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

[cambrianera]

At the time this was explained as needg 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.

Likely a way to validate CFD flow inside the engine using thermal imaging.
Routinely done when designing heat exchangers.

[woods170]

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.

Carefull there Jim. Adding 'IMO' to your post is advised given that you don't have full insight into how SpaceX flies it's rockets, not even after your stint working on DSCOVR.
And no, I'm not being impolite. Just pointing out that this is not ULA, nor NASA.

[Ben the Space Brit]

Purely FWIW, I would be surprised if SpaceX did not plan from the start that certain elements would need replacement after every flight and have designed them appropriately. The long-term objective of the program is, of course, to work down the number of these 'expended per mission' items to as low a figure as possible and thus minimise the turn-around cost of the cores.

It's worth noting that all previous insights into what items would be needed to be replaced and what it would cost to turn around a fly-back core are notional and based on 'best guess' simulations. SpaceX is the first launch provider to actually have a real world core that they want to try to refurbish to flight condition.

I wouldn't be surprised if NASA were watching closely in order to see if these lessons can be applied to its own programs. I understand from various things that I've seen on the 'Net that SpaceX is providing supersonic retro-propulsion and EDL data to NASA as part of the Mars lander development program.

[Jim]

And no, I'm not being impolite. Just pointing out that this is not ULA, nor NASA.

Have the same insight into Spacex as ULA.

[OxCartMark]

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).

Speculation or fact?  To me it seems it would be necessary to vent the LOX and TEA/B before people approached and probably best to vent the nitrogen.  All are inexpensive.  The nitrogen already has vents, the thrusters, and I presume the downward venting was the nitrogen gas being vented out of the thruster direction that would be least likely to tip the stage over.  That (my presumption) downward venting of nitrogen would be through some of the same nozzles used to settle propellent to the bottom of tanks before relighting the engines.  And it looked similar to the nitrogen jet we saw as the CRS-6 stage fought to stay upright on the ASDS.  But helium, that seems to me to be something they'd not want to vent.  First, Elon has said that helium for a flight is a higher cost item than the propellent.  Secondly, unlike all of the other fluids, helium is a limited resource, and if SpaceX has ambitions as large as their ambitions seem to be they wouldn't want to run out the world's supply or raise its price appreciably.  Third, there is little sense in venting it since it (or something else) needs to be in place to keep the tanks structurally tight, and at that point most of the helium would be in those tanks rather than in high pressure storage.  Even if the helium were to be removed it would need to be replaced with another gas at the same pressure which would not give any safety advantages.  Fourth, the pressure in the COPVs would be very low at that point (thus relatively safe) because it is possible to calculate very accurately the amount of helium that would be needed in the COPVs (amount needed to fill the empty tanks).  Fifth, if you were to vent the COPVs to zero gauge pressure you'd just be adding to the stress cycles and giving them a shorter lifetime.  Sixthly, if you look ahead to rapid reusability it seems to me that you'd want to keep the helium in the tanks so that it could be cleaned up and re-compressed into the COPVs.

[Archibald]

A new pic. Pretty cool scene I might say.

I hope that, after the static test firing SpaceX will give the stage to the Smithonian.

[meekGee]

A new pic. Pretty cool scene I might say.

I hope that, after the static test firing SpaceX will give the stage to the Smithonian.

Funny.  But.

It belongs in a lab, in pieces, to expedite searching for any close-calls or low-margin situations with the rocket.  Destructive testing as well.

They can send the legs to four museums of choice, to wall-mount them.  "First rocket legs to ever touch down bla bla".

The museum is not the goal... Mars is.

[Dante80]

I hope that, after the static test firing SpaceX will give the stage to the Smithonian.

Preferably after adding the baked legs and without the process of testing ruining the wonderful patina of re-entry soot that the rocket currently has.

Funny.  But.

It belongs in a lab, in pieces, to expedite searching for any close-calls or low-margin situations with the rocket.  Destructive testing as well.

They can send the legs to four museums of choice, to wall-mount them.  "First rocket legs to ever touch down bla bla".

The museum is not the goal... Mars is.

Elon said that its going to be retired for Museum duty (at a SpaceX location or somewhere else). We don't know how much disassembly they are going to do, especially if they manage to return the more important SES9 core by the end of the month.

The schedule is to do a WDR/static fire at the Cape, and then to send it to Texas for more testing and a possible Full static fire test. After that, museum duty.

Speculation or fact?

We saw venting at landing, and we also saw a hose in the after-landing video that suggests RP-1 unloading.

[Comga]

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.

Be careful
Many black anodize treatments are cosmetic, and have no effect on even the Near IR, never mind the thermal IR.
Many thermal radiators are painted white, and have the same emissivity in the thermal IR as visibly black materials.
There is less spectral difference for things that are hot enough to glow.

[Jim]

Speculation or fact?  To me it seems it would be necessary to vent the LOX and TEA/B before people approached and probably best to vent the nitrogen.  All are inexpensive.  The nitrogen already has vents, the thrusters, and I presume the downward venting was the nitrogen gas being vented out of the thruster direction that would be least likely to tip the stage over.  That (my presumption) downward venting of nitrogen would be through some of the same nozzles used to settle propellent to the bottom of tanks before relighting the engines.  And it looked similar to the nitrogen jet we saw as the CRS-6 stage fought to stay upright on the ASDS.  But helium, that seems to me to be something they'd not want to vent.  First, Elon has said that helium for a flight is a higher cost item than the propellent.  Secondly, unlike all of the other fluids, helium is a limited resource, and if SpaceX has ambitions as large as their ambitions seem to be they wouldn't want to run out the world's supply or raise its price appreciably.  Third, there is little sense in venting it since it (or something else) needs to be in place to keep the tanks structurally tight, and at that point most of the helium would be in those tanks rather than in high pressure storage.  Even if the helium were to be removed it would need to be replaced with another gas at the same pressure which would not give any safety advantages.  Fourth, the pressure in the COPVs would be very low at that point (thus relatively safe) because it is possible to calculate very accurately the amount of helium that would be needed in the COPVs (amount needed to fill the empty tanks).  Fifth, if you were to vent the COPVs to zero gauge pressure you'd just be adding to the stress cycles and giving them a shorter lifetime.  Sixthly, if you look ahead to rapid reusability it seems to me that you'd want to keep the helium in the tanks so that it could be cleaned up and re-compressed into the COPVs.

I doubt there are compressors to remove the helium from the vehicle.  The tanks are likely vented down to a pad pressure.  Too much complexity and cost in reusing it.

[meekGee]

Funny.  But.

It belongs in a lab, in pieces, to expedite searching for any close-calls or low-margin situations with the rocket.  Destructive testing as well.

They can send the legs to four museums of choice, to wall-mount them.  "First rocket legs to ever touch down bla bla".

The museum is not the goal... Mars is.

Elon said that its going to be retired for Museum duty (at a SpaceX location or somewhere else). We don't know how much disassembly they are going to do, especially if they manage to return the more important SES9 core by the end of the month.

The schedule is to do a WDR/static fire at the Cape, and then to send it to Texas for more testing and a possible Full static fire test. After that, museum duty.

I know he did...  Maybe they're relying on having more stages to test, but IMO the absolute most important thing right now is to improve fleet reliability through analysis of returned stages.

They've already had a failure.  If there's another daemon lurking in there and it can be flushed out, it's worth all the museums in the world.

If they can do all the testing and still preserve enough metal to make a worthy museum piece then fine, but it's a lower priority.

IMO.
 

[chipguy]

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.

If your semiconductor heatsink is cooling appreciably via radiation compared to convection then you
are having a very bad day.

Most heavy duty heatsinks I see are strip or extruded aluminum, albeit matte rather than polished.

[LouScheffer]

I doubt there are compressors to remove the helium from the vehicle.  The tanks are likely vented down to a pad pressure.  Too much complexity and cost in reusing it.

Back of the envelope calculation:  Assume stage is 3.66 meters in diameter and 50 meters long, and all filled with helium.   That's 525 cubic meters, or 18,500 cubic feet.   I don't know the current helium price, but a few years ago it was about $100 per 1000 cubic feet.  Assume rocket is pressurized to 4 atm absolute.  Then helium cost is 18.5x4x100 = $7400.  So not a top priority to re-use it.

[Johnnyhinbos]

I doubt there are compressors to remove the helium from the vehicle.  The tanks are likely vented down to a pad pressure.  Too much complexity and cost in reusing it.

Back of the envelope calculation:  Assume stage is 3.66 meters in diameter and 50 meters long, and all filled with helium.   That's 525 cubic meters, or 18,500 cubic feet.   I don't know the current helium price, but a few years ago it was about $100 per 1000 cubic feet.  Assume rocket is pressurized to 4 atm absolute.  Then helium cost is 18.5x4x100 = $7400.  So not a top priority to re-use it.

Perhaps this isn't apples to apples, but as a mixed gas technical diver, one reason people are moving to rebreathers is because of helium cost. For a single moderately deep open circuit dive, say 2 x 100 cu ft at 50% He, and a 40 cu ft at 30% He - the rest of the tanks containing O2 / N2 only blends - so 112 cu ft of He, costs in the range of $300, which leads to $2.68 / cu ft. So extending this out to the the above, you get 18,500 x 4 x 2.68 = $198,214. Point being, I don't think your numbers are in the right ballpark.

[mvpel]

Back of the envelope calculation:  Assume stage is 3.66 meters in diameter and 50 meters long, and all filled with helium.   That's 525 cubic meters, or 18,500 cubic feet.   I don't know the current helium price, but a few years ago it was about $100 per 1000 cubic feet.  Assume rocket is pressurized to 4 atm absolute.  Then helium cost is 18.5x4x100 = $7400.  So not a top priority to re-use it.

It's not entirely about the dollar value in the grand scheme of things.

Helium Shortage: Update After One Year - March 2, 2015

Despite the greater production, however, the situation regarding helium availability is still critical. The high demand, combined with shortages, inevitably led to higher prices. Further to that, however, one of the main problems is that there are periods of shortage, during which the suppliers cannot guarantee helium delivery.

This can cause problems, as the activities which rely on helium (not just kids’ birthday parties) are necessarily  suspended/postponed. Some medical equipment, such as Magnetic Resonance Imaging (MRI), for instance, cannot be used without helium.

Not to mention launch vehicles.

Hopefully their work on autogenous pressurization will bear fruit.

[Robotbeat]

Nice thing about recovering the rocket stage is you ALSO can recover the helium that's pressurizing it. The helium fills the ullage volume, it's not expended!

[Lars-J]

Nice thing about recovering the rocket stage is you ALSO can recover the helium that's pressurizing it. The helium fills the ullage volume, it's not expended!

Yes, but it looks like the remaining LOX is vented after landing, so that would also vent the helium.

[Robotbeat]

Nice thing about recovering the rocket stage is you ALSO can recover the helium that's pressurizing it. The helium fills the ullage volume, it's not expended!

Yes, but it looks like the remaining LOX is vented after landing, so that would also vent the helium.

That's an operational decision. If the helium were valuable enough, it'd be feasible to recover the vast majority of it.

[WHAP]

Nice thing about recovering the rocket stage is you ALSO can recover the helium that's pressurizing it. The helium fills the ullage volume, it's not expended!

Yes, but it looks like the remaining LOX is vented after landing, so that would also vent the helium.

That's an operational decision. If the helium were valuable enough, it'd be feasible to recover the vast majority of it.

It's a mix of helium and GOX.  Based on recent prices, you're looking at maybe $20K of helium (http://www.dla.mil/Portals/104/Documents/Energy/Standard%20Prices/E_AerospaceEnergyFY15DODStandardPrices_150818.pdf)
I think the LOX tank was vented before anyone approached - it's probably a safety hazard otherwise.  SX would need to find a way to automatically connect up to capture the vented gas, then separate the different gases.  Not impossible, but I think Jim is right - too much effort for too little gain.

[toruonu]

You do know every other launcher expends the helium if it's used to pressurize nice to even be discussing reuse of helium from the copv bottles