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

[Kabloona]

Come on, lets get back on topic. ICBMs have nothing to do with it.

2. How much propellant (RP-1 & LOX) did they have to unload?

LOX and helium is vented. The amount of RP-1 they had to unload is unknown, I don't think it would be much though (the legs cannot take a very heavy landing, and there is no need for a big reserve).

IIRC, the environmental impact statement for LZ-1 stated a relatively small quantity of RP-1 expected to remain after landing, something like 150 gallons, though it's hard to imagine cutting it that close.

[Lars-J]

Come on, lets get back on topic. ICBMs have nothing to do with it.

2. How much propellant (RP-1 & LOX) did they have to unload?

LOX and helium is vented. The amount of RP-1 they had to unload is unknown, I don't think it would be much though (the legs cannot take a very heavy landing, and there is no need for a big reserve).

IIRC, the environmental impact statement for LZ-1 stated a relatively small quantity of RP-1 expected to remain after landing, something like 150 gallons, though it's hard to imagine cutting it that close.

But still, there is a limit to what the legs can handle. My assumption is that on a high-margin flight like ORBCOMM, the landing burn might be a longer one at lower thrust, to use up the propellant quicker, and that for a low margin flight the final landing burn will be shorter but at a higher thrust level.

[Robotbeat]

Much more important than having 150 or 200 gallons of RP-1 will be the landing velocity. If you can get the landing velocity very close to zero, then it's fine to have a little extra propellant in the tanks.

[Dante80]

A new pic. Pretty cool scene I might say.

And a question. Could someone guess by this pic.

1. How close did the stage land to the center
2. How tall is it when landed on its legs

?

[Jim]

But still, there is a limit to what the legs can handle. My assumption is that on a high-margin flight like ORBCOMM, the landing burn might be a longer one at lower thrust, to use up the propellant quicker, and that for a low margin flight the final landing burn will be shorter but at a higher thrust level.

The margin  for the mission is in the second stage.  The first stage is going to  burn the same total amount of propellant between launch and boost back, which should leave the same fixed amount for landing.  Additionally, the payload mass really doesn't affect the first stage flight profile that much, it should be fairly the same for every mission.

[CameronD]

But still, there is a limit to what the legs can handle. My assumption is that on a high-margin flight like ORBCOMM, the landing burn might be a longer one at lower thrust, to use up the propellant quicker, and that for a low margin flight the final landing burn will be shorter but at a higher thrust level.

The margin  for the mission is in the second stage.  The first stage is going to  burn the same total amount of propellant between launch and boost back, which should leave the same fixed amount for landing.  Additionally, the payload mass really doesn't affect the first stage flight profile that much, it should be fairly the same for every mission.

All good info, but perhaps I should have explained the reason for my question:  Knowing how much was left might be an indication of whether or not they were cutting it fine with their margins on this flight.  After all, they've got a number of "landings" under their collective belts now, so, given that it appears they nailed it, I was curious to know whether or not they were being 'conservative' for this the first FT flight ...or not.

[CameronD]

A new pic. Pretty cool scene I might say.

Indeed!!  ..and our first good look at the leg hold-downs?  That's something that's been the topic of discussion on the ASDS Thread for months.

[meekGee]

Interesting detail on the soot pattern, those white streaks nearer the top of the unsooted area.

[Steven Pietrobon]

Here's an enhanced image of the engine closeup. The upper nozzle blanket definitely appears to have been eroded and likely needs to be replaced. That area is right next to a turbine exhaust outlet. The white stuff in the nozzles appears to be some liquid that has dried, perhaps some leaking TEA-TEB fluid, or an additive in the RP-1. There are also many small white marks on the outside of the engine bells. Not sure if that indicates stuff that has flecked on, or scratches made by some external abrasive material.

[Coastal Ron]

The upper nozzle blanket definitely appears to have been eroded and likely needs to be replaced. That area is right next to a turbine exhaust outlet.

My impression was that the insulation was like a blanket, and that it didn't erode but retracted "up" into the body (or likely pushed by aerodynamic forces), thus pulling away from the lower area of the engine it should have been covering.

Would be interesting to know if it is allowed to move like that.

[Comga]

Here's an enhanced image of the engine closeup. The upper nozzle blanket definitely appears to have been eroded and likely needs to be replaced. That area is right next to a turbine exhaust outlet. The white stuff in the nozzles appears to be some liquid that has dried, perhaps some leaking TEA-TEB fluid, or an additive in the RP-1. There are also many small white marks on the outside of the engine bells. Not sure if that indicates stuff that has flecked on, or scratches made by some external abrasive material.

Wow
Those patterns inside the two outer (what I assume are the numbers 1 and 5) engines are nearly mirror images of each other.
That can't be just a coincidence.
It must be deterministic.

Would there be a reason to inject the TEA-TEB into all three engines on all three restarts, even though the valves are only open for the center (#9?) engine for the entry and landing burns? 
Would that make the system simpler or more complex?

[sdsds]

I agree the whiter areas inside two engines opposite one another hint that those engines were the ones restarted. I assume the center engine has similar white area, but the "clocking" makes it less visible.

Something like ignition fluid sure makes sense, but I'm not sure: is there a way we can prune from the causal tree the possibility that these white areas are associated with second/third/fourth engine shutdown transients?

[Nomadd]

I agree the whiter areas inside two engines opposite one another hint that those engines were the ones restarted. I assume the center engine has similar white area, but the "clocking" makes it less visible.

Something like ignition fluid sure makes sense, but I'm not sure: is there a way we can prune from the causal tree the possibility that these white areas are associated with second/third/fourth engine shutdown transients?

I'd assume the center engine was black like the other six because it was run in the lower atmosphere after re-entry firing cleaned it out. Maybe it's close to the ground that the soot is deposited.
 Pretty weak, I know, but landing is the difference between the center and the other two.

[dorkmo]

how about a little bit of ice formed from the last bit of propellants after shutdown, stayed frozen through landing, coveree in soot, then melted away later, revealingn layer below.

[WBY1984]

I'm wondering whether this engine photo, which has annotation saying that it is for thermal testing -

https://www.instagram.com/p/6gYIwJl8ZH/

- could be to do with reflying sooty engines? The returned stage is pretty mucked up, it'd make sense they'd want to find out a bit about what that'd do to the engines.

[chalz]

The upper nozzle blanket definitely appears to have been eroded and likely needs to be replaced. That area is right next to a turbine exhaust outlet.

My impression was that the insulation was like a blanket, and that it didn't erode but retracted "up" into the body (or likely pushed by aerodynamic forces), thus pulling away from the lower area of the engine it should have been covering.

Would be interesting to know if it is allowed to move like that.

That's what it looks like to me to. To me it would count as part of the F9 design that anticipated reuse - specifically reentry. They want to protect the inner workings from air flow and debris and this solution does that and still allows the engines to gimbal.

[cscott]

I'm wondering whether this engine photo, which has annotation saying that it is for thermal testing -

https://www.instagram.com/p/6gYIwJl8ZH/

- could be to do with reflying sooty engines? The returned stage is pretty mucked up, it'd make sense they'd want to find out a bit about what that'd do to the engines.

At the time this was explained as needing to have a constant thermal emissivity so that IR imaging could obtain correct temperatures for every surface point.  Otherwise you have to calibrate for the emissivity of every different surface separately.

I don't think it's related to soot.

[ugordan]

There are also many small white marks on the outside of the engine bells. Not sure if that indicates stuff that has flecked on, or scratches made by some external abrasive material.

My speculation is that this is stuff that was blown up from the ground by the engine plume and then richocheted off of a leg back toward the engine section. The pattern looks too directional to be random particulate stuff deposited from the dust cloud. On the other hand the dustiness of the inside of a couple of nozzles (including fingerprints at the rim) does look like dust settling after shutdown.

[avollhar]

I'm wondering whether this engine photo, which has annotation saying that it is for thermal testing -

https://www.instagram.com/p/6gYIwJl8ZH/

- could be to do with reflying sooty engines? The returned stage is pretty mucked up, it'd make sense they'd want to find out a bit about what that'd do to the engines.

At the time this was explained as needing to have a constant thermal emissivity so that IR imaging could obtain correct temperatures for every surface point.  Otherwise you have to calibrate for the emissivity of every different surface separately.

I don't think it's related to soot.

With the right paint (higher IR emissivity), you can effectively cool via radiation. One reason why electronic heatsinks are black anodized rather than polished aluminum.

[Ohsin]

Cross posting from Updates thread, (because discussion is not updates.....)

http://forum.nasaspaceflight.com/index.php?topic=38148.msg1469736#msg1469736

This is a great pic! I am fascinated by the stuff revealed with the raceway cover removed. It's possible it's just the exposure of the photo, but it seems pretty sooty under that cover, which is surprising.

If by "raceway cover" you mean the cowlings over the tops of the grid fin pivots, there were no cowlings on the OG2 flight.

No, that's not the raceway. The "raceway" is the external piping that runs the length of the stage, highlighted in green in image #1, and you can see the whole length of it from the bottom to the top in image #2.

I think its other way around. We see 'raceway' from other side uncovered. Away from strong back

You can see it vent after landing @33m5s mark from those bumps on strong back side

EDIT: Sorry raceway is from strong back side as it doesn't have the square patch that is present on other side (Image attached).