the Earth Return Vehicle of Zubrin's Mars Direct plan

[gunsandrockets]

Many space buffs are familiar with Robert Zubrin's plan for manned travel to Mars which is called Mars Direct. If you are not familiar I recommend reading Zubrin's book, "The Case for Mars", which promotes the Mars Direct plan.<br /><br />As bold and ambitious as the Mars Direct plan is, I have thought for some time the most difficult aspect of the plan is the design of the Earth Return Vehicle (ERV). The Mars Society even held a public competition to design the ERV a few years ago.<br /><br />[Mars Society Announces Kepler Design Contest- The Mars Society - Jan.11.03] <br /><br />[The Society just announced that it will sponsor an annual contest to design spaceships that would be involved in Mars missions. The Kepler Design Contest this year will be aimed at the] <br /><br /><br />["design of an Earth Return Vehicle (ERV) for use in piloted Mars missions. In the contest, participants will propose their design for the ERV and have it judged based on set criteria and mission requirements."]<br /><br />[For its first year's contest, the Kepler Prize will be given to the team that presents the best design of an Earth Return Vehicle (ERV) for use in piloted Mars missions. In the contest, participants will propose their design for the ERV and have it judged based on set criteria and mission requirements.]<br /><br />[The ERV is a critical piece of the Mars Direct mission plan, (for details see, The Case for Mars, by Zubrin and Wagner, and/or http://www.nw.net/mars/ ) The ERV flies to Mars autonomously, landing on the surface and using an on-board supply of hydrogen to create fuel, oxygen, and water for extended operations when the crew arrives later. The same fuel and oxygen are used to propel the crew (and the ERV) back to Earth when their mission is complete.] <br /><br /><br />[The winning team will receive a trophy and two slots on the MRDS. Aimed particularly at school projects, the program will start formally at the next Mars

 

[owenander]

I believe Mars Direct would be more then achievable, but I feel like we need to solve the bottleneck issue before anything. All resources possible need to go towards decreasing the amount of energy spent simply getting into orbit. Once we have a spacecraft that can launch, travel, and land on Earth in an efficient means then I believe space travel will be the biggest thing to ever happen. Until then it will continue at a snails pace.

 

[gunsandrockets]

Here are a few baseline facts for Zubrin's ERV<br /><br />Launch via a single Saturn V class rocket<br /><br />46.2 tonnes sent towards Mars<br /><br />aerocapture at Mars<br /><br />28.6 tonnes landed on the Martian surface<br /><br />of that 28.6, 10.8 tonnes are devoted to the nuclear reactor powered rocket propellant production system, and of that 10.8, 6.3 tonnes are the hydrogen feedstock<br /><br />It seems the liftoff mass of the ERV when returning to Earth is 100.2 tonnes, including the crew of 4 people.<br /><br />The ERV has two ascent stages, dry mass 4.5 tonnes total (not each), using liquid propellant rocket engines (LOX/CH4) with an ISP of 380 seconds. This is supposed to be enough to send the 11.5 tonne crew cabin on a sixth month long return voyage to Earth.<br /><br />The cabin has a 1.8 tonne aeroshell for aerocapture at Earth.<br /><br />That is about as detailed information on the ERV as I have available to me at this time. It's fairly skeletal! It lacks some vital details such as -- does the cabin aerocapture into LEO? or does it have parachutes for a direct landing on Earth?<br /><br />The mass margins listed seem on the thin side. In particular for the ERV cabin. Zubrin gets an awful lot of performance out of a slight 11.5 tonnes: 4 crew, 6 months of life support, a 5 kWe solar power system, and a heatshield adequate for Earth return from Mars. For example compare the 11.5 tonne cabin of the ERV to the 8.5 tonne Crew Module of the Orion CEV spacecraft.

 

[gunsandrockets]

"I believe Mars Direct would be more then achievable, but I feel like we need to solve the bottleneck issue before anything."<br /><br />Okay, you seem to be saying that Mars Direct is a misdirection of effort since Mars Direct is based on using two launches of a Saturn V class rocket such as the Ares V. Using heavy lift launch vehicles is at the heart of Zubrin's plan.<br /><br />While I appreciate the critique (and even agree with it), it's fairly off topic for this thread. There are many many other threads addressing the cheap access to space topic.<br /><br />So, do you have any ideas on how to design the ERV?

 

[bpfeifer]

It seams to me, that you could easily include an inflatable module on the ERV that isn't expanded until the crew is on the way home. Think of it like the orbital module on the Soyuz. It'd add substantial living space for the return journey, and you can just get rid of it before you start aerobreaking. <div class="Discussion_UserSignature"> Brian J. Pfeifer http://sabletower.wordpress.com<br /> The Dogsoldier Codex http://www.lulu.com/sabletower<br /> </div>

 

[gunsandrockets]

"It seems to me, that you could easily include an inflatable module on the ERV that isn't expanded until the crew is on the way home."<br /><br />Yes! That's the kind of response I'm looking for.<br /><br />"Think of it like the orbital module on the Soyuz. It'd add substantial living space for the return journey, and you can just get rid of it before you start aerobreaking."<br /><br />Something like an inflatable 'transhab' module or Bigelow 'sundancer' right? That's a good idea. That's one way to maximize usefulness out of the limited mass of the ERV crew cabin. What size/mass module did you have in mind? I think even the smallish sundancer is around 10 tonnes. <br /><br />And what size Earth reentry module did you have in mind? If your goal is to minimize reentry vehicle mass, Soyuz style, then your reentry module is probably going to make a direct landing on Earth. (And if so, sea landing or ground landing or both?) If your Earth aerocapture module was going to recover into LEO instead, it would need a docking port plus a longer lived power and life support system so the module could wait in LEO for an Earth launched recovery spacecraft to come up and dock with it. <br /><br />And how would you package your inflatable habitat module? Where in the ERV does it go? How do you imagine the different modules of the ERV would be arranged with the addition of the inflatable module?<br /><br />And I should point out that even though I think your inflatable module is a good idea, Zubrin would probably frown over it. Because if the ERV uses an inflatable module when returning to Earth, that means the ERV probably doesn't have much useful living space available when on the surface of Mars. And Zubrin envisioned his ERV as a safe haven the crew could retreat to if anything compromised the life support system of the crew's primary habitat, the lab module which the crew lives in for most of the Mars mission.<br /><br />And this brings up a related issue I find difficult to addre

 

[j05h]

Those are some pretty exacting numbers for an undeveloped mars architecture. I understand why they would put such limits in for a school project, but as a more general exercise it is quite limiting. Instead of asking for a boat that gets you back from Mars, they've specified the wood, construction method and shape. It just seems constraining for a vehicle that is 20-30 years from construction. <br /><br />What if you can make the ERV 10x safer and more comfortable with a slight, out-of-bounds change? Will the Mars society accept that. Other reasonable issues include exactly what ISRU gear is included. You don't really need that 6 tons of hydrogen if you land on Elysium or other H2O-rich area, for example. A water harvesting/condenser/drill/doohickey might make more sense. Also, LEO insertion instead of direct descent might make sense (again, depending on constraints). What about aerobraking ballutes, or reusable habitats (non-cycler, stored in LEO)?? <br /><br />Obviously these kinds of architectural changes are beyond a school project but the Kepler contest could include a second level. A lot of system architecture work has been done since Zubrin wrote Case for Mars. Jon Goff's recent writing is one example, another is the software developed at spacelogistics.mit.edu. Seeing what could come out of a general revising of Mars Direct might be beneficial.<br /><br />josh <div class="Discussion_UserSignature"> <div align="center"><em>We need a first generation of pioneers.</em><br /></div> </div>

 

[gunsandrockets]

"A lot of system architecture work has been done since Zubrin wrote Case for Mars...Seeing what could come out of a general revising of Mars Direct might be beneficial." <br /><br />I agree. And such talk is appropriate to this thread, though I would like it to focus on how those architecture changes would change the design of the ERV.<br /><br />"Those are some pretty exacting numbers for an undeveloped mars architecture."<br /><br />The numbers I quoted were from Zubrin's book, "The Case for Mars". I posted those numbers as a baseline for those interested in this thread but who didn't know about or have access to that data.<br /><br />I don't know if the Kepler Prize was based on those numbers or if the prize was only limited by the basic architecture. The winning design is available on a CD-ROM which comes with the book, "On to Mars 2", published by apogee books. But I don't have that book or a working CD-ROM drive at the moment!<br /><br />The fellow that won the Kepler Prize is making comments over at nasaspaceflight.com, including the thread I posted a link to and he has his own blog (the address of which I have misplaced for the moment). It would be cool if he could find this thread and share his ideas. <br /><br />"What if you can make the ERV 10x safer and more comfortable with a slight, out-of-bounds change? Will the Mars society accept that."<br /><br />Well since Zubrin is president of the Mars Society and a rather prickly personality, I doubt it. But so what. We are not so constrained, so let the creativity flow!<br /><br />Look at this for example...<br /><br />Mars For Less<br /><br />...which takes the Mars Direct plan and breaks it down so that medium lift Proton class launch vehicles can do the mission instead of Saturn V class HLV.<br /><br /><br />

 

[gunsandrockets]

"Other reasonable issues include exactly what ISRU gear is included. You don't really need that 6 tons of hydrogen if you land on Elysium or other H2O-rich area, for example. A water harvesting/condenser/drill/doohickey might make more sense."<br /><br />Yes, that's the spirit! Design of the ISRU is a key factor in the ERV.<br /><br />For those who can't follow this acronym heavy discussion here are some definitions...<br /><br />1) ISRU = in-situ resource utilization, or the use of resources located beyond Earth to support the space mission. This is a broad category including ISPP, making air, building construction, etc.<br /><br />2) ISPP = in-situ propellant production, or the production of rocket propellant from resources located beyond Earth<br /><br />Zubrin deserves full credit for popularizing ISRU and making it so key to his Mars architecture.<br /><br />As for the ERV, even Zubrin realizes his initial ISRU design has limitations and he has explored ways to minimize the reliance on the hydrogen feedstock. You have brought up the idea of collecting polar ice or drilling for ice, both good ideas. Other people have approaced the issue too, as a quick google search of 'ISPP Mars' will reveal!<br /><br />If you go with your Mars Polar Rocket idea (which is how I will refer to it!) several implications are apparent aside from no longer having to carry hydrogen feedstock from Earth. General power requirements are reduced because it takes less power to crack water to obtain oxygen than it does to crack carbon dioxide (collected from the air). The methane/oxygen production process outlined by Zubrin required cracking extra carbon dioxide to obtain the right balance of oxygen.<br /><br />Another even more interesting possibility is using straight lox + hydrogen rocket propellant. Even if you only used LOX/LH2 for the second stage of the ERV, the design margins for a two-stage ERV might be a lot easier to manage. And if you don't have to bring hydrogen feedstock from Earth,

 

[gunsandrockets]

"Also, LEO insertion instead of direct descent might make sense (again, depending on constraints). What about aerobraking ballutes, or reusable habitats (non-cycler, stored in LEO)??"<br /><br />You first! Why don't you talk about the tradeoffs? Or your favorite choice? <br />

 

[bpfeifer]

All right, you asked for it… I hadn’t really thought out a full plan, but I’ll gladly answer each question as you pose them. Really, I prefer a full-blown interplanetary transport vehicle (I detailed one on my blog) to the Direct plan, but this is still an interesting and viable method of doing the job.<br /><br />Size and nature of the inflatable module: sure, make it like transhab or sundancer. It should be at least 10 tonnes, and comprises the primary living space for the return voyage. The idea is to limit the hard vehicle to something small.<br /><br />Size and nature of hard vehicle: This craft is as small as is reasonable. It is essentially a capsule bit enough for the astronauts, supplies, engines, etc. I’d stick the inflatable on the nose, and connect the two by a hatch. This keeps the center of mass over the engines. Once you’ve ditched the inflatable, you could use the hatch as a docking port for earth orbit rendezvous. I don’t know which is better, rendezvous, or direct decent, but if you don’t include a docking port, you will be sorry.<br /><br />Because the Martian atmosphere is much thinner, the vehicle doesn’t need to be quite as aerodynamic for launch. This allows you to build a squatter design, and makes it easier for the astronauts to enter the vehicle. Maybe a fat pyramid would work, or a central sphere surrounded by 3-6 globular engine modules. I’ll also add an inflatable airlock mounted outside for surface operations, but left behind before launch.<br /><br />Safe haven concerns: Yes, I’d be nice to have a safe haven with a comfortable living space, but plenty of sailors survived in small open boats (plenty also died, but that’s a separate issue). From a human factors point of view, in emergency situations, we can survive in pretty awful conditions. If things go wrong, I’ll let my astronauts live in awful conditions, as long as they can survive. <br /> <div class="Discussion_UserSignature"> Brian J. Pfeifer http://sabletower.wordpress.com<br /> The Dogsoldier Codex http://www.lulu.com/sabletower<br /> </div>

 

[j05h]

Guns- I'm time-pressed the next couple of weeks (oh, for this topic in February...) but I'll dig in some. It's been years since I read Case for Mars, my ideas are based on that, Energia's Mars plans, Jon Goff's concepts and some common sense. <br /><br />My primary assumption is to maintain the high ground. "Martians" will commute to and from the surface regularly. <br /><br />The ideal system creates the first, extensible segment of an Earth-Mars transit system. It would use ISRU that does not require hydrogen from Earth, whether that is harvesting local ice, atmosphere, using methane, silane, propane, whatever can be cracked locally. My prefered system would involve a pilot plant on Mars and another on Phobos/Deimos. <br /><br />Instead of an Earth-Return-Vehicle, the Mars-orbit segment, Earth return and EDL would be handled by separate vehicles. The only non-reusable segment is the capsule(s) that bring crew back to Earth from LEO, and if you baseline Dragons, even that is reusable. <br /><br />The Mars ascender could be simple, methane or Lox/H powered. It could be both "hopper" and ascender, but that's further along. Energia proposed a Soyuz-derived ascender, whatever works. <br /><br />The Earth-Mars and Mars-Earth vehicle could be based on Energia's solar-electric MarsPost or on a Sundancer/Nautilus/ballute. Other options for the in-space transit include a singular capsule (the ERV) and a large biconic. If we are going to build heavy lift anyway, I'd recommend a 50-100t "ship" that is launched empty and fuelled at each end of the trip, or the Bigelow stack for same. Properly, on arrival at Mars, the crew would use an in-place ascender to land and use it to get back to the orbiting mothership. <br /><br />Options would include using the same vehicles for multiple purposes, ie, the Hopper/Ascender/ERV is capable of travelling anywhere on or around Mars, and returning to Earth. THis is an extension of Mars Direct, instead of a replacement. The other ideas are more of a rep <div class="Discussion_UserSignature"> <div align="center"><em>We need a first generation of pioneers.</em><br /></div> </div>

 

[gunsandrockets]

"Guns- I'm time-pressed the next couple of weeks (oh, for this topic in February...) but I'll dig in some."<br /><br />I appreciate the attention and effort.<br /><br />"I really like Mars Direct, and NASA's DRM. But both of them are about flags-and-footprints."<br /><br />Heh. Zubrin would probably throttle you for saying that about his beloved architecture!<br /><br />I take a slightly different viewpoint on the various manned Mars mission architectures, focusing more on LOC-risk/cost levels than sustainability. I consider the Mars Direct plan a medium risk mission and the NASA NTR plan a low risk mission. For high risk, check out some of the wild plans proposed for flyby-rendezvous!<br /><br />"What we need to look toward is building a system that can keep people and supplies moving to Mars and volatiles coming back to LEO."<br /><br />With this thread I'm trying to avoid detouring into debating the ideal architecture for going to Mars. There are plenty of other threads discussing just that.<br /><br />"Options would include using the same vehicles for multiple purposes, ie, the Hopper/Ascender/ERV is capable of travelling anywhere on or around Mars, and returning to Earth. This is an extension of Mars Direct, instead of a replacement. The other ideas are more of a replacement."<br /><br />See, you can get into the nitty gritty of an ERV design without having to endorse Mars Direct! And I really want this thread to focus on the Mars Direct style ERV.<br /><br />The ERV is the heart of Mars Direct. And a fascinating engineering challenge all by itself. Having a single spacecraft do everything the ERV does in one package is incredible.<br /><br />The ERV has to fit into a launch shroud. It has to be light enough so the launch vehicle can send it on a ten month+ trip to Mars. The ERV has to have a heatshield, landing gear, maybe a parachute and landing rockets for landing on Mars (without tipping over!). The ERV has to include the ISPP system for manufacture rocket fuel for

 

[gunsandrockets]

"Safe haven concerns: Yes, I’d be nice to have a safe haven with a comfortable living space, but plenty of sailors survived in small open boats (plenty also died, but that’s a separate issue). From a human factors point of view, in emergency situations, we can survive in pretty awful conditions. If things go wrong, I’ll let my astronauts live in awful conditions, as long as they can survive."<br /><br />I agree. <br /><br />Making the ERV work period is so tough I think adding the role of a Mars surface safe-haven could be asking too much. I think Zubrin's salesmanship promoting the Mars Direct plan got the better of him when he suggested the ERV as a Mars safe haven. <br /><br />But just for the sake of arguement, what would be the best method of adding a safe-haven function? You have already suggested an inflatable structure for the ERV cabin to save mass. Perhaps an additional inflatable structure can be placed on the Mars surface that could function as a safe-haven?<br /><br />The Zubrin ERV plan already includes placing on Mars tons of equipment: 3.5 tonne nuclear power system; 0.5 tonne truck; 12 tonnes of water, oxygen and methane and associated tankage to hold it. Why not a small inflatable pressurized habitation module too? <br />

 

[gunsandrockets]

"Size and nature of the inflatable module: sure, make it like transhab or sundancer. It should be at least 10 tonnes, and comprises the primary living space for the return voyage. The idea is to limit the hard vehicle to something small."<br /><br />Here is information I have collected on the Bigelow Sundancer inflatable habitat...<br /><br />[Sundancer, 3 man module, 180 cubic meters volume, 10 metric tons mass, first launch 2010.]<br /><br />[The entrepreneurial firm’s habitat plans then lead to Sundancer — a module that will provide 180 cubic meters of habitable space and come fully equipped with life-support systems, attitude control, on-orbit maneuverability, as well as reboost and deorbit capability. This larger module — sporting a trio of windows — could support a three-person crew and be on orbit in the second half of 2010, Bigelow said.]<br /><br />Sounds like we are reducing the crew size of the ERV from 4 down to 3 people! But that's okay, the mass margins of the Zubrin ERV seem too optimistic to me. Reducing crew size is the easiest way to make up the difference.<br /><br /><br />"Size and nature of hard vehicle: This craft is as small as is reasonable. It is essentially a capsule bit enough for the astronauts, supplies, engines, etc. I’d stick the inflatable on the nose, and connect the two by a hatch. This keeps the center of mass over the engines. Once you’ve ditched the inflatable, you could use the hatch as a docking port for earth orbit rendezvous. I don’t know which is better, rendezvous, or direct decent, but if you don’t include a docking port, you will be sorry."<br /><br />The hard vehicle you describe is effectively a Soyuz spacecraft!<br /><br />I suppose there are two ways to go about the division of equipment between the hard vehicle vs the inflatable. One could add an inflatable module to a Soyuz style vehicle, or one could add a Soyuz style reentry capsule to a Bigelow Sundancer inflatable.<br /><br />Since I only have numbers for the latter, we are n

 

[gunsandrockets]

"Because the Martian atmosphere is much thinner, the vehicle doesn’t need to be quite as aerodynamic for launch. This allows you to build a squatter design, and makes it easier for the astronauts to enter the vehicle. Maybe a fat pyramid would work, or a central sphere surrounded by 3-6 globular engine modules. I’ll also add an inflatable airlock mounted outside for surface operations, but left behind before launch."<br /><br />Yes the shape of the ERV is key to easing access to the Martian surface. Not only does the crew need to get into the ERV, the ERV also (defaulting to the Zubrin plan) drops off tons of equipment onto the Martian surface. Making the ERV more squat could help.<br /><br />A squat ERV also makes landing the ERV easier. Keeping the center of gravity of the ERV low and having a wider stance for the landing gear helps to prevent the ERV from tipping over. Even though the landing spot for an ERV no doubt will be carefully pre-surveyed, the ERV should still have some capability to cope with uneven terrain.<br /><br />The kicker to all this discussion though is that the ERV still has to fit into a launch shroud when fired from Earth, and still has to have a shape with heatshield configuration adequate to survive aerocapture at Mars! So how do you reconcile a squat shape on the Martian surface with the Earth launch requirements and the Mars atmosphere entry requirements?<br /><br />

 

[bpfeifer]

"Since I only have numbers for the latter, we are now looking at a total cabin mass of 13 tonnes: 3 tonnes for the RV, and 10 tonnes for the inflatable hab. That's only 1.5 tonnes more than the numbers for Zubrin's ERV cabin, but with a crew of three instead of a crew of four. Not bad! "<br /><br />Are those numbers for the whole soyuz, or just the re-entry module? That's all I'm taking. The inflatable replaces the orbital module, and the globular propulsion modules replace the propulsion module. <div class="Discussion_UserSignature"> Brian J. Pfeifer http://sabletower.wordpress.com<br /> The Dogsoldier Codex http://www.lulu.com/sabletower<br /> </div>

 

[gunsandrockets]

"Are those numbers for the whole soyuz, or just the re-entry module?"<br /><br />10 tonne Sundancer + 3 tonne Soyuz re-entry module = 13 tonnes<br /><br />

 

[docm]

Bigelow could end up selling a lot of his modules if ITAR doesn't get in the way <img src="/images/icons/tongue.gif" /> <div class="Discussion_UserSignature"> </div>

 

[bpfeifer]

"The kicker to all this discussion though is that the ERV still has to fit into a launch shroud when fired from Earth, and still has to have a shape with heatshield configuration adequate to survive aerocapture at Mars! So how do you reconcile a squat shape on the Martian surface with the Earth launch requirements and the Mars atmosphere entry requirements? "<br /><br />As you say, this is the hard question. The Soyuz is listed as having either a 2.2 or 2.7 meter diameter. If we have access to an Ares V class launcher, we'll have 10 meter fairing. That's more than enough room for both the capsule and its surrounding engine modules.<br /><br />If we're limited to a heavy lift varient of Atlas 5, Delta IV, or Falcon 9, then we're limited to a 5 meter diameter fairing. This poses something of a challenge. At this point, to limit the diameter of the overal ERV, we'll have to make the engine modules taller and narrower. Now the ERV looks truly silly. Start with a spherical crew cabin. On top of that stick your inflatable module, like some kind of odd nose sticking up. Then surround it with several cylindrical engin/fuel pods that are taller than crew cabin. Then again, the Apollo LM looked silly too. <br /> <div class="Discussion_UserSignature"> Brian J. Pfeifer http://sabletower.wordpress.com<br /> The Dogsoldier Codex http://www.lulu.com/sabletower<br /> </div>

 

[gunsandrockets]

"...the hard question."<br /><br />Yep.<br /><br />"If we have access to an Ares V class launcher, we'll have 10 meter fairing...If we're limited to a heavy lift varient of Atlas 5, Delta IV, or Falcon 9, then we're limited to a 5 meter diameter fairing."<br /><br />Hmm... Well there was that one scheme from marsdrive.com to chop Mars Direct into bite sized chunks that could squeeze into an EELV, but I don't think we should limit our discussion that way. The ERV is tough enough just to fit inside an HLV class launcher as Zubrin intended.<br /><br />In that regard the most likely payload shroud limitation is the size of the Ares V third stage, which we know better as the EDS or Earth Departure Stage. I believe that stage is the same diameter as the Shuttle external tank, or 8.4 meters diameter. A larger diameter hammerhead-shaped shroud for the EDS could always be introduced, but at the cost of increased drag and reduced payload to orbit. So let's say the practical limit is 8.4 meters.<br /><br />"... The Soyuz is listed as having either a 2.2 or 2.7 meter diameter...more than enough room for both the capsule and its surrounding engine modules."<br /><br />I think it's useful to bring up the old 1967-era Mars Excursion Module (MEM) at this point. It was a Mars lander design based on the Apollo capsule shape. It had a mass of 50 tonnes and a diameter of 9 meters, with the ability to cope with sloping terrain up to 15 degrees. It was supposed to carry 4 men down to Mars from high Mars orbit and after a 30 day stay return to the same high orbit. The MEM carried it's own supply of rocket propellant for this purpose (no ISPP), interestingly enough the same liquid oxygen + liquid methane propellants Zubrin proposes for the ERV.<br /><br />As the ERV approaches Mars from Earth it will probably mass about as much as the MEM (recall the Zubrin calculation of 46 tonnes TMI). But the ERV will probably be even bulkier than a MEM since the ERV has to carry big empty fuel tanks down

 

[rocketman5000]

I had a couple of ideas as I was reading through the post, but most have been captured. The first was using a dual purpose aeroshell.<br /><br />The second would be if you have your engines/crew cabin at the bottom of the stack you could have a ladder attached to the side of the craft or the little indentations with spring hinged to mantain aerodynamics that many fighter jets have to assist cockpit egress. Lastly you'd want to ditch as much stuff on the surface as possible for your return. Much of this might be a given but I'll list it to spur thoughts. Have the propellant production plant capable of being dropped at the surface. Maybe have two smaller inflatable module so that one can be detached and left at the surface. When in Microgravity you probably don't need as much living space as you'd need on Martian surface. Leave your landing legs at the surface. Detach your accent from the ERV after your TEI burn. <br /><br />I would make your attitude thrusters capable of making extended burns for midcourse corrections. You have to carry them along anyhow. No need for a seperate engine. <br /><br />Do one of two things with your inflatable module. First jettison it before aerobraking back into a direct to earth decent. Or secondly you could maybe have it be reconfigurable to deploy into a ballute to reduce the mass of your heatsheild. <br /><br /><br />One final thought that kinda leave me pondering is this. I am not an expert on the Soyuz rocket system or how their spacecraft is fitted out. You have stated 3 tonnes for the Return to Earth Stage. This seems like it is a little heavy for what we need to do. <br /><br />We need to keep crew alive from the time you seperate from your inflatable habitation module to landing by,<br /><br />-providing oxygen for crew. I'd operate the Decent Module (DM) at a reduce atomospheric pressure<br /><br />-removing CO2, have oxygen pumped into mask to eliminate filters and other life supports systems. Use something similiar to

 

[scottb50]

Another idea is using a two stage descent vehicle. A thermally protected vehicle carries the lander through re-entry and releases it after heating concerns have ended. Engines then power the vehicle back into orbit for use on the next descent. The same lander would work on both the moon and Mars. <br /><br />The same idea could work just as easily from Earth orbit allowing a much simpler return vehicle. <div class="Discussion_UserSignature"> </div>

 

[gunsandrockets]

"Another idea is using a two stage descent vehicle. A thermally protected vehicle carries the lander through re-entry and releases it after heating concerns have ended. Engines then power the vehicle back into orbit for use on the next descent. The same lander would work on both the moon and Mars."<br /><br />Yes, some of the lunar lander configurations now being studied could be re-configured to permit the same lander to be used on Mars. The lunar landers which use so-called 'drop stages' to perform most of the delta V deceleration to land on the moon could use a heat-shield and parachute instead.<br /><br />But a lunar-lander or similar sized mars lander is a very different beast from the focus of this thread, a Mars Direct ERV. An ERV has to have enough performance to send the crew all the way back to Earth, sustain the crew for months, and provide an aerocapture method of stopping at Earth. Tall orders all.

 

[gunsandrockets]

It is the detailed work, as many of the items you just listed, that will make or break a Mars ERV. The mass margins of an ERV are so tough that every kilogram saved is vital. Discarding unneeded equipment and finding multiple-uses for the same equipment is a good technique for making the neccessary mass saving goals.