Are hydrogen upper stages worth it or not?

[Robotbeat]

For the record, the hydrogen third stage for New Glenn strikes me as a good idea. Most launches won't need it, but it should /double/the performance to high energy orbit. At least double.

I know you are aware that most launches these days are to high energy orbits. So I'm curious to hear thoughts on why you think most launches will not need the 3rd stage. Do you think that Blue will be doing a different mix of mission types or do you think that the 2 stage NG will still have the performance to do those missions economically?

New Glenn won't be launching just what we launch today. New Glenn will be launching tourists to LEO and is already being marketed for that purpose. And perhaps LEO constellations will take market share from GSO. But anyway, the main reason is that not all payloads will need all 3 stages to get to a high energy orbit. Two stages is enough. It's a big launch vehicle.

[TrevorMonty]

Most launches won't need it

Doesn't that mean that it doesn't get amortized enough (low flight rates)?

I'd surprised if 3rd stage doesn't sharing a lot of NS components, maybe even tanks.

The New Glenn third stage is apparently depicted as having the same diameter as the rest of the rocket (7 m). But yes, the BE-3 is going to be used for both.

Can't locate picture with NG in it but it showed two versions. The 2 stage is same diameter as 1st (7m) but 3rd stage is considerably smaller.

[Pipcard]

Most launches won't need it

Doesn't that mean that it doesn't get amortized enough (low flight rates)?

I'd surprised if 3rd stage doesn't sharing a lot of NS components, maybe even tanks.

The New Glenn third stage is apparently depicted as having the same diameter as the rest of the rocket (7 m). But yes, the BE-3 is going to be used for both.

Can't locate picture with NG in it but it showed two versions. The 2 stage is same diameter as 1st (7m) but 3rd stage is considerably smaller.

The fairing has a smaller diameter for the two-stage version, the third stage in its respective version has a 7 m diameter.

[guckyfan]

I also don't get why an LH2 upper stage is only useful in cislunar space for earth departure burns.

~Jon

What else could it do? It can't brake near Neptun or Uranus. For that you design a long living stage with hypergols or methalox.

[jongoff]

What else could it do? It can't brake near Neptun or Uranus. For that you design a long living stage with hypergols or methalox.

There's more to the solar system than TLI injection and Neptune/Uranus. Once you get away from planetary bodies, passive thermal control alone can suppress LOX boiloff entirely, and get LH2 boiloff down to levels that work for everything this side of the main belt. Active cooling also becomes a lot easier when the amount of heat you have to reject is modest.

But seriously, for the foreseeable future, we're talking Moon and maybe Mars and/or the asteroids. And LOX/LH2 works fine for enough of that system to be worth serious consideration. I probably would go LOX/CH4 for mars landers, but I also wouldn't go with the SpaceX architecture where your launch vehicle upper stage, interplanetary stage, and mars lander are all the same stage. But that's me.

~Jon

[Pipcard]

but I also wouldn't go with the SpaceX architecture where your launch vehicle upper stage, interplanetary stage, and mars lander are all the same stage. But that's me.

But I was told that it would save on development costs, and that the requirements "overlap" anyway?

[Robotbeat]

They do overlap if your upper stage is VTVL reusable anyway.

[oldAtlas_Eguy]

For the near and even farther into the future on-way outer solar system the use of hydrolox for the US to get fast transits for low cost is a definite positive. But once you start talking re-usability and inner solar system then the systems are more specific to their task and the planetary bodies they service. For airless bodies that have water/ice then a hydrolox system does make some sense. But for Mars it does not.

[Patchouli]

While avoiding that hydrogen did allow Spacex to get flying sooner it also forced some design decisions such as densified propellants that later came to haunt them when they decided to upgrade their vehicle to EELV class payloads.

Though the need for stuff like precooled lox also probably could have been eliminated by simply adding a third stage for missions to high energy orbits.

[jongoff]

but I also wouldn't go with the SpaceX architecture where your launch vehicle upper stage, interplanetary stage, and mars lander are all the same stage. But that's me.

But I was told that it would save on development costs, and that the requirements "overlap" anyway?

That's the theory, but generally trying to make a hyper-optimized, bleeding edge jack of all trades, doesn't always work out as well as people expected. And now the requirements don't necessarily overlap.

~Jon

[jongoff]

While avoiding that hydrogen did allow Spacex to get flying sooner it also forced some design decisions such as densified propellants that later came to haunt them when they decided to upgrade their vehicle to EELV class payloads.

This. For all the talk of how LOX/LH2 is so much harder and more expensive to deal with, ULA had had only a few minor issues with Centaur (knock on wood), and SpaceX has had a ton of challenges with densified propellants, failures due to having to bury their pressurant bottles inside the tanks, etc. Sometimes you end up with more complexity in your attempt to avoid other complexity.

~Jon

[Robotbeat]

Perhaps that's because RL-10 on Centaur and Atlas has half a century of heritage. Its first flights had problems (only ONE of the first five flights actually fully succeeded, and most of those failures were problems with Centaur). I bet if highly densified propellants had half a century of heritage, they'd be basically problem-free, too.

Concern-trolling because SpaceX advances some new technology and it's not perfect out of the gate.

[Oli]

Perhaps that's because RL-10 on Centaur and Atlas has half a century of heritage. Its first flights had problems (only ONE of the first five flights actually fully succeeded, and most of those failures were problems with Centaur). I bet if highly densified propellants had half a century of heritage, they'd be basically problem-free, too.

Concern-trolling because SpaceX advances some new technology and it's not perfect out of the gate.

Stainless steel common bulkhead balloon tanks haven't exactly taken the world by storm.

[savuporo]

If you just count how many earth departure burns LOX/LH2 upper stages have delivered over decades, i think it's clear its worth it.

[sdsds]

I very much admire how F9 has gotten so much performance without hydrogen. (Just a few years ago I would have described as "essentially impossible" what now looks to be almost routine.) The payoff from the techniques providing that performance will be worth the bumps they introduce along the way!

But we know there are also techniques (e.g. IVF) which could improve the capabilities of hydrogen stages too. I acknowledge my perspective is shaded by being a Moon First thinker. But a stage with a lifetime so long it could provide propulsion for lunar orbit insertion? That kind of hydrogen upper stage is definitely "worth it!"

Oh. And providing that would be "essentially impossible" for the F9 upper stage.

[pippin]

Perhaps that's because RL-10 on Centaur and Atlas has half a century of heritage. Its first flights had problems (only ONE of the first five flights actually fully succeeded, and most of those failures were problems with Centaur). I bet if highly densified propellants had half a century of heritage, they'd be basically problem-free, too.

Concern-trolling because SpaceX advances some new technology and it's not perfect out of the gate.

Well, the track record for the first Atlas flights with kerolox wasn't exactly better in those days so I don't think attributing that to hydrolox isn't exactly fair, that's how first flights were in these days.

And densified propellants do have half a century of flight history, just not in the US

[TrevorMonty]

Both Methane and Hydrogen upper stages can use IVF to elimate He (SpaceX curse) and hydrazine. Both fuels would allow for long lived stages capable of multiple refuelling from ISRU fuel. This thread is more about Methane vs Hydrogen than RP1.

For stages that use aerobraking to reenter and land then Methane is superior as stage will be smaller and therefore lighter than Hydrogen. Large light weight stainless tanks are great in vacuum but don't work to well when they have to be integrated into a airframe with heat sheilding.

For lunar missions hydrogen gives better performance plus long term there is option of ISRU fuel. Mars missions long term have option of either ISRU fuel but aerobraking favours Methane.

[Pipcard]

For stages that use aerobraking to reenter and land then Methane is superior as stage will be smaller and therefore lighter than Hydrogen. Large light weight stainless tanks are great in vacuum but don't work to well when they have to be integrated into a airframe with heat sheilding.

For lunar missions hydrogen gives better performance plus long term there is option of ISRU fuel. Mars missions long term have option of either ISRU fuel but aerobraking favours Methane.

The question is whether it is better to spend money on developing and having an extra production line for an optimized lunar lander, or use the same methalox Mars vehicle for your lunar missions, even if only the LOX is available for ISRU (but it would be great if the carbon seemingly found by LCROSS was verified). I guess it would depend on the scale of the operations.

________________

some more food for thought

You don't make a a single engine and shoehorn a way oversized vacuum version of it onto a second stage that's made with identical tooling to  your first stage (when you could lighten it by using other tooling) if you're not driven by producibility/commonality over performance.  You don't use a kerolox upper stage that gets neither long coasts of hypergols nor the performance of hydrolox unless you're not driven by optimization.  The mantra is three fold and clear as day: lower cost, lower cost and lower cost.

[jongoff]

For stages that use aerobraking to reenter and land then Methane is superior as stage will be smaller and therefore lighter than Hydrogen. Large light weight stainless tanks are great in vacuum but don't work to well when they have to be integrated into a airframe with heat sheilding.

For lunar missions hydrogen gives better performance plus long term there is option of ISRU fuel. Mars missions long term have option of either ISRU fuel but aerobraking favours Methane.

Yes and no. If MSNW's magnetoshell aerocapture technology pans out (I'm bullish but you probably already knew that), hydrogen could actually have an advantage over methane for aerocapture/aerobraking, and maybe even aeroentry.

~Jon

[jongoff]

For stages that use aerobraking to reenter and land then Methane is superior as stage will be smaller and therefore lighter than Hydrogen. Large light weight stainless tanks are great in vacuum but don't work to well when they have to be integrated into a airframe with heat sheilding.

For lunar missions hydrogen gives better performance plus long term there is option of ISRU fuel. Mars missions long term have option of either ISRU fuel but aerobraking favours Methane.

The question is whether it is better to spend money on developing and having an extra production line for an optimized lunar lander, or use the same methalox Mars vehicle for your lunar missions, even if only the LOX is available for ISRU (but it would be great if the carbon seemingly found by LCROSS was verified). I guess it would depend on the scale of the operations.

I'm pretty confident the answer is an optimized lunar lander. The amount of benefit you get by being able to do full ISRU refueling instead of having to still carry your own fuel is huge. LOX ISRU helps, but full ISRU shines especially with reusable vehicles. And the benefit of full ISRU is added to the top of the benefit from using LH2 vs Methane in the first place.

Both ULA and Blue Origin will have LOX/LH2 upper staged vehicles flying, so developing a kit to enable lunar landings for one of those stages shouldn't break the bank. It might be harder for SpaceX to compete for lunar missions, but that's why it's good to have an industry with multiple providers taking multiple approaches.

~Jon