Author Topic: Earth-Moon two segment (ion[Cargo]/chemical[Crewed]) mission design  (Read 24343 times)

Offline A_M_Swallow

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Lampyridae - 2/4/2008  8:01 AM

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Once the transfer vehicle works make a larger version and use it to send astronauts to Mars.

If you say so, but the transfer vehicle is a short-term taxi, not a multi-year self-contained life support. Maybe some of the hardware could be carried over but it's still not really viable, IMHO.

Unless it is fully automated the pilot and crew would live aboard the transfer vehicle.  It will cost too much to bring them back to Earth more than say once every 6 months.  Multi year is mostly bigger store cupboards, since regular trips through the Van Allen Belts will necessitate heavy shielding.

The main complexity of the system comes from refuelling the reusable vehicles making regular trips.  Passenger aircraft on the Earth undergo similar sequences when they land at airports.  Fuel is normally transported to airfields in road tankers, which like the ferries are slower but use less fuel to carry the propellent.  There are known solutions to the organisational problem, otherwise railways would not work.

The proposed system does not have to use Jupiters, the Orion can be replaced by a Dragon on a Falcon 9.  Since the Falcon 9 does not have have an EDS everything would have to go through the LEO depot or ISS.  Without a heavy lift the system could still be made to work but all the extra launches will cost a fortune.

The Ares V is an obvious rival to the J-232.  The Orion can be sent to EML1 by launching it on a Ares I and launching the EDS on a Ares V.  The depots and landers can also be lifted by Ares Vs.

The ion/chemical mixture can made work without an Ares V.  The lunar landers, propellent depots, consumables and the various fuels being lifted on EELV and COTS LV.  The Ares I takes the Orion to the LEO depot.  This option makes developing the transfer vehicle an alternative to both the Ares V & EDS.

I suspect that the J-232 can be cost justified on the money saved by the fewer launches its big lift permits if regular trips to the Moon are organised.

Offline A_M_Swallow

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Lampyridae - 2/4/2008  8:01 AM

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Once the transfer vehicle works make a larger version and use it to send astronauts to Mars.

If you say so, but the transfer vehicle is a short-term taxi, not a multi-year self-contained life support. Maybe some of the hardware could be carried over but it's still not really viable, IMHO.

I was assuming the Mars transfer vehicle used chemical thrusters and refuelled at Mars.  A Mars transfer vehicle using ion thrusters would be a very different design.

Offline Lampyridae

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Well, this thing throws the whole CEV concept out of the window. I do not like the idea of a transfer vehicle unable to make atmospheric entry. And the chemical propellant requirements are still astronomical for a chemically-fuelled non-aerobraking transfer vehicle. Besides, the VSE specifically states the need for a CEV. Furthermore there is no need to duplicate functionality in another vehicle (the Ares I lesson) when you have something that is perfectly capable of doing the job.

Anyway, I digress. The airliner principle of operations is OK, but airliners operate in a large turnover environment where you have a constant stream coming and going. Ferries consist of fuel trucks and so on; simple infrastructure. In space, even the design of an unmanned "truck" costs hundreds of millions - just look at the ATV. So I would avoid adding too many elements to an infrastructure the greatest strength of which is simplicity. I guess the engineers would say you are adding too many critical items into the development line.

I would set things up in stages: first an orbital ion propellant depot (or even chemical for landers), then an EML-1 depot and then one on the moon (which would be quite easy). Build up infrastructure in gradual phases.
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Offline A_M_Swallow

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:Lampyridae wrote - 3/4/2008  7:47 AM

: Well, this thing throws the whole CEV concept out of the window. I do not like the idea of a transfer vehicle unable
: to make atmospheric entry.

The whole transfer vehicle does not need to make atmospheric entry - just the lifeboat module.  There is a second compromise, put the engines and fuel tanks in a sort of service module.  The habitation module can be given a single landing heat shield/thermal protection system.

: And the chemical propellant requirements are still astronomical for a chemically-fuelled non-aerobraking transfer vehicle.

I have no objection to aerobraking but I simply did not include a new technology in the critical path.

50 mT dry weight for the transfer vehicle was just a token figure that fitted the upper limit in the question.  Designing a reusable manned LEO - EML1/2 transfer vehicle sounds like a fun subject for a new thread.  Chemical thrusters are being used to reduce the flight time.

If you are going non-reusable EDS instead of a transfer vehicle then the J-232 will be man-rated but the Ares-V probably will not.  The Ares-I and probably the J-120 cannot reach EML1/2.

: Besides, the VSE specifically states the need for a CEV. Furthermore there is no need to duplicate functionality in
: another vehicle (the Ares I lesson) when you have something that is perfectly capable of doing the job.

Are you assuming Aves V or J-232 exists?
I thought Orion was the CEV.  In the main plan the Orion is being used to carry people between Earth and LEO.  Dragon is a back up if Orion or Ares-I do not fly.


: Anyway, I digress. The airliner principle of operations is OK, but airliners operate in a large turnover environment
: where you have a constant stream coming and going. Ferries consist of fuel trucks and so on; simple
: infrastructure. In space, even the design of an unmanned "truck" costs hundreds of millions - just look at the ATV.
: So I would avoid adding too many elements to an infrastructure the greatest strength of which is simplicity. I guess
: the engineers would say you are adding too many critical items into the development line.

Does 4 flights to the Moon a year count as a large turnover?

: I would set things up in stages: first an orbital ion propellant depot (or even chemical for landers), then an EML-1
: depot and then one on the moon (which would be quite easy). Build up infrastructure in gradual phases.

Minimal system

Stage 1 - GEO satellites
1 off LEO depot + tug

Once deployed and some fuel has been procured it can start selling propellent.

The depot will need station keeping fuel.
The tug will need refuelling each time it collects fuel, docks a satellite or SEP ferry.


Stage 2 - Cargo to the Moon
1 off lunar cargo SEP ferry

Start selling 22 mT cargo landings on the Moon.
Large (40 mT) lunar satellites can be carried to various lunar orbits.

Each flight will need an expendable cargo lander.
The SEP fuel and lander propellent are purchased from the LEO depot.


Stage 3 - Build Lunar Base
Start building the lunar base including depot and rovers.  Also land scientific probes on the Moon.
This hardware is probably outside the scope of this thread

Use Step 2 lunar cargo SEP ferry to move items to the Moon.


Stage 4 - Build EML depot (concurrent with Stage 3)
1 off EML1/2 depot + tug + human transfer module
1 off EML cargo SEP ferry
1 off EML fuel SEP ferry
1 off reusable lunar ascent stage - man rated.
Plus first expendable lunar descent stage - man rated.

Use the SEP ferries to carry above hardware to EML1 (or EML2).  Purchase SEP fuel at LEO depot.
Start purchasing lander and transfer vehicle fuel at LEO depot and moving it to EML depot.
Spares will be needed to repair vehicles and depots.


Stage 5 - People to the Moon
Either
  1 off human transfer module to LEO depot or ISS
  1 off LEO - EML transfer vehicle
Or use Orion with EDS to get to EML depot.

Start selling trips of people and equipment to the Moon via EML.
Start refuelling Orion Service Module or transfer vehicle at EML.

Each trip will require an expendable lunar descent stage to be sent EML ahead using the EML cargo SEP ferry.
Each trip needs SEP fuel, descent stage propellent, ascent stage propellent, return from EML propellent and possibly transfer vehicle propellent.


Stage 6 - Full system
As more cargo and people travel launch a full set of SEP ferries, transfer vehicles and lunar ascent stages.

Other than the cargo bay/propellent tanks the SEP ferries should be very similar.

 :cool:

Offline tnphysics

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One must ensure that an SEP failure doesn't strand the crew w/o return propellant.

Offline A_M_Swallow

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tnphysics - 4/4/2008  4:24 AM

One must ensure that an SEP failure doesn't strand the crew w/o return propellant.

When there is only one fuel SEP ferry this is a significant risk, all machines break down.  When there are two SEPs covering the route the crew simply has to wait for the fuel to arrive.  Since we are running planned missions the best places to wait are on the Moon, on Mars and on the Earth; mission control needs to check before authorising manned take-off.

The depot's tanks should be sized to have sufficient fuel that they always carry a reserve sufficient to permit one crew to return.  The depot operator should be under written instructions to maintain this reserve - loss of reserve leading to automatic closure of the depot until the fuel tanks have been refilled.  Setting this up requires a once off increase in the initial capital price to cover the larger propellent tanks and reserve fuel.

Offline Zach

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It seems to me that combining the high ISP of electric propulsion with the efficient propellant storage capability of propellant depots is highly advantageous.  Two depot locations supporting lunar exploration make a lot of sense:
1) LEO: use this depot to fuel the EDS that sends Orion on its quick 3-4 day journey to the moon.  One would only need enough propellant in the EDS/SM to get to LLO and rendezvous with the LLO depot. LEO is also where the LLO depot is fueled prior to shipping it to LLO.
2) LLO: This depot provides the Earth return propellant for Orion as well as the propellant for Altair.  Until the lunar base can provide insitu propellant cost effectively, the LLO depot provides propellant for the round trip to the lunar surface.  Propellant for the LLO depot would be brought from LEO using the electric propulsion.  

The simple depot concept presented by Frank at the Space Access conference http://selenianboondocks.blogspot.com/2008/03/space-access-2008-propellant-depot.html would make a particularly attractive transfer container as well, storing the LO2 or LH2 during the lengthy journey from LEO to LLO.  This LLO depot would be launched from Earth.  Use of Ares V or  J-232 could place a fully depot in LEO in one launch, alternatively the depot could be launched on an EELV class rocket, and filled with multiple commercial launches. I donít want this thread to go down the Ares vs. Direct vs EELV debate black hole, any of these launch architectures can support this concept. Passive ZBO for LO2 is readily achievable with Frankís depot concept, while LH2 would have very low boil-off (could feed a VASIMR engine) or one could add low power active cooling as suggested by Dallas to achieve ZBO for the LH2 as well.

Iím not convinced that reusable, either for the tug or the depot, is the way to go, at least not from the beginning.  The depot concept presented by Frank is very light weight and inexpensive.  Why would one want to haul it back to LEO?  Just replace it once the propellant has been consumed.  I envision a regular train of ďdepotsĒ being brought from LEO to supply the propellant requirements.  For the electric tug, once you get a ~100 kw power plant to LLO I would much prefer for one to get creative on how to use this there rather than bring it back to LEO.  Power for the lunar base is going to be one of the greatest challenges facing exploration, especially through the lunar night.  One option would be to re-stow the solar array, and then use Altair to land it on the lunar surface for use.  My preference would be to use the solar array as is in lunar orbit to beam power down to the lunar base.

Offline A_M_Swallow

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Zach - 5/4/2008  3:11 PM
Iím not convinced that reusable, either for the tug or the depot, is the way to go, at least not from the beginning.  The depot concept presented by Frank is very light weight and inexpensive.  Why would one want to haul it back to LEO?  Just replace it once the propellant has been consumed.  I envision a regular train of ďdepotsĒ being brought from LEO to supply the propellant requirements.  For the electric tug, once you get a ~100 kw power plant to LLO I would much prefer for one to get creative on how to use this there rather than bring it back to LEO.{snip}

Once the depot is in place it does not move.  Fuel and customers come to it.  This makes reuse relatively easy.

The proposed system contains both tugs and ferries.

The tugs are short range vehicles that live at the depots and use chemical thrusters.  They pull the rockets into place using arms.  Since the tugs do the manoeuvring during docking the rockets and fuel tanks do not need complex RCS thrusters and LIDAR short range navigation.  Deciding whether the tug should use liquid or gas propellent will make an interesting trade study.

The SEP ferries are long range vehicles that use electric propulsion (ion/VASIMR) to transport fuel and cargo between the depots and LLO.  Like sea ferries the cargo is stored inside the ferry.

As for reuse of the SEP ferries, on launch costs alone it is cheaper to fly them back to LEO than to launch a second.  The manufacturing cost would be on top of that.

Using the figures from post #264036, earlier in this thread.
The fuel required to return a 15 mT SEP ferry from LLO to LEO is 2.4 mT (metric tons).  The total fuel for the round trip is estimated as 33.6 mT.

Mass for an expendable SEP with cargo
Out [no return] is (126 + 15 + 50) * e^(4040 / (2750 * 9.81)) = 221.9 mT
SEP fuel is 222 - (126 + 15 + 50) = 31 mT

Difference in total mass is 33.6 - 31 = 2.6 mT

During testing there may a single SEP ferry that only goes one way.

Offline Zach

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A_M_Swallow - 5/4/2008  12:30 PM
Once the depot is in place it does not move.  Fuel and customers come to it.  This makes reuse relatively easy.

One must contain the LH2 or LO2 in something that can very efficiently store it during the 3+ month SEP transfer from LEO to LLO.  The "depot" concept outlined by Frank can also simply be considered an efficient storage vessel.  If the SEP can provide >10E-5 G's during the transit, this would be enought to settle the liquid, enabling settled pressure control.

Offline Zach

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A_M_Swallow - 5/4/2008  12:30 PM
As for reuse of the SEP ferries, on launch costs alone it is cheaper to fly them back to LEO than to launch a second.  The manufacturing cost would be on top of that.

You make the assumption that the alternative to bringing the SEP back to LEO for reuse is to throw it away.  A lunar base is going to require 100's of KW, or potentially many WM of power with any form on insitu production or food growth.  One has the choice of launching dedicated missions to provide the power infrastructure, or using the solar arrays from the SEP.  By reusing the SEP for this lunar base power, you get the benefit of the solar arrays during transit to the moon as well as at the moon and you aren't further burdened by needing to provide the tonnes of propellant for the SEP return trip.  Likewise, the SEP only must survive one series of trips through the Van Allen belts, not multiple.

Offline A_M_Swallow

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Zach - 5/4/2008  6:50 PM

You make the assumption that the alternative to bringing the SEP back to LEO for reuse is to throw it away.  A lunar base is going to require 100's of KW, or potentially many WM of power with any form on insitu production or food growth.

The solar arrays account for about 20% to 25% of the mass of a SEP ferry.  The rest of the mass only gets in the way, the chemical fuel needed to land just the solar arrays is greater than the propellent needed to return the entire SEP ferry to LEO.

Although the same solar cells are used in space solar arrays and ground solar arrays the supporting structure is very different.  Ground solar arrays need legs able to take a gravity of 1.6 m/s/s.  The systems that rotates the arrays to follow the sun are also different.

It is simpler and cheaper to develop made for moon surface solar arrays than add complex hardware to refold the space arrays and then reopen on land.

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 One has the choice of launching dedicated missions to provide the power infrastructure, or using the solar arrays from the SEP.  By reusing the SEP for this lunar base power, you get the benefit of the solar arrays during transit to the moon as well as at the moon and you aren't further burdened by needing to provide the tonnes of propellant for the SEP return trip.  Likewise, the SEP only must survive one series of trips through the Van Allen belts, not multiple.

Solar power satellites supplying energy to the Earth are described as searching for the holy grail in the Advanced forum on this newsgroup because the systems are so complex.  Doing it on the Moon is even harder.  It is much easier to just aim solar panels straight at the sun.

Offline Zach

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A_M_Swallow - 5/4/2008  11:59 PM
Solar power satellites supplying energy to the Earth are described as searching for the holy grail in the Advanced forum on this newsgroup because the systems are so complex.  Doing it on the Moon is even harder.  It is much easier to just aim solar panels straight at the sun.

I donít want to turn this into a SPS discussion, but how do you aim solar panels straight at the sun during the 2 week lunar night?  Yes, there are a few mountains at the poles that get more illumination, but that winds up being very limiting.  

SPSís competing with 10c/kwh power on Earth doesnít make any sense.  A little more promising in a few nitch markets on Earth.  But what is a kwh worth on the moon during the lunar night?  $100? $1,000?  A lot more than here on Earth.  The alternatives arenít very attractive.  Try supporting 100 kw through the lunar night using fuel cells and you wind up with 100ís of tones of fuel required.  Nuclear is really the other viable alternative.

Offline wingod

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Zach - 6/4/2008  10:00 AM

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A_M_Swallow - 5/4/2008  11:59 PM
Solar power satellites supplying energy to the Earth are described as searching for the holy grail in the Advanced forum on this newsgroup because the systems are so complex.  Doing it on the Moon is even harder.  It is much easier to just aim solar panels straight at the sun.

I donít want to turn this into a SPS discussion, but how do you aim solar panels straight at the sun during the 2 week lunar night?  Yes, there are a few mountains at the poles that get more illumination, but that winds up being very limiting.  

SPSís competing with 10c/kwh power on Earth doesnít make any sense.  A little more promising in a few nitch markets on Earth.  But what is a kwh worth on the moon during the lunar night?  $100? $1,000?  A lot more than here on Earth.  The alternatives arenít very attractive.  Try supporting 100 kw through the lunar night using fuel cells and you wind up with 100ís of tones of fuel required.  Nuclear is really the other viable alternative.

All current outpost plans are to locate it at the lunar poles on the peaks of eternal light.  Therefore the solar array needs a pivot joint for sun following with a modest (if at all) tilt for the angle to the sun.



Offline Lampyridae

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Zach - 6/4/2008  3:50 AM

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A_M_Swallow - 5/4/2008  12:30 PM
As for reuse of the SEP ferries, on launch costs alone it is cheaper to fly them back to LEO than to launch a second.  The manufacturing cost would be on top of that.

1. You make the assumption that the alternative to bringing the SEP back to LEO for reuse is to throw it away.

2. One has the choice of launching dedicated missions to provide the power infrastructure, or using the solar arrays from the SEP.  

3. By reusing the SEP for this lunar base power, you get the benefit of the solar arrays during transit to the moon as well as at the moon and you aren't further burdened by needing to provide the tonnes of propellant for the SEP return trip.  

1. An individual SEP would cost *much* more than an equivalent performance chemical stage. Reusability in space is easy.

2. Which weigh a fraction of the lunar hardware landed mass, are designed for zero G and space (no dust) and would require a spacewalk to stow them in a lander. This is DIRECT we are talking about, with SEP we can land a 30 tonne nuclear reactor on the moon with one launch.

3. Tonnes? Flying back empty, it would only need a few hundred kg of propellant.
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Offline Mr Natural

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I'm getting closer to defining my baseline architecture and am looking for a bit more discussion. I'll try to summarise it succintly.

CREW
Launch System - DIRECT and EELV (Propellant depot at L1) - Commercial companies contracted to create, maintain and service L1 propellant depot using Ion propulsion.

Orion CEV - however SM and EDS combined into one. Restartable EDS stays with Orion till Earth re-entry. Potential to fuel at L1 for LLO and TEI for return home.

CARGO
Launch System - DIRECT takes RSLAM and 20 mT Cargo to L1 using Ion Propulsion.

CEV RSLAM rendezvous at L1 - both vehicles sent to LLO- RSLAM lands drops, off cargo - 7 days lunar surface activities - ascends with 5mT cargo, LOR - transfer to L1 - Cargo pod rendezvous with SEP while Crew return home - Direct Entry. EDS/CM burn up in atmosphere Cargo returns to Earth a few months later.

I ended up taking segments from all three main architectures. The combination of the EDS/SM only hit me a few hours ago.
One theme that seems less important in existing architectures is International Participation. It was one of the requirements of the VSE.

Offline A_M_Swallow

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Mr Natural - 29/4/2008  12:55 PM
{snip}
Orion CEV - however SM and EDS combined into one. Restartable EDS stays with Orion till Earth re-entry. Potential to fuel at L1 for LLO and TEI for return home.

{snip}
I ended up taking segments from all three main architectures. The combination of the EDS/SM only hit me a few hours ago.

If the SM and EDS use the same fuel they can use the same engines.  The EDS can then be simplified to a set of fuel tanks, possibly drop tanks.

The advantage of L1 over L2 is that the trip is shorter, this matters to people not cargo.  The L2 depot needs a communications satellite to talk to Earth but communication links to the far side of the Moon are needed anyway.

The advantage of L2 is less fuel is needed allowing larger cargoes.

Offline PaulL

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Mr Natural - 29/4/2008  6:55 AM

I'm getting closer to defining my baseline architecture and am looking for a bit more discussion. I'll try to summarise it succintly.

CREW
Launch System - DIRECT and EELV (Propellant depot at L1) - Commercial companies contracted to create, maintain and service L1 propellant depot using Ion propulsion.

Orion CEV - however SM and EDS combined into one. Restartable EDS stays with Orion till Earth re-entry. Potential to fuel at L1 for LLO and TEI for return home.

CARGO
Launch System - DIRECT takes RSLAM and 20 mT Cargo to L1 using Ion Propulsion.

CEV RSLAM rendezvous at L1 - both vehicles sent to LLO- RSLAM lands drops, off cargo - 7 days lunar surface activities - ascends with 5mT cargo, LOR - transfer to L1 - Cargo pod rendezvous with SEP while Crew return home - Direct Entry. EDS/CM burn up in atmosphere Cargo returns to Earth a few months later.

I ended up taking segments from all three main architectures. The combination of the EDS/SM only hit me a few hours ago.
One theme that seems less important in existing architectures is International Participation. It was one of the requirements of the VSE.

The idea of combining the SM and EDS is interesting, specially if you have a high payload capable rocket such as the J-120 to start with. However, I don't see why you want to send the CEV from L1 to LLO. That would cost a lot of delta V and force you to do LLO rendez-vous after ascent. If you are returning the RSLAM to L1, you may as well use it to return the astronaut at L1 too where they can transfer to the CEV waiting there.

PaulL

Offline Mr Natural

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PaulL - 30/4/2008  10:44 AM
The idea of combining the SM and EDS is interesting, specially if you have a high payload capable rocket such as the J-120 to start with. However, I don't see why you want to send the CEV from L1 to LLO. That would cost a lot of delta V and force you to do LLO rendez-vous after ascent. If you are returning the RSLAM to L1, you may as well use it to return the astronaut at L1 too where they can transfer to the CEV waiting there.
PaulL

You are perfectly right and something i mignt not have considered entirely all the way through. My early reasoning for the 100 km circular LOI was safety however that is a kind of negated mute point if consideration is made that an elliptical transfer orbit from L1 will result in a return to L1 if the descent engine misbehaves at perigee. With a 57,731 x 17.5 km transfer orbit I'll have to work out the new delta V's to get the RLSAM to the lunar surface and return to L1. I'm hoping that the generic descent profile from 17.5 km wont change too much.

Offline Lampyridae

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Looking at your architecture I think that you would need to baseline long-term storage of LH to make it work. A RLSAM will really need to use that if you want to land *and* return. However, using CH4 might make more sense in terms of storability and mass. To land and return, you need a lot of propellant. Maybe you need a dedicated propellant lander to refuel the manned lander?

Just a thought that occured to me now, having lots of propellant on the ground would be great from a radiation shielding standpoint. The best design to that end is the wide "cigar" lander design with cabin in the centre and fuel tanks and motor on either side. That shields a fairly large chunk of sky if the tanks are arranged properly. Spare propellant could also be stored in tanks above a habitat roof.
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Offline A_M_Swallow

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Zach - 5/4/2008  6:44 PM

One must contain the LH2 or LO2 in something that can very efficiently store it during the 3+ month SEP transfer from LEO to LLO.  The "depot" concept outlined by Frank can also simply be considered an efficient storage vessel.  If the SEP can provide >10E-5 G's during the transit, this would be enought to settle the liquid, enabling settled pressure control.

Force (thrust) F = mass * acceleration = m a

There are plenty of SEP sizes so I will use a worst case 20 metric tons for the Ferry and 110 tonne for the J-232 cargo including SEP propellent.

F = (20000 + 110000) * 10^-5 * 9.81 = 12.8 N

Depending on which type is chosen that is going to take between 4 and 13 ion thrusters.

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