Rocket Propellant Discussion

[Dilandu]

Not exactly about SpaceX, but just wanted to ask - what do you guys think about
propalox (liquid propane & liquid oxygen) propellant in concentric tanks (i.e. oxygen tank being placed inside propellant tank)?

 

[Byeman]

Not exactly about SpaceX, but just wanted to ask - what do you guys think about
propalox (liquid propane & liquid oxygen) propellant in concentric tanks (i.e. oxygen tank being placed inside propellant tank)?

not worth the effort. No advantage for concentric tanks and it makes the vehicle wider.

 

[Dilandu]

not worth the effort. No advantage for concentric tanks and it makes the vehicle wider.

Well, they simplify propellant feed (both tanks bottom on the same level), they made rocket better resist acceleration, and they solve the problem of oxygen tank insulation/fuel tank cooling.

 

[Byeman]

Well, they simplify propellant feed (both tanks bottom on the same level), they made rocket better resist acceleration, and they solve the problem of oxygen tank insulation/fuel tank cooling.

Draining the outer tank will be complicated.
Oxygen tanks aren't insulated. Space shuttle was a special case.
LOX will freeze propane. Hence, will require insulation for the propane and it will be internal, complicating construction.
It make the tanks have thermal stresses to due different temperatures if they use the same bulkheads. There goes the "better resistance to acceleration".

 

[Dilandu]

LOX will freeze propane. Hence, will require insulation for the propane and it will be internal, complicating construction.

Erm, liquid propane freeze at -188 C. Liquid oxygen boil at -183 С.

 

[Michel Van]

propane is mostly proposed for SSTO as Tripropellant engines
were Lox is burn with Propane and hydrogen

But it got some disadvantage
First it burn far hotter as Methane, means need more cooling.
the triproellant engines need hydrogen to cool it

Second there is no Propane on Mars (yes its in Titan lakes...)
manufacture it on Mars is complex, while Methane production is far easier there

 

[Byeman]

Erm, liquid propane freeze at -188 C. Liquid oxygen boil at -183 С.

SpaceX used densified LOX which is cold than -188C

 

[Dilandu]

SpaceX used densified LOX which is cold than -188C

As I mentioned above - I was asking generally, not particularly about SpaceX.

 

[publiusr]

propane is mostly proposed for SSTO as Tripropellant engines

But it got some disadvantage
First it burn far hotter as Methane, means need more cooling.

Perhaps propane could be used in a RENE set up.
Might propane be stored in a fall away RENE hoop?

This would eliminate the hot staging ring by venting gases upward to slow the first stage?

 

[Byeman]

As I mentioned above - I was asking generally, not particularly about SpaceX.

Still has the other structural issue with the temp differences.

 

[Michel Van]

Perhaps propane could be used in a RENE set up.
Might propane be stored in a fall away RENE hoop?

like Air breathing rocket engine RENE ?
there were several proposal since 1960s

 

[Dilandu]

Still has the other structural issue with the temp differences.

Hm. Would the difference between evaporating liquid oxygen and super-cooled liquid propane be significant enough?

 

[Michel Van]

Hm. Would the difference between evaporating liquid oxygen and super-cooled liquid propane be significant enough?

Lox start boil at −182.96 °C and freezing at −218.79 °C
Propane start boil at −42.04 °C and freezing at −187.7 °C

 

[Dilandu]

Lox start boil at −182.96 °C and freezing at −218.79 °C
Propane start boil at −42.04 °C and freezing at −187.7 °C

I know, that's the whole idea - we could surround oxygen tank with fuel tank, and oxygen would keep propane cooled and dense.

 

[publiusr]

like Air breathing rocket engine RENE ?
there were several proposal since 1960s

Yes...I was even thinking propane could be inside a RENE "afterburner" deal

I do like the idea of concentric tanks for strength.

I think India had a solid first stage with liquid boosters---from propellant efficiency you want the opposite--but structurally speaking--having a strong first stage is a good example of out-of-the-box thinking.

Propane burns hot--kerosene cokes up--but if you use a cleaner base propellant that doesn't burn as hot--then adding them to an ablative RENE ring that widens from combustion and therefore is a wider intake as the atmosphere thins can give Gnom style advantage to LVs perhaps.

I wonder if a ring surrounding an annular aerospike would be quieter...

 

[Byeman]

Hm. Would the difference between evaporating liquid oxygen and super-cooled liquid propane be significant enough?

the LOX doesn't become gas until in the engine.

And there is still the freezing issue.

 

[Byeman]

Yes...I was even thinking propane could be inside a RENE "afterburner" deal


Propane burns hot--kerosene cokes up--but if you use a cleaner base propellant that doesn't burn as hot--then adding them to an ablative RENE ring that widens from combustion and therefore is a wider intake as the atmosphere thins can give Gnom style advantage to LVs perhaps.

I wonder if a ring surrounding an annular aerospike would be quieter...

For what end purpose?
the challenge isn't to eek out every last second of ISP, but to increase the mass to orbit on every dollar spent or said another way lower the cost to put mass into orbit.

A cheaper "inefficient" rocket is better than a "maxed" out rocket that cost more for the same mass.

Juno 1 was an inefficient rocket but it was cheaper than the Vanguard and they both had the same payload capability.
Redstone could have flown more payload if it had better upper stages than the Juno 1 but it would have cost more.

 

[publiusr]

An all liquid alternative to solid augmentation.
The hot staging ring--an erstwhile "temporary" bodge, is true dead weight --but a ring used for nastier combustion products might pay for itself mass-wise if it also serves as tankage for nasty propellants.

Further--perhaps a largely spent ring could also double as a thrust reverser to allow a cooler interface between the first and second stages.

Once stage separation is done, the ring falls away like SH's hot stage ring--and the first stage can land with cleaner Methalox engines--all the heat and/or coking damage happens only to something that you were going to cast off anyway.

Space Freighter being in-line was to have something along the lines of a hot staging ring/join...though a parallel staged Space Freighter may not have needed ANY such ring--or used what I described to at least get a bit of Air- breathing without the whole airframe having to look like a chisel.

Two-Stage-and-a-Half to Orbit

Both winged--belly to belly, no Boostback burn.
Kerosene wet wings--but no coking of the main engines--that just fouls two rings that fall away from the bottom of each winged stage.

The spent rings are like Atlas sustainers and hold the craft up for vertical launch, but are no longer there when the two stages glide back--any remaining kerosene goes to small jets.

Keep what is reusable clean--use nastier propellants on what you cast off anyway.

 

[Byeman]

An all liquid alternative to solid augmentation.
The hot staging ring--an erstwhile "temporary" bodge, is true dead weight --but a ring used for nastier combustion products might pay for itself mass-wise if it also serves as tankage for nasty propellants.

Further--perhaps a largely spent ring could also double as a thrust reverser to allow a cooler interface between the first and second stages.

Once stage separation is done, the ring falls away like SH's hot stage ring--and the first stage can land with cleaner Methalox engines--all the heat and/or coking damage happens only to something that you were going to cast off anyway.

Space Freighter being in-line was to have something along the lines of a hot staging ring/join...though a parallel staged Space Freighter may not have needed ANY such ring--or used what I described to at least get a bit of Air- breathing without the whole airframe having to look like a chisel.

Two-Stage-and-a-Half to Orbit

Both winged--belly to belly, no Boostback burn.

nobody needs solid augmentation.
the ring isn't large enough to hold propellants.

And again, you are trying to optimize the wrong thing.
the hot staging ring is not "true" dead weight. It is not a "new" addition. Regardless, whether normal staging or hot staging, there has to be an interstage between Starship and the Superbooster. With normal staging, there has to be some mechanism that separates the stages. Normally, it is either or combinations of retrorockets on the lower stage, sep/ullage rockets on the upperstage or push rods/springs. SpaceX abhors solid rocket motors (hazards and operational costs) and specific thrusters for this event doesn't make sense. So retro and ullage rockets are out. Push rods/springs for the size Starship would be unmanageable due to their size. That is why SpaceX tried the fling maneuver. When that didn't work, SpaceX went to hot staging and the existing interstage had to have holes added and beefed up and a dome added to protect the booster.

 

[Michel Van]

For what end purpose?

in 1960s were several proposal for RENE engines mostly on air launched shuttle and one for NOVA class launcher
The idea behind is that RENE produce additional thrust using the air during launch and jettison
on Paper it was dynamite, in realty it gain only little on rocket performance, chancel out by mass of RENE device...

 

[Michel Van]

I know, that's the whole idea - we could surround oxygen tank with fuel tank, and oxygen would keep propane cooled and dense.

yes sound good idea, what worry me here, is the close temperature window of 4°c between Propane and LOX
Temperature control is needed to prevent Propane forming ice on Lox tank
You don't want have ice pieces in tank, what is suck into turbo-pumps of engine
what happen with water ice in Booster 11 during IFT-2

 

[Byeman]

in 1960s were several proposal for RENE engines mostly on air launched shuttle and one for NOVA class launcher
The idea behind is that RENE produce additional thrust using the air during launch and jettison
on Paper it was dynamite, in realty it gain only little on rocket performance, chancel out by mass of RENE device...

I was asking him for now, the current timeframe.

 

[Byeman]

yes sound good idea, what worry me here, is the close temperature window of 4°c between Propane and LOX
Temperature control is needed to prevent Propane forming ice on Lox tank
You don't want have ice pieces in tank, what is suck into turbo-pumps of engine
what happen with water ice in Booster 11 during IFT-2

Current launch vehicles that use 'Methane" really use LNG (Vulcan, Starship, NG). And even with tandem propellant tanks, they have issues with propane other minor constituents separating out when near plumbing with LOX in it.

 

[Michel Van]

I was asking him for now, the current timeframe.

ehh so far i know none with RENE...

But there Chinese company that want to use ramjet that use gas generator exhaust as propellant for thrust augmentation.
it more a pipe were Gas generator outlet is in it.

 

[publiusr]

If the Starships mounted atop SuperHeavy used kerolox Falcon engines temporarily--would the recent Starships have stayed in one piece--no explosions?

 

[Byeman]

If the Starships mounted atop SuperHeavy used kerolox Falcon engines temporarily--would the recent Starships have stayed in one piece--no explosions?

Why? What is the purpose?
There is no possible answer, because Starship cannot use Merlin engines.
a. Raptor is greater than 2 1/2 times more thrust
b. Raptor has higher ISP than Merlin
c. RP-1vs Methane have different mixture ratios, hence different tank sizes
d. It would require a separate launch pad for RP-1 and densified propellants.

 

[publiusr]

Musk is flexible..yes, I know it would take some doing...Merlin's have a pretty good track record--though that kerosene could get too cold perhaps?

My overall point was to use more mature engines so as to concentrate of Starship's flight profiles without something else to worry about.

Little Joe tests did not need Apollo/ Saturn hardware beyond the (rump) capsule and it's abort system.

 

[martinbayer]

Musk is flexible..yes, I know it would take some doing...Merlin's have a pretty good track record--though that kerosene could get too cold perhaps?

My overall point was to use more mature engines so as to concentrate of Starship's flight profiles without something else to worry about.

Little Joe tests did not need Apollo/ Saturn hardware beyond the (rump) capsule and it's abort system.

Musk matures liquid rocket propulsion by operationally (re)using engines and designs frequently in high numbers. I *really* don't like the man as a person, but I understand and applaud his rapid evolution design philosophy. He makes design choices as he sees fit and either validates them in operational use or revisits them after failures, because he operates on the principle of continuous improvement. The better is the enemy of the good. In other words, he emulates natural evolution, and more power to him in that particular area of his various and sundry endeavors.

 

[Byeman]

Musk is flexible..yes, I know it would take some doing...Merlin's have a pretty good track record--though that kerosene could get too cold perhaps?
My overall point was to use more mature engines so as to concentrate of Starship's flight profiles without something else to worry about.

The "some doing" would be negative work and Musk is against that. Because it would still take many flights to work out issues with the RP-1 Starship before it can concentrate on flight profiles.
edit:
Additionally, flight profiles of a vehicle using RP-1 would be different due to different burn times and acceleration. So the point is moot, it provides no benefit as you suggest. And there are other reasons, see below.

My overall point was to use more mature engines so as to concentrate of Starship's flight profiles without something else to worry about..

Raptor is a mature engine. It has flown more times than F-1, J-2, RS-68, RD-180, and H-1even with including RS-27.
The issue is more stage propulsion system integration and plumbing and not the individual engines. Switching engines and propellants isn't going to help resolve that.

Little Joe tests did not need Apollo/ Saturn hardware beyond the (rump) capsule and its abort system.

Non sequitur. Starship 7 failed as a launch vehicle. The launch system part has to be worked out before they worry about the "spacecraft" part and recovery. Any orbital and recovery testing is a bonus.

SpaceX philosophy is to be flight hardware rich. They rather spent money doing flight tests than ground tests. It is cheaper for them to try to fly the SB/SS multiple times than build massive stands and non flight stages for full duration static tests. This is just a further expansion of the Saturn V "all up" testing concept. SpaceX just prefers to build only launch pads and flight stages and not the 4 sets of test stages and multiple test stands of Saturn V.