Storing LOX-LH2 as water

Quaoar · 2014-04-27 15:02:36

Storing hydrogen as a liquid at 20°K is very nasty, so there are many study on storing water and electrolyzing it on demand to produce liquid hydrogen and oxygen.

https://ia600603.us.archive.org/10/item … 026039.pdf

According to the study above, a 500 ton/year hardware needs almost 100 KW of electric power.

I like the idea of using water: in a precedent post I have explored the possibility of a water propelled nuclear spaceship: it seem possible, but there are still many technologies to develop. On the contrary, we can build until now a solar powered LOX-LH2 chemical rockets propelled spaceship that gets her propellant from water electrolysis.

like the nuclear steam spaceship, or water electrolyzing LOX-LH2 spaceship can be a very versatile vehicle that can find the return propellant from Mercury pole to Jovian satellites. Water is also a very good cosmic ray shielding material: so we can imagine a multiple shells propellant tank that surround the habitat, solving another nasty issue. Using the same substance for propulsion and for life support is also very safe: imagine a Ship returning to Earth that fail orbital insertion burn for rockets failure: the unused water can keep astronauts alive for years, giving time to set-up a rescue mission.

Power is not a problem, there are many very large deployable solar arrays on the market (http://www.nasa.gov/offices/oct/home/feature_sas.html#.U1voz6KG-M0 ), and water is a very cheep propellant. The only issue is the oxygen/hydrogen ratio of 8:1 that doesn’t match the 6:1 ratio of chemical rocket. Burning LOX and LH2 at 8:1, would result in a slightly lower specific impulse (almost 10 seconds) but a too high combustion temperature that can damage rocket chamber.

Surfing on Internet, I found 3 possible solution:

1) fixing the oxidizer/fuel ratio adding at the mixture 6% LCH4 or 8% of RP1: the result is a tri-propellant rocket like Russian RD-171 (http://www.astronautix.com/engines/rd701.htm ). We can avoid the complicated turbo-pump machinery having it pressure feed: for a in-space propulsion a high expansion ratio is more important than pressure chamber, so we can regain the specific impulse loss with a very high expansion ratio nozzle 1:250 or more.

2) burning LH2 with 75% of LOX inside the chamber in the classical ratio of 6:1 and using the remaining 25% in the nozzle as a LOX afterburner (something like the LOX afterburner of a LANTR). Specific impulse will be slightly lower, but we can use all the propellant without risking chamber damage.

3) burning LH2 with 75% of LOX inside the chamber in the classical ratio of 6:1 and divert the remaining 25% of O2 to feed an electric thruster, resulting a chemical-electric hybrid spaceship, that can be very useful for interplanetary exploration.
Oxygen has a first ionization energy of 1313.9 KJ/mol, higher than 1170 KJ/mol of xenon but lower than 1350.8 KJ/mol of Krypton. Hall effect thrusters and ion thrusters have been adapted to run with oxygen, that is less and less expensive than xenon and krypton and can be extracted from Lunar regolith ( http://arc.aiaa.org/doi/abs/10.2514/6.1998-3994 http://dspace.mit.edu/handle/1721.1/74748 )

SpaceNut · 2014-04-27 16:20:58

Not quite sure where to start whether it is on storage or creation... but in either case we have talked about both.

quotes from methane magic topic for creation

JoshNH4H wrote:

Manufacturing methane is fairly easy, and a process to do so was detailed by Dr. Zubrin in The Case For Mars. The raw materials are water and carbon dioxide, and the setup is mostly steel pipes. I believe a ruthenium catalyst (probably imported from earth for a while, since ruthenium is a hard to find, rare metal) is required.
Electrical to chemical energy conversion efficiency is 35-40 percent, because the sabatier reaction wastes a lot of hydrogen.
Methane-oxygen is a high density, simple energy storage method. But it's not energy efficient and it does necessitate cryogenic cooling.
I never understood the notion of characterizing an economy based on its preferred method of energy storage. Surely there are many much more significant ways to characterize a society?

SpaceNut wrote:

Finding the energy to make methane is the problem. When we look at Earth having 1367 W/m2 while Mars is at about half of what we see in summer and less under atmospheric conditions but winter seems to drop down to only 1/4th. Table 2.2-1. on page 6 gets the change in location
http://spaceclimate.net/Mars.solar.2005.pdf
Then for man to survive we need power to make water, air and heat on top of the initial values being recieved being very low from solar means we are trying to over come quite a deficit.
Storage of the energy for later use will be of great importance and methane is just one of the many choices that we can make.

quotes from compressed gas storage topic...

SpaceNut wrote:

I am thinking that compressed gas is a temporary method and that we should be saving it as just as much water as possible if we are not making fuels.

JoshNH4H wrote:

I think water will be something that well actually have a relative abundance of, seeing as its fairly easy to make/obtain and purify and once we locate a suitable reserve there will no reason to be sparing with it.

Now of course creating it while enroute or returning is more to where are the base engreidiences are to be gathered from.

JoshNH4H · 2014-04-27 23:17:03

In general, I think that the idea of storing your H2/LOX rocket fuel as water for as long as possible before electrolyzing is a good one. Water is much denser, much easier to handle, and much warmer than its component elements.

However, it's well worth noting that certain things are either impossible or unreasonable. For example, you can't electrolyze as you burn. It's simply unfeasible. Even if you are keeping the fuel as water for the transit from, say, the Moon to LEO, you will reap significant gains by leaving it in the form of Water for that time.

Tom Kalbfus · 2014-04-28 06:39:30

JoshNH4H wrote:

In general, I think that the idea of storing your H2/LOX rocket fuel as water for as long as possible before electrolyzing is a good one. Water is much denser, much easier to handle, and much warmer than its component elements.
However, it's well worth noting that certain things are either impossible or unreasonable. For example, you can't electrolyze as you burn. It's simply unfeasible. Even if you are keeping the fuel as water for the transit from, say, the Moon to LEO, you will reap significant gains by leaving it in the form of Water for that time.

You could store the water as ice. say on an asteroid or comet. An icy asteroid would be better. As you know the average distance of the Earth from the Sun would give you an average temperature of 0 Celsius if there was no greenhouse effect. I believe this means that asteroids just a little farther from the Sun could have frozen water in them. What you could do is mount a hydrogen-oxygen rocket engine to an asteroid, cover the asteroid with solar panels, electrolyze the water mined from the asteroid and feed the hydrogen and oxygen into the rocket motor and you can push the asteroid into Earth orbit with that rocket engine, use what remains to build a space station out of.

JoshNH4H · 2014-04-28 06:59:35

Because of the low pressure in space, water has a tendency to sublime away. Ice isn't actually stable in a vacuum until about 5 AU.

Regarding your idea, why not use your solar panels to run a mass driver? It would be much more efficient...

Tom Kalbfus · 2014-04-28 07:22:22

Ice buried deep in a asteroid would be under greater pressure than in a vacuum. Now the surface exposed to the vacuum would be ice free, but if you go under the crust, especially in large asteroids, I am sure ice can be found, and other hydrogen compounds as well. As for a rocket motor, they can be delivered a part of the rocket vehicle that arrives at the asteroid. NASA has yet to use a mass driver for anything. One idea has been to mount a space shuttle main engine to an asteroid, then feed it hydrogen and oxygen separated from compounds within the asteroid Most asteroids just need a little nudge in their orbits to be useful, and the space shuttle main engine can run for hours to get the job done.

Quaoar · 2014-04-28 07:41:59

JoshNH4H wrote:

In general, I think that the idea of storing your H2/LOX rocket fuel as water for as long as possible before electrolyzing is a good one. Water is much denser, much easier to handle, and much warmer than its component elements.
However, it's well worth noting that certain things are either impossible or unreasonable. For example, you can't electrolyze as you burn. It's simply unfeasible. Even if you are keeping the fuel as water for the transit from, say, the Moon to LEO, you will reap significant gains by leaving it in the form of Water for that time.

I know "real time electrolysis" is impossible unless having a multi GW range nuclear reactor. I imagine a big modular orbit-to-orbit reusable spaceship, with 100-200 KW of solar (or nuclear) electric power, who has to spend hundreds days in low planetary orbit waiting for the launch window: it can be safer to store propellant as water and electrolyze it in LOX-LH2 2-3 months before living, even if the spacehip has a good cryogenic cooling system.

If in a future we will discover ice on Phobos or Deimos, this ship can be also refueled melting it.

If the ship has an hybrid chemical-electric propulsion system (like in option 3) and the electrolysis is done only douring orbital stay, the ship will be free to use all her power for electric propulsion douring the transfer.

Another option may be to envoy the return water to low mars orbit using a solar electric space-tug. Then the manned spaceship docks the water tank and start electrolysis 3-2 month before leaving.

Last edited by Quaoar (2014-04-28 08:02:29)

Quaoar · 2014-04-28 08:10:47

Tom Kalbfus wrote:

Ice buried deep in a asteroid would be under greater pressure than in a vacuum. Now the surface exposed to the vacuum would be ice free, but if you go under the crust, especially in large asteroids, I am sure ice can be found, and other hydrogen compounds as well. As for a rocket motor, they can be delivered a part of the rocket vehicle that arrives at the asteroid. NASA has yet to use a mass driver for anything. One idea has been to mount a space shuttle main engine to an asteroid, then feed it hydrogen and oxygen separated from compounds within the asteroid Most asteroids just need a little nudge in their orbits to be useful, and the space shuttle main engine can run for hours to get the job done.

If ice is present as a pack (even buried under some meters of regolith) melting, extraction and propellant production can be easly done with on board hardware (I imagine some kind of specialized lander-tanker). But if ice is diffused between regolith grains it may be very difficoult to get it in useful amount, without having a permanent base on the asteroid, with all the extraction and processing hardware.
We have to know more about asteroid structure, before relaying on local resources.

Last edited by Quaoar (2014-04-28 08:11:53)

JoshNH4H · 2014-04-28 08:21:19

The iissue that comes to mind with a chemical-electric hybrid rocket is that you're either going to end up with the low thrust of an electric rocket or the low Isp of a chemical one, with no real in-between. Let's say the thrust to weight ratio of an ion engine is 0.0005* including power plant and an exhaust velocity of 30 km/s, and an electric to kinetic efficiency of 75%. Let's say your chemical rocket has an exhaust velocity of 4.5 km/s and a thrust-to-weight ratio of 100. To increase your effective exhaust velocity to 5 km/s, 2% of your total thrust will have to come from the electric drive. Sounds reasonable, right?

Well, it's not. The thrust to weight ratios being as they are, your engine mass will increase by a factor of 4000 (To be precise, 4000.98) to give a mean thrust-to-weight value of .025.

If 25% of the LOX (22% of total propellant mass) is used in the ion drive, the mean exhaust velocity will increase to 10.1 km/s, which is nice, but your thrust to weight value will fall by a factor of 44,000 to 0.00023.

I'd like to propose a better form of electrochemical propulsion, called arcjets. In an arcjet, electrical energy is used to heat chemical fuel after it combusts. This has a lower electrical cost than separating them, although it is still prohibitively high most of the time.

*Assuming the values given and a powerplant capable of 100 W/kg combined with an engine capable of 200 W/kg, the figure would be more like .00035

Tom Kalbfus · 2014-04-28 08:56:07

The advantage of chemical rockets is they have to operate only for a short time, while the fuel they burn can be collected over a longer time. These asteroids have plenty of Solar Energy, and solar photovoltaic cells are quire reliable, they take as long as they take to crack the rocket fuel, then the chemical motors burn for a few hours to get the asteroid in the right orbit, perhaps to a lunar orbit intercept. the Moon's gravity can slow the asteroid into orbit around the Earth, and then the chemical rocket will fire up to lower the maximum distance of the orbit to put it out of reach of the Moon's gravitational influence so it doesn't get flung back out into interplanetary space. Probably Geosynchronius orbit would be a good one to put the asteroid in.. From the asteroid we could extend a space elevator cable.

JoshNH4H · 2014-04-28 11:05:16

I think you're getting a bit ahead of yourself, seeing as we don't have the ability to manufacture materials even remotely strong enough to build a space elevator out of yet.

GW Johnson · 2014-04-28 12:12:38

Why not do it as solar-powered electrolysis between burns? And, "hybridize" by doing LOX-LH2 liquid rockets at 6:1, keeping the leftover O2 for both an oxygen electric thruster and life support makeup O2. Two kinds of engines: chemical and electric, one ultimate propellant source (water).

Do your departure and arrivals burns as impulsive (short-duration) LOX-LH2, to avoid the gravity losses of a long-extended electric "burn". That way you do not waste months spiraling out and in on straight electric propulsion.

In between, run the electric thruster continuosly over the long transit time to shorten it, at high Isp. LOX is far easier to keep in cryo storage than LH2.

The only downside I see to this would be the electric power. You'll need a much larger solar-electric rig to handle both the electrolysis rig and the electric thruster at the same time during the long transit.

I'm not sure about 40-day trips to Mars, but 60-90 days would be a lot better than 6-9 months.

Nicest thing is every bit of this is essentially off-the-shelf technology.

GW

JoshNH4H · 2014-04-28 13:57:37

Of course, there is still the question of engine mass. Doing the burns at separate times doesn't change the fundamental power issues with electric propulsion, namely that it is incapable of shortening transit times that much.

Quaoar · 2014-04-28 15:04:29

JoshNH4H wrote:

Of course, there is still the question of engine mass. Doing the burns at separate times doesn't change the fundamental power issues with electric propulsion, namely that it is incapable of shortening transit times that much.

This work is about a still experimental but very promising advanced electric propulsion, where propellant is not used directly for thrusting, but to generate a plasma sail that deflect solar wind protons, gaining almost 1N/KWe. The ship depart and arrive with chemical rockets, but douring the transfer use electric propulsion to add energy to the transfer orbit, shortening transit time.

http://www.lpi.usra.edu/publications/re … wash01.pdf

Quaoar · 2014-04-28 15:16:40

GW Johnson wrote:

The only downside I see to this would be the electric power. You'll need a much larger solar-electric rig to handle both the electrolysis rig and the electric thruster at the same time during the long transit.
I'm not sure about 40-day trips to Mars, but 60-90 days would be a lot better than 6-9 months.
Nicest thing is every bit of this is essentially off-the-shelf technology.
GW

I think a copule of 15-20 m radius Megaflex solar array, that can be easly fitted in a Falcon launced module can easly support both, electrolysis and electric propulsion.

If the ship has to go in the asteroid belt or beyond we can add one or two SAFE-400.

Tom Kalbfus · 2014-04-29 08:03:12

JoshNH4H wrote:

I think you're getting a bit ahead of yourself, seeing as we don't have the ability to manufacture materials even remotely strong enough to build a space elevator out of yet.

We could build a space elevator of some length and as we develop stronger materials, we can make it longer.

JoshNH4H · 2014-04-29 08:08:41

That doesn't make any sense at all because a fraction of a space elevator is pretty much worthless.

GW Johnson · 2014-04-29 08:45:12

OK, back to water as a chemical propellant source. Here's a really oddball notion: why keep the water as liquid in tanks? For that portion of the mission's propellant that you are storing longer-term, just freeze it into a shaped iceberg, and keep it sheeted in metallized reflective plastic balloons for the 6 mbar vapor pressure to prevent sublimation at 0 C. That portion of the propellant source is thus modules at 99+% propellant mass fraction.

When the time comes, undock your iceberg, move it inside your processing tank (you only need the one), melt it, and electrolyze it. Liquify the gases. Use them as we have been discussing here. This is a great fit with a modular orbit-to-orbit transport design. It reduces inert weight, which greatly reduces total weight required of the design. It'll be a big effect, due to the logarithmic nature of the rocket equation.

So, your ship has a big hab module or modules, a big storage module or modules for life support supplies, some water tanks, a whole train of bagged icebergs, an engine module with both LH2-LOX and an oxygen ion thruster, an iceberg melt module, a gas liquification module, an electrolysis module, and a nice big solar array module or two. Arrange it in baton shape for spin to artificial gravity, and park some of the bagged icebergs around the hab for radiation shielding. You can carry landers, or send them separately. It'll just be a skinnier baton coming home, unless you find water you can mine and refine "out there". Impulsive chemical burns for departures and arrivals, low electric thrust to shorten the interplanetary transits.

I might even locate the electric thruster at the spin center, 90 degrees to the spin plane. I think I'll keep the LOX-LH2 engines at one end, for structural reasons, firing through the long axis of the stack when it is not spinning. Spin-up can be by big thrusters at the ends. Maybe that's an application of the lithium-aluminum stuff being addressed in the other thread. The fuel is easily storable for the long term. The H2O2 can be made "at need" as you go in the electrolysis module or in its own "peroxide plant module", since its storage lifetime is short. It was hypergolic, the very thing you need for thrusters, just more efficient than MMH-NTO. But you can always use MMH-NTO for thrusters.

Landers being larger in diameter than payload shrouds is not a problem. I posted about an excellent and easy LEO assembly facility for things like that on "exrocketman". It's got some MCP suit stuff in it as well, which we would need for the assembly facility and for any interplanetary mission. In point of fact, the orbit-to-orbit transport ought to have a similar facility as part of its design, for purposes of self-rescue and self-repair.

The idea is still forming, not gelled yet. Comments? Suggestions?

GW

JoshNH4H · 2014-04-29 09:31:01

How do you think the mass savings from lighter tankage will compare to the mass penalty from an electrolysis and power generation unit, and how much do you expect the ion thruster to shorten the travel time by?

Tom Kalbfus · 2014-04-29 09:59:38

JoshNH4H wrote:

That doesn't make any sense at all because a fraction of a space elevator is pretty much worthless.

It could have value as a research program. Capture an asteroid and start making cable with its material, see how long a cable you can make before it breaks, then work on stronger material that can make a longer cable. This is called an incremental approach. Now NASA wants to capture an asteroid, I don't think it wants to sell its ore, so its a research project. I don't see why making cable couldn't be part of a research project in space. Perhaps we could hang a space station from that cable, at a certain length there will be some sort of gravity, maybe one tenth of a Gee, maybe greater. At a certain point we can demonstrate the ability to make a cable off sufficient strength for use on Mars and later for Earth, and we can do that research right in Earth orbit.

Last edited by Tom Kalbfus (2014-04-29 10:00:06)

JoshNH4H · 2014-04-29 10:05:41

It seems to me that you're grasping at straws now. The biggest challenge with a space elevator is finding a material with sufficient tensile strength. The actual construction is a much lower order of difficulty, so it doesn't make sense to experiment with that now. Development of new materials is best done in labs on Earth, for the most part.

Tom Kalbfus · 2014-04-29 10:39:04

But they get distracted from the main purpose, they'll find other uses for nanotubes and the research will head in that direction, for instance superconducting wires and such, the research into making stronger materials will get neglected.

SpaceNut · 2014-04-29 19:05:04

From the link in the first post which Quaoar openned the topic with.

A propellant depot utilizing solar power technologies is discussed in this paper. The depot will be deployed in a 400 km circular equatorial orbit.

yes fuel is a critical item for on orbit refueling but so are other gasses which are use not only as tank pressurizers but also for buffer gasses for the crew. So tanks with nitrogen,helium, argon ect would also be needed.

JoshNH4H · 2014-04-29 20:43:34

Tom Kalbfus wrote:

But they get distracted from the main purpose, they'll find other uses for nanotubes and the research will head in that direction, for instance superconducting wires and such, the research into making stronger materials will get neglected.

Materials science is such a booming and important area that we work on all of those at the same time.

By the way, if nanotubes are conductive that greatly simplifies space elevator technology by making it easier to send power to each vehicle

SpaceNut · 2018-09-23 09:29:31

Since we need cryrogenic cooling to stop boil off on each tank of fuel it makes more sent to have a common platform that has these on them and solar or nuclear power source for electrolysis for converting the water into fuel on demand.

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#1 2014-04-27 15:02:36

Storing LOX-LH2 as water

#2 2014-04-27 16:20:58

Re: Storing LOX-LH2 as water

#3 2014-04-27 23:17:03

Re: Storing LOX-LH2 as water

#4 2014-04-28 06:39:30

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#5 2014-04-28 06:59:35

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#6 2014-04-28 07:22:22

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#7 2014-04-28 07:41:59

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#8 2014-04-28 08:10:47

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#9 2014-04-28 08:21:19

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#10 2014-04-28 08:56:07

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#11 2014-04-28 11:05:16

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#12 2014-04-28 12:12:38

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#13 2014-04-28 13:57:37

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#14 2014-04-28 15:04:29

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#15 2014-04-28 15:16:40

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#16 2014-04-29 08:03:12

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#17 2014-04-29 08:08:41

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#18 2014-04-29 08:45:12

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#19 2014-04-29 09:31:01

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#20 2014-04-29 09:59:38

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#21 2014-04-29 10:05:41

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#22 2014-04-29 10:39:04

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#23 2014-04-29 19:05:04

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#24 2014-04-29 20:43:34

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#25 2018-09-23 09:29:31

Re: Storing LOX-LH2 as water

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