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Use of hydrogen by CEV/LSAM
by
OrenT
on 14 Jun, 2006 21:42
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The current LSAM design uses hydrogen for the descent engine to increase total payload to the lunar surface. The ascent engine is supposed to be identical to the CEV engine and uses the same storable propellant combination (originally lox/methane, now probably hypergolics).
It makes sense to use hydrogen (with its higher Isp but rapid boiloff) on the way to the moon and use the storable propellants for the return engines that will have to sit around on the surface or in lunar orbit for the duration of the visit.
But insertion into lunar orbit is done by the CEV engine. Wouldn't it make sense to use the higher Isp of hydrogen at this point?
I can see two potential practical issues with this option:
1. Using the LSAM engine to brake into lunar orbit would require making its propellant tanks larger. The LSAM is already pretty tall and unwieldy. This would also have some penalty in the tank weight.
2. While this reduces total mission mass it moves some of the propellant mass from the smaller CLV to the larger CaLV. This may require some redesign of the launchers. I'm not sure which one of them is more weight constrained at the moment.
A possible solution for the first problem is to use drop tanks on the LSAM. Another possibility is to use a lunar crasher stage to perform both LOI and most of the descent delta-V, switching to the LSAM engine for final approach and landing. The LSAM would land with relatively full tanks and the descent engine is ow much smaller and doesn't need deep throttling. In fact, it's about the right size to be used for ascent, staging just the landing gear and some surface-only equipment.
With a smaller CEV delta-V requirement it might be less of an overkill for ISS crew replacement and supply runs.
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#1
by
hyper_snyper
on 14 Jun, 2006 21:58
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Lunar orbit insertion is done by the LSAM descent stage. I'm pretty sure it's designed this way in order to better facilitate outpost construction. There will be a common descent stage and then you just put the outpost module on top and fire them off on a CaLV. So when you go to the moon with CEV you already have the ability to do LOI and land with the LSAM. CEV SM is just for TEI and orbit circularization at launch.
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#2
by
OrenT
on 14 Jun, 2006 22:28
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It seems the information I was using was not up to date. The current plan is for LSAM to do the LOI burn.
I wonder how much this extra delta propellant and low density of hydrogen contribute to the LSAM being to tall.
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#3
by
Jim
on 14 Jun, 2006 22:58
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most of it
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#4
by
rumble
on 15 Jun, 2006 02:46
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Using the LSAM for LOI... Clever. Drop tanks would make this a no-brainer.
That way we use hydrogen for as much of the mission as is practical, and can use methane for the later parts.
Question: Doesn't this still introduce an issue if CaLV is launched, but there's a delay before the CEV launches & makes its rendezvous? I guess the problem is no more severe than it would be for the earth departure stage or the landing. But it makes me wonder how long is "too long" for the CaLV (2nd stage) + LSAM to hang around in orbit...I assume fuel boils off?
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#5
by
nacnud
on 15 Jun, 2006 05:10
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I think the answer to that is too long would be in the months rather than weeks. Anyway there could be another CEV in the flow to take over from a duff one, this is especialy true if the ISS is still being used at the time.
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#6
by
Jim
on 15 Jun, 2006 11:37
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rumble - 14/6/2006 10:33 PM
Using the LSAM for LOI... Clever. Drop tanks would make this a no-brainer.
That way we use hydrogen for as much of the mission as is practical, and can use methane for the later parts.
Question: Doesn't this still introduce an issue if CaLV is launched, but there's a delay before the CEV launches & makes its rendezvous? I guess the problem is no more severe than it would be for the earth departure stage or the landing. But it makes me wonder how long is "too long" for the CaLV (2nd stage) + LSAM to hang around in orbit...I assume fuel boils off?
Other threads have covered this but the EDS and LSAM are to be sized for 95 days on orbit
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#7
by
Kayla
on 15 Jun, 2006 23:16
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rumble - 14/6/2006 9:33 PM
Using the LSAM for LOI... Clever. Drop tanks would make this a no-brainer.
That way we use hydrogen for as much of the mission as is practical, and can use methane for the later parts.
Question: Doesn't this still introduce an issue if CaLV is launched, but there's a delay before the CEV launches & makes its rendezvous? I guess the problem is no more severe than it would be for the earth departure stage or the landing. But it makes me wonder how long is "too long" for the CaLV (2nd stage) + LSAM to hang around in orbit...I assume fuel boils off?
LM's analysis showed that passive cryo storage with a well designed stage would be viable for up to ~1 year in space.
http://www.lockheedmartin.com/data/assets/12382.pdfActive storage would extend this.
I also believe that NASA's analysis that showed LO2/CH4 as being better for the ascent vehicle & the CEV/SM was flawed. The higher ISP of H2, ISP=460 sec vs 370, is very compelling. One does need to develop a truly integrated design though to enable the long duration storage while on the lunar surface or in space with reasonable weight and low boil-off. This technology is common between the EDS, LSAM and CEV/SM.
The last 40 years of H2 propulsion experience is something that should be taken into consideration as well when considering the 2 most critical elements of returning to the moon. The ascent vehicle and the CEV/SM are the 2 elements of exploration that have no abort scenarios. The absolutely have to work!
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#8
by
wannamoonbase
on 16 Jun, 2006 00:06
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rumble - 14/6/2006 9:33 PM
Using the LSAM for LOI... Clever. Drop tanks would make this a no-brainer.
I like tanks on the surface, they can be refilled or the metals reprocessed into other useful things. Consume and use everything you take. Remeber we live and think like a disposable society. Think like a person contrained by cash and resources (reduce, reuse, recycle.)
Makes sense when your budget is limited and things cost $1000's per pound.
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#9
by
HailColumbia
on 16 Jun, 2006 01:13
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wannamoonbase - 15/6/2006 7:53 PM
I like tanks on the surface, they can be refilled or the metals reprocessed into other useful things. Consume and use everything you take. Remeber we live and think like a disposable society. Think like a person contrained by cash and resources (reduce, reuse, recycle.)
Makes sense when your budget is limited and things cost $1000's per pound.
ok, people say that all the time. Please explain how that is practical. You would need to bring all the hardware needed to melt down the tank, and then like forge it into whatever you want to "reprocess" it into. plus, what could you actually make that wouldent suck? It couldent be in anyway complex. maybe you could make yourself a shovel or somthing, at great expense.
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#10
by
Kayla
on 16 Jun, 2006 03:16
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Certainly the concept of cannibalizing components, such as computers, pressure vessels, valves, etc. makes a lot of sense. If common components are used throughout the exploration process this is possible. Not utilizing common components means that you must bring an incredible number of different kinds of spares. Inevitably you will run out of things that are experiencing a higher than anticipated failure rate.
Relatively simple robotic production of solar cells has been proposed using insitu derived materials. Use of aluminum for example from left over structure may make this even more probable.
Eventually the reforming of materials for large scale production may make sense. It seems a lot easier to utilize metals and other materials from left over stages is a lot easier than the insitu production. Having a junk yard on the lunar surface (same for Mars) will be the modern day gold mine.
Whether or not any of the more exotic proposals come to pass really depends on how extensive the exploration (dare we say colonization) program is.
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#11
by
meiza
on 16 Jun, 2006 08:28
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#12
by
wannamoonbase
on 16 Jun, 2006 18:38
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HailColumbia - 15/6/2006 8:00 PM
wannamoonbase - 15/6/2006 7:53 PM
I like tanks on the surface, they can be refilled or the metals reprocessed into other useful things. Consume and use everything you take. Remeber we live and think like a disposable society. Think like a person contrained by cash and resources (reduce, reuse, recycle.)
Makes sense when your budget is limited and things cost $1000's per pound.
ok, people say that all the time. Please explain how that is practical. You would need to bring all the hardware needed to melt down the tank, and then like forge it into whatever you want to "reprocess" it into. plus, what could you actually make that wouldent suck? It couldent be in anyway complex. maybe you could make yourself a shovel or somthing, at great expense.
I think you are thinking too high tech and too short term. There is going to be a need for lower quality (i.e. Not Aluminum Lithium or Titanium) materials for things like bunks, vehicles, hab structures, tunneling machines etc. Framing and structure for machines. I agree that early on nearly 100% of material will be from the Earth. But if you want to stay on the surface for more than a few weeks you have to start making and using stuff there. Oxygen, metals, solar panels, etc.
Regarding high tech not everything needed to live on the moon needs to be engineered to the Nth degree. A lot of tried and true equipment from Terra firma will work fine, like pumps, pipe, fans, electronics. They wont have to pay 14 billion to NASA to contract a company to make a gold plated platinum pump for the water reclaim system. Just go get the best one off the shelf and in the worst case send two and a few parts.
We that love space and exploration sometimes fall into a trap of thinking that everything needs to be really cutting edge and stupidly expensive. It doesn't have to be that way.
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#13
by
Jim
on 16 Jun, 2006 18:56
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wannamoonbase - 16/6/2006 2:25 PM
Regarding high tech not everything needed to live on the moon needs to be engineered to the Nth degree. A lot of tried and true equipment from Terra firma will work fine, like pumps, pipe, fans, electronics. They wont have to pay 14 billion to NASA to contract a company to make a gold plated platinum pump for the water reclaim system. Just go get the best one off the shelf and in the worst case send two and a few parts.
We that love space and exploration sometimes fall into a trap of thinking that everything needs to be really cutting edge and stupidly expensive. It doesn't have to be that way.
Yes, they have to be.
1. They need to be light. Transportation costs are high
2. They have to last a long time. Because transportation costs are high, spares are not viable
3. Unless the habitat is operating at sea level atmosphere, this has to be taken into account in the design for cooling, flammability, etc
4. 1/6 gravity has to be taken into account
5. Materials have to be screen for outgassing since it will be a closed system
Submarines has similar requirements
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#14
by
mlorrey
on 16 Jun, 2006 19:13
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HailColumbia - 15/6/2006 8:00 PM
wannamoonbase - 15/6/2006 7:53 PM
I like tanks on the surface, they can be refilled or the metals reprocessed into other useful things. Consume and use everything you take. Remeber we live and think like a disposable society. Think like a person contrained by cash and resources (reduce, reuse, recycle.)
Makes sense when your budget is limited and things cost $1000's per pound.
ok, people say that all the time. Please explain how that is practical. You would need to bring all the hardware needed to melt down the tank, and then like forge it into whatever you want to "reprocess" it into. plus, what could you actually make that wouldent suck? It couldent be in anyway complex. maybe you could make yourself a shovel or somthing, at great expense.
Are you an engineer? From the sounds of it, I doubt it. Ever been a metalworker? Doubt it.
A cylindrical tank is primarily sheet metal, which can be disassembled with a basic plasma cutter rather easily, and cut and welded into many other structures and assemblies. The only odd shapes are the hemispheres, which can be used as:
a) regolith scoops
b) welded back together for spherical tanks to store lunar water, lunox, or other volatile fuels and gasses in.
d) used as pressure modules if large enough. Small ones are light enough to be used as sunshades/radshields by astronauts on the outside, like umbrellas.
Once more, it all comes down to who has the vision...
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#15
by
simonbp
on 17 Jun, 2006 04:59
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Re recycling fuel top domes:
The Von Braun's Astronautical Society's planetarium dome is built from the top of a S-IVB stage; it's not quite spherical, but pretty awesome...
Simon
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#16
by
darkenfast
on 18 Jun, 2006 08:00
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The talk about recycling components on the Moon is similar to the "why don't we re-use deep space vehicles by re-fueling them at a space staion?" comments that pop up occasionally. When you start adding up the costs, the risks and the complexities, it soon becomes apparent that for now, it's science fiction.
Slicing up a fuel tank with a plasma cutter or some other tool? How much did it cost to develop a safe version of that tool and send it to the Moon? Where are you going to do it? If under cover, whats it going to do to the atmosphere? If outside, can an astronaut handle it in a suit, and safely? How much does it cost to maintain that astronaut in that suit on the surface of the Moon per hour, and would that money be better spent elswhere?
Someday these things (like that gas station in orbit), will happen. But not yet. Thinking these things through, and adding up the costs and hazards isn't "lack of vision". It's reality.
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#17
by
CuddlyRocket
on 18 Jun, 2006 10:19
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mlorrey - 16/6/2006 8:00 PM
A cylindrical tank is primarily sheet metal, which can be disassembled with a basic plasma cutter rather easily, and cut and welded into many other structures and assemblies.
Welding? That's sophisticated. It's not called the metal-
bashing industry for nothing!
Of course, an oxygen tank
is an oxygen tank, and can therefore be re-used to store in-situ produced oxygen (which is highly likely to be one of the first ISRU products, possibly after dirt for radiation shielding). And if you have plenty of oxygen production, no need to take that heavy water, just take extra hydrogen and produce water by running it through a fuel cell (giving you power as a bonus). And where would you put the water? In an empty hydrogen tank. If it'll hold LH it will hold water. And perhaps carbon dioxide, or nitrogen or methane or ethanol or some other gas or liquid you may have a use for.
And the fuel cells can be re-used as fuel cells. And batteries as batteries. And temperature and pressure sensors as such. Even the structural material that holds all this in place on the LSAM can be re-used to hold stuff in place (including wiring - great for tying things together).
And we always think of the complex things, whereas it's the simple stuff that is often most missed. For instance, a bit of piping capped off would make a fine pen-holder. Handy things pen-holders. People have them for a reason. Bit of sheet metal - nice tray. Or perhaps a plate.
Scavenging is an art. Look at any materially deprived culture on Earth and what they can make from other people's rubbish.
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#18
by
mlorrey
on 18 Jun, 2006 19:45
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darkenfast - 18/6/2006 2:47 AM
The talk about recycling components on the Moon is similar to the "why don't we re-use deep space vehicles by re-fueling them at a space staion?" comments that pop up occasionally. When you start adding up the costs, the risks and the complexities, it soon becomes apparent that for now, it's science fiction.
Slicing up a fuel tank with a plasma cutter or some other tool? How much did it cost to develop a safe version of that tool and send it to the Moon? Where are you going to do it? If under cover, whats it going to do to the atmosphere? If outside, can an astronaut handle it in a suit, and safely? How much does it cost to maintain that astronaut in that suit on the surface of the Moon per hour, and would that money be better spent elswhere?
Someday these things (like that gas station in orbit), will happen. But not yet. Thinking these things through, and adding up the costs and hazards isn't "lack of vision". It's reality.
"Safe" versions of plasma cutters usable in vacuum are already developed, so no cost there (been in that business, I know the technology). They weigh about 30-40 lbs. However, the types developed for use in zero g are unnecesssary on the Moon, since the Moon has gravity, so there is no need to neutralize the thrust of the plasma (plasma cutters have a lot of similarities to arc-jet and similar electric propulsion systems).
Plasma cutters operable in atmosphere are in existence, quite common (you can buy them at Home Depot). Plasma cutting and various welding tools put lots of ozone and oxygen ions in the atmosphere, and depending on the gas used, possibly helium, argon, etc as well as metal oxide dust, which needs to be filtered out of the atmosphere.
The problem with your uninformed cynicism is that your "not yet"-ism has been keeping us on the ground for decades, despite that plasma cutters, and other technologies, have been around for a long, long time. Plasma cutters are a WWII technology. There is no need to waste millions or billions reinventing technology that already exists, to work on the Moon. It is not zero g.
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#19
by
darkenfast
on 19 Jun, 2006 04:26
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Well gee, I guess that put me in my place. It will be a shame if this forum starts sounding like SDC.
