the Earth Return Vehicle of Zubrin's Mars Direct plan

gunsandrockets · Apr 9, 2007

[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.] Aha! I found again who it was that won the Kepler Prize for best design of an Earth Return Vehicle, he's Kent Nebergall. And I found the address for his blog too... http://earthreturn.blogspot.com ...though it looks like he hasn't updated it for over a year. I may just email him and invite him to join our discussion. I haven't seen his winning ERV design yet, but I imagine with that kind of effort he must have valuable insight. Knebergall@ameritech.net

gunsandrockets · Apr 10, 2007

I figured I would now throw another issue into the boiling ERV pot. What kind of rocket propulsion should the ERV use? I'll try to frame the issue... Just as the Earth Return Vehicle is the heart of the Mars Direct Plan, propulsion is the heart of the Earth Return Vehicle. The whole purpose of the ERV is to return a crew to Earth from Mars. To achieve this goal Zubrin proposed the ERV would land on Mars basically empty and manufacture it's own rocket propellant from the Martian atmosphere in combination with a small feedstock of liquid hydrogen. This process is powered by a 100 kilowatt electric power system, furnished by a portable nuclear reactor which the ERV deploys by a rover hundreds of meters away on the surface of Mars. The baseline Zubrin ERV propulsion plan is for a 100 tonne, two stage vehicle using oxygen and methane liquid propellant rocket engines. It's not very clear but it seems the Zubrin ERV uses the descent engines for the 1st stage ascent engines. At the very least the descent engines also burn liquid oxygen and liquid methane. Now the baseline Zubrin plan is all well and good, but can it be improved? Here are the basic questions... 1) Is there a better oxydizer than oxygen or a better fuel than methane that could be manufactured at Mars for the ERV? 2) Is there a better method than carrying 6 tonnes of hydrogen feedstock to support propellant production on Mars? 3) Is there a better power system than a portable nuclear reactor for supporting propellant production on Mars? 4) What is the best combination of rocket engines and stages to support the Earth to Mars mid-course flight, the descent to Mars surface, ascent from Mars surface and the return to Earth? What makes this really tough is that all four questions are inter-related. So the best overall answer may not be the same as the best answer for any one question. Here are some iss

scottb50 · Apr 10, 2007

1) Is there a better oxydizer than oxygen or a better fuel than methane that could be manufactured at Mars for the ERV?>> Oxidation is combining Oxygen with another element. I can't think of a better oxidizer than Oxygen. 2) Is there a better method than carrying 6 tonnes of hydrogen feedstock to support propellant production on Mars? />>> If you carry water you can produce both Hydrogen and water when you need it. Water is pretty stable and easy to transport and all you need is electrical power to break it down. 3) Is there a better power system than a portable nuclear reactor for supporting propellant production on Mars? />>> See 2) You could carry a lot of water for the weight of a reactor and if you repeatedly recycled it a fixed amount would last indefinitely. Carry more and convert it to propellant, in Mars orbit, and you could have the ability to support surface operations that eventually could take Mars water to orbit for conversion to propellant. 4) What is the best combination of rocket engines and stages to support the Earth to Mars mid-course flight, the descent to Mars surface, ascent from Mars surface and the return to Earth? />>> I think it should be done with a combination of a single type of rocket engine that uses Hydrogen and Oxygen propellant. The upper stage propellant tanks and engines would be kept in Space and used to build transit cyclers, landers, return to orbit vehicles and surface and orbital facilities. Though having been chastised for not ridgedly following the Zubrin plan I'm sure I will be charged with blasphemy. <div class="Discussion_UserSignature"> </div>

gunsandrockets · Apr 10, 2007

[Though having been chastised for not ridgedly following the Zubrin plan I'm sure I will be charged with blasphemy.] The whole point of this thread is to improve the Mars Direct plan, not to blindly follow Zubrin's catechisms. [Oxidation is combining Oxygen with another element. I can't think of a better oxidizer than Oxygen.] By oxydizers I meant the portion of the rocket propellant which is used to oxydize the fuel portion of the rocket propellant. Examples of other rocket propellant oxydizers besides liquid oxygen are hydrogen peroxide, nitric acid, nitrous oxide, nitrogen tetroxide, fluorine, chlorine tetrafluoride, etc. [If you carry water you can produce both Hydrogen and water when you need it. Water is pretty stable and easy to transport and all you need is electrical power to break it down.] Even though water carries hydrogen in even greater density than liquid hydrogen, water is an extremely mass inefficient method for storing hydrogen feedstock. You would need 8 times more mass of water than of liquid hydrogen to carry the same mass of hydrogen. Remember that in the Mars Direct plan the ERV aquires all the oxygen needed for the return trip to Earth by processing the Martian atmosphere. The Zubrin plan converts 6 tonnes of hydrogen feedstock into more than 90 tonnes of rocket propellant by exploiting the resources found on the Martian surface. [ You could carry a lot of water for the weight of a reactor and if you repeatedly recycled it a fixed amount would last indefinitely.] Water is not an energy storage system nor an electrical power generating system and therefore could not substitute for a nuclear reactor electric power system. [I think (propulsion) should be done with a combination of a single type of rocket engine that uses Hydrogen and Oxygen propellant.] Even though liquid hydrogen and liquid oxygen have an excellent ISP rocket performance, hydrogen has lousy den

j05h · Apr 10, 2007

I've been sketching out the "Sled" ERV/Lander craft a little and struck on a possible 1st stage for getting it off the surface: advanced Armadillo Pixel craft or Fregat stages. Several units could be docked to the base of the ERV and dropped as expended.These stages go on to become tugs and hoppers. Fregat is limited because it is currently hypergolic, but both craft might be adapted in concept to run on Lox/CH4. Following the heatshield we discussed above (metal, nose-mounted, flippable seats in the ERV cockpit), these stages would ride attached to the base of the much wider ERV, land and accept fuel. Using this concept, the "first stage" could simply be a set of drop tanks instead of actual rockets. I'd recommend an existing engine, but am not a propulsion expert. My sketch of the "Sled" includes 4 linear aerospikes for engines, but pick your poison. Fuel density shouldn't fully be viewed as a problem, the bulkier the ERV, the easier the aerobraking. Lox-Methane is probably the best choice for now. Nitrous Oxide-Methane might work, but making it on Mars is going to immediately compete with breathing and crop needs. If you HAVE to bring hydrogen from Earth, perhaps a block of plexiglas or other plastic is the right choice for feedstock? You could get Hydrgen from plastic panels that double as green-house cover. Especially in light of recent Mars discovery, it would appear that every drop of propellant can be mined on Mars itself, no feedstock needed. Josh <div class="Discussion_UserSignature"> <div align="center">We need a first generation of pioneers. </div> </div>

gunsandrockets · Apr 23, 2007

<Fuel density shouldn't fully be viewed as a problem, the bulkier the ERV, the easier the aerobraking.> http://www.dunnspace.com/alternate_ssto_propellants.htm I guess I didn't make myself clear on the importance of fuel density. The above link to dunnspace is an analysis of performance of various propellants based upon a SSTO vehicle with a fixed dry mass and therefore a fixed propellant tank volume. Though not the same thing as an ERV, the SSTO shares enough similarities that the dunnspace study is very instructive. Just like the SSTO an ERV is also a fixed mass and fixed volume vehicle (as it lands upon the Martian surface). If you look at the dunnspace study results, the methane + LOX propellant combination has one of the lowest performance numbers because of it's low density. Propellants with higher density have a higher performance than methane even though those propellants may have a slightly lower ISP.

gunsandrockets · Apr 23, 2007

Analysis of Solar Electric Propulsion as an ERV Upper Stage Right now our tentative modification of the Zubrin ERV leaves the habitat section and re-entry capsule in Mars orbit as a weight saving measure, both in mass landed on the Martian surface and mass lifted off the Martian surface when the ERV returns to Earth. The NASA DRM 3.0 is somewhat similar to our modification. The NASA DRM splits functions between a Mars orbital spacecraft, and a Mars Ascent Vehicle which takes off from Mars. But unlike our modification the NASA orbital spacecraft has it's own large rocket system for propelling it on a trajectory back to Earth. Our orbital vehicle at the moment contains no significant propulsion section and all the propulsion neccessary for Earth return is supplied by the Mars landing segment of our ERV. Hopefully I haven't lost anyone by this point. As a means of examining propulsion and staging variations I decided to look at adding a solar electric propulsion system (SEPS) to our Orbital segment, sort of functioning as an upper stage for our ERV. My goal was to see how the numbers worked out by adding 1 km/s of delta-V via this SEPS. My hope was to find another way to lighten the burden on the Mars landing segment of our ERV. This additional SEPS would come along with the Orbital segment from Earth. When our crew leaves for Earth, I imagined the Mars landing segment of our ERV would rendezvous with our Orbital segment in high Mars orbit, then apply enough delta-V to return the whole combination on a slow ~240 day return trajectory to Earth. The empty Lander segment would then be jettisonned and the Orbital segment would use it's SEPS to add 1 km/s of delta-V to shorten the trip time to ~180 days. So to our 13 tonne Orbital segment I added a 2.5 tonne SEPS mostly based upon numbers derived from the Deep Space One (DS1) vehicle. I quickly abandoned the 3,000 ISP ion-engine of DS1 because the accelerati

scottb50 · Apr 24, 2007

Right now our tentative modification of the Zubrin ERV leaves the habitat section and re-entry capsule in Mars orbit as a weight saving measure, both in mass landed on the Martian surface and mass lifted off the Martian surface when the ERV returns to Earth.... That seems to be exactly what I have been saying. Three dedicated vehicles. A TSTO Earth launcher, an LEO-LMO Transport and a Single Stage Mars lander and launcher. If they are all built from the same Modules it becomes quite simple. LEO facilities to launch to and prepare for a Mars transit and LMO facilities for the same purpose complete the system. As long as the facilities and vehicles, use the same Modules, which start out as Second Stage Tanks for the TSTO vehicle it could be done a whole lot cheaper that Subrins plan. Where I have a difference is depending on Mars resources, at some point that might very well become possible, but being able to exploit Martian resources is going to take time and equipment. I think it is far better to get a foothold and expand from there rather than expect to set up business in one fell swoop. I also think electric engines enroute would not be worth their weight between LEO and LMO, especially when you figure the added propellant needed to slow down. I would rather stick with Hydrogen and Oxygen. <div class="Discussion_UserSignature"> </div>

gunsandrockets · Apr 24, 2007

"That seems to be exactly what I have been saying. Three dedicated vehicles. A TSTO Earth launcher, an LEO-LMO Transport and a Single Stage Mars lander and launcher. If they are all built from the same Modules it becomes quite simple." Sorry, I'm afraid you misunderstood my description. What I was describing was in every way identical to Zubrin's ERV of Zubrin's Mars Direct Plan with a slight alteration. The alteration of not landing all of the ERV structure onto the Martian surface and instead leaving a Sundancer size inflatable habitat with a Soyuz size reentry capsule in high Mars orbit.

j05h · Apr 24, 2007

I'd still like to see discussion of a common aerobraking/lander stage that can bring all the components to Mars' surface and carries the crew back to Earth with redundant reentry vehicles, the main "Sled" and a smaller capsule. Instead of dedicated Hab and ERV landers, make a 10-20 ton Sled that can bring all the components (in succession) to the ground. It requires a rethink of Mars Direct but seems like it makes sense. I'll post pics soon. josh <div class="Discussion_UserSignature"> <div align="center">We need a first generation of pioneers. </div> </div>

gunsandrockets · Apr 25, 2007

There is such a burning desire expressed in this thread for architectures other than Zubrin's Mars Direct that I have started another thread just for that purpose. http://uplink.space.com/showflat.php?Cat=&Board=businesstech&Number=704737&page=0&view=collapsed&sb=5&o=0&fpart= Please post discussion of your favorite plans on that thread, so that way this thread can remain focused on the Mars Direct ERV. Thanx!

j05h · Apr 25, 2007

Guns- I just think a lot has changed in the 15 years, and that we can use a common architecture for getting stuff to and from Mars. Even Zubrin would admit that, I hope. <div class="Discussion_UserSignature"> <div align="center">We need a first generation of pioneers. </div> </div>

gunsandrockets · May 2, 2007

Methanol instead of Methane? At first glance methanol is a mediocre fuel. It's ISP is inferior to methane and even slightly inferior to RP-1. But after looking at methanol more closely and I now see why Zubrin is so interested in ISPP of methanol. I don't know if methanol is best of all but it's looking very superior to methane as an ERV fuel. Methanol is like methane, but with an extra oxygen atom. Burned in a rocket engine, methanol only needs half the oxydizer that methane does. In other words with the same size tank of oxygen you could burn twice as much methanol as you could methane. Chilled methanol is very much more dense than methane too. The bottom line is, for the same size propellant tanks an ERV could carry twice the mass of LOX/methanol compared to LOX/methane. That adds up to an enormous advantage in mass ratio for a methanol fueled ERV. Even though methanol has about 8% less ISP compared to methane, the doubling of mass ratio from methanol would more than make up for that. If the ERV is multistaged at the very least the 1st stage should be methanol fueled. Perhaps the numbers work out so that methane is superior for an ERV second stage, I don't know since I haven't worked the numbers yet but I wouldn't be surprised if an all methanol ERV is better.

j05h · May 2, 2007

Guns- I've been thinking about this in the downtime. Suggesting reusable ERVs is no more radical a change to Mars Direct than our collective suggestion of Dragon/Sundancer. If you absolutely hate the idea, I'll never mention it again, but that other thread is not the right place for it. Integrating a lot of the mass that Zubrin suggests dropping (aeroshell for instance) and working toward reusability from the start makes for a far more robust, forward looking architecture. What we have done so far in this thread is reinvent NASA's Mars Semi-Direct (the Design Reference Mission). Since Mars Direct plans from the start for redundancy, having a multirole ERV from the start makes a lot of sense. If towards the end of the first expedition, there would be 3 ERVs on Mars. The crew could theoretically take one of the fully or half-fueled vehicles to a secondary site for some backup ground truth. If they based in Elysium, maybe they do a sortie to Valles Marineris, return to base and use one of the other ERVs to fly home. This is actually combing two of Zubrin's concepts, MD and the Gashopper. Wherever possible, the Hab and ERV should have compatible hardware, whether it is rocket stages or life support, it adds another level of redundancy to the system. I think that planetary-level mobility is something Mars explorers are going to need practically from the start. I also very much enjoy exploring using commercially available/nearly space products for Mars exploration. At what point does it stop being Mars Direct? Zubrin draws that line before the DRM (he wants all hardware to reside on Mars), where do you put it? Josh <div class="Discussion_UserSignature"> <div align="center">We need a first generation of pioneers. </div> </div>

gunsandrockets · May 7, 2007

<What we have done so far in this thread is reinvent NASA's Mars Semi-Direct (the Design Reference Mission).> I have to strongly disagree with that. The NASA DRM is very far from what we have come up with. Our mission has a smaller crew size than Mars Direct. The NASA DRM has a larger crew than Mars Direct. The NASA DRM uses six launches of HLV to assemble three nuclear powered spacecraft in LEO. Mars Direct uses two HLV launches, each of which go direct to Mars. Our ERV manufactures enough propellant on Mars for a delta-V of over 7 km/s. The NASA 'ascent vehicle' only manufactures propellant for about 4 km/s. The NASA DRM is so different from Mars direct that the main similarity is a long surface stay on Mars. The elements of Mars Direct which are so key, such as massive ISRU and a focus on Mars Surface Rendezvous (MSR), are only a pale shadow in the NASA DRM. The NASA plan is much more an Earth Orbital Rendezvous plus Mars Orbital Redezvous plan. < At what point does [a plan] stop being Mars Direct? Zubrin draws that line before the DRM (he wants all hardware to reside on Mars), where do you put it? /> That is a very fair question. What is inside and outside the boundaries of Mars Direct? I think the key to understanding that boundary is that Mars Direct is intended as a 'let's go to Mars today' plan rather than an idealized plan relying on new technology. There are two long poles in the technology tent that Zubrin requires to accomplish his Mars Direct plan: a light nuclear powerplant for Mars surface electric power, and a Saturn V class heavy lift launch vehicle. Any plan which requires more advanced technology than that, such as the NTR propulsion of NASA's DRM, I would say is outside the boundary of Mars direct. A plan which uses LESS advanced technology, such as solar power instead of nuclear or Proton class launch vehicles instead of Saturn class, could still be considered Mars Direct if i

j05h · May 10, 2007

<What we have done so far in this thread is reinvent NASA's Mars Semi-Direct (the Design Reference Mission).> I have to strongly disagree with that. The NASA DRM is very far Only in the round: orbital rendevous for Earth-return and such. It wasn't meant as a direct comparison and frankly it's been a long time since I looked at the DRM so probably shouldn't have mentioned it at all. Making Mars architectures happen quickly versus extensive new research is an important point. One of my root critiques is that any system like this needs to be somewhat "future proofed" so that it can support further activity. This includes being able to modularize cargo and routine access. I don't think Zubrin's surface powerplant is unreasonable. The SP 100 was designed and tested. The tech is basically there, but it's probably a political non-starter. Maybe a private company working with the military and GE could do it, but I doubt NASA would be allowed to. It'd actually be a good use for launching from Kwaj. Zubrin called for direct TMI burns from the "Ares" upper stage. LEO staging of vehicles changes the equation of what should be reusable, hence my suggestion of a common aerobraking stage/lander. My working assumption is that, regardless of ESAS, in the near future there will be propellant depots on orbit, while we cannot be assured of HLV. Everything else follows. I agree that the initial ELV is a tough bird to develop, but would like to see it as future-proof as possible. >What is inside and outside the boundaries of Mars Direct? I think the key to understanding that boundary is that Mars Direct is intended as a 'let's go to Mars today' plan rather than an idealized plan relying on new technology. .... That's the point of Mars Direct. The idea of going to Mars now instead of some unknown time in the future. Absolutely! I'm all for humans-to-Mars, the sooner the better. Pushin <div class="Discussion_UserSignature"> <div align="center">We need a first generation of pioneers. </div> </div>

gunsandrockets · May 11, 2007

I'm still pretty hazy on exactly what your ERV concept does. I've got a rough idea of the layout, a nose mounted heatshield and two stages. But I'm completely lost on where each part your ERV flies to. (1st stage hoppers?) Does your ERV even do the basic ERV function of returning a crew to Earth? Or is it just a Mars surface to Mars orbit vehicle?

j05h · May 11, 2007

You've got the basic idea. This ERV functions as a common aerobraking, lander and ascent stage. It returns the crew to Earth orbit (or the ground, but why waste the craft? It's much smarter to use a standard capsule to complete Earth reentry) . I'm assuming that on-orbit refits would allow it to bring new cargo to Mars after the first mission. It would bring a Sundancer and Dragon to Mars orbit, then land with the rest of the cargo. I envision one craft that can carry crew and cargo depending on needs. It's designed to bring labs, habs , nukes and exploration kit to the surface. It may very well be to many roles for a 15t craft. Anyway, here are a couple of sketches done in manga style: http://www.wakeshield.net/sandbox/ERV_Manga_Big.jpg Josh <div class="Discussion_UserSignature"> <div align="center">We need a first generation of pioneers. </div> </div>

JonClarke · May 14, 2007

As I mentioned in the other thread, my recollection was that a solar thermal power systems was a feature of one of the contenders for the Mars Society's Kepler prize a few years ago. My memory was that it had actually won the prize. I got the report at work today, and my memory played me false. The study does indeed use a type of STP, but it did not win the Kepler prize, but was merely an entry in the competition. Some salient points to the discussion: Given the concerns that the original MD ERV was too small, it is interesting that study study has an ERV that starts out at 51 tonnes on the surface of Mars and is 183 tonnes fully fuelled. The proposal uses a solar thermal concentrator to generate electricity using gas turbines, these power a plasma propulsion system to shorten the transit time. the same collector also provides surface power on Mars. Also of interest is the use of inflatable extensions to the ERV to increase habitable volume. Is quite a comprehensive report, running to 77 pages. I have permission to forward it to interested parties, about it is large, 500 kB in a zip drive. Please contact me by PM if you are interested. Jon <div class="Discussion_UserSignature"> 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 Arthur Clarke </div>

gunsandrockets · May 14, 2007

Thanx for the info! <As I mentioned in the other thread, my recollection was that a solar thermal power systems was a feature of one of the contenders for the Mars Society's Kepler prize a few years ago. /> So it wasn't Solar Thermal Propulsion (STP) but Solar Dynamic Power (SDP). Huh. I could see how those two things could get confused for each other. I wonder what kind of power to mass ratio the SDP system has in comparison to Nuclear Electric Power. <My memory was that it had actually won the prize. I got the report at work today, and my memory played me false. The study does indeed use a type of [SDP], but it did not win the Kepler prize, but was merely an entry in the competition. /> Ah. You wouldn't by chance have any info on the Kepler Prize winning design would you? If you do please share it with us! <The proposal uses a solar thermal concentrator to generate electricity using gas turbines, these power a plasma propulsion system to shorten the transit time. the same collector also provides surface power on Mars. /> Woah! Solar electric propulsion (SEP)? That's interesting. What kind of propellant did the SEP use? Was the SEP propellant derived via ISPP? I admit that it's clever to get dual use out of the electric power system, for both ISPP and SEP. But from my own limited analysis of exploiting SEP for the ERV (that I posted about earlier in this thread) I concluded SEP doesn't shorten the Earth return trip time any better than using chemical propulsion. <Also of interest is the use of inflatable extensions to the ERV to increase habitable volume. /> Is that during surface ops on Mars? Or during the return to Earth flight? Or both?

JonClarke · May 14, 2007

Well, I will plead an 18 month lapse since I last read it! Do, I don't know anything about what idea actually won the prize. The ERV used ISPP produced methane and LOX. In inftables were yoused to increase volume on the way back, they were small pop-outs along the side. Sorry for the short response. I am off for 10 days tomorrow for work and am running low on time. I'll try and check in tonight. Jon <div class="Discussion_UserSignature"> 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 Arthur Clarke </div>

gunsandrockets · May 14, 2007

<Sorry for the short response.> All information is welcome, no matter how sketchy. Fill in any blanks whenever it is convenient. I look forward to hearing more. <The ERV used ISPP produced methane and LOX. /> Even for the electric propulsion? What kind of electric propulsion was it? I can understand the LOX+CH4 propellant for the basic chemical rocket propulsion, but for the 'plasma rocket' propellant too? I'm trying to wrap me head around that one.

gunsandrockets · May 14, 2007

From nasaspaceflight I found some interesting information posted by someone with the moniker of 'propforce' who favors propane fuel over methane... bar graph of tank volume vs fixed delta-V for several propellants graph of propellant ISP vs oxydizer/fuel mixture ratios for several propellants thread, Methane: the ultimate fuel? perhaps the nasaspaceflight.com 'propforce' is our own space.com propforce? propforce profile

JonClarke · May 15, 2007

It would appear so. From page 3: Our propulsion system uses chemical propellant combined with heat and electricity generated from the solar-thermal reactor assisted for energy efficiency â€“ the spaceship equivalent of a hybrid, solar-powered car. This also allows for throttling of the thrust so the system produces a high thrust at low efficiency or low thrust at a high efficiency. By superheating the propellant and ionizing the resulting gas, we achieve an Isp into the thousands at the high efficiency end. This will have the nearly the same efficiencies as nuclear thermal, with a modest thrust of 59 Newtons. This represents two areas of tested and developed technologies combined into one efficient package. Although this unique and innovative combination has never before been attempted, we show mathematically the result with this design as being very much advantaged over using either solar thermal alone (which has lower thrust), or chemical propulsion alone (having lower Isp). From page 67. The ERV launches from the surface of Mars like a conventional rocket. Chemical rockets, burning Liquid Methane CH4 and Liquid O2 fuel is used to reach a Martian escape velocity orbit. Once the burn has completed but while still in Low Mars Orbit, the first stage rocket module is jettisoned followed by a maneuver that turns the craft 90 degrees so that its long axis is perpendicular to its direction of travel. Next, the craft rolls on its long axis until its transit engine, located midship, is aligned to stern. The transit engine rocket nozzle is prepared for operation through the removal of protective, spring-loaded dust covers. Directly forward of the rocket nozzle, the solar collector storage cylinder swings outward 90 degrees so that it points in the direction of travel. Finally, the solar collector is deployed in a manner similar to a blossoming flower. Now the Solar Thermal generator is brought back into active operation, w <div class="Discussion_UserSignature"> 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 Arthur Clarke </div>

JonClarke · May 15, 2007

Mars entry configuration. <div class="Discussion_UserSignature"> 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 Arthur Clarke </div>

the Earth Return Vehicle of Zubrin's Mars Direct plan

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