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

[acsawdey]

Pressurization is going to be interesting. -340 F is 66.5 K and at that temperature the vapor pressure of a liquid oxygen appears to be about 0.03 bar. So they're going to need to introduce some additional gas to pressurize the tank.

[kdhilliard]

https://twitter.com/elonmusk/status/677663227271118848

Elon Musk ‏@elonmusk  1m1 minute ago
@PaigeANjax -340 F in this case. Deep cryo increases density and amplifies rocket performance. First time anyone has gone this low for O2.

And further down that twitter thread:

Luke @lukealization: Are you chilling RP-1 also?
Elon Musk ‏@elonmusk: yes, from 70F to 20 F

That's the first time I've seen a specific temperature mentioned for the RP-1 chill.

~Kirk

[LouScheffer]

On an operational rocket, he means.  NASA built a test plant and even a mock stage IIRC, so the basic idea was vetted.  Always a surprising distance between theory and practice, of course.

EDIT: and the Russians apparently used supercooled LOX on an upper stage... just not *as* cooled, apparently.

I believe Antares also used sub-cooled LOX, needed by the engines.   And since those engines were from the N-1, that probably used sub-cooled LOX as well.  The sub-cooling was needed for turbopump lubrication, if nothing else.

[northenarc]

https://twitter.com/elonmusk/status/677663227271118848

Elon Musk ‏@elonmusk  1m1 minute ago
@PaigeANjax -340 F in this case. Deep cryo increases density and amplifies rocket performance. First time anyone has gone this low for O2.

And further down that twitter thread:

Luke @lukealization: Are you chilling RP-1 also?
Elon Musk ‏@elonmusk: yes, from 70F to 20 F

That's the first time I've seen a specific temperature mentioned for the RP-1 chill.

~Kirk

  Haven't been following it too closely, but that's the first I've heard mention of RP-1 chilling. Have they done this at all on previous Falcon 9 flights? If not it's a considerable change, which the LOX subcooling already was. Has anyone done RP-1 chilling for orbital launches before?

[Dante80]

We did know that part of the FT upgrade was propellant densification, happy to see some actual numbers on that now.

More importantly, given the temperatures listed above, could someone make an educated guess about the amount of fuel and oxidizer carried?

Lastly, a question. Would the lower RP1 temp affect S2 endurance at all? I thought that SX had a possible problem with long coasting periods because of RP1 freezing issues.

[brettreds2k]

How far is the static fire testing pushed back? Affects launch I know

[mme]

And now we know the RP-1 temperature too:
https://twitter.com/lukealization/status/677663981293740033

Luke ‏@lukealization  2h2 hours ago
@elonmusk Are you chilling RP-1 also?

https://twitter.com/elonmusk/status/677666779494248449

Elon Musk ‏@elonmusk  2h2 hours ago
@lukealization yes, from 70F to 20 F

[S.Paulissen]

On an operational rocket, he means.  NASA built a test plant and even a mock stage IIRC, so the basic idea was vetted.  Always a surprising distance between theory and practice, of course.

EDIT: and the Russians apparently used supercooled LOX on an upper stage... just not *as* cooled, apparently.

I believe Antares also used sub-cooled LOX, needed by the engines.   And since those engines were from the N-1, that probably used sub-cooled LOX as well.  The sub-cooling was needed for turbopump lubrication, if nothing else.

I recall an article saying that part of the modification of an NK33 to an AJ26 was that they qualified it on standard temperature LOX. Edit: maybe it was just American fuel formulations.

Also, there was an interview of Shotwell where she clearly stated a mild sub cooling of the RP1 in response to a question.

[CameronD]

  Haven't been following it too closely, but that's the first I've heard mention of RP-1 chilling. Have they done this at all on previous Falcon 9 flights? If not it's a considerable change, which the LOX subcooling already was. Has anyone done RP-1 chilling for orbital launches before?

That discussion is all right here in this thread.. back 50-odd pages or so: 

http://forum.nasaspaceflight.com/index.php?topic=38149.40

[toruonu]

Sooo, I'm guessing lack of any news on a static fire means that the launch on 19th is off the table by now? If they manage the fire today can they still try for the launch on 20th?

[Earendil]

I did not see this tweet posted here..

@elonmusk Did you guys get #Falcon9 O2 down to -340F on the test stand at #McGregor? Is this just an integration issue at LC40?

 Elon Musk ‏@elonmusk  6h6 hours ago
@craigcocca It worked in Texas

So.. it should not be a vehicle, but a stand issue?

[Steven Pietrobon]

More importantly, given the temperatures listed above, could someone make an educated guess about the amount of fuel and oxidizer carried?

That's not an easy question! For the RP-1 density I used two sources:

http://kinetics.nist.gov/RealFuels/macccr/macccr2008/Bruno2.pdf
http://atlasbases.homestead.com/Analysis_of_RP-1_Fuel_Density_-_SAWE0323.pdf

The first report gives a density range from 0.8236 to 0.8436 kg/L at -6.7 C. The second report gives a range from 0.8176 to 0.8265 kg/L. At 21.1 C, the range for the second report is 0.7968 to 0.8056 kg/L. The 0.8056 kg/L density is close to other values I have seen, so I believe the second report is more valid with the value of 0.8256 kg/L being very close to the low end of the first report. Thus, I will assume the following values

dfl = 0.8056 kg/L (low fuel density at 21.1 C)
dfh = 0.8265 kg/L (high fuel density at -6.7 C)

For the LOX density, I used the equation given in Section 3.3 of

http://www.nist.gov/srd/upload/jpcrd423.pdf

I get the following densities (pascal program attached).

dol = 1.1420 kg/L (LOX low density at -183.0 C)
doh = 1.2539 kg/L (LOX high density at -206.7 C)

The Merlin 1C mixture ratio is 2.2.

http://iacse.commercial-space.net/wp-content/uploads/2008/10/iac-08d213.pdf

malu5531 worked out a ratio of 2.36 for the Merlin 1D+. I couldn't find a source for the actual ratio.

https://forum.nasaspaceflight.com/index.php?topic=32983.0

Assuming a ratio of 2.2 we get

dl = 1.0102 kg/L (low density)
dh = 1.0795 kg/L (high density)

For a ratio of 2.36 we get

dl = 1.0158 kg/L (low density)
dh = 1.0867 kg/L (high density)

That gives increases of 6.86% and 6.98%, respectively. According to

http://spaceflight101.com/spacerockets/falcon-9-v1-1-f9r/

the v1.1 first stage propellant mass is 395.7 t. Thus, the increase in propellant mass could range from 27.1 to 27.6 t.

The second stage was already reported to have a 10% increase in propellant volume.

http://www.spacelaunchreport.com/falcon9ft.html

The second stage v1.1 has a propellant mass of 92.67 t. Thus, the increase would be from 16.25 to 16.38 t.

[FutureSpaceTourist]

https://twitter.com/elonmusk/status/677663227271118848

Elon Musk ‏@elonmusk  1m1 minute ago
@PaigeANjax -340 F in this case. Deep cryo increases density and amplifies rocket performance. First time anyone has gone this low for O2.

Here's an interesting response to Elon's tweets:

https://twitter.com/george_sowers/status/677724984165330944

George Sowers ‏@george_sowers 4h4 hours ago

.@elonmusk Thats why we don't bother. Lots of complexity for little gain.

https://twitter.com/george_sowers/status/677730399242457089

George Sowers ‏@george_sowers 4h4 hours ago

.@rocketrepreneur @elonmusk Tough to know the conditions of LOX at liftoff.

[laika_fr]

So it worked in Texas, weather data :

TX
relative humidity : 70%
pressure : 1026hpa
temp : 4°C
Dew point : 0°C
wind : ~15Km/h

FL 
relative humidity : 90% 
pressure : 1012hpa
temp : 23 C°
Dew point : 21°c
wind : 20-40Km/h

[rpapo]

Texas: Add dust.
Florida: Add salt.

[Proponent]

So it worked in Texas, weather data :

TX
relative humidity : 70%
pressure : 1026hpa
temp : 4°C
Dew point : 0°C
wind : ~15Km/h

FL 
relative humidity : 90% 
pressure : 1012hpa
temp : 23 C°
Dew point : 21°c
wind : 20-40Km/h

In other words, that sub-cooled lox is going to cause one heck of a lot more condensation in Florida than in Texas.

[Proponent]

Would the lower RP1 temp affect S2 endurance at all? I thought that SX had a possible problem with long coasting periods because of RP1 freezing issues.

Do we know whether the second-stage propellants are being chilled?  Weight being more critical up there (because it has to be carried longer) than on the first stage, densification won't necessarily help much or at all.  I recall Jim telling us about upper-stage fuel actually being heated on some Delta 2 launches to increase specific impulse.

[Proponent]

Pressurization is going to be interesting. -340 F is 66.5 K and at that temperature the vapor pressure of a liquid oxygen appears to be about 0.03 bar. So they're going to need to introduce some additional gas to pressurize the tank.

Per the Falcon 9 Payload User's Guides, heated helium has long been used to pressurize tanks on both stages.  Does anybody know what ullage pressure(s) Falcon 9 uses?

[Jim]

https://twitter.com/elonmusk/status/677663227271118848

Elon Musk ‏@elonmusk  1m1 minute ago
@PaigeANjax -340 F in this case. Deep cryo increases density and amplifies rocket performance. First time anyone has gone this low for O2.

Here's an interesting response to Elon's tweets:

https://twitter.com/george_sowers/status/677724984165330944

George Sowers ‏@george_sowers 4h4 hours ago

.@elonmusk Thats why we don't bother. Lots of complexity for little gain.

https://twitter.com/george_sowers/status/677730399242457089

George Sowers ‏@george_sowers 4h4 hours ago

.@rocketrepreneur @elonmusk Tough to know the conditions of LOX at liftoff.

I guess Spacex could say the same about LH2.   It is just a matter of figuring the ROI.  LH2 requires more insulation everywhere and haz gas detection, subcooled LOX requires active cooling.

[Mike_1179]

Texas: Add dust.
Florida: Add salt.

don't forget the effects of Solar radiation ie sunshine

It's more than just ambient environmental conditions.

I know it's a totally different vehicle, but think back to the issues around the GUCP. http://www.nasaspaceflight.com/tag/gucp/

Could some of the problems be with the umbilical attachments to the vehicle at the launch site that are different than Texas? For a static fire in McGregor, you can bolt the fill lines directly to the stage while in Florida these lines have to be some sort of quick disconnect that detaches at launch.

The cooled LOX is above the melting point of nitrogen (it's actually right near the boiling point of nitrogen, so maybe they're using LN2 to cool it), so I don't think they're seeing solidification of air around the very cold parts like the GUCP, but if there is water condensing then freezing around areas where it didn't freeze before, you could run into problems keeping a good seal or maintaining electrical conductivity of the umbilicals - you might not see that in McGregor if the lines were bolted.