Author Topic: Lunar Oxygen plus Earth Hydrogen - can't be done?  (Read 8980 times)

Offline Apollo Alum

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Recently I was fooling around with the idea of ISRU - In-situ Resource Utilization as it might apply to acquiring propellants on the moon. Of course Oxygen is easy - the lunar regolith sampled during the Apollo visits is around 40% oxygen, and the reduction of SiO2 into Si + O2 requires about 5.2kWh of electricity per kg of feedstock processed.

Hydrogen also exists in typical lunar regolith, mostly from captured solar wind particles. But its extraction is much more expensive - 2,250kWh per kg of H2 recovered. Of course, if it turns out that substantial quantities of water ice exist in one or both of the polar cold traps (the depressed areas which receive zero sunlight), things look much rosier. Electrolysis of water into H2 and O2 only requires 4.5kWh per kg of H2O processed.

The production of large quantities of LOX and LH2 would make practical reusable LEO-Lunar surface vehicles which would depart the moon fully fueled for the round trip. They would travel to LEO where they would exchange crews and take on cargo - but no fuel! - and then return to the lunar surface. Which means only one CLV launch per trip. More about this as soon as I get a few more simulations finished.

But what if it turns out to be impractical to produce Hydrogen on the moon? Can the production of lunar Oxygen alone substantially lower the cost of lunar exploration?

The traditional answer is that lunar Oxygen could be used as breathing air - not a very substantial benefit. It could also be used to fuel the earth-return vehicle, which would substantially reduce the mass required at TLI. But this does not yield what I was looking for - a long-term, reusable lunar shuttle.

I wanted to take this line of thought a step farther. I tried to model the following scenario on my simulator: size a vehicle with a dry mass of 30 metric tons (mT) plus propellant tanks which gets a full load of LOX on the lunar surface and a full load of LH2 at LEO. That is, the vehicle leaves the moon with enough LOX for the round trip (LS - LEO - LS) but just enough LH2 for the LS - LEO half of the trip. The LH2 tanks are then filled at LEO and the vehicle departs LEO with enough LH2 for the LEO - LS - LEO round trip, but just enough LOX for the LEO - LS half of the trip. Assuming a direct-ascent, direct-descent trajectory (no stop in LLO, therefore no plane-change maneuvers), this trip costs 6,250 m/s of delta-vee each way including a bit of a safety factor.

After grinding away for a long (by today's desktop workstation standards) time, my simulator came back with a surprising answer - there is no solution! I could not find a model that balanced - one where the vehicle arrived in LEO with essentially no LH2 and arrived at the moon with essentially no LOX. I looked at representative models all the way up to the ridiculous level of 10,000 mT of LOX at lunar departure! For the record, I also tried LOX/CH4 with likewise no solution.

So here's my question - is my simulator wrong? Does such a solution exist? Has anyone found a vehicle size which works in this scenario? If such exists and the fuel load at LEO is within the ETO capabilities of the proposed CaLV, it would dramatically reduce the cost of subsequent lunar trips, making the moon that much more accessible.

Anybody?
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Offline Bill White

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Re: Lunar Oxygen plus Earth Hydrogen - can't be done?
« Reply #1 on: 07/07/2007 03:54 am »
Try it with EML-1 and/or EML-2 as the transfer point. I would be very interested in your answer.

Bringing lunar LOX back to LEO may not be viable however I suspect that a re-useable LSAM shuttling between the lunar surface and an L point will give you much better numbers for Terran H2 or CH4 and lunar LOX. A different vessel is used for LEO to/from the L point.

Add: Terran LOX may well be needed for the LEO to EML-1 or EML-2 leg of the journey with lunar LOX used only for EML-1 or EML-2 back to LEO and to/from Luna however look at the overall fuel consumption needed to deposit payload on the lunar surface.

= = =

Add -- here is an excellent thread on EML-2:

http://forum.nasaspaceflight.com/forums/thread-view.asp?tid=1337&posts=206&start=1
EML architectures should be seen as ratchet opportunities

Offline MTKeshe

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Re: Lunar Oxygen plus Earth Hydrogen - can't be done?
« Reply #2 on: 07/07/2007 08:03 am »
Interesting piece of work .

May be what  can be add to your detailed work is the new way of thinking in the production, or more precisely, extraction of matter in the space technology.

In this new approach there is no need for KW of energy to extract or separate matter or atoms from their environment.

What has been tested in lab, there is a much easier way to extract hydrogen and oxygen and even CO2 from the surrounding environment anywhere , without a need for energies you have mentioned above.

What the concept has been is that now we produce within a dynamic reactor the gravitational or the magnetic field attraction of the matter which one likes to capture.

Then what is achieved, is that the system will be extraction system for that given matter.

Then one can change the configuration of the atomic magnetic field of the system to another matter which one needs to extract.

I think this is a more realistic and easier approach.

Do not forget this is exactly how different planets and solar systems gather around them certain given matter.

That is why Saturn holds on to more helium and the earth to more oxygen and so on.

The fact is now we have the knowledge in how to produce what we call magnet for any material than Iron.

By this method producing or extracting any oxygen and hydrogen mix for colonisation or even water for deep space  travel become space base independent .

We are hopeing to do the first commercial unit for Beijing Olympic for cleaning CO2 in the city.

The technology has been patent applied for to be published sometimes in 2008.

Offline neviden

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RE: Lunar Oxygen plus Earth Hydrogen - can't be done?
« Reply #3 on: 07/07/2007 09:27 am »
2 x 6 km/s delta-v is quite a lot for single stage chemical rockets even if you get part of your fuel on the way. Changing two things might help:

1. Stage your flight. Split 6 km/s into two parts: 3 km/s to get from Moon to LLO/L2 and 3 km/s to get from LLO/L2 to LEO. That way you reduce dry weight you have to carry around. Transfer propellants in orbit.

2. Use non-propulsive/high isp way of moving between orbits. You could use aero braking to get to LEO or you could use electric propulsion to get there and back. The Oxygen and Hydrogen doesn’t have to move very fast ass long as everything is designed for a long-term storage.

You increase the complexities (you need LLO/L2 and LEO fuel depot + tanker) but the reduction in needed mass from Earth could make it worthwhile.

Offline Apollo Alum

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Re: Lunar Oxygen plus Earth Hydrogen - can't be done?
« Reply #4 on: 07/07/2007 02:52 pm »
To Bill White and Neviden: I did look at at least one LOR model. It only increases the delta-vee cost (LTO plus LOM = 1,900 m/s, TEI = 1,650 m/s, EOI + EOM = 3,200 m/s + 10% safety = 7,300 m/s). L2R might be cheaper, but by definition cannot be cheaper than the direct flight. I will take a look at using two reusable vehicles - one for LS - LLO (or L2) - LS, one for LEO - LLO/L2 - LEO, but will be quite surprised if it makes an appreciable difference.

The problem with carrying supplemental LOX ETO is that you very quickly surpass the ETO capability of the HLLVs on the drawing board, especially the CaLV (100 - 125 mT). The whole point of this exercise is long-term cost reduction and the single biggest factor in that is avoiding the second ETO launch per mission. If you need 1.5 or 2 launches per mission, you're right back where you started from.

To MTKeshe: your process seems quite promising for separating molecules, such as pulling water ice or SiO2 from the lunar soil. The power requirements I quoted were for dissociating the SiO2 or H2O molecules into their component atoms. However you do it you have to overcome the molecule's bonding energy, which requires at least the powers I quoted. I don't see how you can do that centrifugally or magnetically for less. Something about conservation of energy. If you can dissociate a molecule for less energy than the component atoms give off when they recombine, you have made a perpetual motion machine. No further comment.

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Offline neviden

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Re: Lunar Oxygen plus Earth Hydrogen - can't be done?
« Reply #5 on: 07/07/2007 06:46 pm »
Quote
Apollo Alum - 7/7/2007  4:52 PM
To Bill White and Neviden: I did look at at least one LOR model. It only increases the delta-vee cost (LTO plus LOM = 1,900 m/s, TEI = 1,650 m/s, EOI + EOM = 3,200 m/s + 10% safety = 7,300 m/s). L2R might be cheaper, but by definition cannot be cheaper than the direct flight. I will take a look at using two reusable vehicles - one for LS - LLO (or L2) - LS, one for LEO - LLO/L2 - LEO, but will be quite surprised if it makes an appreciable difference.
While it looks like you will get half of the propellant in the LEO, this is not true. The mass of the Hydrogen in the H2/O2 combination is about 10% of the whole mass. But since you would carry that extra H2 from LEO you can basically discount that saving (when looking from the vehicles point of view).

The problem is that you basically want a SSTO that can make 12 km/s with 450 isp. Compare this with all attempts to make a 9,7 km/s SSTO (from Earth to LEO) and you will get why this comes out with “does not compute”. The ratio of dry weight to propellant needed for 12 km/s is way too high (not even counting your +10% reserve).

So, you either make an equivalent of a multi stage rocket (with propellant transfer in orbit) to reduce dry mass, try to reduce delta-v (aero braking) or increase isp (SEP/NEP). Preferably all of the above.

Offline MTKeshe

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Re: Lunar Oxygen plus Earth Hydrogen - can't be done?
« Reply #6 on: 07/07/2007 07:52 pm »
You are correct.

What we have achieved is very similar to what our planet does which has been and will be doing for billions of years.

A system which perpetually rotates and at  the same time creates magnetic and gravitational field within the centre of the system.

Offline Bill White

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Re: Lunar Oxygen plus Earth Hydrogen - can't be done?
« Reply #7 on: 07/08/2007 04:23 am »
I am partial to brute force LOX extraction via vapor phase pyrolysis.

Inexpensive mylar mirrors given a parabolic shape by inflatable structures allows the collection of significant quantities of solar energy with: (a) low cost for materials and (b) low IMLEO to deploy.

Other solutions are more elegant yet require much more massive and sophisticated (= expensive) hardware. Nuclear reactors for example. I am not anti-nuke in any sense except I don't see how nuclear power can be cost effective taking into account the IMLEO needed to get one to the Moon ( and service and re-fuel it from time to time) as compared with generating 2000 degrees F with a few dozen kg worth of Mylar that costs maybe $500 at Lowes.

As for the heat exchangers and plumbing, you need that either way.

Therefore, for electric power, I am partial to the idea of simple heat engines (Stirling cycle) with the hot end at the focal point of mylar parabolas and the cold end in the lunar shade. Create a 1000 degree F temperature differential and a simple little heat engine should purr like a Porsche.

= = =

As for mission architectures, I favor bringing as much to Luna as possible and return as little to Earth as possible. (Every time I watch orbiter land, I cringe at all the delta V expended to get all that dry mass to climb uphill, only to fly it back down again.)

A BIG reuseable LSAM parked at EML-1 or EML-2 (LLO just isn't stable, long term and lacks global lunar access) and little tiny taxis (Soyuz sized) to ferry crew and H2 to the LSAM. which gets its LOX from Luna.

HLLVs (Jupiters) would be needed to periodically toss big bulldozers and additional LSAMs to the L points. A robust spacefaring civilization will need Earth-to-LEO lift in many different sizes and Jupiters can toss those big LSAMs and lunar surface habs to the L point transfer station while routine crew transfers use the smallest vehicles feasible.

= = =

Longer term, MXER tethers and simple momentum exchange tethers offer the "cheapest" transport system between Luna and LEO -- IMHO.

Incoming lunar payloads are caught and slowed by LEO tethers (which have their orbital energy increased) and those tethers later toss new payloads back to Luna, perhaps after further electromagnetic reboost.
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Offline Apollo Alum

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Re: Lunar Oxygen plus Earth Hydrogen - can't be done?
« Reply #8 on: 07/09/2007 01:44 am »
Neviden: you miss the point. It IS possible to build a single-stage vehicle with an Isp of 450 and a delta-vee of 12.5km/s. It just would be quite large. Mass ratio on the order of 17:1. Big, but not impossible. The problem here is you don't start out with all your mass and then progressively burn it off. Halfway through the mission you fill either the LOX tank or the LH2 tank. Turns out the bird seems to even theoretically impossible to build, not just an engineering nightmare.

To all: Using LLO for staging and propellant storage actually makes the thing theoretically possible, just WAY to big to ever be built. The scenario:

Lunar ascent with all the LOX for the entire round trip plus just enough LH2 to reach LLO.

Rendezvous with a tank containing the LH2 for TEI + EOI. Drop off a tank containing the lunar descent LOX. Depart LLO with the LH2 for TEI + EOI plus the LOX for TEI, EOI, TLI, and LOI.

Arrive in LEO with the LOX for TLI, and LOI. No LH2 left.

Tank up with the LH2 for the entire round trip.

Depart LEO with the LH2 for the entire round trip plus the LOX for TLI and LOI.

Arrive in LLO with the LH2 for LD, LA, TEI and EOI. Rendezvous with the LOX tank left behind earlier. Drop off a tank containing the LH2 for TEI and EOI. This tank will be picked up by the next flight. See step 2 above.

Begin Lunar Descent with the LOX for LD plus the LH2 for LD and LA.

Land on the moon with only the LH2 for LA. Tank up with the LOX for the entire round trip. See step 1 above.

Complex as it is, the numbers do work! That's the good news. The bad news is this scenario requires 126 times the dry mass of the vehicle in LH2 and 756 times the dry mass of the vehicle in LOX. To keep the LH2 load within the 100mT capacity of the CaLV, the dry mass of the vehicle, including crew and cargo, is limited to 793kg. Anybody have experience doing structural design using aluminum foil? Anybody know any Hobbits who want to be astronauts?

For the record, the lunar take-off mass of my baseline 30mT dry vehicle would be 26,500mT (equivalent to 13 fully loaded CaLVs) and would require 38 CaLV launches to lift enough LH2 to refuel it in LEO. Possible? Yes. Practical? I don't think so.

So in conclusion it looks like the production of lunar oxygen is of only marginal benefit to a long-term lunar program unless an in-situ source of an appropriate fuel, preferably Hydrogen, can also be located and mined. At the best lunar oxygen would obviate the need to bring breathing oxygen from Earth and could allow the LSAM to land with the acent stage LOX tanks empty, which would raise the cargo-carrying capacity of the LSAM by 3,690 kg. Considering the current LSAM descent stage cargo capability is around 2,300 kg, this is not an inconsiderable amount. But it is an infield single compared to the home run I was hoping to hit.

So I'm back to studying my reusable LS - LEO - LS vehicle using in-situ propellants in the hopes large quantities of water ice turn out to exist there.

More when I have more.

BTW - I think I will not post here any longer. I will look for a more appropriate forum.
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Offline Bill White

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Re: Lunar Oxygen plus Earth Hydrogen - can't be done?
« Reply #9 on: 07/09/2007 03:24 am »
So in conclusion it looks like the production of lunar oxygen is of only marginal benefit to a long-term lunar program unless an in-situ source of an appropriate fuel, preferably Hydrogen, can also be located and mined.

IF and ONLY IF you insist on lugging your entire spaceship with you on every leg of the journey. Why would anyone desire to do that?

So I'm back to studying my reusable LS - LEO - LS vehicle using in-situ propellants in the hopes large quantities of water ice turn out to exist there.

Why park your LSAM in LEO when EML-1 and EML-2 are so much more convenient?
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Offline Apollo Alum

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Re: Lunar Oxygen plus Earth Hydrogen - can't be done?
« Reply #10 on: 07/09/2007 02:38 pm »
Bill, it is not "if and only if". Read what I wrote! I am not insisting on lugging my entire spaceship on every leg of the journey. 95% of the mass you can park is propellant and tankage. Having separate but identical crew facilities makes no sense. The Apollo and ESAS models of leaving the CM in LLO do make sense because otherwise you are lugging the mass of the re-entry equipment (heat shield, parachutes, etc) down to the surface and back to LLO again. In this case, you would have to entirely duplicate the crew facility, which actually has a negative cost benefit. So parking the propellant is the best you can do.

I did not look in detail at the option of parking propellant at LS-2. But my quick back-of-the-envelope calculations tell me the benefit is at best marginal and still results in a ridiculously large spacecraft requiring 35 or so CaLV launches to refuel.

The one big risk with using L-2 at this point is that we have absolutely no experience there. Since it is a stable "trojan" point, it may well have collected quite a bit of debris over the years. I am an old member of the L-5 Society, and I remember one of the early concerns was sweeping the L-5 point clear of debris prior to beginning construction. The same might apply here. I think the first thing you should be lobbying for is an unmanned probe to visit L-2, survey the area, and begin accumulating station-keeping data. Only once we know what is already there and what it actually costs to do station-keeping there can we begin to assess the risk of using the point.

This also applies to L-1 with the additional problem that L-1 is out of radio contact with Earth. Parking propellants (or anything for that matter) at either point requires either a completely autonomous probe (high risk) or a radio link with Earth for telemetry and C/C. This works for L-2. It does not work for L-1 without a relay satellite either in lunar orbit, at L-4, or at L-5.

At to my forward work, my first study is LS - LEO - LS because it is the simplest and lowest risk case and provides a baseline. Following that, I will look at LS - LLO - LEO - LLO - LS, parking the LLO - LS propellants in LLO. While this should reduce the lunar lift-off mass of the vehicle, it does increase the delta-vee cost of the mission as well as increasing its risk.

Following that I may compare that mission profile to your LS - L2 - LEO - L2 - LS mission. If you're really that interested, do the work yourself. At least dig up for me the LEO - L2 and LS - L2 delta-vee requirements and transit times. A quick run on my simulator, simply using L-2 as the apogee of a highly-elliptical earth orbit whose perigee is the ISS orbit shows some rather alarming transit times. And my own back-of-the-envelope work tells me the LEO - L2 - LS delta-vee is quite a bit larger than the direct profile, and seems to be larger than the LEO - LLO - LS profile, because in the LLO profile your LOI maneuver and your de-orbit maneuver are both 180 degrees from the instantaneous velocity vector, so they accumulate. In the L2 profile the burn to put you into L2 and the burn to take you out of L2 towards the moon are out of phase, so you are spending fuel countering yourself. I don't have the time right now to do the detailed work on this, but I would be very interested id you could point me to a reliable publication describing these maneuvers.
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Offline Apollo Alum

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Re: Lunar Oxygen plus Earth Hydrogen - can't be done?
« Reply #11 on: 07/09/2007 03:35 pm »
Oops! I just realised I mixed up L-1 and L-2. Please mentally correct the prior post. Thanks.
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Offline neviden

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Re: Lunar Oxygen plus Earth Hydrogen - can't be done?
« Reply #12 on: 07/09/2007 04:50 pm »
Quote
Apollo Alum - 9/7/2007  3:44 AM
Neviden: you miss the point. It IS possible to build a single-stage vehicle with an Isp of 450 and a delta-vee of 12.5km/s. It just would be quite large. Mass ratio on the order of 17:1. Big, but not impossible. The problem here is you don't start out with all your mass and then progressively burn it off. Halfway through the mission you fill either the LOX tank or the LH2 tank. Turns out the bird seems to even theoretically impossible to build, not just an engineering nightmare.
Look, it's simple physics. Delta-V is too high for that kind of isp to make anything practical possible even if it is theoretically possible. You can calculate anyway you like but will still get “does not compute”. And like you discovered it gets better if you don’t bring the whole thing back to the LS, but it is still hard.

17:1 is too big. Since most of your mass is propellant, try to reduce maximum delta-v per flight to about 3 km/s and increase number of flights (they are reusable, remember). That should bring everything in the “it is possible” land. Try something like this:

1)   LS -> LLO/L2. Launch full to bring payload or extra O2
2)   LLO/L2 -> LEO. Refuel to full tanks, bring either payload or extra O2
3)   LS -> LEO (optional – 6 km/s!). Refuel to full tanks, bring (smaller) payload
4)   LEO -> LLO/L2. Refuel to full tanks, bring either payload or extra H2
5)   LEO -> LS (optional – 6 km/s!). Refuel to full tanks, bring (smaller) payload
6)   LLO/L2 -> LS. Pick up payload and refuel with enough O2 and H2 to land.
7)   LLO/L2 -> LS. Refuel with extra H2 and enough O2 to land.

Lots of flights and lots of H2 from Earth. I don’t think it is economical. Your only hope is if you can reduce delta-v of 2) flights by aero-braking or reduce mass transferred (or number of flights) by using SEP/NEP with 2) and 4).

Ok, what if we have both H2 and O2 on the moon. Then you get something like this:

1)   LS -> LLO/L2. Launch full to bring payload or extra O2+H2
2)   LLO/L2 -> LEO. Refuel to full tanks, bring either payload or extra O2+H2
3)   LS -> LEO (optional). Refuel to full tanks, bring (small) payload
4)   LEO -> LLO/L2. Refuel to full tanks, bring the payload
5)   LEO -> LS (optional). Refuel to full tanks, bring (small) payload
6)   LEO -> LLO/L2. Refuel with enough O2+H2 to get back to LLO/L2 empty.
7)   LLO/L2 -> LS. Pick up payload (or go empty) and refuel with enough O2 and H2 to land.

Still lot’s of flights, but at least you don’t need to bring any propellant past the LEO from Earth. Might work even without aero-braking or SEP/NEP. You would be also able to move pieces of Mars/Asteroid missions to LLO/L2, assemble them, refuel them and launch them from there. They would have a 3 km/s advantage compared to launch from LEO.

It would also be possible to also get H2/O2 from places (Asteroids/extinct comets - NEO) that have lower delta-v then from the LS to LLO/L2/HEO.

Quote
Apollo Alum - 9/7/2007  4:38 PM
The one big risk with using L-2 at this point is that we have absolutely no experience there. Since it is a stable "trojan" point, it may well have collected quite a bit of debris over the years.
Both L1 and L2 are unstable. I think they require something like 30 - 100 m/s stationkeeping per year. And I think that you should really read the thread that Bill White posted. It explains why the L2...

http://forum.nasaspaceflight.com/forums/thread-view.asp?tid=1337&posts=206&start=1

Quote
Apollo Alum - 9/7/2007  4:38 PM
This also applies to L-2 with the additional problem that L-2 is out of radio contact with Earth.
You can use halo orbit around L2 to avoid that problem.

Offline Apollo Alum

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Re: Lunar Oxygen plus Earth Hydrogen - can't be done?
« Reply #13 on: 07/09/2007 09:39 pm »
Neviden: it sounds good, but do the math. Calculate how much mass you are moving from point A to point B to handle all your refuelings. It is easy to say "refuel here." It is quite another thing to calculate how much it costs to get all that propellant where you need it. Do the math.

I did read the Farquhar article. Actually, I think I read it in 1972 when I still subscribed to A&A! I'm not convinced there is enough of an advantage to using L1 to justify the increased risk for a crewed mission until we have more experience with it using robots.  I also think L2 is definitely out because it is out of line-of-sight with Earth, which greatly increases the C&C issues.

Likewise aerobraking a vehicle this size needs a LOT of risk-reduction experience.

Solar and Nuclear are a bit too far out (time-wise) to be of interest to me for this undertaking. Ditto asteroids, comets, ...

As I said, when I am ready to publish some hard data regarding a reusable LEO - LS shuttle using lunar oxygen and hydrogen, I will start a new thread, probably in this forum, unless Dennis has a more appropriate one by then.
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Offline neviden

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Re: Lunar Oxygen plus Earth Hydrogen - can't be done?
« Reply #14 on: 07/10/2007 06:53 am »
Quote
Apollo Alum - 9/7/2007  11:39 PM
Neviden: it sounds good, but do the math. Calculate how much mass you are moving from point A to point B to handle all your refuelings. It is easy to say "refuel here." It is quite another thing to calculate how much it costs to get all that propellant where you need it. Do the math.
I did do the math. It's a LOT of flights. That's why I keep telling you that the delta-v is too high for that kind of isp, but this way it is at least possible (which doesn't mean it is economical).

My guess is that LS -> LLO/L2 and LLO/L2 -> LS would be economical. Maybe even economical enough to deliver extra propellant to LLO/L2. For anything else you have to either increase flight rates considerably or apply some new technologies.

Offline GraphGuy

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Re: Lunar Oxygen plus Earth Hydrogen - can't be done?
« Reply #15 on: 08/16/2007 07:30 pm »
I think that you can ignore LH2 and use pure LOX in a NERVA style engine.  You probably would not want to land near a base though.

Offline kfsorensen

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Re: Lunar Oxygen plus Earth Hydrogen - can't be done?
« Reply #16 on: 08/17/2007 04:29 pm »
Quote
GraphGuy - 16/8/2007  2:30 PM

I think that you can ignore LH2 and use pure LOX in a NERVA style engine.  You probably would not want to land near a base though.

The key to high Isp in a nuclear thermal engine in the low molecular weight of the exhaust gas.  This compensates for the lower stagnation temperature in the rocket chamber.

Molecular hydrogen has a molecular weight of 2, water has a MW of 18, and O2 would have an MW of 32.  Significantly worse performance.

In addition, oxygen at 2500K would not only dissociate, but would eat through the graphite fuel elements of the NERVA engine like acid on flesh.

Offline khallow

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Re: Lunar Oxygen plus Earth Hydrogen - can't be done?
« Reply #17 on: 08/17/2007 06:54 pm »
Ok, I have a couple of questions. First, suppose you can impart some velocity to a vehicle launching from the Moon. How much velocity do you need to make the numbers work? There are a few possibilities, eg, rail guns, linear motors, or space guns (powered by oxygen reacting with lithium, calcium, or aluminum). As I see it, if you could somehow impart the full velocity at start, then there would be little need for propulsion (perhaps you could resort to compressed oxygen for course corrections and skip the need for hydrogen). So somewhere between zero velocity boost and full velocity is the threshhold where your model starts to work.

Second, while toying with the idea of introducing lithium (perhaps as some sort of hybrid motor afterburner running on oxygen-rich exhaust from the LOX/LH2 engine), I wonder if just compressed oxygen might fill the gap (it depends how much of a delta-v gap there is). Eg, you use up the LH2 you brought to the surface and then go the rest of the way on compressed oxygen.
Karl Hallowell

Offline meiza

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Re: Lunar Oxygen plus Earth Hydrogen - can't be done?
« Reply #18 on: 08/17/2007 08:26 pm »
Compressed oxygen? You have to heat it, it's not helium you know. :)

Offline khallow

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Re: Lunar Oxygen plus Earth Hydrogen - can't be done?
« Reply #19 on: 08/20/2007 12:15 pm »
Quote
meiza - 17/8/2007  1:26 PM

Compressed oxygen? You have to heat it, it's not helium you know. :)

I see a couple of ways this could be done. First, it could be heated while on the Moon and installed in its own tank. You could carry some lithium and in an ultra-safe procedure, toss that into your LOX tank and have the resulting reaction pressurize the tank. Both add weight to the vehicle obviously so they may be impractical on mass grounds.
Karl Hallowell

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