SpaceX (Vol. 2)
Discussion
annodomini2 said:
Talksteer said:
Tim's not an engineer, there have been numerous air launched studies by serious outfits which address all of this. Virgins approach of firing a multi-stage rocket was a little odd but if you look at air launching a re-usable single stage to orbit (SSTO, though arguably air launching is cheating in this regard) craft it starts to make sense.
1: If you are air launching a re-usable single stage to orbit space plane your "stage one" is likely to be a used A380, this is widely available at knock down values and will fly thousands of missions without heavy maintenance with incredibly high reliability.
2: One of your vehicles is already designed for you
3: There are some potential ways to handle the different loading cases, firstly you have you carrier aircraft pull up before landing. The launched SSTO craft then flies a semi-ballistic course for quite while which mean that the wings don't need to support the fueled weight of the craft. The different load cases make less of a difference to a SSTO which doesn't have the weak point of multi-stage rocket which separates at the interstages.. For a single stage the propellant tanks are pressurised in flight and proof against the full rocket thrust in the lateral direction, this makes them perfectly capable of holding their filled mass in the horizontal direction. The wings only have to support the craft at relatively high velocities so don't need to be massive.
4: The rocket equation is logarithmic, so an extra 5% of delta V makes a much bigger impact on payload. Launching from 35,000ft also means that you can run higher expansion ratio engines which gives you a better ISP and the aero-dynamic loads are much lower so you can trim weight from other parts of the structure.
The upshot of all this is that if you air launch you move an SSTO design from being a non starter to being completely plausible with a useful payload. This means that you now only have to design a single vehicle which doesn't split in flight. If you extrapolate from the 80's Teledyne Brown air launched space plane with modern technology and an A380 launch platform you are looking about15 tonnes LEO. You would achieve this with a single engine of the same thrust as a Raptor, which does indicate that in terms of equipment employed it may trade favorably with a two stage re-usable rocket.
The weight of a delta wing is likely a bit higher than a Starship style "Elonaron" but this is more than offset by the lack of need for landing propellant which you also don't need to maintain for the whole flight. The biggest advantage is however that a gliding landing is considerably safer than a propulsive landing, both from a statistical basis (thousands of landings per mishaps, the Shuttle obviously stuck every landing even with equipment failures) and and also from a a consequence of failure basis (if a glider landing fails an inert vehicle skids down the runway, if a propulsive landing fails fiery explosive death awaits)
The only real issues with a gliding landing is, you can't land anywhere other than earth and once you exceed the size of what can be carried by commercially available aircraft you stop being able to use COTS technology. It's probably best for putting up satellite constellations and moving people about in vast numbers.
1. Air launching makes it Two stage as the plane would be the first stage. It's not SSTO.1: If you are air launching a re-usable single stage to orbit space plane your "stage one" is likely to be a used A380, this is widely available at knock down values and will fly thousands of missions without heavy maintenance with incredibly high reliability.
2: One of your vehicles is already designed for you
3: There are some potential ways to handle the different loading cases, firstly you have you carrier aircraft pull up before landing. The launched SSTO craft then flies a semi-ballistic course for quite while which mean that the wings don't need to support the fueled weight of the craft. The different load cases make less of a difference to a SSTO which doesn't have the weak point of multi-stage rocket which separates at the interstages.. For a single stage the propellant tanks are pressurised in flight and proof against the full rocket thrust in the lateral direction, this makes them perfectly capable of holding their filled mass in the horizontal direction. The wings only have to support the craft at relatively high velocities so don't need to be massive.
4: The rocket equation is logarithmic, so an extra 5% of delta V makes a much bigger impact on payload. Launching from 35,000ft also means that you can run higher expansion ratio engines which gives you a better ISP and the aero-dynamic loads are much lower so you can trim weight from other parts of the structure.
The upshot of all this is that if you air launch you move an SSTO design from being a non starter to being completely plausible with a useful payload. This means that you now only have to design a single vehicle which doesn't split in flight. If you extrapolate from the 80's Teledyne Brown air launched space plane with modern technology and an A380 launch platform you are looking about15 tonnes LEO. You would achieve this with a single engine of the same thrust as a Raptor, which does indicate that in terms of equipment employed it may trade favorably with a two stage re-usable rocket.
The weight of a delta wing is likely a bit higher than a Starship style "Elonaron" but this is more than offset by the lack of need for landing propellant which you also don't need to maintain for the whole flight. The biggest advantage is however that a gliding landing is considerably safer than a propulsive landing, both from a statistical basis (thousands of landings per mishaps, the Shuttle obviously stuck every landing even with equipment failures) and and also from a a consequence of failure basis (if a glider landing fails an inert vehicle skids down the runway, if a propulsive landing fails fiery explosive death awaits)
The only real issues with a gliding landing is, you can't land anywhere other than earth and once you exceed the size of what can be carried by commercially available aircraft you stop being able to use COTS technology. It's probably best for putting up satellite constellations and moving people about in vast numbers.
Edited by Talksteer on Wednesday 15th May 20:53
2. You're not going to be able to launch much more than what Virgin Orbit did with Launcher one, 500kg-1000kg to orbit. Obviously non-reusable. Less to support reusability (probably nothing).
3. The benefits of initial speed and drag are limited by the lift capability of aircraft. You also cannot consume all the remaining take off mass of the aircraft as you're limited by how and where to mount the rocket such that it can be safely deployed. Without designing a dedicated aircraft you're very limited in what you can lift and deploy.
4. Single stage from the launch aircraft would be less mass efficient to orbit. As you have to get more mass to orbital velocity. If your inter-stage outweighs the rest of your rocket's 1st stage, then you haven't designed it correctly.
Prior to SpaceX landing the first stage of Falcon 9, air launch or SSTO were considered the future, and landing the first considered borderline impossible.
With that the game changed.
With a reusable 5 km/s dv first stage, air launch at 0.27km/s the benefit is insignificant for massively increased complexity.
SSTO may one day be practical, but not till we have a working solution for having 600+Secs of ISP and high thrust in the propulsion system, it's not going to happen any time soon.
I agree glider landing is more efficient on Earth, but Musk has stated directly that the goal of Starship is to land on other planets. Mars being the primary goal. Which doesn't have enough atmosphere or runways for that matter to support it.
The TDE concept was going to launch from the Shuttle carrier aircraft, interim Hotol from an AN225. Since both those concepts have been developed A380's capable of lifting 250 tonnes (cargo A380 payload, PAX variant will be able to get that into the air it doesn't need to be able to land with it),have become relatively easy to purchase. Virgin Orbit's rocket used a tiny fraction of a 747's lifting capability (about 25 tonnes) in no way can you extrapolate anything about any other air launched concept from them.
The TDE concept is relatively detailed proposal (they use extrapolated masses from the shuttle stack, and shuttle aerodynamics which is a detriment as it's much heavier and not optimised for aero on the way up, which done right cuts gravity losses down a lot) and the concept has a weight breakdown that doesn't need magic technology. The plan was to use a single SSME and some RL10's. There are now COTS closed cycle H2 engines. You'd be looking at at least 10 tonnes to LEO from an A380 launched vehicle, with the potential to get a fair bit more.
The way to look at it is that you have a 250 tonne upper stage using hydrogen. That is an absolutely massive upper stage, the only larger one pre Starship was the SII on the Saturn V. That size means that the stage will be structurally very efficient and you can offset the mass of the wings and the landing gear. Both of those are only really stressed for a 35 tonne landing vehicle, so the landing gear may be as little as 600kg. As stated before heat shield is only resisting ~700 degrees C so does a double duty as tank insulation it also means that it can be something tougher like a nickel alloy honeycomb.
As to why you would do it:
- Safer than propulsive landing
- Only have one stage with rockets on it,
- Ground equipment is some sort of crane to lift the rocket back onto the top of the A380 and a fuel supply.
- The rocket can be based anywhere including the majority of countries in the world that don't have east coasts over ocean. You don't have to go through all the red tape associated with lighting a rocket on the ground or even on the sea.
Edited by Talksteer on Friday 24th May 11:41
GTO-3R said:
Flight 4 about 10 days away according to Elon. How far they getting this time? If they can have control of Starship in orbit this time then it's an advancement and if it can make it through re-entry then it'll be a huge step 
My suspicion is that it would have been regarded as very successful on IFT3 had Starship entered at the correct (and stable) angle. If things go better this time the footage of the plasma glow is going to be spectacular. GTO-3R said:
Flight 4 about 10 days away according to Elon. How far they getting this time? If they can have control of Starship in orbit this time then it's an advancement and if it can make it through re-entry then it'll be a huge step
I suspect it’ll be another successful step forward, no point launching otherwise. I read earlier in the thread they were waiting on the FAA mishap report, have I missed that and all the changes detailed somewhere?
Can’t wait!
LivLL said:
I suspect it’ll be another successful step forward, no point launching otherwise.
I read earlier in the thread they were waiting on the FAA mishap report, have I missed that and all the changes detailed somewhere?
Can’t wait!
SpaceX do the mishap investigation and support their report to the FAA for review. They've published a public summary tonight:I read earlier in the thread they were waiting on the FAA mishap report, have I missed that and all the changes detailed somewhere?
Can’t wait!
https://www.spacex.com/updates/#flight-3-report
In other news today, SpaceX official twitter says they're now targeting NET 5 June pending regulatory approval.
https://x.com/SpaceX/status/1794000049858597253
Hill92 said:
SpaceX do the mishap investigation and support their report to the FAA for review. They've published a public summary tonight:
https://www.spacex.com/updates/#flight-3-report
In other news today, SpaceX official twitter says they're now targeting NET 5 June pending regulatory approval.
https://x.com/SpaceX/status/1794000049858597253
Thanks Hill92, this seems to suggest the regulatory approval isn't a problem. Roll on the 5th.https://www.spacex.com/updates/#flight-3-report
In other news today, SpaceX official twitter says they're now targeting NET 5 June pending regulatory approval.
https://x.com/SpaceX/status/1794000049858597253
SpaceX said:
Following the flight test, SpaceX led the investigation efforts with oversight from the FAA and participation from National Aeronautics and Space Administration (NASA) and the National Transportation and Safety Board (NTSB). During Flight 3, neither vehicle’s automated flight safety system was triggered, and no vehicle debris impacted outside of pre-defined hazard areas. Pending FAA finding of no public safety impact, a license modification for the next flight can be issued without formal closure of the mishap investigation.
Talksteer said:
I suggest that you try to find the papers on the Teledyne Brown Engineering space plane or for that matter the interim Hotel concept.
The TDE concept was going to launch from the Shuttle carrier aircraft, interim Hotol from an AN225. Since both those concepts have been developed A380's capable of lifting 250 tonnes (cargo A380 payload, PAX variant will be able to get that into the air it doesn't need to be able to land with it),have become relatively easy to purchase. Virgin Orbit's rocket used a tiny fraction of a 747's lifting capability (about 25 tonnes) in no way can you extrapolate anything about any other air launched concept from them.
The TDE concept is relatively detailed proposal (they use extrapolated masses from the shuttle stack, and shuttle aerodynamics which is a detriment as it's much heavier and not optimised for aero on the way up, which done right cuts gravity losses down a lot) and the concept has a weight breakdown that doesn't need magic technology. The plan was to use a single SSME and some RL10's. There are now COTS closed cycle H2 engines. You'd be looking at at least 10 tonnes to LEO from an A380 launched vehicle, with the potential to get a fair bit more.
The way to look at it is that you have a 250 tonne upper stage using hydrogen. That is an absolutely massive upper stage, the only larger one pre Starship was the SII on the Saturn V. That size means that the stage will be structurally very efficient and you can offset the mass of the wings and the landing gear. Both of those are only really stressed for a 35 tonne landing vehicle, so the landing gear may be as little as 600kg. As stated before heat shield is only resisting ~700 degrees C so does a double duty as tank insulation it also means that it can be something tougher like a nickel alloy honeycomb.
As to why you would do it:
Ok let's assume you could use the full remaining ~200t for the launch vehicle including propellant.The TDE concept was going to launch from the Shuttle carrier aircraft, interim Hotol from an AN225. Since both those concepts have been developed A380's capable of lifting 250 tonnes (cargo A380 payload, PAX variant will be able to get that into the air it doesn't need to be able to land with it),have become relatively easy to purchase. Virgin Orbit's rocket used a tiny fraction of a 747's lifting capability (about 25 tonnes) in no way can you extrapolate anything about any other air launched concept from them.
The TDE concept is relatively detailed proposal (they use extrapolated masses from the shuttle stack, and shuttle aerodynamics which is a detriment as it's much heavier and not optimised for aero on the way up, which done right cuts gravity losses down a lot) and the concept has a weight breakdown that doesn't need magic technology. The plan was to use a single SSME and some RL10's. There are now COTS closed cycle H2 engines. You'd be looking at at least 10 tonnes to LEO from an A380 launched vehicle, with the potential to get a fair bit more.
The way to look at it is that you have a 250 tonne upper stage using hydrogen. That is an absolutely massive upper stage, the only larger one pre Starship was the SII on the Saturn V. That size means that the stage will be structurally very efficient and you can offset the mass of the wings and the landing gear. Both of those are only really stressed for a 35 tonne landing vehicle, so the landing gear may be as little as 600kg. As stated before heat shield is only resisting ~700 degrees C so does a double duty as tank insulation it also means that it can be something tougher like a nickel alloy honeycomb.
As to why you would do it:
- Safer than propulsive landing
- Only have one stage with rockets on it,
- Ground equipment is some sort of crane to lift the rocket back onto the top of the A380 and a fuel supply.
- The rocket can be based anywhere including the majority of countries in the world that don't have east coasts over ocean. You don't have to go through all the red tape associated with lighting a rocket on the ground or even on the sea.
Edited by Talksteer on Friday 24th May 11:41
@35t for the launch vehicle without payload.
With Hydrolox, and ISP 455secs.
Gives you a DeltaV of about 7.7km/s assuming constant ISP and no drag (which is obviously not real).
You need a DeltaV iro 9.4km/s for LEO with a de-orbit burn, your air launch basically gives you a free de-orbit burn.
So to make it work without payload requires either:
1. You increase the efficiency of the engines to 550s. (This is still without payload)
2. You decrease the mass of the launcher and increase the fuel mass.
For 455s @ 200t all up for the launcher, the empty mass + payload would max out at 23t.
So if you wanted a 10t payload, your ship can weigh no more than 13t when empty.
There is no margin for error in these figures.
Starship launch 4 will be a bit different than before. No experimental Starlink doors or internal fuel transfers.
They're going to be jettisoning the hot-stage ring off the booster after separation this time too. That's a temporary weight reduction measure for the booster it seems. The booster will then attempt a soft water landing at 7:04 minutes after launch.
However they are going to try a Starship reentry, flip over and landing burn into the Pacific. The latter being at 01:05 hours after launch.
The proposed timeline is here:
https://www.spacex.com/launches/mission/?missionId...
I notice that MECO now seems to stand for "most engines cut off" instead of "main engine(s) cut off"
Seems the problems with launch 3 were predominantly valve or filter related (I'm sure Boeing sympathises).
The Booster:
"Following stage separation, Super Heavy initiated its boostback burn, which sends commands to 13 of the vehicle’s 33 Raptor engines to propel the rocket toward its intended landing location. All 13 engines ran successfully until six engines began shutting down, triggering a benign early boostback shutdown.
The booster then continued to descend until attempting its landing burn, which commands the same 13 engines used during boostback to perform the planned final slowing for the rocket before a soft touchdown in the water, but the six engines that shut down early in the boostback burn were disabled from attempting the landing burn startup, leaving seven engines commanded to start up with two successfully reaching mainstage ignition. The booster had lower than expected landing burn thrust when contact was lost at approximately 462 meters in altitude over the Gulf of Mexico and just under seven minutes into the mission.
The most likely root cause for the early boostback burn shutdown was determined to be continued filter blockage where liquid oxygen is supplied to the engines, leading to a loss of inlet pressure in engine oxygen turbopumps. SpaceX implemented hardware changes ahead of Flight 3 to mitigate this issue, which resulted in the booster progressing to its first ever landing burn attempt. "
And for flight 4:
"Super Heavy boosters for Flight 4 and beyond will get additional hardware inside oxygen tanks to further improve propellant filtration capabilities. And utilizing data gathered from Super Heavy’s first ever landing burn attempt, additional hardware and software changes are being implemented to increase startup reliability of the Raptor engines in landing conditions."
The Ship:
"Several minutes after Starship began its coast phase, the vehicle began losing the ability to control its attitude. Starship continued flying its nominal trajectory but given the loss of attitude control, the vehicle automatically triggered a pre-planned command to skip its planned on-orbit relight of a single Raptor engine.
Starship went on to experience its first ever reentry from space, providing valuable data on heating and vehicle control during hypersonic reentry. The lack of attitude control resulted in an off-nominal entry, with the ship seeing much larger than anticipated heating on both protected and unprotected areas. High-definition live views of entry and a considerable amount of telemetry were successfully transmitted in real time by Starlink terminals operating on Starship. The flight test’s conclusion came when telemetry was lost at approximately 65 kilometers in altitude, roughly 49 minutes into the mission.
The most likely root cause of the unplanned roll was determined to be clogging of the valves responsible for roll control. "
And for flight 4:
"SpaceX has since added additional roll control thrusters on upcoming Starships to improve attitude control redundancy and upgraded hardware for improved resilience to blockage."
Source:
https://www.spacex.com/updates/#flight-3-report
They're going to be jettisoning the hot-stage ring off the booster after separation this time too. That's a temporary weight reduction measure for the booster it seems. The booster will then attempt a soft water landing at 7:04 minutes after launch.
However they are going to try a Starship reentry, flip over and landing burn into the Pacific. The latter being at 01:05 hours after launch.
The proposed timeline is here:
https://www.spacex.com/launches/mission/?missionId...
I notice that MECO now seems to stand for "most engines cut off" instead of "main engine(s) cut off"
Seems the problems with launch 3 were predominantly valve or filter related (I'm sure Boeing sympathises).
The Booster:
"Following stage separation, Super Heavy initiated its boostback burn, which sends commands to 13 of the vehicle’s 33 Raptor engines to propel the rocket toward its intended landing location. All 13 engines ran successfully until six engines began shutting down, triggering a benign early boostback shutdown.
The booster then continued to descend until attempting its landing burn, which commands the same 13 engines used during boostback to perform the planned final slowing for the rocket before a soft touchdown in the water, but the six engines that shut down early in the boostback burn were disabled from attempting the landing burn startup, leaving seven engines commanded to start up with two successfully reaching mainstage ignition. The booster had lower than expected landing burn thrust when contact was lost at approximately 462 meters in altitude over the Gulf of Mexico and just under seven minutes into the mission.
The most likely root cause for the early boostback burn shutdown was determined to be continued filter blockage where liquid oxygen is supplied to the engines, leading to a loss of inlet pressure in engine oxygen turbopumps. SpaceX implemented hardware changes ahead of Flight 3 to mitigate this issue, which resulted in the booster progressing to its first ever landing burn attempt. "
And for flight 4:
"Super Heavy boosters for Flight 4 and beyond will get additional hardware inside oxygen tanks to further improve propellant filtration capabilities. And utilizing data gathered from Super Heavy’s first ever landing burn attempt, additional hardware and software changes are being implemented to increase startup reliability of the Raptor engines in landing conditions."
The Ship:
"Several minutes after Starship began its coast phase, the vehicle began losing the ability to control its attitude. Starship continued flying its nominal trajectory but given the loss of attitude control, the vehicle automatically triggered a pre-planned command to skip its planned on-orbit relight of a single Raptor engine.
Starship went on to experience its first ever reentry from space, providing valuable data on heating and vehicle control during hypersonic reentry. The lack of attitude control resulted in an off-nominal entry, with the ship seeing much larger than anticipated heating on both protected and unprotected areas. High-definition live views of entry and a considerable amount of telemetry were successfully transmitted in real time by Starlink terminals operating on Starship. The flight test’s conclusion came when telemetry was lost at approximately 65 kilometers in altitude, roughly 49 minutes into the mission.
The most likely root cause of the unplanned roll was determined to be clogging of the valves responsible for roll control. "
And for flight 4:
"SpaceX has since added additional roll control thrusters on upcoming Starships to improve attitude control redundancy and upgraded hardware for improved resilience to blockage."
Source:
https://www.spacex.com/updates/#flight-3-report
Beati Dogu said:
The most likely root cause for the early boostback burn shutdown was determined to be continued filter blockage where liquid oxygen is supplied to the engines, leading to a loss of inlet pressure in engine oxygen turbopumps. SpaceX implemented hardware changes ahead of Flight 3 to mitigate this issue, which resulted in the booster progressing to its first ever landing burn attempt. "
Can you enlighten me. What is causing the blockage of the filters? I, maybe naively, thought that the liquid oxygen would be pure so would not block the filter. Is it solid Oxygen, if so how cold does it need to be for that to form, or some other contaminant such as water ice from air in the tank at filling? Valve problems I can understand as the cold makes it a pretty hostile environment, but filters I would like to know what causes this.
bill swizz said:
Beati Dogu said:
The most likely root cause for the early boostback burn shutdown was determined to be continued filter blockage where liquid oxygen is supplied to the engines, leading to a loss of inlet pressure in engine oxygen turbopumps. SpaceX implemented hardware changes ahead of Flight 3 to mitigate this issue, which resulted in the booster progressing to its first ever landing burn attempt. "
Can you enlighten me. What is causing the blockage of the filters? I, maybe naively, thought that the liquid oxygen would be pure so would not block the filter. Is it solid Oxygen, if so how cold does it need to be for that to form, or some other contaminant such as water ice from air in the tank at filling? Valve problems I can understand as the cold makes it a pretty hostile environment, but filters I would like to know what causes this.
At a wild guess; there's probably plenty of opportunity for contamination from entry point to combustion, and no matter how clean your assembly plant is, no matter how well you clean your equipment after assembly, there's always going to be room for contamination from an external source that the liquids/gasses will pick up and run through a system.
AJLintern said:
Would it be moisture somehow getting into the system so ice blockages in the filter...?
Depending on how cold the LOX is, potentially Nitrogen ice. I do some work with Liquid Helium, and you get ice of pretty much everything accumulating on cold heads and the like.I wonder if they've got a problem with an air pocket in the tank/lines when they load propellants?
xeny said:
Depending on how cold the LOX is, potentially Nitrogen ice. I do some work with Liquid Helium, and you get ice of pretty much everything accumulating on cold heads and the like.
I wonder if they've got a problem with an air pocket in the tank/lines when they load propellants?
I think it was this Helium vat that freaked me out a little on a walk around Oxford when it did a vent, although it might have been one of the several liquid nitrogen tanks dotted around.I wonder if they've got a problem with an air pocket in the tank/lines when they load propellants?
Starship mission to Mars is never happening. Musk and SpaceX know this but they'll do whatever is necessary to keep the external investment coming in.
https://www.nature.com/articles/s41598-024-54012-0
But hey big rocket go bang is cool right.
https://www.nature.com/articles/s41598-024-54012-0
But hey big rocket go bang is cool right.
RumbleOfThunder said:
Starship mission to Mars is never happening. Musk and SpaceX know this but they'll do whatever is necessary to keep the external investment coming in.
https://www.nature.com/articles/s41598-024-54012-0
But hey big rocket go bang is cool right.
That paper analyses until 2030. So "never happening" is "not in the next 6 years".https://www.nature.com/articles/s41598-024-54012-0
But hey big rocket go bang is cool right.
However, that paper seems to go into the ISRU rabbit hole without really considering alternative options. If SpaceX can achieve their goal of rapid launch cadence with Starship, then I think the easiest way around the return flight issue is yeeting more Starships to Mars. That would be far more proven technology.
Now, it seems that delta-v would still be prohibitive. However. The article seems to go a bit weird about aerocapture, referring to a maximum 7.5 km/s velocity. My reading of the SpaceX article cited is that this is more of a ballpark figure. However, the Martian atmosphere is thin, and the right aerocapture window could distribute the heating across multiple passes, while expending a negligible quantity of propellant. This could vastly increase the delta-V budget available (by the 1.39 km/s Mars arrival value below).
Edited by Solocle on Wednesday 29th May 16:53
RumbleOfThunder said:
Starship mission to Mars is never happening. Musk and SpaceX know this but they'll do whatever is necessary to keep the external investment coming in.
https://www.nature.com/articles/s41598-024-54012-0
But hey big rocket go bang is cool right.
That analysis is based on “original Starship” - Musk has already set out the roadmap for Starships v2 & v3, which would seemingly overcome some of the problems identified in that paper.https://www.nature.com/articles/s41598-024-54012-0
But hey big rocket go bang is cool right.
Sending a “cargo Starship” ahead of / alongside the crewed Starship would head off some of the other issues.
The paper is wonderfully detailed, but reads like an MSc project & not an especially useful paper.
I wonder if the clogging issue is because they use supercooled liquid oxygen, which is below the temperature at which methane solidifies, and the tanks share a common pressure structure. Presumably when the engines are run, this reduces the tank pressure(s) which drops the temperature further, possibly causing the fuel to go waxy or mushy.
Gassing Station | Science! | Top of Page | What's New | My Stuff