Author Topic: Any benefit to Launching water ice to depot?  (Read 8531 times)

Offline JohnFornaro

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Any benefit to Launching water ice to depot?
« on: 07/28/2009 03:05 pm »
I followed my own advice [gasp] and started a new thread to discuss this possiblity.

There has been much discussion of the benefits of fuel depots at L1 and other places.  Not in my backyard, of course.  There's also plenty of debate regarding cryogenics, hypergolics, and a buncha other stuff.  But here I just consider H2/O2 propulsion, which is sufficiently efficient for many purposes, and ask that other fuels be discussed elsewhere.  Further, a depot would not have to be limited to storing only one fuel, nor would it be limited to storing fuel only, and not other expendables, including landers, tugs, rescue vehicles, a repair facility, and so forth.

Arthur C. Clarke has already proposed my favorite type of depot, a 1200m radius ring, rotating at about .25 rpm providing about .88G, and featuring a relatively static hub for crew and cargo transfers.  Multiple levels provide opportunities to study various gravitational levels.

Again, the design of the hub is not the question at hand, at the moment.

I thought that launching huge dumb cargos of water ice  from Antarctica (Edit 08-03-09  REmove all penguins first before harvesting ice)  might be a good way to get large quantities of a valuable fuel precursor up to L1 at a significantly lower launch cost.  The downside is the addditional complexity of having a solar powered cracking station as a part of the depot.

Ice, having already expanded, will not present significant problems due to expansion.  Water ice does sublime in a vacuum, but water vapor is not as an aggresive permeator, if that's the word, as H2.

The issue of comparison is twofold.  Long term storage, and ease of cracking the ice into its constituent molecules.  The system I am talking about is new, but as always, newness is far less important than theoretical practicality.  The comparison should be thought of in terms of getting an equal amount of energy at the end of the process for either system. 
The comparison is only between H2/O2 propulsion systems. 

Unfortunately that 100,000 acre chunk of ice I bought off the Ross ice shelf last year cracked off, and I lost my investment, so I have no skin in the game, so it's just a preliminary discussion of general merit.  Naturally, the decision to use fuel depots is the same in both cases.  Since we're dealing with the same amount of cryogenics in space, the means to handle these materials are assumed to be equal. 

The upside:

1. Ice is easier to store for the long term space.

a. It merely needs to be shaded, not refrigerated, thus requiring less infrasturcture.

b. Water vapor is easier to contain in the vacuum of space than is liquid H2 and O2, and will have less boiloff.

c. Ice is easier to launch than cryogenics because the container can be less complex.

d. Ice requires less container mass than cryos to launch, increasing either payload or reducing propellant needs.

The downside:

2. An in space solar powered cracking facility will be required to be launched to L1, or wherever, and assembled in space, probably requiring human presence. 

a. The additional complexity needs to be amortized over the expected number of fuel trips necessary to provide the same amount of H2/O2 to the depot location.  This is where the cost comparison is made.

A similar calculation can be made regarding the amount of expected water ice on the Moon.  in this case, it will have to be first determined how difficult it is to extract the lunar water, and compare that with launching the ice from Earth to  the lunar based cracking station, which will be the same in either case.

Edit 08-03-09  And ice is just the initial idea.  Is tap water a better idea, since it is readily available, and it's eventual expansion upon freezing could be accomodated.
« Last Edit: 08/03/2009 03:40 pm by JohnFornaro »
Sometimes I just flat out don't get it.

Offline Jim

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Re: Any benefit to Launching water ice to depot?
« Reply #1 on: 07/28/2009 03:28 pm »
Just send water.  Easier to handle

Offline JohnFornaro

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Re: Any benefit to Launching water ice to depot?
« Reply #2 on: 07/28/2009 03:48 pm »
Water, probably sea water is easier to handle.  Its freezing and subsequent expansion should also be relatively easy to deal with.  However, what to do with the leftover salt?
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Offline GI-Thruster

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Re: Any benefit to Launching water ice to depot?
« Reply #3 on: 07/28/2009 04:11 pm »
I covered this just a couple weeks ago in a thread concerning containers.  One correction: we do not recover almost all the energy when cracking H20.  The water->constituents process is vastly more energy intensive than the energy liberated once the parts are combined.  Even closed cycle H2 fuel cells do not approach 100% conversion and they are vastly more efficient than reaction motors.

The process of liberating H2 and O2 from water is in fact so inefficient that most H2 is taken not from water, but from methane.  Gives you an idea how expensive it is to generate fuel from water.

And except for launch, you don't need a container.  It's possible it will one day be practical to loft ice blocks direct from the lunar poles with a maglev.

Offline Jim

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Re: Any benefit to Launching water ice to depot?
« Reply #4 on: 07/28/2009 04:13 pm »
Water, probably sea water is easier to handle.  Its freezing and subsequent expansion should also be relatively easy to deal with.  However, what to do with the leftover salt?

Just tap water.  The amounts aren't going to be that big.  Cruise ships take on more than any LV could launch.

Offline mmeijeri

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Re: Any benefit to Launching water ice to depot?
« Reply #5 on: 07/28/2009 04:21 pm »
There are obvious advantages of using ice compared to liquid hydrogen and liquid oxygen: the boil-off issue is eliminated and density is much higher. IIRC original plans for Space Station Freedom included gaseous oxygen and hydrogen propulsion, with the hydrogen and oxygen being stored as water until needed and then separated by electrolysis. Bigelow is planning something similar for its space stations.

I'm still not seeing the advantage of ice over water. Is the idea that you want to store it as chunks of ice without needing a container? Water has high density, so the mass of the tankage shouldn't be too much of a problem.
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Offline JohnFornaro

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Re: Any benefit to Launching water ice to depot?
« Reply #6 on: 07/28/2009 06:04 pm »
No, I just thought ice from Antarctica, as originally conceived, would be easier to deal with.  But really, tap water is probably easier to deal with.  You launch from KSC rather than the pole, for one thing, or for another, you don't have to drag the stuff up to KSC.

So I'm right about the simplicity of the container.  But all those solar panels, and an electrolysis station?  Does that tip the scales in favor of launching H2 and O2 separately?
Sometimes I just flat out don't get it.

Offline alexterrell

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Re: Any benefit to Launching water ice to depot?
« Reply #7 on: 07/28/2009 11:12 pm »
Water > Hydrogen and Oxygen needs 285KJ / mole. Accounting for inefficiencies, call it 500KJ/18g. Let's say you want 20 tons per month of fuel for visiting launchers (this is the same as in the Profac Revisited thread - http://forum.nasaspaceflight.com/index.php?topic=17984.0).

So in one month you need 5.55E11 Joules. Assuming constant power, that's 215 KW of electrical power needed. If you're in Low Earth Orbit, you need to double that.

That seems quite feasible - just bring up water on whatever is the cheapest launcher per kilo, store it in a big tank, and produce Hydrogen and Oxygen on demand.

The 215 KW needs about  1,000m2 of solar array weighing a mere ton. With the appropriate deployment technology (http://forum.nasaspaceflight.com/index.php?topic=18022.0) this array could go up on a Falcon 1 (depending on where sited, of course).

But forget about ice. Have you tried electrolysing ice? You'd probably use distilled water.

From the Profac revisited thread I think the alternative is to capture atmospheric air, bring up some hydrogen, convert it into Nitrous Oxide and Hydrazine, and store these.

Offline Jim

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Re: Any benefit to Launching water ice to depot?
« Reply #8 on: 07/28/2009 11:31 pm »

The 215 KW needs about  1,000m2 of solar array weighing a mere ton. With the appropriate deployment technology  (http://forum.nasaspaceflight.com/index.php?topic=18022.0) this array could go up on a Falcon 1 (depending on where sited, of course).

Based on what?  These mass and volume estimates are laughable.  There hasn't been any arrays with that weight.  Falcon 1 as an LV is a joke.  Power conditioning and batteries have been ignore. 

Offline alexterrell

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Re: Any benefit to Launching water ice to depot?
« Reply #9 on: 07/29/2009 12:05 am »

The 215 KW needs about  1,000m2 of solar array weighing a mere ton. With the appropriate deployment technology  (http://forum.nasaspaceflight.com/index.php?topic=18022.0) this array could go up on a Falcon 1 (depending on where sited, of course).

Based on what?  These mass and volume estimates are laughable.  There hasn't been any arrays with that weight.  Falcon 1 as an LV is a joke.  Power conditioning and batteries have been ignore. 
Since when do you need batteries for electrolysis?

Note also that pumps, electrolysis equipment, tanks, cooling, radiators, comms gear, attachment, gyroscopes have also been "ignored".

Power conditioning is an interesting area. Electrolysis requires DC. Can you switch the individual cells between parallel and serial mode to give the right voltage? Especially as cells give fairly constant voltage output. 

Online MP99

Re: Any benefit to Launching water ice to depot?
« Reply #10 on: 07/29/2009 07:34 am »
Water > Hydrogen and Oxygen needs 285KJ / mole. Accounting for inefficiencies, call it 500KJ/18g. Let's say you want 20 tons per month of fuel for visiting launchers (this is the same as in the Profac Revisited thread - http://forum.nasaspaceflight.com/index.php?topic=17984.0).

So in one month you need 5.55E11 Joules. Assuming constant power, that's 215 KW of electrical power needed. If you're in Low Earth Orbit, you need to double that.


Your vehicle needs the mass of both water & H2 / O2 tanks.

You need to liquefy the gases before they're stored.

You also need to refrigerate the H2 / O2 tanks as part of the startup of your fuel preparation phase, I suspect this might be quite a pain (ie development required to achieve this without GSE).

cheers, Martin

PS and there's a thread somewhere on NSF where I asked the same question!

Offline JohnFornaro

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Re: Any benefit to Launching water ice to depot?
« Reply #11 on: 07/29/2009 02:23 pm »
Yes, you do have to melt the ice first.  That's what the parabolic reflectors are for.  I just thought that ice was easier to launch.  But the price difference between launching ice and water is fairly small, I think, and can be neglected.  What is the price difference between launching ice and the equivalent in LH2 and LOX?

Yes, the resulting gasses have to be liquified and stored, but this process requires the exact same energy of electolysis, assuming tap water, in either location.  It probably needs less energy to refrigerate in space, because the solar array provides shading. 

Is it cheaper to do this on Earth, and subsequently launch the cyros, or is it cheaper to do this in orbit?

Yes, the orbiting factory has to include the mass of ice storage in addition to fuel tankage.  Although it is an additional mass cost, it is relatively inexpensive.

I can't do the math, Alex, but you may be able to.  Tighten up on your array estimate, and Jim will have to agree, if your calculations are correct.
Sometimes I just flat out don't get it.

Offline GI-Thruster

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Re: Any benefit to Launching water ice to depot?
« Reply #12 on: 07/29/2009 03:54 pm »
The energy required to strip water into LOX and H2 is huge.  Especially if you intend to burn it and not use it as part of a closed cycle system, ie. fuel cells; you'll obviously want to do the energy intensive stuff here and launch components only.  On the other hand, if you have a closed cycle system, you need to be able to crack water anyway so you need to have the equipment including the power source for this in situ and what exactly you launch, water or components; doesn't matter so much.

We need a way to store vast amounts of energy for any extended stays on the Moon.  Solar and a closed water cycle might serve until there's a reactor in situ but a SAFE type system makes more sense, IMHO.

Offline alexterrell

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Re: Any benefit to Launching water ice to depot?
« Reply #13 on: 07/29/2009 05:07 pm »
The energy required to strip water into LOX and H2 is huge.  Especially if you intend to burn it and not use it as part of a closed cycle system, ie. fuel cells; you'll obviously want to do the energy intensive stuff here and launch components only.  On the other hand, if you have a closed cycle system, you need to be able to crack water anyway so you need to have the equipment including the power source for this in situ and what exactly you launch, water or components; doesn't matter so much.

We need a way to store vast amounts of energy for any extended stays on the Moon.  Solar and a closed water cycle might serve until there's a reactor in situ but a SAFE type system makes more sense, IMHO.
The energy may be huge, the power is quite achievable - 215KW for 20 tons / month.

More of an obstacle is the need (as MP99) points out for cooling and storing. To date NASA has not deployed (AFAIK) any Liquid Hydrogen refrigeration system in space. Rather they rely on boil off to keep it cool. Another research job for ISS?

Offline alexterrell

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Re: Any benefit to Launching water ice to depot?
« Reply #14 on: 07/29/2009 05:18 pm »
Y
I can't do the math, Alex, but you may be able to.  Tighten up on your array estimate, and Jim will have to agree, if your calculations are correct.
The enthaltpy of the reaction H2 + 1/2 O2 <-> H2O is easy. I believe electrolysis is about 60% efficient, so am reasonably confident in 200-300KW for 20 tons per month, but that's just for the chemistry.

Solar cell masses are in Wikipedia or elsewhere. (Space solar power was budgeted in at 100KW / ton in the 70s, and since then has improved a lot, including microwaves etc.) I agree there'll need to be additional equipment, but am baffled why Jim thinks batteries are needed for this.


Offline Jim

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Re: Any benefit to Launching water ice to depot?
« Reply #15 on: 07/29/2009 05:25 pm »
I agree there'll need to be additional equipment, but am baffled why Jim thinks batteries are needed for this.

So it is ok for the whole spacecraft and depot to be unpowered for 1/2 of each orbit.  Or even the electrosis process to stopped and started every 45 minutes.

Offline Patchouli

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Re: Any benefit to Launching water ice to depot?
« Reply #16 on: 07/29/2009 05:31 pm »
It might be easier to use propellants like LOX and propane lower ISP but it's easier to store.
But if you were to keep water depots why split it and burn it in chemical engines?
A solar thermo or NTR rocket can use water as a propellant.

Offline JohnFornaro

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Re: Any benefit to Launching water ice to depot?
« Reply #17 on: 07/29/2009 05:54 pm »
My first idea about the water/ice launches was to the lunar outpost on Shackleton, "Seward's Folly".  Figuring that it would be easier to prime the pump for the outpost's drinking water.  I hadn't even considered water as a propellant for the rockets that Patchouli is thinking about.

But I don't think batteries, other than standby backup batteries, are necessary on the depot, which would be at L1.  Solar radiation would fall while in the Earth's shadow, but isn't the orbit inclined enough so that the ratio of unpowered time would be far less than 1/2?

Is there a good animated link showing The Earth, Moon, Sun in orbit, plus L1?  For those of us who don't get these things just yet.  Because also, I don't have a good idea of the period of L1 either.
Sometimes I just flat out don't get it.

Offline Jim

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Re: Any benefit to Launching water ice to depot?
« Reply #18 on: 07/29/2009 06:12 pm »
The depot would have to be in LEO.  The moon isn't going to have enough business for decades to support a depot at L1

Offline randomly

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Re: Any benefit to Launching water ice to depot?
« Reply #19 on: 07/29/2009 06:16 pm »
Don't forget that 40-50% of your energy input for electrolysis is going to end up as heat. You'll need radiators to deal with that.
You will need power conditioning for load matching to the photo cells to maintain efficiency. That will also need cooling.
Energy required to cool and liquify the hydrogen is about 30% of it's contained chemical energy. Liquefying the Oxygen also takes considerable energy, although less than the hydrogen. You will also need radiators to dump the heat from the cryostats.

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