Author Topic: The best method to transfer Methalox Fuel in space?  (Read 21970 times)

Offline Norm38

  • Full Member
  • ****
  • Posts: 1108
  • Liked: 471
  • Likes Given: 660
Re: The best method to transfer Methalox Fuel in space?
« Reply #80 on: 09/29/2017 04:09 PM »
You mean the fill and vent lines?  And they're bidirectional?  I have no idea if the valves can support that or not.
« Last Edit: 09/29/2017 04:10 PM by Norm38 »

Offline rakaydos

  • Full Member
  • ***
  • Posts: 399
  • Liked: 161
  • Likes Given: 3
Re: The best method to transfer Methalox Fuel in space?
« Reply #81 on: 09/29/2017 04:27 PM »


4 pipes for fuel transfer. You can see in the render which side flares and which side narrows for mating the pipes.

Online John Alan

  • Full Member
  • ****
  • Posts: 701
  • Central IL - USA - Earth
  • Liked: 382
  • Likes Given: 1669
Re: The best method to transfer Methalox Fuel in space?
« Reply #82 on: 09/29/2017 05:39 PM »
You mean the fill and vent lines?  And they're bidirectional?  I have no idea if the valves can support that or not.

On the rocket... yes... all liquid rated and capable of flow in either direction... use valves that allow this on the rocket...
Back them together in space... latch the connectors... and open all 4 valve lines...

On edit... added pic of my... 60 second yes that works... paper stand in
Apply thrust and fluid can be transferred in either direction by "gravity"...
« Last Edit: 09/29/2017 05:57 PM by John Alan »

Offline shooter6947

  • Full Member
  • *
  • Posts: 107
  • Idaho
  • Liked: 75
  • Likes Given: 429
Re: The best method to transfer Methalox Fuel in space?
« Reply #83 on: 09/29/2017 05:47 PM »
So Musk confirmed tanker and spaceship will mate end-to-end and use ullage thrusters to settle the propellant down into the empty tanks of the ship.

He said the plan is to reuse the existing plumbing from the booster to transfer fuel.  But in the image here, if say CH4 is on the left and O2 is on the right, when the ship and tanker dock end-to-end, then those connections don't line up.  They might if the tanker rolled over, but that's not what's shown.

Discuss.

Just put CH4 on the top, and O2 on the bottom.

Offline DanielW

  • Full Member
  • ****
  • Posts: 477
  • L-22
  • Liked: 338
  • Likes Given: 62
Re: The best method to transfer Methalox Fuel in space?
« Reply #84 on: 09/29/2017 06:18 PM »
I find it interesting that the spaceship will be fueled by the booster on earth. I would assume that means that all other umbilical connections for power/data etc will also come from the booster.

Offline Jim

  • Night Gator
  • Senior Member
  • *****
  • Posts: 32227
  • Cape Canaveral Spaceport
  • Liked: 10882
  • Likes Given: 324
Re: The best method to transfer Methalox Fuel in space?
« Reply #85 on: 09/29/2017 06:25 PM »
You mean the fill and vent lines?  And they're bidirectional?  I have no idea if the valves can support that or not.

They are called fill and drain lines.  The tanks have to be emptied for scrubs.

Offline envy887

  • Senior Member
  • *****
  • Posts: 4100
  • Liked: 2121
  • Likes Given: 1269
Re: The best method to transfer Methalox Fuel in space?
« Reply #86 on: 09/29/2017 06:32 PM »
And they won't use milligees of this to do the actual transfer. The thrust is to settle the propellant. The transfer is driven by pressure differential.

Offline Norm38

  • Full Member
  • ****
  • Posts: 1108
  • Liked: 471
  • Likes Given: 660
Re: The best method to transfer Methalox Fuel in space?
« Reply #87 on: 09/30/2017 04:10 AM »
You mean the fill and vent lines?  And they're bidirectional?  I have no idea if the valves can support that or not.

They are called fill and drain lines.  The tanks have to be emptied for scrubs.

Got it. So when the separate ships are fueled for launch on Earth, are they filled from the top or the bottom?  From John Alan's sketch, they will fill from the bottom due to ullage thrust. 
« Last Edit: 09/30/2017 04:12 AM by Norm38 »

Offline Lars-J

  • Senior Member
  • *****
  • Posts: 4032
  • California
  • Liked: 3329
  • Likes Given: 2092
Re: The best method to transfer Methalox Fuel in space?
« Reply #88 on: 09/30/2017 05:45 AM »
You mean the fill and vent lines?  And they're bidirectional?  I have no idea if the valves can support that or not.

They are called fill and drain lines.  The tanks have to be emptied for scrubs.

Got it. So when the separate ships are fueled for launch on Earth, are they filled from the top or the bottom?  From John Alan's sketch, they will fill from the bottom due to ullage thrust.

F9 fills its stages from the bottom, as does most (all?) liquid launch vehicles.

Offline Semmel

  • Full Member
  • ****
  • Posts: 1385
  • Germany
  • Liked: 1191
  • Likes Given: 3129
Re: The best method to transfer Methalox Fuel in space?
« Reply #89 on: 09/30/2017 11:35 AM »
They could just mount the pipes at the front and back if rotating 180 degrees is a problem. I dont think the tanker will have reversed pipes  because this makes the ground equipment more complicated. Just have them front and back and you can stick the two second stages together as shown in the image.

Online Nibb31

  • Full Member
  • **
  • Posts: 244
  • France
  • Liked: 142
  • Likes Given: 8
Re: The best method to transfer Methalox Fuel in space?
« Reply #90 on: 09/30/2017 11:40 AM »
There is no need to rotate. The male/female connections are symmetrical, as shown in SpaceX's slide. It's quite clear.

Offline speedevil

  • Senior Member
  • *****
  • Posts: 2148
  • Fife
  • Liked: 1056
  • Likes Given: 1184
Re: The best method to transfer Methalox Fuel in space?
« Reply #91 on: 03/01/2018 09:43 PM »


The image is 507 pixels across, and though presumably not a final design, I thought it interesting to do some approximate numbers.
Measuring the internal diameter of the two narrow pipes, I came to an approximate figure of 11 pixels, and around 18 pixels for the wider outside.
As these are tapered connectors, 14 pixels seems a reasonable approximation for the ID of the pipe, leading to a diameter of 26.7cm.
For no particularly good reason, I'm assuming it's in fact 25cm.

Only calculating liquid oxygen,and assuming one pipe flow of 18m long, with around 1 bar across the pipe, assuming the receiving tank is vented, this flows around 70 tons a minute. (oxygen viscosity is 188*10-6 kg/ms, density 1.1, http://www.pressure-drop.com/Online-Calculator/ )

For both pipes, this is probably conservative, if the system is properly designed.
I did not bother calculating methane, as oxygen dominates.

This assumes autogenous pressurisation works, and the engines are OK with starting up with less than nominal pressure if you're transferring a lot of fuel, or some autogenous pressurisation device that works without the engines being on.

I was idly wondering in the context of my silly speculations on using BFS SSTO, refuelling suborbitally, and if it only takes two minutes, plus a couple of minutes  to rendevous from close flight, this might be quite plausible.

Online douglas100

  • Senior Member
  • *****
  • Posts: 2168
  • Liked: 222
  • Likes Given: 102
Re: The best method to transfer Methalox Fuel in space?
« Reply #92 on: 03/01/2018 10:11 PM »

....This assumes autogenous pressurisation works, and the engines are OK with starting up with less than nominal pressure if you're transferring a lot of fuel, or some autogenous pressurisation device that works without the engines being on.

I was idly wondering in the context of my silly speculations on using BFS SSTO, refuelling suborbitally, and if it only takes two minutes, plus a couple of minutes  to rendevous from close flight, this might be quite plausible.

I think it would much longer than two minutes. Propellant would only flow at that rate if the main engines were running and the flow was being driven by their turbopumps. You emphatically would not be doing that during orbital refuelling. (I won't comment on your suborbital proposal.) Pressure differential is all that is required to transfer settled propellant. It doesn't matter in principle whether the pressure differential is caused by autogeneous  pressurisation or a pressurant like helium. In the case of BFS it would be autogeneous. Note that the tanks must be pressurised anyway before any main engine start however it is done. Same for prop transfer.
Douglas Clark

Offline speedevil

  • Senior Member
  • *****
  • Posts: 2148
  • Fife
  • Liked: 1056
  • Likes Given: 1184
Re: The best method to transfer Methalox Fuel in space?
« Reply #93 on: 03/01/2018 10:19 PM »

....This assumes autogenous pressurisation works, and the engines are OK with starting up with less than nominal pressure if you're transferring a lot of fuel, or some autogenous pressurisation device that works without the engines being on.

I think it would much longer than two minutes. Propellant would only flow at that rate if the main engines were running and the flow was being driven by their turbopumps.

I am assuming the receiving tank is vented to vacuum, and the originating tank is pressurised to somewhere above 1 bar, and propellant simply flows due to difference in pressure.
10" pipes flow quite a lot of liquid at 1 bar head, especially if low viscosity like liquid oxygen, even if 20m long or so.

The originating tank nominal pressure pretty much has to be pressurised significantly over 1 bar in order to handle even atmospheric loads.

No pumps at all.


I note F9 fills in apparently 15 minutes for 200+ tons of LOX, so unless BFS is significantly slower, 70 tons a minute would be a reasonable figure, and indeed quite slow for BFR.

'In real life' performance, even assuming unchoked pipes is complex, and would need to make assumptions about things like pressurant being very non ideal-gas-like as the temperature drops and more wants to condense into the propellant.

At some total amount of transfer relative to the initial tank volume, you're going to need to start actively pressurising, or the gas will just drop out as it rapidly cools. (or boiling will occur, which is bad)

The engines have to be able to cope in some manner with varying tank pressurisation, as it's explicitly mentioned at IAC that they'll dump them to vacuum.

Perhaps the fill lines go to the main tanks, and the 'landing' tanks remain pressurised through some system, while allowing rapid main tank gas heating when the engines are on through heat exchangers.

I consider the suborbital refuelling idea very very unlikely to happen.
« Last Edit: 03/02/2018 10:54 AM by speedevil »

Offline livingjw

  • Full Member
  • ***
  • Posts: 356
  • Liked: 384
  • Likes Given: 166
Re: The best method to transfer Methalox Fuel in space?
« Reply #94 on: 03/02/2018 11:17 AM »
The tanks won't be at zero pressure. Main tank pressures are about 30-45 psi. Receiving tank could be dropped 10 to 20 psi below that. Once transfer is complete, pressure can be raised back up using warm GOx and GCH4. Main engines would never be operated until design tank pressures have been reestablished. Small pressure fed vernier motors would use a different tank system, probably pressurized to a few hundred psi.

John
« Last Edit: 03/02/2018 11:24 AM by livingjw »

Offline the_other_Doug

  • Senior Member
  • *****
  • Posts: 2726
  • Minneapolis, MN
  • Liked: 1782
  • Likes Given: 3387
Re: The best method to transfer Methalox Fuel in space?
« Reply #95 on: 03/02/2018 04:10 PM »
The tanks won't be at zero pressure. Main tank pressures are about 30-45 psi. Receiving tank could be dropped 10 to 20 psi below that. Once transfer is complete, pressure can be raised back up using warm GOx and GCH4. Main engines would never be operated until design tank pressures have been reestablished. Small pressure fed vernier motors would use a different tank system, probably pressurized to a few hundred psi.

John

When dealing with tanks partially filled (separately, of course) with super-cooled liquid methane and with LOX, at what temperature and pressure does each freeze into a solid?  I get the feeling that it's a sliding scale, depending on the amount of fluid vs. gas in each tank.

I'm assuming that the freezing point goes higher as pressure decreases.  At a vacuum and super-cooled temps, I'd think you'd flash-freeze a lot of each liquid...
-Doug  (With my shield, not yet upon it)

Offline speedevil

  • Senior Member
  • *****
  • Posts: 2148
  • Fife
  • Liked: 1056
  • Likes Given: 1184
Re: The best method to transfer Methalox Fuel in space?
« Reply #96 on: 03/02/2018 04:29 PM »
When dealing with tanks partially filled (separately, of course) with super-cooled liquid methane and with LOX, at what temperature and pressure does each freeze into a solid?  I get the feeling that it's a sliding scale, depending on the amount of fluid vs. gas in each tank.

I'm assuming that the freezing point goes higher as pressure decreases.  At a vacuum and super-cooled temps, I'd think you'd flash-freeze a lot of each liquid...

You would need to let a moderate amount of liquid boil off in order to chill the bulk liquid to freezing point.

The reference to 'vacuum' above was a bit misleading - you wouldn't go all the way to vacuum - it will boil - just 14PSI (or whatever) lower than the other tank.
The concern which makes it somewhat more complex to calculate what happens is that as the volume of gas in the tank changes in the 'sending' tank, if you are not using pumps, it can rapidly cool to below the point at which it becomes liquid as it expands, and pressure collapses.
This means you need some means of maintaining pressure in the tank.

In practice, if the propellant is actually chilled below the boiling point, you in addition have a large flow of pressurant gas condensing in the tanks, so 'steady state' is only occurring with the pressurant boiling system - however it's designed - active.

As a rough number, this system needs to provide in a normal launch, 1000m^3 over 5 minutes, 3m^3/s. At STP, this volume of pressurant gas would be around 4.5kg/s, at 100K, ideal gas law says around 15kg/s, and a quick google says 200kJ/kg, so the heater needs to provide about 3MW, equivalent to burning about a hundred grams of methane a second, if the heater were to be an isolated system.





Offline rakaydos

  • Full Member
  • ***
  • Posts: 399
  • Liked: 161
  • Likes Given: 3
Re: The best method to transfer Methalox Fuel in space?
« Reply #97 on: 03/02/2018 06:44 PM »
Why would they NOT use turbopumps to accelerate fuel transfer? Spend a little fuel via turbopump, save a bit of fuel in ullage thrust, save time because the pumping is faster, and hot partially burned methalox makes for more efficent ullage.

Offline envy887

  • Senior Member
  • *****
  • Posts: 4100
  • Liked: 2121
  • Likes Given: 1269
Re: The best method to transfer Methalox Fuel in space?
« Reply #98 on: 03/02/2018 06:49 PM »
Why would they NOT use turbopumps to accelerate fuel transfer? Spend a little fuel via turbopump, save a bit of fuel in ullage thrust, save time because the pumping is faster, and hot partially burned methalox makes for more efficent ullage.

Tank pressure is more than enough to empty the tanks in minutes. How do you think the booster tanks empty in less than 2 minutes during ascent? Hint: the turbopumps are not "sucking" it out...

Online Steve D

  • Member
  • Posts: 96
  • Liked: 36
  • Likes Given: 1
Re: The best method to transfer Methalox Fuel in space?
« Reply #99 on: 03/02/2018 08:38 PM »
As the liquid flows from the tanker why would you not just transfer gas into the tanker from the BFS? I thought there were 4 connections between tanker and BFS. 1 supply and 1 return line for o2 and methane.

Tags: