Falcon Heavy Cross-Feed

[Dmitry_V_home]

Angara-5 cross-feed version 

[MP99]

Answer this: what happens to a cryogen in a feed line while the valve is closed and it sits there warm soaking?  When that valve is opened, what does the inlet side see from the valve?

Well if I were designing it, I'd look into allowing a small flow through the valve to keep everything cold.

Would a cryo valve have to be closed on the ground? Once closed in-flight, I don't think it would need to be opened again?

IFF some of the engines were to be switched from the side tanks to the core tanks (as opposed to being shut down) the LOX main tank feeds to them would start out shut on the ground, then opened in flight so there's the question of keeping them chilled.

Ah, of course.

I presume the main tank feeds could be left open until seconds before launch, so presumably can be kept chilled at this phase? However, I can see that could be a problem in the (presumably hot) environment during cross-fed flight. Re "small flow" - how much flow is required to maintain cryo temps?

cheers, Martin

[Jim]

Angara-5 cross-feed version 

That shows that the boosters have to be at a higher pressure than the core.

[cuddihy]

Wouldn't it be simpler to just run a single line each RP1 and LOX from the outboard tanks to the core, then distribute the fuel/lox from there? That would only require two couplings rather than six on each side. Perhaps with valving, the current fill/empty lines could be expanded a bit and used?

Simpler conceptually, but much more expensive.

That certainly doesn't seem obvious.

Assuming the fill/empty lines can be enlarged and are used for the cross feed to 3 engines in the core, then single cross feed for fuel and LOX requires for each booster:

Probably enlarging the 2 fill/empty lines
2 T's
2 line separation system
2 1x3 manifolds in the core
Space and support for 2 lines

and how do you go about enlargening the drain/fill line to that extent (take a look, the other feed lines are the same size and are in the way). In effect you would be creating a new RP1 plenum. Not so with LOX because of the big downcomer. But again you still would end up having to extend the thrust structure.

Running separate lines using the booster feed lines requires

Probably enlarging 6 feed lines
6 1x2 manifolds
6 line separation system
Space and support for 6 lines

[Dmitry_V_home]

That shows that the boosters have to be at a higher pressure than the core.

Not necessarily.

[RDoc]

and how do you go about enlargening the drain/fill line to that extent (take a look, the other feed lines are the same size and are in the way). In effect you would be creating a new RP1 plenum. Not so with LOX because of the big downcomer. But again you still would end up having to extend the thrust structure.

It appears that the flow velocity is pretty low, so taking a SWAG I'd say the flow rate was pretty proportional to the area. So, assuming the fill/empty lines are the same as the downcomers, to increase the flow by a factor of 3 would require an increase in diameter of one line by 1.73, so an increase of .73. To increase the area of 3 lines by a factor of two would be 3 * 1.41 = 4.2 so an increase of 1.2. For 10 inch lines, this would be 7.3 inches total, .73 inches per line vs 12 inches total, or 1.2 inches per line.

The fuel lines probably aren't a big deal since there seems to be plenty of room to tighten up the spacing. I don't see how this would be particularly expensive in either case.

The LOX line is a different matter though I'd think. My guess is the feed/fill line is the one on the lower left of the aft-most hub of the octopus. There seems to be plenty of room to increase that. However, to increase 3 LOX lines would require either re-spacing the forward LOX lines which seem pretty tightly spaced, or increasing the diameter of the plenum. Changing the diameter would change the geometry and might require increasing the fuel header circle diameter.

There's no doubt that any cross/side feed system would require changes to both the fuel and LOX lines, but I doubt these are off the shelf items that are bought at a bulk discount. It does seem though that enlarging a single line for each would be somewhat less disruptive to the existing geometries than doing 3 each. I don't see where the significant increase in cost would lie in the smaller change vs the larger.

It's certainly also true that either design would require changing the thrust structure, but again, accommodating two larger lines isn't obviously a lot more expensive than 6 smaller lines.

[Jim]

That shows that the boosters have to be at a higher pressure than the core.

Not necessarily.

Huh?  if not, the core will use its own propellants

[go4mars]

That shows that the boosters have to be at a higher pressure than the core.

Not necessarily.

Huh?  if not, the core will use its own propellants

I don't read Russian, but is that a valve labelled on the middle tank (just below where the green feedlines come over)? 

[aga]

That shows that the boosters have to be at a higher pressure than the core.

Not necessarily.

Huh?  if not, the core will use its own propellants

I don't read Russian, but is that a valve labelled on the middle tank (just below where the green feedlines come over)? 

if i got it right, and according to wiki, the thing in the middle is in english called "butterfly valve"... sorry, not familiar with english terminology in this area

[go4mars]

That shows that the boosters have to be at a higher pressure than the core.

Not necessarily.

Huh?  if not, the core will use its own propellants

I don't read Russian, but is that a valve labelled on the middle tank (just below where the green feedlines come over)? 

if i got it right, and according to wiki, the thing in the middle is in english called "butterfly valve"... sorry, not familiar with english terminology in this area

Thanks.  That sounds right.  I assume it allows flow from the boosters and disallows flow from the middle core until the boosters are empty and gone (then it folds its wings and opens its back). 

[Jim]

The fuel tank on the core does not have an equivilent valve

[Dmitry_V_home]

I assume it allows flow from the boosters and disallows flow from the middle core until the boosters are empty and gone (then it folds its wings and opens its back). 

Exactly!

[Dmitry_V_home]

One more possible scheme of the cross-feed rocket:

[RDoc]

Am I correct in thinking that the biggest mechanical issue with cross/side feed would be the umbilical separation systems between the boosters and core?

The other components seem pretty standard, manifolds, valves and pipes. Even the systems for dropping the boosters has a lot of industry precedents, although perhaps SpaceX might use hydraulics to lock and release the boosters?

Presumably FH would use something like the Shuttle external tank system couplings with explosive bolts, low pressure shutoff valves, coupling retractors, and fairing doors on both the core and boosters. That all seems like a lot of complex moving parts, but perhaps it could be simplified with an integrated cam/lever mechanism actuated by the hydraulic system. I wouldn't think they'd want to have any pieces jettisoned at that point that could hit the core or boosters as they fell away, although probably some RP1 and LOX would be spilled.

In any case it seems a bit tricky to get right and reliable.

[Jim]

Am I correct in thinking that the biggest mechanical issue with cross/side feed would be the umbilical separation systems between the boosters and core?

The other components seem pretty standard, manifolds, valves and pipes. Even the systems for dropping the boosters has a lot of industry precedents, although perhaps SpaceX might use hydraulics to lock and release the boosters?

Presumably FH would use something like the Shuttle external tank system couplings with explosive bolts, low pressure shutoff valves, coupling retractors, and fairing doors on both the core and boosters. That all seems like a lot of complex moving parts, but perhaps it could be simplified with an integrated cam/lever mechanism actuated by the hydraulic system. I wouldn't think they'd want to have any pieces jettisoned at that point that could hit the core or boosters as they fell away, although probably some RP1 and LOX would be spilled.

In any case it seems a bit tricky to get right and reliable.

no, see heritage Atlas

[RDoc]

no, see heritage Atlas

That seems like a very different system.

[Jim]

no, see heritage Atlas

That seems like a very different system.

No, it would have similar disconnects.

[Jim]

1.  The other components seem pretty standard, manifolds, valves and pipes. Even the systems for dropping the boosters has a lot of industry precedents, although perhaps SpaceX might use hydraulics to lock and release the boosters?

2.  Presumably FH would use something like the Shuttle external tank system couplings with explosive bolts, low pressure shutoff valves, coupling retractors, and fairing doors on both the core and boosters. That all seems like a lot of complex moving parts, but perhaps it could be simplified with an integrated cam/lever mechanism actuated by the hydraulic system. I wouldn't think they'd want to have any pieces jettisoned at that point that could hit the core or boosters as they fell away, although probably some RP1 and LOX would be spilled.

In any case it seems a bit tricky to get right and reliable.

1.  no, too complex and unneeded.  See Titan solids and Delta IV boosters.  Explosive nuts are all that is needed with some sep motors

2.  Again, no doors or hydraulics, too complex and unneeded.  No coupling retraction needed.

See heritage Atlas.  LOX and RP-1 disconnects.  Separation is done after engine cutoff (no flow conditions).

[go4mars]

See heritage Atlas.  LOX and RP-1 disconnects.  Separation is done after engine cutoff (no flow conditions).

So a re-light is required for the boost-back phase?  I guess that could be lower risk.  I was picturing only 6 engines shutting off on the outside cores...3 just keep firing. 

These 1D's are made for re-starting easily anyways right?  ?     

?

[Jim]

See heritage Atlas.  LOX and RP-1 disconnects.  Separation is done after engine cutoff (no flow conditions).

So a re-light is required for the boost-back phase? 

What boost-back phase?