Methalox Falcon 9 family

[Hyperion5]

The SpaceX Mars BFR could also be configured like the Saturn-INT 20/21 concept. If so that could eliminate the Falcon Heavy if BFR is reusable. That is the two stage version and not the tri-core concept that is being speculated.

Converting the F9 or FH US to LCH4/LOX could be used as a third stage for BLEO on the BFR launches. I don't see it being used on the F9/FH.

Well then how do we explain Shotwell's comments about having a methalox upper stage on the Falcon 9 family?  Spacex leadership appears to be in the midst of some severe cognitive dissonance.  On the one hand we get denials that there is a smaller methalox engine being under design.  On the other hand we suddenly have Shotwell talking about an upper stage for the Falcon 9 family being methalox.  You don't have to be a rocket engineer to figure out that it a Raptor would be an utterly ridiculous choice to power that stage.  It's simply too powerful.  But you know what would be a perfect choice?  A methalox Merlin or FFSC methalox engine would work, but they're denying such an engine is under consideration.  They can have the Raptor and no methalox F9 upper stage, or they can power a F9 methalox upper stage with a new engine, but they can't power that stage with a Raptor. 

After F9/FH and Mars BFR I think they will come up will a new concept to replace F9/FH with lower cost, faster launch rate, and greater mass to LEO while being fully reusable.

So for this thread, compare mass to LEO and GTO. Compare payload mass to orbit for same size launcher with different fuels.

F9 v1.1 RP-1/LOX to LEO payload mass and GTO payload mass?
F9 LCH4/LOX to LEO payload mass and GTO payload mass?

So if there is not much differance then why convert?

It might be worth it to convert because a methalox engine would trim turnaround times and allow more reuses of a stage.  Currently it's likely that the 20 reuse-rated Merlins are the limiting factor in reusability.  However, swap in some methalox engines, and it's likely you could get even more reuses (due to lack of coking) and modestly more performance.  You'd also simplify pad infrastructure and tear pads up with modestly less thrust.  There's a lot to like about the possibilities of a methalox Falcon 9 family offering improved reusability and greater capability. 

[Lars_J]

The SpaceX Mars BFR could also be configured like the Saturn-INT 20/21 concept. If so that could eliminate the Falcon Heavy if BFR is reusable. That is the two stage version and not the tri-core concept that is being speculated.

Converting the F9 or FH US to LCH4/LOX could be used as a third stage for BLEO on the BFR launches. I don't see it being used on the F9/FH.

Well then how do we explain Shotwell's comments about having a methalox upper stage on the Falcon 9 family?  Spacex leadership appears to be in the midst of some severe cognitive dissonance.  On the one hand we get denials that there is a smaller methalox engine being under design.  On the other hand we suddenly have Shotwell talking about an upper stage for the Falcon 9 family being methalox.  You don't have to be a rocket engineer to figure out that it a Raptor would be an utterly ridiculous choice to power that stage.  It's simply too powerful.  But you know what would be a perfect choice?  A methalox Merlin or FFSC methalox engine would work, but they're denying such an engine is under consideration.  They can have the Raptor and no methalox F9 upper stage, or they can power a F9 methalox upper stage with a new engine, but they can't power that stage with a Raptor. 

C'mon.  There is a massive gulf between "not working/planning on it" and "not ruling it out for the future". It would be silly for her to say that they would NEVER do something. No contradiction there.

[Hyperion5]

The SpaceX Mars BFR could also be configured like the Saturn-INT 20/21 concept. If so that could eliminate the Falcon Heavy if BFR is reusable. That is the two stage version and not the tri-core concept that is being speculated.

Converting the F9 or FH US to LCH4/LOX could be used as a third stage for BLEO on the BFR launches. I don't see it being used on the F9/FH.

Well then how do we explain Shotwell's comments about having a methalox upper stage on the Falcon 9 family?  Spacex leadership appears to be in the midst of some severe cognitive dissonance.  On the one hand we get denials that there is a smaller methalox engine being under design.  On the other hand we suddenly have Shotwell talking about an upper stage for the Falcon 9 family being methalox.  You don't have to be a rocket engineer to figure out that it a Raptor would be an utterly ridiculous choice to power that stage.  It's simply too powerful.  But you know what would be a perfect choice?  A methalox Merlin or FFSC methalox engine would work, but they're denying such an engine is under consideration.  They can have the Raptor and no methalox F9 upper stage, or they can power a F9 methalox upper stage with a new engine, but they can't power that stage with a Raptor. 

C'mon.  There is a massive gulf between "not working/planning on it" and "not ruling it out for the future". It would be silly for her to say that they would NEVER do something. No contradiction there.

But that would mean that this thread's premise is actually plausible, Lars, and that would mean...(gasps)...that the thread shouldn't be shut down!   

---

I keep hearing how Spacex hasn't approved any such smaller methalox engine, which is true.  However this thread is about the plausibility of needing such an engine for the MCT, and I think that's extremely plausible.  You would have to set a new record in throttling to use a single Raptor to land the MCT Apollo-style.  Now you could avoid doing so, but that would require you to land the MCT perfectly every time.  It would also endanger the engine and gouge a big hole directly beneath the lander during landing.  In contrast multiple angled-out engines have been proven to be a safe alternative thanks to MSL.  Plus there's one really big reason not to use a single Raptor engine to land the MCT: no engine-out capability.  If you're going to use multiple smaller methalox engines to land on Mars, then you might as well put one of those engines on a Falcon 9 or Falcon Heavy.  If not on the whole rocket then at least on the upper stage. 

[Lars_J]

Oh I'm not disagreeing with that. I have always been on record here as preferring a Mars lander with multiple smaller engines instead of a big one. But based on what she said, any Such vehicle is over a decade away anyway, so it is all fluid at this point.

(Sorry to drag this off topic, I will end it here)

[ArbitraryConstant]

Well then how do we explain Shotwell's comments about having a methalox upper stage on the Falcon 9 family?  Spacex leadership appears to be in the midst of some severe cognitive dissonance.  On the one hand we get denials that there is a smaller methalox engine being under design.  On the other hand we suddenly have Shotwell talking about an upper stage for the Falcon 9 family being methalox.

I don't know where you're getting that but it's not the 3/21 space show interview. I listened to that.

The only mention of a methane US for F9/H was that it's not being worked on and there's no plans to work on it. It's not completely ruled out in any possible future but we are given the extremely robust impression that SpaceX considers all current Earth orbit launches pretty much wrapped up with the advent FH and reusability, and there is very little interest in further distractions from the Mars mission. Someone called in to ask if they'd do methane work for a F9/H US if someone hired them to do it and even then that got a skeptical response because it would pull people off other stuff.

However this thread is about the plausibility of needing such an engine for the MCT, and I think that's extremely plausible.

There's other landing concepts that have been discussed. Whatever your or anyone else's analysis, if Shotwell says they want to work on the Mars ship and not a smaller methane engine, that suggests strongly that the Mars ship doesn't have a smaller methane engine. Even if you can make a case it's a good engineering idea, you're not making a case that SpaceX sees it as one or that it aligns with what they want to do. Which is ultimately necessary if you want to suggest that it has a chance of happening.

[MP99]

So, a thought.

Raptor, as a gas-gas engine, will have two gas generators & turbopump assemblies.

Could one of those assemblies be used in a gas-liquid engine of around half the thrust? I assume not, as it would be such a different transport / injection / combustion architecture. Probably much easier to just build a smaller gg/turbopump assembly, and reuse the experience with Raptor.

Cheers, Martin

[cuddihy]

I don't believe a methalox Merlin, or other GG engine, buys enough in Isp (IIRC only 10-20 sec or so) to be worth re-designing stages and pads.

Does anyone know if an expander cycle based methane is any better?

*edit* I've done a fair bit of googling& haven't found anything about expander methalox specific impulse. It seems an expander cycle is limited to about 300 psi in the chamber. RL-10A has apparently been run on methalox but no data on pressure or Is.

I DID find a fascinating 1999 usenet thread back &forth between Gary Hudson& Henry Spencer which led me to the original 1990 Zubrin Mars proposal (with Martin Marietta logo no less)

But no specifics about expander methane performance...

Sigh...going to have to dig the Sutton out of the books in the garage.

[Oli]

What about a third stage similar to Proton's Briz-M but with a pressure-fed methane engine?

Seems like Falcon could benefit a lot from such a stage, in particular the version with reusable first stage.

[docmordrid]

If you're going pressure fed for a 3rd stage why not KISS and do a SuperDraco based "Briz-X"?

[Hyperion5]

I don't believe a methalox Merlin, or other GG engine, buys enough in Isp (IIRC only 10-20 sec or so) to be worth re-designing stages and pads.

Does anyone know if an expander cycle based methane is any better?

*edit* I've done a fair bit of googling& haven't found anything about expander methalox specific impulse. It seems an expander cycle is limited to about 300 psi in the chamber. RL-10A has apparently been run on methalox but no data on pressure or Is.

I have to agree that gas generator cycle is probably not going to provide enough of an improvement to be worth it.  It's going to have to be some form of staged combustion cycle or expander cycle, and only the latter if on the upper stage.  I don't know if expander cycle is any better mainly because there's been very little work with methalox engines before the last 15 years.  If you can't find anything regarding a methalox RL-10A, I would suggest looking into the RD-0146 engine from Russia.  If my memory serves, Russiaspaceweb.com has the actual performance numbers for a methalox version.  If you fail to find it, please contact fregate here on NSF.  He was one of the original authors on Russiaspaceweb's RD-0146 article. 

So, a thought.

Raptor, as a gas-gas engine, will have two gas generators & turbopump assemblies.

Could one of those assemblies be used in a gas-liquid engine of around half the thrust? I assume not, as it would be such a different transport / injection / combustion architecture. Probably much easier to just build a smaller gg/turbopump assembly, and reuse the experience with Raptor.

Cheers, Martin

It's probably only worth it if you apply Raptor tech to any possible smaller engine.  They might as well reuse their experience gained with the Raptor for such an engine.

---

I was just trying to figure out a few details about any possible methalox Falcon 9.  If using a FFSC methalox engine on both stages, then the mass of the LV should drop substantially.  But how much?  We know the propellant mass load will be 17% less, but how much structural mass would the Falcon 9 gain?  Presumably you can just use the same thermal insulation from the O2 tanks.  Anyone have a good idea about the mass of that insulation per m^2 of tanks? 

If memory serves, a Falcon 9 v1.1 is 95.5% propellant sans payload. 

Known takeoff mass: 505.846 mt
~=estimate
Falcon 9 propellant mass: ~470.5 mt
Falcon 9 structural mass: ~22.2 mt
Falcon 9 v1.1 payload mass: 13.15 mt

For now, the only thing we can be fairly sure of with a Falcon 9M is the propellant mass.  We know the payload mass will be more than 13.15 mt, but not by how much.  If anyone wants to take a stab at figuring out how much structural mass and payload this rocket would gain, that would be great. 

Takeoff mass: ??
Falcon 9M propellant mass: ~390 mt
Falcon 9M structural mass: ??
Falcon 9M payload mass: 13.15 mt+

[cuddihy]

 If you can't find anything regarding a methalox RL-10A, I would suggest looking into the RD-0146 engine from Russia.  If my memory serves, Russiaspaceweb.com has the actual performance numbers for a methalox version.  If you fail to find it, please contact fregate here on NSF.  He was one of the original authors on Russiaspaceweb's RD-0146 article.

Thanks, I had no idea there was so much on RD-0146 on line, it's fascinating stuff. But no stats for methane related to efficiency, or pressure.

Also, Sutton doesn't have anything either except Methane physical properties and a table of RL-10B2 stats, so I'll have to calculate/guesstimate based on that. But clearly you're not going to get the pumping power from expansion of methane that you do from LH2. That may be why RD-0146 works for methane because it's also partly Lox-expansion driven as well. So that probably works in your favor for methane since the heat capacities and pumping powers are matched up.

[RocketmanUS]

To answer some of the above posts.

1 ) F9/FH reusable prototype

2 ) BFR two stage to LEO first generation reusable rocket

3 ) F9/FH replaced by LCH4/LOX second generation reusable launch rocket

That is the order I see things that could happen. F9 when being reused does not deliver enough mass to orbit to be cost effective. The FH would be to costly and has more LOM risk compared to a two stage RLV. So I see the second generation RLV as a two stage to orbit able to deliver some were between 25mt to 53mt based on future market and over all cost. Then a new 2nd generation BFR would go on to be the 3rd generation RLV  ( with possible tri-core ).

So why convert F9/FH or just the US when it should be better to just replace them in the future with a new generation RLV, upgrades all around and desigen for the propellants it would use from it's beginning and it's .

It is a good idea to compare the F9 RP-1/LOX to what could be a F9 LCH4/LOX and the SAT-INT-21 5/5. This is to get a better understanding of the performances between these propellant combinations. Also to compare the differances when use with the small launcher to the much larger launcher.

[Oli]

If you're going pressure fed for a 3rd stage why not KISS and do a SuperDraco based "Briz-X"?

Hypergolics? ISP?

[docmordrid]

Works for Briz-M, and SD is regenetatively cooled.

[Oli]

Works for Briz-M, and SD is regenetatively cooled.

So? Besides the obvious advantages, SpaceX may want a pressure-fed methane engine anyway (hint: Mars). Also SD is designed for abort and landing.

[cuddihy]

So I found this great paper on US methalox: www.dtic.mil/dtic/tr/fulltext/u2/a558199.pdf

It's a parametric flow analysis of a LCH4/LOX  dual expander cycle US engine with aerospike. But a very intriging discussion of other standard nozzle engines included.

Dual expander is similar to FFSC in that pumping power for fuel and lox are provided by separate pumps/turbines powered by expanded fuel and LOX  from separate heat exchangers--i.e. it also avoids the possible mixing of fuel and oxidizer in the same way as FFSC, but without the mass and complexity of pre-burners.

Table 24: Comparable Engine Performance.
Engine   MDEAN   RD-185   RD-167   RD-160   NGEDer   NGE  H-DEAN
Fuel   CH4   CH4   CH4   CH4   CH4   H2   H2
Thrust (lbf)   25K   40,344   79,366   4,409   25K   25K   4,694
Isp (s)   349.3   378   379   380.6   383   465   429.8
T/W   120.7 44   63   15.5 108   N/A   142.2
Mass (lbm)   207   917   1260   284   231
N/A   314
Mprop (lbm)   22,323   17,715   17,588   17,388   N/A   N/A   20,600