Alternative Methods Of Heating Hydrogen For High Efficiency Rockets

[Skye]

Are there other ways you could heat hydrogen to 2-3000 K for use in a high-efficiency rocket without the use of a nuclear reactor? The idea here is to have a rocket as efficient as an NTR, but having it be able to be used in the atmosphere, being able to land and be reused, and to be not deadly radioactive. I think that having it be able to do these things could make it worth using (unlike NTRs, which are kinda useless, just refuel). They could potentially be used on first stages with Methalox side boosters? (Picture SLS but replace solids with Methalox and replace Hydrolox with LH2 and these rockets (HVRs? - Hydrogen Vapour Rockets?) and also on second stages, and large kick stages, potentially.

My dad jokingly suggested filling a tank with hundreds of gerbils, soaking them in liquid hydrogen, igniting them, and then using the heat to warm the hydrogen! 

[Jim]

Are there other ways you could heat hydrogen to 2-3000 K for use in a high-efficiency rocket

yes, just burn it.  You aren't going to find a better solution.

[Skye]

Are there other ways you could heat hydrogen to 2-3000 K for use in a high-efficiency rocket

yes, just burn it.  You aren't going to find a better solution.

I choose to remain hopeful, because burning won’t leave pure H2 as exhaust 

[Proponent]

Solar-thermal propulsion with hydrogen as a working fluid was proposed long ago for in-space propulsion, but it does not seem to pencil out very well for any particular application. For one thing, the thrust-to-weight ratio is terrible, and keeping hydrogen liquid for long periods isn't fun either.

https://forum.nasaspaceflight.com/index.php?topic=52349.msg2156478#msg2156478
https://forum.nasaspaceflight.com/index.php?topic=16081.msg370859#msg370859
https://forum.nasaspaceflight.com/index.php?topic=55131.msg2305917#msg2305917

One amusing idea is to use LiH as a propellant. It's a solid at room temperature but dissociates at a a few hundred degrees Celsius, IIRC. Maybe you could dissociate it into Li and H₂ (gaining some energy from H + H -> H₂) and heat the gas. Li is not quite as light as H₂, but it's still lighter than typical chemical exhaust products, and it has the advantage of being monatomic. Maybe it would even be worthwhile refining the Li to the fairly abundant ⁶Li isotope. Somewhere there is a thread about this, in connection with a peri-solar pass for an outer-solar-system mission, IIRC. This all good fun, but again, it doubt it works out well when you look into the details.

[edzieba]

I would recommend looking through Atomic Rockets' Engine List. There are a lot of propulsion architecture both studied and proposed already, and not much reason to retread the same ground without something new to add.

[Paul451]

There are proposals to use ground-based lasers to heat the propellant in a launch vehicle. Presumably something like that is the only non-nuclear answer to your suggestion. But the practicalities of both generating sufficient heat density onto the vehicle via the laser and efficiently moving that heat to the propellant while retaining that heat density seems like a show-stopper to me.

In practice, you don't need especially high Isp for the first stage, and certainly not for boosters, you need high thrust-density propellants. And chemical fuels are already nearly perfect. It's why solid propellant boosters are so useful, even though their Isp is garbage.

(For upper stages, higher Isp helps, especially for BLEO. Likewise for interorbital manoeuvres. But that wasn't your question.)

[Skye]

There are proposals to use ground-based lasers to heat the propellant in a launch vehicle. Presumably something like that is the only non-nuclear answer to your suggestion. But the practicalities of both generating sufficient heat density onto the vehicle via the laser and efficiently moving that heat to the propellant while retaining that heat density seems like a show-stopper to me.

In practice, you don't need especially high Isp for the first stage, and certainly not for boosters, you need high thrust-density propellants. And chemical fuels are already nearly perfect. It's why solid propellant boosters are so useful, even though their Isp is garbage.

(For upper stages, higher Isp helps, especially for BLEO. Likewise for interorbital manoeuvres. But that wasn't your question.)

What about using mirrors to reflect the sun?

[edzieba]

There are proposals to use ground-based lasers to heat the propellant in a launch vehicle. Presumably something like that is the only non-nuclear answer to your suggestion. But the practicalities of both generating sufficient heat density onto the vehicle via the laser and efficiently moving that heat to the propellant while retaining that heat density seems like a show-stopper to me.

In practice, you don't need especially high Isp for the first stage, and certainly not for boosters, you need high thrust-density propellants. And chemical fuels are already nearly perfect. It's why solid propellant boosters are so useful, even though their Isp is garbage.

(For upper stages, higher Isp helps, especially for BLEO. Likewise for interorbital manoeuvres. But that wasn't your question.)

What about using mirrors to reflect the sun?

Solar Thermal and Laser thermal are known propulsion architectures.

[Jim]

There are proposals to use ground-based lasers to heat the propellant in a launch vehicle. Presumably something like that is the only non-nuclear answer to your suggestion. But the practicalities of both generating sufficient heat density onto the vehicle via the laser and efficiently moving that heat to the propellant while retaining that heat density seems like a show-stopper to me.

In practice, you don't need especially high Isp for the first stage, and certainly not for boosters, you need high thrust-density propellants. And chemical fuels are already nearly perfect. It's why solid propellant boosters are so useful, even though their Isp is garbage.

(For upper stages, higher Isp helps, especially for BLEO. Likewise for interorbital manoeuvres. But that wasn't your question.)

What about using mirrors to reflect the sun?

not at outer planets.

[Jim]

Are there other ways you could heat hydrogen to 2-3000 K for use in a high-efficiency rocket

yes, just burn it.  You aren't going to find a better solution.

I choose to remain hopeful, because burning won’t leave pure H2 as exhaust 

false hope
 there is nothing new under the sun when comes to chemical and thermal propulsion. 

[ShadowAndFlame]

Keep a little anti-hydrogen onboard and feed slowly into the chamber?

Please ignore the glaring issue of containment.

I would recommend looking through Atomic Rockets' Engine List. There are a lot of propulsion architecture both studied and proposed already, and not much reason to retread the same ground without something new to add.

Oh look it's on the list! https://projectrho.com/public_html/rocket/enginelist3.php#amplasma

[Vultur]

Yeah, many of these things have been considered.

But for first stages hydrogen is not a great idea (yeah, SLS, but it's kind of a Frankenstein design). Even if you didn't care about radiation, NTR first stages would be bad (even with an Isp of 800 or so) because the dry mass is so huge.

Laser launch might work since the "engine" mass has basically been offloaded to the ground, but that's a ton of development and cost needed. You can't really start with a "Falcon 1" for that.

[Skye]

What about using mirrors to reflect the sun?

not at outer planets.
[/quote]

You’re right. Damnit!

[Twark_Main]

For solar thermal, see also the TransAstra Omnivore thruster and architecture.

[lamontagne]

Are there other ways you could heat hydrogen to 2-3000 K for use in a high-efficiency rocket without the use of a nuclear reactor? The idea here is to have a rocket as efficient as an NTR, but having it be able to be used in the atmosphere, being able to land and be reused, and to be not deadly radioactive. I think that having it be able to do these things could make it worth using (unlike NTRs, which are kinda useless, just refuel). They could potentially be used on first stages with Methalox side boosters? (Picture SLS but replace solids with Methalox and replace Hydrolox with LH2 and these rockets (HVRs? - Hydrogen Vapour Rockets?) and also on second stages, and large kick stages, potentially.

My dad jokingly suggested filling a tank with hundreds of gerbils, soaking them in liquid hydrogen, igniting them, and then using the heat to warm the hydrogen! 

Have you looked at the lunar oxygen rocket, LANTR?  It uses hot hydrogen from a nuclear reactor to react with oxygen to get higher ISP.  Same result, inverse process. 

[tenkendojo]

Are there other ways you could heat hydrogen to 2-3000 K for use in a high-efficiency rocket without the use of a nuclear reactor? The idea here is to have a rocket as efficient as an NTR, but having it be able to be used in the atmosphere, being able to land and be reused, and to be not deadly radioactive. I think that having it be able to do these things could make it worth using (unlike NTRs, which are kinda useless, just refuel). They could potentially be used on first stages with Methalox side boosters? (Picture SLS but replace solids with Methalox and replace Hydrolox with LH2 and these rockets (HVRs? - Hydrogen Vapour Rockets?) and also on second stages, and large kick stages, potentially.

My dad jokingly suggested filling a tank with hundreds of gerbils, soaking them in liquid hydrogen, igniting them, and then using the heat to warm the hydrogen! 

Yes. There is a paper from a few years back about using novel conventional explosives to trigger pure fusion pulses for rocket propulsion, the fuel would be lithium deuteride of course.

If you want to get more speculative, I guess theoretically you can use Antihydrogen as antimatter fuel, just 1 gram should get you  43 kilotons of output, as close to E = MC^2 efficiency as you can get. That said, we are only able to produce trace amount of antihydrogen with those huge particles colliders right now.

[edzieba]

In between fusion-heats-remass and antimatter-photon rockets would be 'fusion fragment' rockets, where you try and corral the high energy fusion products into an exhaust stream directly without needing to thermalise them and heat additional reaction mass. May be viable for charged fusion products (e.g. p-B and its trip of emitted Alphas), not much good for Neutrons or gamma emission.

[Paul451]

My dad jokingly suggested filling a tank with hundreds of gerbils, soaking them in liquid hydrogen, igniting them, and then using the heat to warm the hydrogen!

Gerbils are a complex hydrocarbon, they won't burn in a reducing atmosphere like hydrogen. You still need an oxidiser.

[Skye]

You could probably shoot them out through the nozzle, spraying them with LOX & rapidly disintegrating them on the way 

Not that it”d be highly efficient - or efficient at all, really

[lamontagne]

You could probably shoot them out through the nozzle, spraying them with LOX & rapidly disintegrating them on the way 

Not that it”d be highly efficient - or efficient at all, really

The Gerbils are, after all, mostly water.  So masswise the combustion would be inefficient.  It's something of an inefficient variation of the LANTR.

[Skye]

Ok, hear me out - dried, (edit: dried of water) dead gerbils! 

(Still soaked in LH2, of course! )

[Vultur]

That would basically become a tripropellant - dried gerbil/LOX/LH2.

[Skye]

lol - wonder how well it would work?

Get DARPA on this now! 

[Vultur]

Tripropellants with H2 where you have a really high energy chemical reaction to heat the H2, which is the low molar weight propellant, were actually tried, in the 60s I think -- though not involving gerbils.

"Ignition" talks about this, a lithium/fluorine/H2 system was actually measured at 542 seconds Isp! (But talk about a handling and environmental nightmare...)

[Skye]

Yup, Ignition! is a great book 

Why not just the FLiH system but replace H with B5H9 & replace Li with Cs?

Oh and add (CH3)2Hg to reduce performance!

I mean, if you want the most immoral rocket engine ever, just make one that burns dried humans - or puppies

[redneck]

On paper, one could burn aluminum and oxygen for the energy and use hydrogen for the reaction mass. Retain the AL2O3 on board and use the long coast periods to refine it back to aluminum and oxygen. Per mass, aluminum and oxygen create a lot of energy when burned, though the mechanism for using that to heat the hydrogen AND keeping it on board could get entertaining.

[Skye]

You could combust them in a chamber above the main chamber, then have a filter that filters out the Al2O3 (& other heavy particles) and vacuums(?) them back & filters them out after combustion, while allowing the H2 to pass through? Would be quite interesting to see!

[Vultur]

On paper, one could burn aluminum and oxygen for the energy and use hydrogen for the reaction mass. Retain the AL2O3 on board and use the long coast periods to refine it back to aluminum and oxygen. Per mass, aluminum and oxygen create a lot of energy when burned, though the mechanism for using that to heat the hydrogen AND keeping it on board could get entertaining.

Beryllium/oxygen/hydrogen was actually tested but had really disappointing performance compared to theoretical calculations, according to "Ignition!".

[redneck]

On paper, one could burn aluminum and oxygen for the energy and use hydrogen for the reaction mass. Retain the AL2O3 on board and use the long coast periods to refine it back to aluminum and oxygen. Per mass, aluminum and oxygen create a lot of energy when burned, though the mechanism for using that to heat the hydrogen AND keeping it on board could get entertaining.

Beryllium/oxygen/hydrogen was actually tested but had really disappointing performance compared to theoretical calculations, according to "Ignition!".

The concept with the aluminox>hydrogen was that the aluminox would create the temperatures that would heat the hydrogen to >SSME temperatures. Then the hydrogen at 1/9 the molecular mass would have 3 times the Isp going by the square root of temperature over molecular mass. Even duping the AL2O3 overboard would net a 50% net gain.  Many people argued against the concept quoting various programs that disn't seem to address the actual idea. It took me going to a chemistry book to figure out that the problem was in the heat capacity of hydrogen. The net temperatures would have been so low that the Isp would be down in the 300s.

[Vultur]

There is a non-hydrogen aluminum/oxygen rocket idea around. Isp isn't great, but the idea is that both propellants can be processed from the lunar regolith and you don't need great Isp for a lunar takeoff.

[Skye]

On paper, one could burn aluminum and oxygen for the energy and use hydrogen for the reaction mass. Retain the AL2O3 on board and use the long coast periods to refine it back to aluminum and oxygen. Per mass, aluminum and oxygen create a lot of energy when burned, though the mechanism for using that to heat the hydrogen AND keeping it on board could get entertaining.

Beryllium/oxygen/hydrogen was actually tested but had really disappointing performance compared to theoretical calculations, according to "Ignition!".

Indeed it was, but, well, Beryllium…

[Apollo22]

There is a non-hydrogen aluminum/oxygen rocket idea around. Isp isn't great, but the idea is that both propellants can be processed from the lunar regolith and you don't need great Isp for a lunar takeoff.

Specific impulse is 285 seconds BUT lunar orbit & escape velocities are merely 2400 m/s, which really helps. I have this idea stuck in my head for a long time, of Al-Lox lunar SSTOs ; eventually manufactured on the Moon.

[Skye]

Could absolutely work, though you’d need to be able to manufacture a hybrid rocket on the moon, and ideally make it reusable 

[redneck]

Could absolutely work, though you’d need to be able to manufacture a hybrid rocket on the moon, and ideally make it reusable 

You may not care about reusable depending on the goals to be achieved. If delivering aluminum to orbit for process into structure, you may consider a thick walled aluminum hybrid that delivers the remaining wall thickness to the orbital facility. LOX cooling of the aluminum throat and nozzle. Detachable brain and control systems for reuse.

There are a lot of possible ideas out there. I wish I had more time to discuss them. 750 seconds?
 https://selenianboondocks.com/2008/10/tetherocket/     

[Skye]

I suppose, though Reusability would be nice for certain situations

759 seconds sounds nice? 

[Apollo22]

Could absolutely work, though you’d need to be able to manufacture a hybrid rocket on the moon, and ideally make it reusable 

You may not care about reusable depending on the goals to be achieved. If delivering aluminum to orbit for process into structure, you may consider a thick walled aluminum hybrid that delivers the remaining wall thickness to the orbital facility. LOX cooling of the aluminum throat and nozzle. Detachable brain and control systems for reuse.

There are a lot of possible ideas out there. I wish I had more time to discuss them. 750 seconds?
 https://selenianboondocks.com/2008/10/tetherocket/   

Spot on. You know, I'm just a pragmatic who started from lunar regolith composition (as detailed here - https://en.wikipedia.org/wiki/Lunar_resources#Resources ) and wondered what could be done  with oxygen aluminum and silicium - the three most abundant resources.

The answer ? solar arrays, SBSP for a lunar base, and lunar SSTOs running on aluminum and LOX.  Bringing lunar LOX to EML-1 or EML-2 to fuel Mars-bound spaceships.

Mining regolith further, two interesting byproducts might be a) the ill-named rare earths (REE) and of course, b) PGM from asteroid impacts (see Dennis Wingo 20 years old book Moonrush)