Should launch providers switch to common methalox engines?

[Pipcard]

Musk says that overhead starts with how the launch vehicle is designed. The workhorse Atlas V, for example, used for everything from planetary probes to spy satellites, employs up to three kinds of rockets, each tailored to a specific phase of flight. The Russian-built RD-180 first- stage engines burn a highly refined form of kerosene called RP1. Optional solid-fuel strap-on boosters can provide additional thrust at liftoff, and a liquid hydrogen upper stage takes over in the final phase of flight. Using three kinds of rockets in the same vehicle may optimize its performance, but at a price: “To a first-order approximation, you’ve just tripled your factory costs and all your operational costs,” says Musk.

Instead, from the very beginning, SpaceX designed its Falcon rockets with commonality in mind. Both of Falcon 9’s stages are powered by RP1 and liquid oxygen, so only one type of engine is required. Both are the same diameter and are constructed from the same aluminum-lithium alloy, reducing the amount of tooling and the number of processes and resulting in what Musk calls “huge cost savings.”

If that is true, if having three different types of engines really triples the operating costs...

then why aren't others thinking of "optimizing for (manufacturing and operating) costs" for their next-generation launch vehicles by switching to a common propellant?

Let's say there was a launch provider that used a hydrolox+kerolox+solid combination. They managed to become a major player in the launch industry (case in point: Ariane 4 used multiple types of engines and still took over 50% of the market). Now let's say they were designing a next-generation rocket, and that they realized that they should optimize for cost through commonality, in order to stay competitive.

If they were to switch to an all-hydrolox rocket (without any solids), the first stage wouldn't be optimal because of liquid hydrogen's low density and the relatively low thrust of hydrolox engines. It is also apparently "hard to handle," which was why SpaceX abandoned the idea.

If they were to switch to an all-kerolox rocket, they would sacrifice the performance given by the high-energy upper stage.

Methalox is not the most optimal for either stage. But it is a compromise. Its density and specific impulse are in-between that of kerolox and hydrolox. There hasn't been a methalox engine used in any rocket before, but judging by the in-development Raptor, it can have a good thrust for first stages, too. SpaceX is planning for their next generation launcher (BFR) to be all-methalox. It has the additional benefit with being common with Mars ISRU and having less residue buildup than kerolox, good for reusability. The reason that they didn't start out with it is that it was easier for them, as a startup, to develop kerolox engines.

For major launch providers based in countries that, in general, have relatively higher labor costs (i.e. not China, Russia, or India):
- Ariane 6 and H-III will have hydrolox and solids because of heritage (less development costs).
- Vulcan will have methalox (because it's an "in-between" fuel for the first stage), hydrolox, and solids (the latter two also because of heritage).

The main thing I want to ask is, is it worth it for a provider to abandon their hydrolox/kerolox/solid manufacturing and processing infrastructure and replace that with a methalox-based one? I know that solid rocket manufacturing can have synergy with the defense industry (i.e. missiles), though.

[woods170]

Musk says that overhead starts with how the launch vehicle is designed. The workhorse Atlas V, for example, used for everything from planetary probes to spy satellites, employs up to three kinds of rockets, each tailored to a specific phase of flight. The Russian-built RD-180 first- stage engines burn a highly refined form of kerosene called RP1. Optional solid-fuel strap-on boosters can provide additional thrust at liftoff, and a liquid hydrogen upper stage takes over in the final phase of flight. Using three kinds of rockets in the same vehicle may optimize its performance, but at a price: “To a first-order approximation, you’ve just tripled your factory costs and all your operational costs,” says Musk.

Instead, from the very beginning, SpaceX designed its Falcon rockets with commonality in mind. Both of Falcon 9’s stages are powered by RP1 and liquid oxygen, so only one type of engine is required. Both are the same diameter and are constructed from the same aluminum-lithium alloy, reducing the amount of tooling and the number of processes and resulting in what Musk calls “huge cost savings.”

If that is true, if having three different types of engines really triples the operating costs...

then why aren't others thinking of "optimizing for (manufacturing and operating) costs" for their next-generation launch vehicles by switching to a common propellant?

The answer is simple. Until just a few years ago nobody took SpaceX seriously. There was no need for "optimizing for cost". Now that SpaceX has begun taking bites from the revenues of the usual suspects, the need for "optimizing for cost" is slowly but ever so gradually beginning to sink in with the rest of the industry.

[Rocket Science]

My problem with this is if an issue with the engine crops up all the launchers using it would be grounded...

[nadreck]

The main thing I want to ask is, is it worth it for a provider to abandon their hydrolox/kerolox/solid manufacturing and processing infrastructure and replace that with a methalox-based one? I know that solid rocket manufacturing can have synergy with the defense industry (i.e. missiles), though.

This depends on the volume of business you will be doing, the amount of extra capital needed to switch, and the difference in unit cost at the end. If the company currently launches 10 of the hydrolox/kerolox/solid combination vehicles and owns the plants that make the engines and tanks (not the actual case in the real world) then one might assume that there is less retooling expense when they go to a new design that uses the same mix of propulsion than replacing everything with methalox. So if the new vehicle would cost $100M each and require an extra $1B in capital in retooling if it was a methalox rocket, but instead cost $120M each if it stayed hydrolox/kerolox/solid, then it would, at 10 flights a year, take 5 years to pay off the difference in up front capital at a 0% discount rate and about 6 years at a 5% discount rate. If the difference was either $2B in capital or the hydrolox/kerolox/solid rocket only cost $110M then it would take 10 years at a 0% discount rate, or more than 15 years at a 5% discount rate. It really might not be worth going to methalox if it was 15 years before the benefits would start to pay off as you might be into a redesign by then. Double the flight rate and it all changes back to the first case, halve  the flight rate and the first case looks like the 2nd.

[Oli]

Musk says that overhead starts with how the launch vehicle is designed. The workhorse Atlas V, for example, used for everything from planetary probes to spy satellites, employs up to three kinds of rockets, each tailored to a specific phase of flight. The Russian-built RD-180 first- stage engines burn a highly refined form of kerosene called RP1. Optional solid-fuel strap-on boosters can provide additional thrust at liftoff, and a liquid hydrogen upper stage takes over in the final phase of flight. Using three kinds of rockets in the same vehicle may optimize its performance, but at a price: “To a first-order approximation, you’ve just tripled your factory costs and all your operational costs,” says Musk.

Instead, from the very beginning, SpaceX designed its Falcon rockets with commonality in mind. Both of Falcon 9’s stages are powered by RP1 and liquid oxygen, so only one type of engine is required. Both are the same diameter and are constructed from the same aluminum-lithium alloy, reducing the amount of tooling and the number of processes and resulting in what Musk calls “huge cost savings.”

If that is true, if having three different types of engines really triples the operating costs...

We don't have enough data to say whether that is true or not. From a development cost point of view he's certainly right though. There's no way SpaceX could have afforded to develop RD-180, RL-10, AJ-62 equivalents.

[nadreck]

Musk says that overhead starts with how the launch vehicle is designed. The workhorse Atlas V, for example, used for everything from planetary probes to spy satellites, employs up to three kinds of rockets, each tailored to a specific phase of flight. The Russian-built RD-180 first- stage engines burn a highly refined form of kerosene called RP1. Optional solid-fuel strap-on boosters can provide additional thrust at liftoff, and a liquid hydrogen upper stage takes over in the final phase of flight. Using three kinds of rockets in the same vehicle may optimize its performance, but at a price: “To a first-order approximation, you’ve just tripled your factory costs and all your operational costs,” says Musk.

Instead, from the very beginning, SpaceX designed its Falcon rockets with commonality in mind. Both of Falcon 9’s stages are powered by RP1 and liquid oxygen, so only one type of engine is required. Both are the same diameter and are constructed from the same aluminum-lithium alloy, reducing the amount of tooling and the number of processes and resulting in what Musk calls “huge cost savings.”

If that is true, if having three different types of engines really triples the operating costs...

Exactly, if you are the incumbent with sunk costs (but really no except SpaceX fully is since they all buy the different engines from an array of other companies) then it makes less sense to change unless you are sure of the volume, but if you are the new guy then whatever you choose you have to tool up for so you have incentive to minimize the manufacturing capitalization.

We don't have enough data to say whether that is true or not. From a development cost point of view he's certainly right though. There's no way SpaceX could have afforded to develop RD-180, RL-10, AJ-62 equivalents.

[muomega0]

The answer depends on the launch manifest and destination and long term plans.  Two different engines exist to avoid common failure modes.

ISP rules in space, so depending on the deltaV one can increase IMLEO by 25% using methane vs LH2, so is the NASA 'market' 0, 50, or 500mT/year?  The relative importance of I_sp and propellant density depends on the application (e.g., first stage or upper stage) and the mission (e.g., heavy payload to low orbit or small payload to escape).

Another consideration is the common configuration for Class A cargo and crew to find that unknown unknown.  Perhaps solids are not used for crew due to LAS mass, but are used for performance gains in the heavy variant. 

Another consideration is methane vs water for ISRU, and choosing the former pretty much eliminates LH2 option.  Type of fuel for landers, if any?

If launching mass to BEO is not in the future plans, then its entirely driven by DOD needs, which has what, 8 heavy flights over 13 years, and lacks cash for space assets.   

In this case, the choices are narrowed further to how many $ are available in the short term, and even further to those with semi-deep pockets, who can fund, err, 'commercial' engines and LVs.

Another consideration is where the components are built, where they are launched, and how many $$ can be diverted from state funding to tax breaks, like using rockets to round up cows or planting farms around pads.

Long term planning for NASA and the USG is not possible until campaign finance and gerrymandered districts are corrected.   It will be interesting to see what answer industry tells the USG, but right now its Vulcan v0 and Falcon.

[Jim]

The main thing I want to ask is, is it worth it for a provider to abandon their hydrolox/kerolox/solid manufacturing and processing infrastructure and replace that with a methalox-based one? I know that solid rocket manufacturing can have synergy with the defense industry (i.e. missiles), though.

No.  Do all land vehicles use the same fuel?

[rayleighscatter]

I'm not sure I'd want to put all my eggs in the methane basket, it's becoming a real environmental bugaboo.

[nadreck]

I'm not sure I'd want to put all my eggs in the methane basket, it's becoming a real environmental bugaboo.

I'm not sure I'd want to put all my eggs in the methane basket, it's becoming a real environmental bugaboo.

It has a much smaller GHG footprint than any other fossil fuel between how it is gathered and burned. The fact that it in and of itself is a greenhouse gas is irrelevant as the vast majority of it that is removed from the ground (more than 99.9%) is burned to become mainly water, half as much CO₂, and in the case of other applications there are trace amounts of other chemicals being burned as well as nitrogen combining in as it is being burned giving us some other pollutants, but when you use it in a rocket engine it is presumably more refined with just traces of ethane left in and no nitrogen is being mixed in with it during combustion.

[rayleighscatter]

I'm not sure I'd want to put all my eggs in the methane basket, it's becoming a real environmental bugaboo.

I'm not sure I'd want to put all my eggs in the methane basket, it's becoming a real environmental bugaboo.

It has a much smaller GHG footprint than any other fossil fuel between how it is gathered and burned. The fact that it in and of itself is a greenhouse gas is irrelevant as the vast majority of it that is removed from the ground (more than 99.9%) is burned to become mainly water, half as much CO₂, and in the case of other applications there are trace amounts of other chemicals being burned as well as nitrogen combining in as it is being burned giving us some other pollutants, but when you use it in a rocket engine it is presumably more refined with just traces of ethane left in and no nitrogen is being mixed in with it during combustion.

Don't underestimate the US government, especially when methane has already been singled out for stricter scrutiny from production to transportation to storage and use. It might seem absurd, but few also thought in 1960 that barely a decade later their brand new jet aircraft would be banned for being too noisy.

[Nilof]

I'm not sure I'd want to put all my eggs in the methane basket, it's becoming a real environmental bugaboo.

I'm not sure I'd want to put all my eggs in the methane basket, it's becoming a real environmental bugaboo.

It has a much smaller GHG footprint than any other fossil fuel between how it is gathered and burned. The fact that it in and of itself is a greenhouse gas is irrelevant as the vast majority of it that is removed from the ground (more than 99.9%) is burned to become mainly water, half as much CO₂, and in the case of other applications there are trace amounts of other chemicals being burned as well as nitrogen combining in as it is being burned giving us some other pollutants, but when you use it in a rocket engine it is presumably more refined with just traces of ethane left in and no nitrogen is being mixed in with it during combustion.

Keep in mind though, that to get optimal Isp, methalox has to burn fuel-rich. So you are releasing the excess methane directly into the atmosphere.

The rocket company (the book) had a methane RLV and this issue did turn up once reuse became common, with the trades involved when switching to an oxidizer-rich mode.

[Steven Pietrobon]

Keep in mind though, that to get optimal Isp, methalox has to burn fuel-rich. So you are releasing the excess methane directly into the atmosphere.

The oxygen in the atmosphere will quickly burn with the very hot excess methane. The main problem is boil off on the ground. That is solved by piping the gaseous methane to a burn off point, just like what is done for hydrogen boil off.

As to the question of the thread, the rocket builder should be free to use whatever propellant combination they think is best, although moving away from toxic propellants should be encouraged.

[Proponent]

Don't underestimate the US government, especially when methane has already been singled out for stricter scrutiny from production to transportation to storage and use. It might seem absurd, but few also thought in 1960 that barely a decade later their brand new jet aircraft would be banned for being too noisy.

Given that unburnt methane is a powerful greenhouse gas, I don't see what's fundamentally irrational about paying close attention to the parts of the methane cycle leading up to combustion.  Likewise, since commercial aviation grew rapidly in the decade after 1960, it's not obvious to me that jet-engine noise might not have gone from being a minor annoyance to a significant problem over the same period.

[Robotbeat]

Hydrogen is also an indirect greenhouse gas that by mass is worse than CO2 (not by molar mass or volume, though, if I recall correctly). But like methane, that's only if it's unburnt.

This is all overblown. There are inexpensive ways to counteract the effect, such as burying biochar. It's not significant.

[Lars-J]

To answer the question posed by the thread starter: NO.

Think of it this way... Should early car manufacturers have been forced to use one or two shared engines? Of course not. That would not have benefitted anyone.

[Pipcard]

To answer the question posed by the thread starter: NO.

Think of it this way... Should early car manufacturers have been forced to use one or two shared engines? Of course not. That would not have benefitted anyone.

It's not about sharing the same engine between launch providers, it's about each provider having a common engine & propellant for their rocket stages to "optimize for cost."

(I'm sorry if you read the title wrong)

[Stan-1967]

Keep in mind though, that to get optimal Isp, methalox has to burn fuel-rich. So you are releasing the excess methane directly into the atmosphere.

The rocket company (the book) had a methane RLV and this issue did turn up once reuse became common, with the trades involved when switching to an oxidizer-rich mode.

How do you arrive at the conclusion that methane, in any significant amount, will being released into the air?  Any hydrocarbon undergoing combustion can have intermediate carbon compounds like CO as they combust fully to CO2.   It is not supportable that a fuel rich cycle will somehow miraculously fully combust some portion of CH4 completely to C02 and H20 and the balance of the CH4 will not experience any combustion at all?

The combustion gasses will be primarily a mixiture of CO2, H20, & CO, with CH4 being the least plausible of all emitted gasses. CH3, 0, OH, & CH20 are all more probable than CH4. 

[TrevorMonty]

Most Hydrogen is extracted from methane with CO2 being by product.
Then there is shipping and extra energy required to cool LH. As a rocket fuel is methane is more environmentally friendly if burnt direct compared to converting to LH.
 
https://en.m.wikipedia.org/wiki/Hydrogen_production

[Nilof]

The oxygen in the atmosphere will quickly burn with the very hot excess methane.

Not necessarily. The exhaust of an upper stage rocket engine with a high expansion ratio is generally colder than the flammability point of methane, as the expansion in the nozzle converts most of the thermal heat into mean mechanical motion. The methane will only combust if it hits atmosphere at a high enough speed that it becomes compression heated.

If the exhaust velocity is say, 3.6 km/s, then the exhaust will be released at velocity ~zero when the vehicle is traveling at 3.6 km/s halfway through the launch. That portion of the exhaust will make it into the atmosphere without combusting.