies in the flow dynamics of the exhaust and atmospheric gasses around the core during descent. I'm no expert on laminar flow dynamics, but isn't it possible that there was a 'cool void' of trapped low-energy gas around the middle of the vehicle during re-entry that stopped fusion and combustion products from depositing on that part of the hull? The gas flow curved back towards the hull towards the top of the vehicle and, of course, were nearly in contact close to the engines, meaning that burns appeared on those parts of the hull.

[andrewsdanj]

Just an idle observation, but I note the grid fins retained hydralic pressure (stayed 'stuck out') after landing, rather than drooping as per the F9R Dev 1/2 landings. Probably means nothing but it's just the sort of thing that jumps out!

[GORDAP]

Photo of booster with crane:

Most of it is covered in soot except for a wide white band in the middle, why is that? I've seen some speculation that this was due to ice covering the LOX tonk but all the fuel should have been drained by now. Maybe a layer of ice prevented soot deposition earlier?

I wonder if the top soot was actually caused by the 2nd stage exhaust.  I recall hearing that the 2nd stage fired up when the 1st stage was still quite close.

[TrevorMonty]

I know they've been making landing improvements each time, but the Falcon came down so perfectly vertical and dead center on the pad, that I can't believe they didn't land on the barge before this.

All previous landing failures seem to have been specific hardware issues, which have been since rectified.

And it seems they can do barge landings now if they need the extra performance for heavier payloads.
I wonder if that'll be in the mix, or if they'll only come back to the pad?

I'm not sure if it's been confirmed but the general consensus at this point seems to be that the SES-9 launch may use the ASRD barge.

Should be a mix of barge and land landings. With upgrade to v1.2 a lot of expendable V1.1 GTO flights will now be recoverable.

[mnelson]

I suggest a new color scheme for the Falcon 9 first stage: black with a large white band in the middle. It would hide the soot better. Used rockets with unmarred paint jobs have a much higher resale value. 

[bstrong]

Looking back at the last launch, you can definitely see some darkening during ascent. It really starts to pick up as the atmosphere thins/disappears, which makes sense when you think about it.

I'm not sure that the source really matters. I'm more curious about what the sharp banding indicates. I'm not buying that it was the LOX level at the time of boost-back or re-entry burns, since that would indicate much more LOX was present at those times than seems plausible to me.

[rst]

The "important test" of the 2nd stage re-entry burn might have been just to verify that the stage *could* relight in vacuum, without problems like those encountered on the first v1.1 launch (due, iirc, to frozen TEA/TEB igniter fluid).

[Antilope7724]

Even if it turns out the rocket body has metal fatigue or stress cracks that might prevent reuse, they still got back 9-rocket engines they could probably use again.

[Kaputnik]

Even if it turns out the rocket body has metal fatigue or stress cracks that might prevent reuse, they still got back 9-rocket engines they could probably use again.

That's an interesting point. Elon has ruled out reusing the stage a a whole, but I would love to be able to track what happens to the engines- will they go into a pool like the SSMEs did, or will stages remain intact after assembly?

[jimbowman]

Chris, don't know if you said anything about it yet but how did the servers do?

Edit: Nm, saw you posted about it last night and everything was good.

[Comga]

Another image taken a short while ago:

Where is this?
It's doesn't look like LX-1.  There is no tank there that we have seen, and little need for one.
These look like the mounts from the now abandoned ASDS base at Jacksonville.
SpaceX must have carried the stage via the crane.  That should be great video if they show it.

edit: Less certainty, more questioning

[rpapo]

Where is this?
It's definitely not LX-1.  There is not tank there.
These look like the mounts from the now abandoned ASDS base at Jacksonville.
SpaceX must have carried the stage via the crane.  That should be great video if they show it.

Those tanks don't need to be really close to the pad.  Think telephoto lens...

Besides, we only saw less than half the perimeter of the pad in yesterday's picture.  From the helicopter shot you can see there are other things there, and that in only a small additional part of the perimeter not visible in yesterday's daylight photos.

[edkyle99]

Looking back at the last launch, you can definitely see some darkening during ascent. It really starts to pick up as the atmosphere thins/disappears, which makes sense when you think about it.

I'm not sure that the source really matters. I'm more curious about what the sharp banding indicates. I'm not buying that it was the LOX level at the time of boost-back or re-entry burns, since that would indicate much more LOX was present at those times than seems plausible to me.

I believe it has to do with the tank wall temperature, which would be indicated by an external frost layer.  LOX doesn't have to be up to that level, the tank wall just has to be down to that temperature.  My guess is that these deposits were laid either during the boostback burn in near vacuum or during the reentry burn, or possibly even during second stage ignition.  When the frost layer melted, it took away the soot.  Given the height of the "temperature line", I wouldn't be surprise to learn that it was during second stage ignition or during the first, boostback burn.

 - Ed Kyle

[AncientU]

Even if it turns out the rocket body has metal fatigue or stress cracks that might prevent reuse, they still got back 9-rocket engines they could probably use again.

The stage tanks were fully pressurized at landing -- metal fatigue/stress cracks would likely compromise the integrity of the tanks, leading to failure before landing.  Bet the tanks are in tact and reusable.

[meekGee]

Another image taken a short while ago:

Where is this?
It's doesn't look like LX-1.  There is no tank there that we have seen, and little need for one.
These look like the mounts from the now abandoned ASDS base at Jacksonville.
SpaceX must have carried the stage via the crane.  That should be great video if they show it.

edit: Less certainty, more questioning

Well you either have to bring the rocket to the ground mount, or the ground mount to the rocket.  Since the rocket is not connected to the ground, and is only one piece, I vote for door #1.

I think this answers the question of why use a lattice crane - since they are track-mounted and can move while carrying a load.  Or alternatively, can have a longer reach, and thus swing the rocket to the launch mount.