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#1020
by
Proponent
on 18 Dec, 2015 12:47
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I wonder whether Falcon 9's sub-cooled RP-1 might be the thickest liquid propellant (excluding thixotropics) used in modern rocket history. Per the attached paper, the kinematic viscosity of RP-1 at 20
oF is 3.3 cP, as opposed to 1.7 cP at 70
oF. I wonder whether the chilling of the RP-1 is limited by viscosity.
EDIT: Corrected viscosity figures (they were both slightly too small, as a result of an underlying error in the calculation of density).
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#1021
by
Eagandale4114
on 18 Dec, 2015 13:16
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Is there a window for today's attempt?
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#1022
by
MarekCyzio
on 18 Dec, 2015 13:30
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Weather detoriated significantly today - we have an upcoming cold front. It rains hard at this moment.
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#1023
by
Chris Bergin
on 18 Dec, 2015 13:35
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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.
Oh the GUCP! That brings back "fun" memories!
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#1024
by
Michael.Kalenty
on 18 Dec, 2015 13:39
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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.
Oh the GUCP! That brings back "fun" memories!
Certainly brings back memories of STS-133 for me...
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#1025
by
Chris Bergin
on 18 Dec, 2015 14:01
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Weather detoriated significantly today - we have an upcoming cold front. It rains hard at this moment.
A few people noting that at me now. Wonder if it becomes an issue for the preps.
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#1026
by
WHAP
on 18 Dec, 2015 14:30
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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?
It could be either. Or both.
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#1027
by
WHAP
on 18 Dec, 2015 14:34
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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.
I'd venture that the use of LH2 (over RP1) is a whole lot more gain than the subcooling/densification that SpaceX is pursuing. And most of the extra effort required to handle LH2 has been known for decades - but we still "learn" some interesting things every so often (stuff we should have known).
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#1028
by
notsorandom
on 18 Dec, 2015 14:56
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Can they do the test fire even when the Weather is red for launch? Certainly don't want the wind blowing the rocket around on take off. If the rocket it still held down what weather concerns would there be aside from maybe lighting?
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#1029
by
Lars-J
on 18 Dec, 2015 15:05
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Can they do the test fire even when the Weather is red for launch? Certainly don't want the wind blowing the rocket around on take off. If the rocket it still held down what weather concerns would there be aside from maybe lighting?
The rocket is only held down by 4 points at the base. There is a limit to how much wind it can handle when not held by the erector arms.
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#1030
by
abaddon
on 18 Dec, 2015 15:13
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It's hardly unprecedented for it to take a little extra time to shake down new equipment at a launch site. I feel people are getting a little silly about "crazy LOX subcooling!!!". To be fair, Elon was being a bit silly when he tweeted about how nobody has ever gone this cold before; while technically true, it feeds into this hyperbole. Sowers' mild trolling doesn't help either.
And please, let's not start the LH2 vs LOX thing. Both have advantages and drawbacks.
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#1031
by
LouScheffer
on 18 Dec, 2015 15:15
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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.
I've wondered about this as well. If you want 6-10% more fuel, why not make the rocket 6-10% longer? There are several possibilities:
(a) The rocket is already long and thin. Longer makes the bending moments and modes worse, maybe requiring other changes.
(b) Added mass of longer tanks. This seems pretty small.
(c) There might be volume constraints to pumping through the engine. So perhaps you need the higher density to get higher thrust.
(d) Don't want to fiddle with the attachment points, transporter, umbilicals, etc. yet again
(e) Transportation might be harder (road transport, fitting under bridges, etc.)
At least the additional complexity is on the ground side, and not on the rocket itself.
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#1032
by
Proponent
on 18 Dec, 2015 15:15
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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.
I'd venture that the use of LH2 (over RP1) is a whole lot more gain than the subcooling/densification that SpaceX is pursuing. And most of the extra effort required to handle LH2 has been known for decades - but we still "learn" some interesting things every so often (stuff we should have known).
I think that's likely true, but I can see SpaceX's rationale: developing an LH2 engine would have been an expensive undertaking for a fledgling commercially-oriented rocket company. ULA's hydrogen upper-stage engine, in contrast, was originally developed during the cost-plus era. Given their respective origins, it makes sense that SpaceX densifies lox and RP-1 while ULA uses hydrogen.
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#1033
by
MarekCyzio
on 18 Dec, 2015 15:30
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It could be either. Or both.
Or none. Maybe tweaking various parameters just takes more time than planned.
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#1034
by
RedLineTrain
on 18 Dec, 2015 15:40
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And please, let's not start the LH2 vs LOX thing. Both have advantages and drawbacks.
At risk of bringing this up again, is there a temperature between -340F (F9 LOX) and -434F (hydrogen) where handling of liquids goes from relatively easy to relatively challenging?
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#1035
by
davey142
on 18 Dec, 2015 15:42
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And please, let's not start the LH2 vs LOX thing. Both have advantages and drawbacks.
At risk of bringing this up again, is there a temperature between -340F (F9 LOX) and -434F (hydrogen) where handling of liquids goes from relatively easy to relatively challenging?
And the fact that Hydrogen atoms are small. It's the same thing that makes handling Helium challenging.
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#1036
by
Lars-J
on 18 Dec, 2015 15:53
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And please, let's not start the LH2 vs LOX thing. Both have advantages and drawbacks.
At risk of bringing this up again, is there a temperature between -340F (F9 LOX) and -434F (hydrogen) where handling of liquids goes from relatively easy to relatively challenging?
And the fact that Hydrogen atoms are small. It's the same thing that makes handling Helium challenging.
Again, can we keep the LH2 vs KeroLox talk in a more appropriate thread?
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#1037
by
Lar
on 18 Dec, 2015 16:10
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Everything ties together of course, but I agree, let's try to stay focused. Stuff about why LH2 is hard to handle probably is not on topic for a RTF thread. Thanks!
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#1038
by
rkoenn
on 18 Dec, 2015 17:27
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LH2 engines are a big step up in difficulty to design and build. Kerosene fueled engines are much easier to do but plenty difficult in their own right. Also LH2 propellant is far less dense which means you need larger tankage. LH2 fueled engines do give much higher performance but between the engine design and manufacturing difficulties and the larger tanks required kerosene is an easier fuel to work with. If this new version Falcon has the tanks sized, which I assume it has, for the higher density LO2 then they have to put that in the rocket. The propellant ratios would be sized for that and if they don't get the higher density during the engine burn they will run out of LO2 before kerosene which of course causes numerous problems primarily not getting to orbit.
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#1039
by
Kabloona
on 18 Dec, 2015 17:31
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