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Panel

SLS return to the moon

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I ran some numbers based on data I could find online and some rough estimates. I think that an SLS could be used to send Orion and a 20 metric ton lander to the moon by using a NTR as a third stage.

The block 1B SLS will be able to lift 105 metric tons to orbit. I guesstimate that the NTR stage could have a dry mass of about 10 metric tons. An Isp of 850 and the mass of the fuel at 40 tons, Orion spacecraft and a twenty ton lander could be propelled into lunar orbit entirely using this stage. Storage of cryogenic fuels over three days would give a test opportunity for NASA, who could the tech developed for this on a trip to Mars.

The lander could be, at maximum, 20 tons. I think this is easily doable for the support of 4 crew during a 14 day lunar surface stay. This would allow for a deep study of the surrounding area on earlier missions, later ones being used to build and resupply a base. Also, it would allow for polar landings, since a new return window opens up every 14 days.

The lander would launch from the surface, and dock with Orion in orbit. The lander would be discarded, and Orion could return to Earth under it's own power. 3 days there, a stay of 14 days, and 3 days back adds the total mission time to 20 days, within Orion's planned capabilities.

Does this seem plausible for a return to the moon? I definitely had very rough estimates when I couldn't find good info on the mass of a dry NTR tank and engine.

Edited by Panel
Updated title to better reflect discussion

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49 minutes ago, Panel said:

I ran some numbers based on data I could find online and some rough estimates. I think that an SLS could be used to send Orion and a 20 metric ton lander to the moon by using a NTR as a third stage.

The block 1B SLS will be able to lift 105 metric tons to orbit. I guesstimate that the NTR stage could have a dry mass of about 10 metric tons. An Isp of 850 and the mass of the fuel at 40 tons, Orion spacecraft and a twenty ton lander could be propelled into lunar orbit entirely using this stage. Storage of cryogenic fuels over three days would give a test opportunity for NASA, who could the tech developed for this on a trip to Mars.

The lander could be, at maximum, 20 tons. I think this is easily doable for the support of 4 crew during a 14 day lunar surface stay. This would allow for a deep study of the surrounding area on earlier missions, later ones being used to build and resupply a base. Also, it would allow for polar landings, since a new return window opens up every 14 days.

The lander would launch from the surface, and dock with Orion in orbit. The lander would be discarded, and Orion could return to Earth under it's own power. 3 days there, a stay of 14 days, and 3 days back adds the total mission time to 20 days, within Orion's planned capabilities.

Does this seem plausible for a return to the moon? I definitely had very rough estimates when I couldn't find good info on the mass of a dry NTR tank and engine.

Anything that uses an NTR third stage, let alone expendable, will:

1. Cost a fortune to build and develop, it'd be cheaper to get the extra Delta-V via advanced 5.5m RP-1/Lox boosters, which were proposed for SLS (shunned for ASRBs), and allow for up to 150 T to LEO depending on the engine cycle. If that's not enough, add 1-2 more SSMEs to the core, and replace the upper stage with a J-2X powered upper stage- the engine was 90% complete, and you could have up to 3 J2-X upper stage engines. Or you can replace the core with a 10 m diameter core, Ares V did that and managed 180T to LEO before its cancellation.

http://www.dynetics.com/_files/insights/papers/Enabling%20an%20Affordable,%20Advanced%20Liquid%20Booster%20for%20NASA%27s%20Space%20Launch%20System.pdf

https://en.wikipedia.org/wiki/Earth_Departure_Stage

2. Be unpopular publicly.

3. Be a serious hazard, for example during a launch failure.

 

Also, your dry mass seems to be... off.

http://www.astronautix.com/engines/nerva2.htm

This engine has 2x the thrust of the SLS Block IB upper stage- BUT, it's probably around the correct size due to the low TWR of NTRs. It's 11T, and that's just the engine.

 

The lander is also too small, https://www.nasa.gov/pdf/604643main_2-Panel%202_Donahue_Final.pdf

That report shows a Boeing proposal for a lunar lander. The high ISP SLS upper stage is used as a crasher stage, so the 15 T lander can get away with only having a few hundred m/s above a conventional LEM-style lander (and also be reusable, as a bonus). Try that s**t with NTR, and you'll have a chunk of radioactive waste on the moon very close to your landing site.

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41 minutes ago, fredinno said:

The lander is also too small, https://www.nasa.gov/pdf/604643main_2-Panel%202_Donahue_Final.pdf

That report shows a Boeing proposal for a lunar lander. The high ISP SLS upper stage is used as a crasher stage, so the 15 T lander can get away with only having a few hundred m/s above a conventional LEM-style lander (and also be reusable, as a bonus). Try that s**t with NTR, and you'll have a chunk of radioactive waste on the moon very close to your landing site.

mmh, that's an interesting lander, however, how do they plan to make it 'reusable' ? it's barely reusable if you need to send a crasher stage each time :) - guess it has the delta-V to land, and refuel it on the ground if you manage to put storage / isru on the moon. (though, methane isru on the moon :() - still, if you try to land it without a crasher stage, does it still has a separate emergency mean for abort (preferably to orbit from any point of the descent) ? - it was not explained in the .pdf :) (i don't know if they could pack an hypergolic engine + propellants that they could use in an emergency after ditching the methane section)

Edited by sgt_flyer

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23 minutes ago, sgt_flyer said:

mmh, that's an interesting lander, however, how do they plan to make it 'reusable' ? it's barely reusable if you need to send a crasher stage each time :) - guess it has the delta-V to land, and refuel it on the ground if you manage to put storage / isru on the moon. (though, methane isru on the moon :() - still, if you try to land it without a crasher stage, does it still has a separate emergency mean for abort (preferably to orbit from any point of the descent) ? - it was not explained in the .pdf :) (i don't know if they could pack an hypergolic engine + propellants that they could use in an emergency after ditching the methane section)

No, they reuse the lander, and get Ch4 lox propellant from Earth. It's barely reusable, yes, but it's not like there's going to be more than 2 missions a year. Reuse is not essential, and is a bonus the design is capable of doing.

ISRU is a pain for early lunar missions- there is no atmosphere, meaning you need the much more expensive, complex, and heavy equipment to extract stuff from the soil. And even then, it'll only give you the oxidizer (thankfully the majority of the fuel mass), as the moon lacks volatiles.

 

And you can't land this without a crasher, (except maybe as a cargo lander, sacrificing ascent back to LLO), so abort without a crasher is pointless.

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Alright, so this wouldn't work with a single launch. How much mass would the lander need to have? Altair was so big because it was used for lunar orbit insertion. 

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35 minutes ago, Panel said:

Alright, so this wouldn't work with a single launch. How much mass would the lander need to have? Altair was so big because it was used for lunar orbit insertion. 

I would just use the boeing proposal, TBH, and use a dual SLS Block I/IB, and call it a day. Since the Block I is most likely retired post Europa Clipper (not economical to keep an entire rocket stage in production just for 1 mission every 3 years), it'll be SLS Block IBx2.

Thus, the mass to LEO would be 200T. Huge, but not unprecedented for a moon mission. It's far more mass to LEO than the 160T to LEO of the Constellation program, allowing for a huge amount of margin, more features (lunar hopper/emergency escape device?) and longer duration missions (possibly into the lunar night!) than Altair provided. It also makes boil-off less of a concern.

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The Boeing proposal would work, but it requires a station at L1 or L2. Would NASA realistically manage to get that funded? Also, the SLS 3rd stage in the proposal is the same as the Block 1 stage, right?

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To get the tiny Apollo lander, command capsule etc etc etc.... took a massive rocket called...Saturn.... it was one, if not the, biggest rocket they have ever built.

 

800px-Ksc-69pc-442.jpg

 

If you want another Moon mission, bigger, then you're going to have to build a bigger rocket OR split it into multiple launches.

Don't forget, you have to take it with you or do without, every kilo means more fuel.

Given the budgets of space agencies nowadays, I cannot see it happening.

Edited by kiwi1960
typos

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33 minutes ago, kiwi1960 said:

To get the tiny Apollo lander, command capsule etc etc etc.... took a massive rocket called...Saturn.... it was one, if not the, biggest rocket they have ever built.

 

800px-Ksc-69pc-442.jpg

 

If you want another Moon mission, bigger, then you're going to have to build a bigger rocket OR split it into multiple launches.

Don't forget, you have to take it with you or do without, every kilo means more fuel.

Given the budgets of space agencies nowadays, I cannot see it happening.

It's basically already known that any SLS lunar return will be via EOR of 2 launches. Even Block II is too small  (which has a similar payload capacity to LEO as the Saturn V, as Orion is much larger than the CM, and you want to have a lander that can stay with 4 people for at least a week, thank you very much.

1 hour ago, Panel said:

The Boeing proposal would work, but it requires a station at L1 or L2. Would NASA realistically manage to get that funded? Also, the SLS 3rd stage in the proposal is the same as the Block 1 stage, right?

Yes. Considering ARM is pretty much doomed, SLS needs a post-2023 mission. It needs to be made quickly, have multiple missions, and be worth using a SLS/Orion on, and also be useful for future missions. Nothing else fits that checklist other than Lunar Space Stations. We have lots of heritage with space stations via the ISS, and have the BS-330, and figuring out long-term space without resupply is essential to any Mars/Asteroid mission, or Lunar Bases.

I'd go so far to say it's the only choice, if you don't want the SLS program to lay fallow for 5+ years.

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What is the cost of a BA-330-DS? They usually quote leasing prices. I'd think it would be a bargain-basement item for SLS, as it would be dirt cheap at even a couple billion.

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8 minutes ago, tater said:

What is the cost of a BA-330-DS? They usually quote leasing prices. I'd think it would be a bargain-basement item for SLS, as it would be dirt cheap at even a couple billion.

????

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The Bigelow hab is the BA-330, the deep space variant is the -DS (they add water tiles all around, not just the sleeping quarters). Bigelow usually quotes a leased price, that's their business model. 

Edited by tater

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The Moon is pretty much the only place Orion/SLS can go to. Mars is out of reach, and Orion is useless for a Mars mission, regardless of NASA's PR. So yes, it does make sense.

I'd personally go for a dual launch architecture, where one SLS brings a large reusable lander to EML. Later missions only need to take the SLS and a refuel tank for the lander.

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Yeah, dual launch would be really simple to engineer. The only big-ticket item would be developing the lander, launched on its own flight (an expendable lander, of course), making the crewed launch basically the EM-2 baselined right now, but with a couple rendezvous with the lander added, and a lower lunar parking orbit, something which the upcoming EUS should be able to allow. The lander could thus be big and beefy, carrying a sizeable payload to the surface, probably some of it built into the descent stage.

A reusable lander in EML changes the architecture a great deal, Nibb31, requiring some fuel depot to be built... you know as well as I do, that "lunar gateway" would turn into ISS 2.0, so the cost would rival that of the program to develop the NTR, methinks.

 

Rune. That would be the original LOR architecture, which IHMO always made the most sense since it allows unmanned cargo flights and the smallest launcher.

Edited by Rune

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9 minutes ago, Rune said:

A reusable lander in EML changes the architecture a great deal, Nibb31, requiring some fuel depot to be built... you know as well as I do, that "lunar gateway" would turn into ISS 2.0, so the cost would rival that of the program to develop the NTR, methinks.

Not necessarily. The lunar gateway isn't required. The crew rotation flight could theoretically carry the propellant to resupply the lander.

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13 minutes ago, Nibb31 said:

Not necessarily. The lunar gateway isn't required. The crew rotation flight could theoretically carry the propellant to resupply the lander.

So the lander is a single stage? Then what propulsion were you thinking about? Because I can tell you right now, H2/LOX won't do, on account of the propellant transfer and surface boiloff. So you are probably looking at storables, and thus a pretty massive Mass ratio, so a lot of lander fuel to be moved around.

And how do you take the fuel to the lander, exactly, and insert that into EML? What does the stationkeeping between missions for the lander? What re-certifies the lander after each flight, and how many flights can it be used? And what, exactly, handles the fuel transfer? Equipment on the lander that you take to the surface and back, or you envision some kind of tanker bolted to an EUS?

Also, note that an expendable two-stage lander can be used for unmanned cargo flights, landing big items on the surface for, say, extended stays or the construction of lunar bases. I don't know how payload delivery would work in your scenario...

 

Rune. I'd stick to the expendable for the first missions, at least.

Edited by Rune

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I'd probably go with some sort of replaceable landing stage (you would get new engines on each mission), or a replaceable tank with sidemounted engines. I haven't thought it through to be honest. Stationkeeping at EML-1 would be minimal.

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The Boeing proposal used a crasher stage, using a modified Delta Cryogenic Second Stage. However, the architecture would require a space station at L1 or L2. 

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3 hours ago, Nibb31 said:

I'd probably go with some sort of replaceable landing stage (you would get new engines on each mission), or a replaceable tank with sidemounted engines. I haven't thought it through to be honest. Stationkeeping at EML-1 would be minimal.

That sounds like assembly in space, and that always sounds easier than it ends up being...

Nope, at lest for the first flights, the lander won't be reused. It could probably be single stage, tough, the dV budget is not that bad.... what is it, a bit more than 5km/s to go to  the surface from EML1/2 and back? Let's actually throw some numbers:

On storables (Isp ~320s, the only thing that has actually been used in space after and extended in-orbit period), that would be a Mass Ratio of around 5, or 20% payload (engine weight and tankage are counted as payload, BTW, so final usable payload will be more like 10%). With two stages, however, you get Mass ratio of 2.2 on each, which works out to ~4.9 when you square it. Yeah, just about the breaking point, the two-stage vehicle will be only slightly smaller for the same payload, or have about the same payload fraction, to within one percent or so. But, use the landing stage with a payload on top like a habitat, and you are looking at 45% of the lander weight being useful payload on the ground, for the price of not building the upper stage for that flight (basically, you build a surface payload the same size as the upper stage). Seems convenient, but as I said, you are looking at very similar vehicles down to the thrust level.

On both cases, refueling the vehicles saves you building a new one, mostly, since whichever way you cut it the empty weight of the lander is pretty much trivial, because you still have to push 90% of its weight to EML1/2 every time you want to pull of a mission, and you add complexity to its design and the mission architecture. And frankly, the cost of the lander will be mostly R&D, making it reusable will save you very little. Maybe when we are launching to the moon monthly, but you are not going to get anywhere close to such a mission cadence with SLS, so better to save some money and keep things simple.

Plus, if you don't make the lander reusable, you can do the rendezvous in LLO, which has its own advantages. Mainly, it offers the possibility of free return trajectories to it and a smaller dV budget for the lander (which actually is awesome for the storable single stage case, drops mass ratio to around 4), but it also allows an orbit that lets you do science from, and you can also get global access by inserting the lander for each mission into a different orbit.

Advanced fuel for the lander means advanced headaches, of course. Those might be worth it if you have a ready source of fuel nearby, but unless and until we build the fabled polar fuel refineries (and then the lander would be based on the ground, not EML1/2), and/or put a water-rich carbonaceous chondrite in orbit around it (and actually develop the tech to mine it), most of what you are doing is wasting your Isp advantage in the form of boiloff between missions and extra tankage mass. All of it, of course, at the cost of extra R&D money for the lander, which is something that doesn't exist in the first place, of course...

A lunar lander is one thing that has a (slim) chance to get funded by the next administration. But if you put a big sticker cost on it with fancy technologies that aren't already there and will need their own development program (and schedule), then I'm afraid you would be killing it before it is born.

 

Rune.Not a bad idea for the next NASA administrator to propose.

Edited by Rune

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I agree that the next administration will have to redirect its manned effort towards the Moon, or else they'll be going nowhere for another 30 years.

They need to kill the "Journey to Mars" PR rubbish, whose sole purpose is to hide the fact that Orion/SLS is a lunar vehicle and can't do much else. It's time to give themselves goals that are actually achievable rather than pipedreams that are never going to get funded.

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Yeah, there was a show on sat TV I saw in the schedule (I watched only a few minutes of it) last week, Impossible Engineering, about "NASA's rocket to Mars." It was about Orion/SLS. I wanted to throw the remote at the TV.

The moon is doable with what we have (and what we had before) in a short time span, well within current budgets. Mars is also doable, and we could probably do it within current budget limitations if NASA could spend money as they chose, not how Congress tells them to. They'd not have built an arbitrary lifter, however (SLS), then worked to figure out how to make a Mars vehicle that fit that launcher, though. They'd have designed a Mars vehicle(s), then designed a launcher ideally suited to that vehicle (still multiple launches, obviously).

Edited by tater

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3 hours ago, Nibb31 said:

I agree that the next administration will have to redirect its manned effort towards the Moon, or else they'll be going nowhere for another 30 years.

They need to kill the "Journey to Mars" PR rubbish, whose sole purpose is to hide the fact that Orion/SLS is a lunar vehicle and can't do much else. It's time to give themselves goals that are actually achievable rather than pipedreams that are never going to get funded.

Meh... not the only option. And in my obviously very particular mind, not the best one either. Wanna hear my two cents?

A lunar lander is a dead-end technology, only applicable to lunar missions. A transit hab and stackable in-space propulsion stage (some refuelable tug like ACES, or a more mature and low cost storable one) would probably be about the same development cost and time, since they are both dumb simple, and examples of all the technologies they would use are already flying in one form or another, or under development by private industry. Furthermore, both items would greatly benefit from the huge amount of ISS experience (the russkies have been doing fuel transfer for decades now, as little as it is mentioned).

Such a (relatively) small expense would open up a whole lot of interesting places for flybys and orbital missions, not to mention be applicable to missions anywhere else. You could fulfill the president's request of visiting an asteroid much more sanely, conduct remote exploration of the moon (probably as an excuse to test the long endurance missions), even put people around Mars in a couple decades, and still have a budget that could, maybe, in the future, probably with international participation, allow the extra expenditures of meaningful surface operations, be they on the moon (a lander does not a base make) or Mars (ditto, and ISRU should really be looked at there IMO).

And of course, we have known that this are the obvious next things to build from the seventies, there's that. ;)

 

Rune. Plus, the US gets a fleet of spaceships, if they come up with good names for the habs and reuse them. USS Enterprise, anyone?

Edited by Rune

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16 hours ago, Rune said:

Yeah, dual launch would be really simple to engineer. The only big-ticket item would be developing the lander, launched on its own flight (an expendable lander, of course), making the crewed launch basically the EM-2 baselined right now, but with a couple rendezvous with the lander added, and a lower lunar parking orbit, something which the upcoming EUS should be able to allow. The lander could thus be big and beefy, carrying a sizeable payload to the surface, probably some of it built into the descent stage.

A reusable lander in EML changes the architecture a great deal, Nibb31, requiring some fuel depot to be built... you know as well as I do, that "lunar gateway" would turn into ISS 2.0, so the cost would rival that of the program to develop the NTR, methinks.

 

Rune. That would be the original LOR architecture, which IHMO always made the most sense since it allows unmanned cargo flights and the smallest launcher.

Why would it become an ISS 2.0? The proposals for a lunar space station are usually only a few modules (far smaller), and can be based off ISS modules or Cygnus.

A fuel depot might complicate things though.

11 hours ago, Rune said:

That sounds like assembly in space, and that always sounds easier than it ends up being...

Nope, at lest for the first flights, the lander won't be reused. It could probably be single stage, tough, the dV budget is not that bad.... what is it, a bit more than 5km/s to go to  the surface from EML1/2 and back? Let's actually throw some numbers:

On storables (Isp ~320s, the only thing that has actually been used in space after and extended in-orbit period), that would be a Mass Ratio of around 5, or 20% payload (engine weight and tankage are counted as payload, BTW, so final usable payload will be more like 10%). With two stages, however, you get Mass ratio of 2.2 on each, which works out to ~4.9 when you square it. Yeah, just about the breaking point, the two-stage vehicle will be only slightly smaller for the same payload, or have about the same payload fraction, to within one percent or so. But, use the landing stage with a payload on top like a habitat, and you are looking at 45% of the lander weight being useful payload on the ground, for the price of not building the upper stage for that flight (basically, you build a surface payload the same size as the upper stage). Seems convenient, but as I said, you are looking at very similar vehicles down to the thrust level.

On both cases, refueling the vehicles saves you building a new one, mostly, since whichever way you cut it the empty weight of the lander is pretty much trivial, because you still have to push 90% of its weight to EML1/2 every time you want to pull of a mission, and you add complexity to its design and the mission architecture. And frankly, the cost of the lander will be mostly R&D, making it reusable will save you very little. Maybe when we are launching to the moon monthly, but you are not going to get anywhere close to such a mission cadence with SLS, so better to save some money and keep things simple.

Plus, if you don't make the lander reusable, you can do the rendezvous in LLO, which has its own advantages. Mainly, it offers the possibility of free return trajectories to it and a smaller dV budget for the lander (which actually is awesome for the storable single stage case, drops mass ratio to around 4), but it also allows an orbit that lets you do science from, and you can also get global access by inserting the lander for each mission into a different orbit.

Advanced fuel for the lander means advanced headaches, of course. Those might be worth it if you have a ready source of fuel nearby, but unless and until we build the fabled polar fuel refineries (and then the lander would be based on the ground, not EML1/2), and/or put a water-rich carbonaceous chondrite in orbit around it (and actually develop the tech to mine it), most of what you are doing is wasting your Isp advantage in the form of boiloff between missions and extra tankage mass. All of it, of course, at the cost of extra R&D money for the lander, which is something that doesn't exist in the first place, of course...

A lunar lander is one thing that has a (slim) chance to get funded by the next administration. But if you put a big sticker cost on it with fancy technologies that aren't already there and will need their own development program (and schedule), then I'm afraid you would be killing it before it is born.

 

Rune.Not a bad idea for the next NASA administrator to propose.

Why do you need advanced fuels? This report: http://www.sei.aero/eng/papers/uploads/archive/AIAA-2013-5479_Presentation.pdf

shows that the best choice for a lunar lander would be RP-1 (very well understood) or CH4 (less well understood due to new engine, but slightly better performance) I would choose CH4 if you want to refuel using ISRU eventually and do reuse (I would choose this one), or RP-1 if you want to get boots to the ground sooner at a slightly lower cost.

Boil off is not a problem for ~15 day lunar missions, though lunar base missions would complicate things and require better insulation to mitigate boil off.

LH2 might also work, it has the lowest mass of them all, but it's probably bad for the longer term when building a base due to higher boil off rate.

It also shows a single stage lander is infeasible due to ~10T higher launch mass.

7 hours ago, Rune said:

Meh... not the only option. And in my obviously very particular mind, not the best one either. Wanna hear my two cents?

A lunar lander is a dead-end technology, only applicable to lunar missions. A transit hab and stackable in-space propulsion stage (some refuelable tug like ACES, or a more mature and low cost storable one) would probably be about the same development cost and time, since they are both dumb simple, and examples of all the technologies they would use are already flying in one form or another, or under development by private industry. Furthermore, both items would greatly benefit from the huge amount of ISS experience (the russkies have been doing fuel transfer for decades now, as little as it is mentioned).

Such a (relatively) small expense would open up a whole lot of interesting places for flybys and orbital missions, not to mention be applicable to missions anywhere else. You could fulfill the president's request of visiting an asteroid much more sanely, conduct remote exploration of the moon (probably as an excuse to test the long endurance missions), even put people around Mars in a couple decades, and still have a budget that could, maybe, in the future, probably with international participation, allow the extra expenditures of meaningful surface operations, be they on the moon (a lander does not a base make) or Mars (ditto, and ISRU should really be looked at there IMO).

And of course, we have known that this are the obvious next things to build from the seventies, there's that. ;)

 

Rune. Plus, the US gets a fleet of spaceships, if they come up with good names for the habs and reuse them. USS Enterprise, anyone?

The amount of fuel needed for HAB reuse is uneconomical unless you use ION drives, and those are pointless for HABs as you need higher thrust engines to make sure the Van Allen doesn't give the astronauts cancer by passing through them too much.

A lunar lander can also be upgraded with more engines, an inflatable heat shield, and a drop tank stage and used as a ISRU using MAV (assuming the lander uses CH4 as fuel), as per se the Boeing proposal. The aerodynamics will be worse, yes, but Mars' atmosphere is very thin. It might not be a huge deal.

 

But yeah, I get where you are coming from. I just support Lunar landings more than HAB+ refueling, as the international community is far more interested in landing on the moon and building a base than asteroid missions, thus allowing for easier international cooperation, and as NASA will have far more reason to build a lunar base to justify the lunar program, and is much less likely to end in itself, like the Apollo Program.

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Fuel depots launched by SLS might make some in Congress have their heads explode, since the people who are for SLS tend to be vehemently against orbital refueling for some inexplicable reason.

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Trying to approach this from another angle. 

I'd go for as many reusable/permanent items in lunar mission architecture, in order to turn it into a pork project that is difficult to cancel after the first successful flight. STS flew for thirty years before it got dumped, ISS is probably going to satay in LEO for 30 years... Apollo got caned early, and its specialized and expendable nature made it easier. Reusables/permanent structures make governments commit to a long-term project. 

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