New info on LSAM, ascent stage engine switched to hydrogen?

[gunsandrockets]

http://www.airandspacemagazine.com/ASM/Mag/Index/2006/AM/soap.html<br /><br />"As for propulsion, NASA will go with the old reliable: liquid hydrogen/liquid oxygen engines for both the descent and the ascent stages. Apollo had to make do with less potent hypergolic fuels, which ignite on contact, because they were the safest and most reliable propellants available at the time. The LSAM descent stage will use a modified version of the venerable RL10 engine, which entered service in 1963, just as Apollo was getting under way. "<br /><br />"The descent engines for the lander have to be throttleable-by the time of touchdown, they'll produce barely enough thrust to keep the vehicle from falling to the surface in the one-sixth gravity of the moon. "<br /><br />"Today's RL10s can throttle down to 20 percent of their full thrust, but the LSAM engines will have to do better: 10 percent. That shouldn't pose a problem, thinks Connolly, but the achievement still requires some development work, and NASA may want to test these highly throttleable engines on robotic landers scheduled to begin visiting the moon as early as 2011."<br /><br />Liquid hydrogen for the ascent-stage seems an odd choice because of storage issues. An LSAM might have to sit on the moon for up to six months before the crew leaves in the ascent-stage. Six months is a looong time to keep the liquid hydrogen from boiling away.

 

[gunsandrockets]

I understand why NASA went for the LSAM design that they did. Mainly, NASA wants the capability to land large amount of cargo on the lunar surface, "In cargo-only mode, with no crew, its [LSAM] carrying capacity will be 21 tons, more than the weight of the entire [Apollo] LM". But I see that capability leading to an old problem, a problem that the Apollo project faced and managed to avoid by virtue of the Lunar Excursion Module. The problem is size, for the LSAM will tower 30 to 40 feet high. It has to in order to get the capability that NASA wants. The LSAM needs a massive descent stage and that stage is made even larger because of the huge tanks needed to store the high-performance (but very low density) liquid hydrogen propellant. <br /><br />Now why should the LSAM height be a problem? Two main reasons, access and stability. The LSAM crew will conduct lunar EVA daily, and climbing up and down a 20 foot ladder each time in a bulky pressure suit is an accident waiting to happen. NASA is aware of the access problem, from the article...<br /><br />"In some designs, says Connolly, "we're talking about just putting an extra bulkhead and a hatch into [the LSAM] cylinder." But it might be preferable to have the airlock hatch closer to the lunar surface instead of placing it 15 or 20 feet off the ground, reachable only with a long ladder. The study team played with different options, including a kind of split-level design in which the astronauts descend a tunnel before heading out the airlock. The spacecraft's designers are still working to determine the exact configuration." <br /><br />And if simple crew access is a problem imagine the trouble with the cargo landers which might have up to 21 tonnes of equipment perched way up yonder.<br /><br />The second problem is stability. As the LSAM is trying to soft-land, the vast bulk of it's remaining mass will be high in it's towering structure, since the descent-engine tanks will be nearly dry. That bad CG factor compl

 

[JonClarke]

Interesting comments. The Russians chose the crash-lander approach with the LK lander. I had not known that F aget came up with this idea as well On a small scale the Surveyor soft landers worked the same way, ditching their braking engine and touching down using verniers..<br /><br />Height is certainly a big issue for safety, not only on the Moon but Mars as well. Most lander designs pay no attention to this issues at all. Obviously the designers have not tried to climb up and down 10 or 20 m landers in space suits. One small step could very easily become one giant leap, with unpleasant consequences. <br /><br />Another solution to the height problem is to have a horizontal rather than vertical lander. For example this layout or this. The advantage of this configuration is that it allows payload to be increased without increasing the height of the spacecraft on the lunar surface, simply by making the spacecraft longer and adding tankage. The only constraint to growth is the overall booster height which will still have to fit the VAB.<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[nacnud]

There is a thread over on nasaspacefligt that deals with the problem, can seem to locate it now...

 

[JonClarke]

Yes, I know the one. There was a study that looked at both vertical and horizontal landers, and settled on a hybrid.<br /><br />Am I right in saying the LSAM design is still completely fluid?<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[mikejz]

I hate to be one looking at this from a different angle: But why do they need a latter? Would not a winch do the job better and with less weight or possibly a basket? With the mini elevator, they could even enter from the top docking port. <br /><br />Also the added height of a lander would allow for a better overview of the local lunar area and allow for longer line-of-site communications between astronauts and the lander.

 

[j05h]

Either lander (vertical or horizontal) will want to be well above the lunar dust. Long landing legs and ladders/elevators may be unavoidable. The dust was almost a EVA-breaker for Apollo and we still haven't started designing new spacesuits to combat it. Moving the lander/hab upward a few feet will increase equipment lifetimes. Of course, as discussed, there are other tradeoffs.<br /><br />josh <div class="Discussion_UserSignature"> <div align="center"><em>We need a first generation of pioneers.</em><br /></div> </div>

 

[josh_simonson]

It seems to me that the storability issues with LH2 will make longer stays on the moon very difficult. The LSAM would have to return to earth in a short period of time, and I can't picture them leaving astronauts on the moon without an emergency ride home.<br /><br />LH2 may be available in situ though, so if they're willing to pay to develop that capability and deploy a reliquification scheme up there, they might be able to use it. The RL-10 does have some restart capability, so it may be a good place to start if one wanted a re-useable LSAM.<br /><br />I guess if they get a lot of funding this could be a good thing, but if they have to squeak by on a small budget this is bad.

 

[JonClarke]

In what way was dust nearly an EVA breaker for Apollo? Can you name one EVA that was abandoned or nearly abandoned because of it?<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[j05h]

have you seen the condition of the suits afterward? The Apollo suits were heavily worn after the missions. I'm not sure about abandoned EVAs, but do think they cancelled one late in a mission. The later Apollo suits were better but still damaged, the dust gets into everything. And yes, Apollo astronauts complained about the wear on their suits andhte trouble with dust. Suit technology has not improved that much since the Apollo suit: it has been a refinement. There are no skinsuits or exoskeletons for astronauts (yet). <br /><br />With this in mind, how in Jove's name are the new Moonwalkers supposed to conduct EVAs? Carry a half-dozen suits for each crew member? this is a huge obstacle right now, and NASA is only addressing it with a cool (but not super relevant) Mark III suit. BioSuit and Phil Nyutten's Exosuit are potential solutions but neither are ready. <br /><br />http://www.wired.com/news/space/0,2697,67110,00.html<br /><br />...Within hours, the dust covered the astronauts' spacesuits and equipment, scratching lenses and corroding seals... "Dust is the No. 1 environmental problem on the moon," said Apollo 17 astronaut Harrison Schmitt...<br /><br />Josh <div class="Discussion_UserSignature"> <div align="center"><em>We need a first generation of pioneers.</em><br /></div> </div>

 

[willpittenger]

* Do you have a drawing of a hybrid lander like your horizontal lander images?<br /><br />* My concern with horizontal landers is a Catch-22. If you put the main engines in the center, they can back each other up. However, if they are on the corners, they can better balance the vehicle.<br /><br />* Unless a workable hybrid lander could be developed, I would like to see the lander be sent down with only enough fuel for the descent. I have to believe that some types of fuel could be made from lunar regolith. Martian regolith can be made into fuel. Perhaps the same can be done with the lunar stuff. Then the ascent stage would <i>be</i> the descent stage. It would also be reusable. Since you might need to return to orbit without waiting for fuel, a crasher would be sent unmanned ahead of time. (Besides, the main lander might fail to start. That was why Grumman went with hypergolic fuels.) It would be cramped with just enough space for three astronauts to squeeze in, on each others laps if needed. It would use hypergolic fuels (and perhaps clones of the 1960's ascent engine) for return to orbit. <div class="Discussion_UserSignature"> <hr style="margin-top:0.5em;margin-bottom:0.5em" />Will Pittenger<hr style="margin-top:0.5em;margin-bottom:0.5em" />Add this user box to your Wikipedia User Page to show your support for the SDC forums: <div style="margin-left:1em">{{User:Will Pittenger/User Boxes/Space.com Account}}</div> </div>

 

[gunsandrockets]

"It seems to me that the storability issues with LH2 will make longer stays on the moon very difficult. The LSAM would have to return to earth in a short period of time, and I can't picture them leaving astronauts on the moon without an emergency ride home."<br /><br />You know I just realized something. Yes, passive liquid hydrogen storage is not going to work for prolonged stays on the moon, and some NASA scenarios contemplate stays as long as six months. But the original design LSAM isn't capable of stays longer than seven days regardless of the type of fuel the ascent stage uses. The LSAM only has enough consumables for a short stay, and much much more importantly the LSAM electrical power is from fuel cells which limits the endurance to the amount of fuel carried. So a switch from methane to hydrogen propellant in the ascent stage isn't really a temporary drawback after all.<br /><br />"LH2 may be available in situ though, so if they're willing to pay to develop that capability and deploy a reliquification scheme up there, they might be able to use it. The RL-10 does have some restart capability, so it may be a good place to start if one wanted a re-useable LSAM."<br /><br />Other than using the (assumed) ice at the lunar poles, there is another scheme for using hydrogen. The LUNOX plan from 1993 (search the forum for various threads on LUNOX) uses hydrogen carried from Earth, combined with oxygen derived from the lunar regolith to refuel a lightweight lunar lander. The same power used to produce lunar oxygen (most likely nuclear power) can also be used for active refrigeration of the liquid hydrogen stock sent from the Earth. Active refrigeration of liquid hydrogen is a technology directly applicable to reusable Nuclear Thermal Rocket tugs for manned missions to Mars.<br />

 

[digitalman2]

I remember a concept piece somewhere about having part of the outer shell of the lander fall away (actually, maybe there wasn't an outer shell covering the suits), having the suits attached to the remaining wall. The astronauts would enter the suit from the back. They would come back in a similar fashion. Since the suit is always outside the lander, very little dust can get inside the lander. <br /><br />It was unclear what sort of airlock mechanism would be used. I imagine getting back in the lander could be tricky since you would have to attach your 'back' to the airlock wall.

 

[gunsandrockets]

"Another solution to the height problem is to have a horizontal rather than vertical lander. For example this layout or this. The advantage of this configuration is that it allows payload to be increased without increasing the height of the spacecraft on the lunar surface, simply by making the spacecraft longer and adding tankage. The only constraint to growth is the overall booster height which will still have to fit the VAB."<br /><br />Because of the layout of the LSAM ascent-stage, my scheme for replacing the LSAM descent-stage with a lunar-crasher stage transforms the LSAM ascent-stage into a 'horizontal lander'. But I get your meaning in any case.<br /><br />You show two different horizontal-lander configurations, and each makes perfect sense in the context of which those landers originated. The only problem is those landers don't fit into the context of the ESAS 1.5-launch lunar-architecture. That's why I proposed the lunar-crasher stage, because it does fit into the ESAS plan.<br /><br />With the ESAS plan, the CEV is docked in line with the LSAM and the EDS for the TLI burn. The center of gravity of the three-vehicle stack is in line with the center of thrust. Then after the EDS is discarded, the LSAM descent-stage conducts the LOC burn for the two-vehicle stack. Once again the stack's center of gravity is lined up with the thrust line.<br /><br />The problem with a very large horizontal-lander is how does it fit into the HLV launch shroud, while still having engines in line for the LOC burn and in line for the lunar landing? I only see two ways around that problem. The first way is redocking the CEV to the Lander, after the TLI burn and before the LOC burn, which is a little clumsy operationally and adds extra weight for the secondary docking port. The second way around the problem is a second set of engines on the Lander offset by 90 degrees, a sort of SPACE: 1999 Eagle-spacecraft configuration which gives rise to other issues which deserve a closer look

 

[gunsandrockets]

"* Do you have a drawing of a hybrid lander like your horizontal lander images?"<br /><br />Are you asking me? I didn't paste any links to horizontal lander images, and I don't know what you mean by 'hybrid lander'. I'm happy enough though to describe my idea of a modified LSAM which uses a lunar-crasher stage in place of the descent-stage.<br /><br />Start with a closer look at the current idea for the LSAM...<br /><br />http://images.spaceref.com/news/2005/nas.esas.21.l.jpg<br /><br />...the ascent-stage crew cabin is a cylindrical structure 3 meters wide and 5 meters long. The very bulky descent-stage is also used for the Lunar Orbit Capture burn which places the CEV + LSAM stack into orbit around the moon.<br /><br />The LSAM descent-stage carries in addition to the liquid-hydrogen and liquid-oxygen for the engines, consumables for lunar surface ops, fuel cells for lunar surface power, landing gear, about a tonne of cargo and four new-design engines based on the RL-10 15,000 lb thrust rocket engine. My crasher stage would be a very simple, roughly spherical in shape, that would only carry propellant and a single RL-10b rocket engine, an engine which is already in service, has a thrust of 25,000 lb and an ISP of 465 seconds. This simple crasher-stage could not only be used with lunar-missions but also serve as a multi-purpose stage for other jobs much as the Centaur upper stage is used today.<br /><br />The ESAS lunar-stack will mass about 55 metric tons, compared to the original Apollo lunar-stack of 45 metric tons. The Apollo used a 22,000 lb thrust engine on the Service Module to conduct the Lunar Orbit Capture burn. The only reason I can see for 60,000 pounds of thrust on the LSAM descent stage has to due with redundancy of the engines for the lunar landing phase, not because that much thrust is needed for the LOC phase. So a single RL-10b should be plenty for LOC, plus have a hi

 

[willpittenger]

Such a design would not be successful in keeping dust out. You need an opening without a vacuum to let the astronaut through. Furthermore, unless you through the module's air outside when they leave (like they did with Apollo), you need a door for each suit.<br /><br />Once in space a cover over the suits is not required except for micrometeorite protection. <div class="Discussion_UserSignature"> <hr style="margin-top:0.5em;margin-bottom:0.5em" />Will Pittenger<hr style="margin-top:0.5em;margin-bottom:0.5em" />Add this user box to your Wikipedia User Page to show your support for the SDC forums: <div style="margin-left:1em">{{User:Will Pittenger/User Boxes/Space.com Account}}</div> </div>

 

[willpittenger]

You bring up some good points about horizontal landers. Some might be solved, though, by installing the lander into the shroud sideways. Let it remain like that until it separates. We are talking about micro-gravity. So astronauts should not have problems with the layout. <div class="Discussion_UserSignature"> <hr style="margin-top:0.5em;margin-bottom:0.5em" />Will Pittenger<hr style="margin-top:0.5em;margin-bottom:0.5em" />Add this user box to your Wikipedia User Page to show your support for the SDC forums: <div style="margin-left:1em">{{User:Will Pittenger/User Boxes/Space.com Account}}</div> </div>

 

[willpittenger]

Sorry. I thought I was replying to another post. I can't find it now. It mentioned hybrid landers.<br /><br />New comments that I want to add to my earlier post in this branch:<br /><br />* Assume the lander will not support any long duration stays. The first stop might be only to checkout the stuff that landed independently and then leave. That would include other landers and a long duration stay facility. Later trips would rely on the base -- which would be left on the moon and reused. Cargo landers (see next item) would send down supplies. Once the astronauts have moved out, the lander would shut down except for some heat and computers. The computers would be up in case the astronauts or Houston need to talk to the lander. For the most part, it would just go to sleep until needed.<br /><br />* I think there should be a variant of the main lander for cargo only. Assume if an astronaut absolutely had to ride it to orbit, he or she would wear a spacesuit for the trip and be exposed to vacuum. It would promise great views of the trip.<br /><br />Together, I think my ideas would reduce the size of the lander some. <div class="Discussion_UserSignature"> <hr style="margin-top:0.5em;margin-bottom:0.5em" />Will Pittenger<hr style="margin-top:0.5em;margin-bottom:0.5em" />Add this user box to your Wikipedia User Page to show your support for the SDC forums: <div style="margin-left:1em">{{User:Will Pittenger/User Boxes/Space.com Account}}</div> </div>

 

[JonClarke]

Have I seen the suits afterwards? Not personally (they were left on the LM AFAIR), but I have seen the photos, spoken to one person who wore one, and read the post mission reports. They did get very grubby, that's for sure!<br /><br />I don't know of any EVAs that were cancelled when on the Moon. the crew that streaked into the CM was Apollo 12, whether they were exceptionally grubby or if the CM pilot (Dick Gordon ) was just fussy, I don't know.<br /><br />The problems with fines can't be eliminated but they can be minimised by some very simple design changes and operational procedures. No stick outer layers to suits (the Apollo suits were fabric, ideal for trapping ground-in dirt), disposable dust covers, electric brushes to rub suits down while the astronauts stand on a grating before entering the airlock. Vaccuming the suit exteriors and the airlock after pressurisation but before entering the main part of the spacecraft. High tech solutions - magnetic bushing, elecxtrostatic replusion might be worth considering as well. <br /><br />Bearings that get exposed to dust should be eliminataed where possible. Tolerances of moving parts that are exposed to dust should be made so tight that dust does not get in, or designed so that the dust falls out again. <br /><br />Dust is an issue, but I don't see it as an unsolvable one. We have lots of experience in living and working in very dusty environments on earth. Not all the experience can be transferred to the Moon, but some of it will. Some lessons will need to be learned as we go, which is why there should not be 6-month lunar stays up front. <br /><br />I suspect that there is a cultural issue here. Astrnuatical engineers are not experienced in dusty environments and are used to working in clean rooms. They are not used to dirty dust envornments on planetary surfaces. That's going to have to change. There may be a degree of self interest as well, if you are lookinbg at getting funding for dust research you <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[JonClarke]

You are thinking of "suit ports". It is a great idea, and has also been trialed at Ames as a way of getting people in and out of areas contaminated by radiation, chemicals, or biological agents. One study investiagtes the use of suit ports in connection with pressurised Mars rovers.<br /><br />The main issue I see is that over the longer term the suits will need to come inside for maintainence. Youw ill also need a back up airlock anyway, in the event of emergencies. But it is a great idea for short missions - a days to a few weeks perhaps. Also for LEO. On the Moon and a space station you would need some sort of unpressurised vestibule to protect the suits from micrometeorites, space debris, UV, and atomic gases of course.<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[j05h]

I agree that the dust/fines issues can be solved, but we are in no way ready for dealing with on-the-ground work and research on Luna. I'm glad that you don't brush off the issue. Luckily, they aren't talking about starting with 6 month tours. <br /><br />I quoted Harrison Schmidt earlier, not "the media". It came from a Wired article, but I can probably find a similiar quote in the Heavens and the Earth if you insist. People have been discussing/troubleshooting lunar dust issues from day 1.<br /><br />Back to original topic: the major flaw with the proposed LSAM is the same as most upper stages: reusability. Not even reuse as a thrust-providing device, but reuse in turning them into storage, habs, tankfarms or anything else. <br /><br />Josh <div class="Discussion_UserSignature"> <div align="center"><em>We need a first generation of pioneers.</em><br /></div> </div>

 

[j05h]

anvel- interesting suggestion, similiar to Phil Bono's assisted SSTOs. It would indeed put the crew closer to the ground. I'm not sure it would need drop tanks. An option would be to build a LEO-Luna-LEO craft that can make many trips, it would aerobrake to meet a capsule return craft at a station. The crew could live in the craft or meet up with robot-delivered Habs. This also gives us a first step to a Mars transfer vehicle and would allow rapid surface-surface (hopper) access. <br /><br />One reason the current LSAM is the way it is because that "big Apollo" craft is a pre-existing design from a decade or so ago. Check out the "habitat" module:<br /><br />http://www.abo.fi/~mlindroo/Station/Slides/sld051f.htm<br /><br />While these designs are the most-obvious solutions, it looks like they just put the capsule in orbit, made the Hab bigger and added an engine. From viewgraph to viewgraph, they can just keep recycling. Some of the trade studies last year were really innovative, instead the presentations NASA gives on VSE look like they ignore that advice. SpaceHab's solution could have been done using current EELVs.<br /><br />I don't want to sound negative to VSE, but I think the next people on the moon are going to be private adventurers in a hacked Soyuz setup. <br /><br />Josh <div class="Discussion_UserSignature"> <div align="center"><em>We need a first generation of pioneers.</em><br /></div> </div>

 

[josh_simonson]

The plans for a lunar base involve a power module and habitation and logistics modules. But unless they provide hydrogen reliquification they will be unable to keep a LSAM on site to evacuate in an emergency, dispite having plenty of food and power.<br /><br />Griffin has indicated he'd like to develop a LEO fuel depot that reliquifies LH2 and LO2, so perhaps he sees the move to LH2 as a way to force the research on in-situ reliquification to be completed and deployed into a working system.<br /><br />Consider the HLV, in it's current design, it burns half the second stage fuel to get to LEO, then the other half is used for TLI. If a fuel depot were in LEO, the HLV could burn all it's stage 2 fuel on the way to LEO or launch half empty, then completely refill the second stage before the earth departure burn. Doubling the fuel will double the available mass to the moon, and using the full second stage burn to get to LEO will improve the non-fuel mass to LEO considerably as well. <br /><br /><br /> />"It seems to me that the storability issues with LH2 will make longer stays on the moon very difficult. The LSAM would have to return to earth in a short period of time, and I can't picture them leaving astronauts on the moon without an emergency ride home." <br /><br /> />You know I just realized something. Yes, passive liquid hydrogen storage is not going to work for prolonged stays on the moon, and some NASA scenarios contemplate stays as long as six months. But the original design LSAM isn't capable of stays longer than seven days regardless of the type of fuel the ascent stage uses. The LSAM only has enough consumables for a short stay, and much much more importantly the LSAM electrical power is from fuel cells which limits the endurance to the amount of fuel carried. So a switch from methane to hydrogen propellant in the ascent stage isn't really a temporary drawback after all. <br />

 

[gunsandrockets]

"Why have two seperable components complete with two seperate engines? Use the drop tank concept that military aircraft use. Replace the ascent stage of the LSAM with the fuel tanks required for descent...Crew/cargo plus fuel for ascent and the one engine are all housed within the lower portion of the LSAM. This would seem to address the CG issues, and put the crew/cargo nearer to the lunar surface. "<br /><br />That is a practical idea and would provide the benefits you mention but there are some drawbacks to your Lander.<br /><br />First off it would require a long pressurized docking tunnel between the cabin of the Lander and the CEV (a minor problem). Second, it would require development of a new highly-throttleable hydrogen engine (no worse a problem than NASA plans). Third, the size of the engine bell would require fairly spidery landing gear for ground clearance (no worse a problem than NASA plans). Finally, the Lander would depend on a single-engine with no redundancy for crew survival (a tiny bit worse problem than the NASA plan, as the NASA single ascent-engine is more protected from damage during landing than yours).<br /><br />My idea for a twin-engined Lander has several key benefits compared to your single-engine Lander. By placing the engine bells at the side, the height of the Lander is reduced compared to placing a single-engine underneath. Cross tank fed twin engines provide an engine out capability. And the simple pressure-fed hypergolic-propellant engines are very very reliable compared to a pump-fed cryogenic-propellant engine.<br /><br />Your single-engine Lander concept should be more mass efficient than mine though, benefitting from fewer engines and the higher ISP of using LOX/LH2 for all phases of Lander operations.<br /> <br />"These [descent fuel tanks] are removable, of course once the craft has landed."<br /><br />I think a slightly different procedure is called for. The drop tanks should be discarded after the bulk of the descent burn, whil

 

[gunsandrockets]

"If a fuel depot were in LEO, the HLV could burn all it's stage 2 fuel on the way to LEO or launch half empty, then completely refill the second stage before the earth departure burn."<br /><br />Heck if an LEO fuel depot were available forget about HLV, as then mere MLV would have enough payload to serve the NASA planned lunar flight architecture.