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kbd512: I don't see Congress paying for yet another spacecraft. They already paid for Orion, Dragon, and CST-100, and there is continuing discussions about DreamChaser. And yes, I want to see DreamChaser fly. That's 4 American spacecraft; I don't see a 5th. But if you want a minimum weight spacecraft to do what you just described, that's Soyuz. Do you realize how cramped Soyuz is? The descent module has 20 minutes of life support, just enough to de-orbit and land. The orbital module has 2 weeks of life support. The Soyuz descent module has a titanium alloy hull, and shaped with hemisphere top, heat shield, and side wall angle optimized for minimum weight. The American designed Apollo D2 (designed one year before Soyuz) had exactly the same shape, because this is the optimum for absolute minimum weight. Soyuz is capable of long term storage in space, and has been proven as the reliable crew return vehicle. And Soyuz needs the service module to deliver it to ISS. Actually, the 1960s version of Soyuz designed to carry Russian cosmonauts to lunar orbit and back, the equivalent to Apollo CSM, had a larger service module. That one was called Soyuz LOK (Lunar Orbit Craft - the Russian word for Craft starts with "K"). The Soyuz model used to service space stations (Salyut/Mir/ISS) has a smaller service module, just enough to do the job. Basically, what you're describing is Soyuz without the orbital module. The orbital module has an aluminum alloy hull, and spheroid shape, so minimum weight and designed to be discarded. If you want astronauts to ride Soyuz to the space station, and breathe while they do so, then the orbital module is required.
Rob,
The only capsule systems that we've developed thus far are all far larger and more sophisticated. Even Soyuz is larger and more sophisticated than necessary for what this capsule would be used for. This is a single man capsule, intended to provide functionality already noted, and not intended to replace the functionality of any existing capsule system.
The question I have for "what if", is under what conditions do we bail and try to land and under what situation do we just seal each module to allow for them to seperate from what would be a disasterous condition? Of course upon seperation each needs there own mini life support, navigation ect until rescue can be achieve or until they can recouple back together again as a station with the offending modules neutralized.
Here's what I see these capsules being utilized for:
1. Emergency return of single crew members from ISS for medical conditions
Ideally we'd have a flight surgeon aboard ISS to contend with medically emergencies, but if that's not always possible then we need a way to return infirm personnel without a lot of fuss.
2. Unscheduled ISS crew additions or transfers/swaps due to changing mission requirements
If several crew members suffer from illness at the same time, perhaps we'd elect to dispatch a doctor if the cost was sane. If a crew member for an outbound exploration flight was injured or ill, maybe we'd just replace him or her with a member of the backup flight crew. Let's say one of our sophisticated life support, power, or propulsion subsystems for our exploration craft doesn't pass a checkout and requires a few parts and a skilled technician to correct the issue. No problem, we'll send him, his tools, and a few parts to fix it.
3. Temporary abandonment of permanently occupied spacecraft due to fire or release of hazardous substances that require an emergency depressurization
This should be pretty self-explanatory.
4. Capability backup to prevent the failure of a more sophisticated landers from scrubbing a necessarily expensive mission
Let's say for a moment that we'll launch landers as separate cargo ahead of the crew that will use them instead of trying to attach them to our deep space transit vehicles so as to keep payload and propulsion system masses sane, thus limiting the cost of missions by forgoing the use of insanely expensive lift vehicles like SLS. If the lander is inserted into the wrong orbit, never makes orbit, or has some other technical problem that inhibits its use, then the crew can still get to the surface.
5. If the capsules were reusable, then our explorers could use surface vehicles and small cranes to retrieve the capsules after landing, attach the capsules to much smaller ascent vehicles on the surface of Mars, and potentially have a second way of returning to the deep space transit vehicle after their surface stay has been completed
I just think that smaller and simpler backup ascent vehicles should also be considered.
Do we necessarily have to put all of our astronauts in one vehicle? I don't think we do. Having options is a good thing. If our Red Dragon has some sort of technical malfunction that prevents us from using it as intended, then the money and effort expended for a surface mission isn't an instant total loss.
Every capsule system developed thus far is completely over the top of what's required for backup and emergency use. The t/Space shuttlecock capsule was the right design for simplified EDL, but it was larger and more sophisticated than necessary.
Rob,
I was thinking about something a little more sophisticated than MOOSE and a lot less sophisticated than Dragon / CST-100 / Orion and significantly smaller. The capsule needs minimal avionics and attitude control for EDL, life support systems so space suits are not absolutely required but still permit use of pressure suits, weigh as little as possible, and be robust enough for long duration space flights.
Rather than containing multiple backup subsystems and weeks of supplies, this is a final alternative for getting to the surface of Earth or Mars from orbit.
At some point, we need to start developing that "portfolio of technologies" that NASA keeps talking about.
As far as sabotage from the defense contractors is concerned, they're not actively developing anything like what is actually required for sustainable space exploration. I'm not aware of any major defense contractor capable of producing a simple, cost-efficient emergency return capsule. SpaceX, t/Space, or some other company will have to develop the technology because the defense contractors won't.
I like the potential utility that Lockheed's proposal could provide, but I can't recall a single program that they've completed on time and within budget in living memory. If NASA gives them a dime for their proposal, it needs to be with the understanding that there's a fixed budget with time constraints applied and that they will either produce or receive nothing.
Cold fusion is not going to pass muster because its proponents are frauds.
I'd be ever so careful about labeling anyone a fraud or any technology a hoax without substantial independent testing.
If the scientists really were evidence driven instead of ego driven, then why not just say that we don't understand what Mr. Rossi's device is doing, but it's obviously putting out quite a bit more power than the conventional chemical reactions we've seen.
I don't consider the physicists and other scientists working on hot fusion to be frauds, either, even though they've yet to come up with a sustainable break even fusion reaction during the last several decades over which serious effort has been devoted towards the goal.
Be very skeptical of anyone who tells you they have a magic energy box, but don't let your ego prevent you from examining the evidence.
Rob,
There are applications that robotic or remotely operated systems are more suitable for than humans, but I would also say that there are certain tasks that are most easily performed by humans or human operators in close proximity to the work site. Obviously design requirements for human rated systems increase, but I think we need to let go of the idea that any particular spacecraft has to be capable of re-entry for it to be man rated. For emergency re-entry, I think the t/Space CXV was the right idea, but it needs to be scaled down to seat one or perhaps two astronauts.
If that thing was man rated and paired with a SEP propulsion unit, I can see it being useful for repair and retrieval of satellites and upper stages. We still need repair and manufacturing modules for ISS and a propellant depot. If service providers and/or the DoD were ever able to design "general purpose" satellites that could be reconfigured or upgraded on-orbit, their costs for launch services would eventually drop.
If cold fusion devices pass peer review, the only thing hot fusion devices will be used for is industrial power generation facilities for established population centers.
Even if He3 could simply be picked up off the lunar surface with little to no processing, which is certainly not the case, it would likely only be used on the moon and Mars for colonies with populations great enough to warrant the expense and effort to construct the infrastructure to support hot fusion. It's hard to say what the state of power generation tech will be when we're at that stage in the game.
No matter how expensive the stuff is or how much better it is than D/T for power generation, barring development of a heavily automated infrastructure for mining, processing, and transporting it, I don't see a market for it on Earth now or in the future.
Don't forget that you might not need a payload fairing at all. A cylindrical module whose skin is not too fragile can be its own "payload fairing", riding naked on top of the launcher. It just needs a small "pointy hat" to reduce air drag some. That would a small conical fairing on its end, covering the docking gear there from supersonic bow waves, going up.
I intended for all three major components to be covered with solar cells and radiators, so that probably means some protection is required during ascent. The swash plate and blades will be somewhat more delicate than the primary or secondary modules, as there are five separate components included that are assembled on-orbit.
Ascent heating is just not that big a deal, since you leave the "dense" air (enough to have significant heating) at about Mach 2-ish at around 100+ kilofeet-ish. Higher and faster the temperatures are high, yes, but the density is actually so low there is little heat actually transferred, plus it's a brief transient. It really is NOT re-entry-in-reverse, we don't ascend with trajectories like that at all!
GW
I don't think it's possible to design an inexpensive deep space habitat, but I'm trying to use available technology. The secondary module is a small ISS module and the primary module is a SLS gas can. The design goals are triple redundancy for subsystems that can put a damper on your exploration activities (like power, consumables, and ECLSS), distribution of consumables, distribution of the crew amongst the modules, and some measure of artificial gravity. The closed loop ECLSS, active radiation shielding, and the swash plate and blades all require further development.
Gravity doesn't help you if you're sleeping... if you're only going to have a centrifuge in part of it, make it at least the exercise area, and ideally put the restrooms and dining area there as well. The crew can sleep in freefall.
The problem with having gravity in the exercise room would be disturbing the orientation of the MTV. The propulsion system is low thrust electric. There's no real issues with tumbling a MTV if impulsive burns are used. Sleeping on an incline will have to suffice.
An inflatable wheel would also work and provide enough space for the crew to work from, but it'd be heavier. I wanted to keep the solution as light as possible to make the loads manageable using three F9H flights.
I'll believe SLS will be available when the funding to use it materializes. There's no funding for an upper stage, so SLS is 70t to LEO, 85t with advanced boosters, and maybe 90t with composite tankage. There's no advantage to using a booster that's more than ten times as expensive to fly as F9H, unless you just want to burn money.
Yes, well, we all saw how Venture Star turned out. Billions spent and nothing to show for it.
Now that we have a company (SpaceX) with leadership that's more interested in whether or not they're actually producing goods and services that have utility for manned space flight and have established a short, albeit highly successful, track record of delivering, I think it's time for NASA to send some of our tax money elsewhere. I think SpaceX has figured out that if they can make access inexpensive, then demand increases.
In any event, our major defense contractors see cost plus contracts as spending programs that funnel money to them rather than a guaranteed way to maintain a profit margin while producing what the government requires. If anyone in management there with but a shred of personal integrity was in charge, they'd look at cost control as a civic duty and not something mandated by regulation.
My only hope is that SLS and Orion don't waste billions and then leave NASA with no capability for manned space flight. However, I also know that SLS and Orion are not the solution for the type of missions that NASA says it wants to perform, so perhaps it's just as well that these two programs die, however painful and wasteful their demise may be. Let's keep our fingers crossed that NASA is forced to deal with reality and that SpaceX turns their BFR into something much more than a paper rocket.
Rob,
No, I want NASA and Congress to incentivize good behavior on the part of the contractors and de-incentivize bad behavior.
If you deliver on-time and within budget, you receive a bonus.
If you overrun your budget more than two times, your contract is automatically cancelled. Call it the three strikes rule.
If you fail to demonstrate progress towards contract goals/objectives for more than a pre-determined period of time, your project is cancelled.
These kinds of things encourage the contractors to provide solutions that have a reasonable chance of working rather than something which might work if enough time and money were thrown at the problem.
Basically, no more cost plus contracts. If Boeing and Lockheed-Martin don't want to play ball, we'll go to SpaceX and they'll get nothing. Trust me, every contractor wants the business.
At some level, you also need executives who are actually interested in the business and making progress in advancing the state of the art. Obviously companies have to turn a profit, but that can't be their only motivation for working with NASA.
If I were NASA, I would have compromised with Lockheed-Martin to permit resumption of work, under the notion that it's better to get something rather than nothing for the taxpayers' money. The entire X-33 concept wasn't flawed, but the material selection for the tanks wasn't workable at the time.
For a crew of six, my design requires a four bladed artificial gravity device. One crew member bunks in each blade tip. Two crew members are on watch at all times in the primary or secondary flight deck, so only four bunks are required. During normal operations, all airlocks are sealed to prevent a penetration in one compartment from endangering the entire crew. Apart from meals and recreation the crew will remain in separate MTV modules for the same reason. All three modules will contain a shower, toilet, and galley. The primary module will be more lavish than the secondary module or swash plate, but a systems casualty won't instantly make the astronauts hate life.
Unfortunately, I don't have any visuals to provide. The term swashplate was only meant to illustrate the concept.
Picture a three or four bladed rotor or propeller with flat blades and hollow cores. Now imagine that this propeller has bulbs/bumps on the tips of the blades and hollow cavity connecting them. The bulbs/bumps are astronaut sleeping quarters. The transfer tunnels leading to the sleeping quarters are just big enough for the astronauts to transit through. The hollow cores contain small cavities for water to equalize mass distribution amongst the propeller blades and provide a secondary source for potable water. The hollow swash plate contains a pumping system for moving water amongst the blades to equalize loading.
Irrespective of whether or not a particular astronaut weighs a little more or less than the astronaut in the blade opposite from him/her, or whether or not the opposing blade is even occupied, the mass distribution system ensures that no net force is applied in a particular direction so as not to disturb the direction of travel.
The interfaces between the blades and swash plates are air locks. The front and back of the swash plate are also air locks connected to the primary and secondary deep space habitat modules.
I wanted triple redundant ECLSS, triple redundant power supply and management, and distribution of consumables amongst the three components to reduce the weight of specific components. If it is possible to lift all three components using F9H and larger payload fairings, that would be ideal. I think three F9H flights and one crewed F9 flight would be sufficient for assembly.
The primary module will be launched first to provide station keeping capability during initial assembly and testing. After assembly has been completed, SLS provides the primary propulsion module. If SLS is not available, then two more F9H flights are required. Irrespective of how the propulsion module arrives in LEO (fully fueled if aboard SLS or partially fueled if aboard F9H), the MTV is then mated to the propulsion module. The propulsion module transfers the MTV to ISS for crew consumables loading and any necessary repairs/manifest additions/software upgrades. From there, the propulsion module transfers the MTV to L1 where tests of the communications systems and active radiation shield are performed. If everything functions as expected, the exploration crew are cleared for departure. The crew are launched in Dragon aboard a F9H outbound to L1. Upon arrival, the propulsion module separates from the MTV to permit Dragon to transfer the crew. The propulsion module is then re-mated to the MTV. The crew performs final checkout and says their goodbyes.
Rather than complicating the architecture with a surface stay, the first mission will be an orbital mission designed to prove that the MTV and propulsion module are up to task. The mission might include exploration of Phobos or Deimos just to say we landed on something or it might not.
Even now, interplanetary travel is a monumental human achievement, so I'm going to divide the task into achievable mission objectives. With tech that will be available within the next five to ten years, this is doable. I imagine that the tech required for surface stays is another ten to fifteen years away after that. Slowly but surely, we'll get there.
I am wondering if congress should feed funds towards the commercial market of Space x ect.. in terms of what they want and just leave NASA out of the steady state applications and bring it back to cutting edge designing that can be propagated down into the commercial market.
Nah, thats crazy talk; as meantioned we can not trust them to be the stewarts that we would want.
I agree. NASA should only concern itself advancing the state of the art and pursuit of science objectives that further human knowledge.
NASA's contractors should continue to provide know-how and services, but NASA needs to issue requirements, solicit bids, and select from amongst the proposals that meet the requirements and are within budgetary limitations. NASA needs administrators who understand rocket and spacecraft tech, but the agency shouldn't actually employ anyone for the purpose of designing or building rockets so long as there are three or more companies capable of providing solutions.
Our aerospace and defense contractors have the know-how and service provisioning aspects of the business covered, but there needs to be an incentive to deliver on-time and within budget.
SpaceX isn't infallible, but there seems to be more independent development going on there than at more established contractors like Boeing and Lockheed-Martin.
I've seen more than a few presentations from NASA that indicate that the agency is attempting to develop a portfolio of technologies for space exploration, but I don't see them actually doing that.
Examples:
Rover/NERVA - high specific impulse and high thrust propulsion
Saturn V - heavy lift launch system
Skylab - space station
STS - sensitive cargo lift/retrieval and partial reusability
X-33 and Venture Star - completely reusable single stage to orbit for sensitive cargo lift/retrieval
There are only a handful of technologies required for sustainable space exploration and precious little funding devoted to them.
Here's what we need:
- dramatically lowered launch costs
- high reliability closed loop life support
- active radiation shielding
- high energy density power generation systems
- high specific impulse and high thrust propulsion systems
- in-situ resource utilization
We live in an age where there are companies and even private individuals who would fund space exploration if the basic technologies required were available for purchase, but the enabling technologies don't exist because we've squandered so many billions of dollars on projects that haven't contributed to the goal of making space flight affordable and attainable.
The greatest barrier to space exploration is and always has been the insane cost of getting to LEO. NASA has been in operation for more than five decades and in that time no completely reusable launch system has been developed. That was step one for sustainable space exploration and we're still not there.
By all means, let's repurpose NASA for tasks they're actually good at.
For purposes of generating artificial gravity for the deep space habitat, I was thinking something more along the lines of a swash plate with rotors and small crew accommodations at the tips, just big enough to bunk one or perhaps two crew members. The rotors would be covered with solar cells for power and the blades would be detachable for on-orbit assembly. The swash plate would attach to the air lock and house secondary ECLSS. The front of the swash plate would contain another air lock with a smaller module attached to it. The smaller module would contain additional consumables, secondary flight deck, telescope, and backup ECLSS. The rotors would use water distribution to maintain precise counterbalance.
The habitat module would contain the primary avionics and flight deck, store the bulk of the consumables for the crew, house the active radiation shield, primary power subsystem for the active radiation shield and primary ECLSS, and attitude control systems. The crew would enter the habitat module from the rear and then the propulsion module would attach to the docking port and seal them in for the transit to Mars.
The general idea is to not require use of a substantial separate counterweight or tether, not use propellant for start/stop, and simultaneously permit the use of SEP or NEP. The end-over-end tumbling concept should also work, but the spin down operations are slightly more complicated.
The same habitat module with a docking adapter in place of a propulsion module could serve as a space station or L1 outpost.
My presumptions are that all propulsion and attitude control systems will be electric, Orion won't be available to serve as a counterweight due to flight costs and its inability to land anywhere but an ocean, and that the heavy lift capability provided by SLS will only be used for the deep space habitat module.
Whether we like it or not, billions of our tax dollars are being squandered on pet projects that this or that bureaucrat has a political/economic interest in. I just want NASA administrators to focus on what's required for real space exploration and pay lip service to the whimsical and insipid requests of Congress. There's no benefits to be had by playing political games. Congress can either choose to defund the manned space program or fund it properly and administer it properly. Let people who are qualified to make mission architecture and technology selections make them. Congress and the President need to set goals, step back, and give people who are qualified to do what they want done a chance to work.
Congress is supposed to be a good steward of the taxpayers' money. They're not supposed to play favorites or dictate every little detail of how to do something to the government agencies and contractors they provide funding for. Our engineers know how to build rockets, spacecraft, and run space programs, but the constant interference from Congress and special interest groups has made their tasks impossible by dictating things to them that should have been their decisions to make.
If a certain technology selection or mission architecture isn't manageable or is cost prohibitive then NASA needs to accept the breaks and Congress needs to be realistic about what can and can't be done for a given level of funding. On that note, if Congress wanted to do something that would benefit not just NASA but the military, too, it would prohibit NASA or the military from letting cost plus contracts. A contractor needs to accurately estimate what a particular technology or tool set costs to develop and build, submit a proposal, and then a proposal that approaches affordability needs to be selected. This isn't the 1960's. Spacecraft aren't completely experimental technology and haven't been for decades. If no suitable solutions are available, then NASA needs to go back to Congress and let them know that what they want accomplished isn't doable with available resources.
For example, is there any reason why the Air Force should be permitted to let contracts to a contractor (ULA) who has violated the law because their cost overruns are so high? There's no reason whatsoever why all contracts that run into the billions of dollars shouldn't be competitively bid and no reason why the contractor overcharging the government should be permitted to dictate operations to potential competitors for certification to bid on contracts.
Like GW said, the giant bureaucracy that NASA has become is simply taking longer to become irrelevant than most of us would like. You can't throw money at the problems that NASA has and expect a result. It's cultural.
I would think if you built the engines on those propulsion sections to be long-life reusable (whatever that might actually mean), there would be little need for refurbishment after every use, until that operating life runs out. Thus you could just do in-space refueling and supply-loading at the L1 point. Returning the stage to LEO for refurbishment should only be occasional. You get to send more propellants and supplies most of the time, if you're not ferrying inert stage weights around.
I'm going to presume relatively small and simple regeneratively cooled pressure fed or expander cycle engines since the methane is moderately cryogenic. The major parts would be 3D printed, so they could be produced at ISS. The engines would be arranged in four banks of two.
Maybe such engines exist and maybe they don't yet. Spacex at least thinks they have one in the Merlin 1D's. We'll see. At small thrust sizes, maybe XCOR has one in their piston-pumped Lynx engine. That's because the highest risk of failure in rocket engines has to do with turbopump machinery. They at least think they can scale up to larger sizes, too. That extends to methane and hydrogen, not just kerosene and LOX.
Something like the XCOR 5M12 (descent/ascent) and XR-3M9 (rcs) are what I had in mind for the propulsion module. A bit more performance or more banks of engines would be required for Mars missions, but we need to concern ourselves with development of the propulsion module first.
One or the other of those approaches, or maybe something else, will give us the long-life, low-maintenance liquid rocket engines we need to make this transportation happen efficiently. And I think it's not very far off. Both companies I mentioned are making good progress.
I think in about three to five years or so, we'll have LOX/LCH4 engines that are suitable for manned spacecraft. NASA moves slowly, so there's plenty of time to design the module while we're developing the engines.
My suggestion does imply that we develop in-space refueling well enough to make it both safe and reliable with mild cryogenics. Most folks are talking LOX and methane these days. The Russian refueling is with simple storables, NTO and one of the hydrazines, if memory serves. NASA has never learned how to do any of this for itself, though. It's this issue, probably more than long-life engines, that limits our ability to do replenishment at L1 instead of coming back every time to LEO.
Yes, on-orbit refueling, purging, and refurbishment of the propulsion module are what make this architecture possible. Transferring the propulsion modules back to LEO for refueling is about efficiency and availability of repair facilities. The SEP tugs can transfer the propulsion modules to L1 with far less propellant mass consumed than with chemical propulsion. There's no advantage to a L1/L2 propellant depot if you're not making the propellant on the moon because you have to expend propellant to get to L1/L2 and you have to have something to store the propellant in. All of this infrastructure also has to get to LEO to begin with. The propulsion module stores the propellant because it's using the propellant. The propulsion module has to be inspected after each use and only ISS will have the facilities to repair or replace damaged parts and crews trained for that task.
We'd have to start with exactly your suggestion, but we'd have to work on long-life engines and in-space cryo-refueling to make it more efficient, which is my suggestion.
Agreed.
Given what I have been saying about NASA declining elsewhere, I think I'd look to the private companies to actually get this done. If one of them sees value going to the moon, something like what we are discussing is the better way to do it. It'll happen then, and not before.
GW
I'm not holding my breath on NASA going anywhere in my lifetime. I believe that the vast majority of our political establishment is completely uninterested in space exploration of any kind and can't or won't provide clear, consistent, and achievable objectives for NASA to accomplish. Leadership has to start at the top and we don't have any.
Relying on international partners for critical functionality is always a mistake. I'm not sure what it would take for that to sink in.
The Russians' leadership is every bit as petulant as our leadership is. If the Russians are intent on treating ISS like some sort of political chess piece instead of the international cooperative effort that NASA intended for it to be, then there is no "International" Space Station. NASA needs to accept this and put forth the effort required to replace the capability the Russians modules provided or de-orbit the facility and save the taxpayers' money for real manned space exploration efforts.
NASA needs to develop its own tech for manned space exploration and Skylab II is a step in the right direction. The capabilities that the Russian modules provide is well within our technological capability.
If NASA is at all serious about its commitment to ISS, it will divert funds to develop a SEP propulsion module and crew accommodations. I'm guessing that it's not and the station will be brought down when the Russians leave. Anyway, screw 'em. Upwards and onwards.
If ISS is brought down, then there is no commercial crew program and no platform to test new technologies on. In nearly two decades of operations, NASA couldn't allocate funding for a crew accommodations module or a propulsion module. Makes perfect sense to me.
This should mean more funding for tech required for a Mars mission, but I'm guessing it means no space station, no commercial crew program, no lunar missions, and no Mars mission.
Maybe Skylab II development work could start, but that's probably too sensible. Oh well, what's a few tens of billions between friends?
Responding to KBD512 in #77 above: Why not leave the landers at L1, and shoot the supplies straight there? Why drag the inert mass of the landers back-and-forth from LEO to L1? Otherwise, I love your idea!
GW
Gee whiz, GW. My brain isn't working today. I finally realized what you were asking. The surface exploration vehicles could stay at L1 with the station keeping tug if they didn't require significant repair or refurbishment, but the chemical propulsion modules have to be ferried back to ISS for refueling and refurbishment.
Responding to KBD512 in #77 above: Why not leave the landers at L1, and shoot the supplies straight there? Why drag the inert mass of the landers back-and-forth from LEO to L1? Otherwise, I love your idea!
GW
I realize that I wasn't clear about the design of the lander and its propulsion hardware, so I'll be more specific. The lander is a wheeled or preferably tracked methalox/electric hybrid vehicle. The propulsion module is a separate piece of hardware that attaches to the top of it.
The propulsion module rests on hydraulic jacks/posts to enable the surface exploration vehicle to attach/detach from it for mobile surface exploration. The propulsion module also provides refueling capability for the surface exploration vehicle. This makes servicing the propulsion module and surface exploration vehicle easier and permits a wider variety of payloads to be carried.
Responding to KBD512 in #77 above: Why not leave the landers at L1, and shoot the supplies straight there? Why drag the inert mass of the landers back-and-forth from LEO to L1? Otherwise, I love your idea!
GW
This is all theoretical and would never be done in real life because it accomplishes too many stated space exploration objectives, tests too many technologies required for interplanetary travel, and isn't complex enough to satisfy the complexity cravings that NASA has.
We build three SEP tugs and four landers. The fourth lander is a contingency spare kept at L1 along with a smaller SEP tug for station keeping (the same design that we'll use to return satellites to ISS for repair/refurbishment/refueling/repurposing).
We're going to design the tugs to be capable of transferring payloads to Mars from the outset rather than wasting time and money screwing around with a bunch of intermediate designs requiring subsequent testing. Every functional part will be designed such that it is on-orbit replaceable without tools, if possible. As new tech comes out of our labs, the tugs are upgraded. Think of it as propulsion legos for astronauts to play with.
The SEP tugs enable LEO/L1/LEO transfers of heavy payloads between refuelings, but you have to be willing to wait a few months for the transfers. This is not a major problem because we can only maintain a relatively low launch cadence for crewed launches. The heavy landers only use chemical propulsion to get to the lunar surface from L1 and then back to L1. This maximizes useable propellant mass for our tugs and landers, as additional propulsion hardware and propellant would be required to supply the depot in any orbit other than LEO. After the initial support infrastructure is in place at ISS, subsequent launches provide consumables and replacement parts only.
If we're willing to launch the landers and SEP tugs with minimal propellant mass and use subsequent launches for fueling, it's possible to make this work with F9H only. When F9 and F9H become reusable, we can purchase ten or more F9H flights for the price of a SLS flight. F9/F9H are the American equivalents of Soyuz and Proton. If the upper stages are also reusable, the crew can launch to ISS aboard a F9, instead of the more expensive F9H.
I was thinking methalox for the landers because it makes the stack shorter since the tankage is smaller and it doesn't have the storage issues associated with LH2. The propellants are moderately cryogenic, but cooling requirements are within the capabilities of existing active cooling systems that NASA's contractors have already expended considerable effort to develop. The attitude control thrusters should also use methalox.
The general idea is to test the propulsion systems and landers through years of actual operations in space in the actual configuration required for a Mars mission, less components unique to atmospheric operations like inflatable heat shields.
Dragon is mass efficient enough that a F9H and RL-10 powered upper stage (or something similar to it that doesn't cost so much) can transfer it between LEO and L1, but more importantly, back to LEO without refueling. Active cooling is required, but we're supposed to be testing that tech because NASA says it's required for mid term space exploration objectives.
If we're doing space exploration on the cheap, we might as well have a concept of operations that makes that possible.
If the premise is to attempt a sustainable exploration program, then I'd go for the "some other configuration" option for lunar missions. The Apollo, L3, and Altair landers were designed for single use.
Use ISS as a propellant depot and repair facility for SEP tugs and reusable landers.
The SEP tug would transfer the lander from ISS to L1 ahead of the crew. After the lander arrives at L1, the crew would then go to L1 in Dragon to transfer to the lander. The single stage lander then descends to the lunar surface from L1 for the surface mission. After the surface mission has been completed, the lander ascends to L1, the crew transfers back to Dragon, and then Dragon returns to Earth. The SEP tug then transfers the lander back to ISS for refueling, consumables resupply, and refurbishment.
This would give Boeing the opportunity to test the technologies required to transfer sizable payloads to Mars and reduce the recurring costs of a lunar exploration campaign. We can also test active radiation shielding and experiment with recovering oxygen from lunar regolith.
If ISS is upgraded with a repair facility module and payloads are sent to ISS before transfer to their ultimate destination, then humans who could actually correct problems can perform final checkout on the payloads. If something is forgotten or broken, it can be added or fixed. It's not a guarantee that a payload will reach its destination or that nothing can subsequently cause a problem that results in loss of the payload, just an additional opportunity to problem solve with greater flexibility.
I would think that the experienced garnered from exercising the capability to fix spacecraft and satellites in space have utility for a sustainable space exploration program, but that's just me. So long as episodes of space road truckers aren't inflicted on the rest of humanity, that is. (edit: I guess a more appropriate analogy would be Spacecraft Overhaulin. If some clown puts a pair of fuzzy dice on Orion or installs a chrome instrument panel, we're pulling the plug.)
I think we can look at a typical resupply mission and easily determine that a significant mass fraction of the cargo is devoted to propellant, breathing gases, and water. It highlights the requirement for any long duration mission requiring a high degree of self sufficiency to use electric thrusters for station keeping and have reliable closed loop ECLSS.
For ISS, or any lunar or Mars missions for that matter, to remain within the far reaches of the realm of affordability, much better propulsion and life support systems need to be tested aboard ISS. All we could establish by tabulating cargo masses would be resupply rate for the consumables. Consumption rates for oxygen were recorded on Expedition 12, although that was a number of years ago and we'd need more data to baseline average oxygen consumption. One would think that NASA would have this information.