Mars Direct Rethought - Fixing the potholes in Zubrin's plan

Bill White · 2002-08-27 09:28:28

The X-38 is an intriguing idea. It doesn't have a regenerable life support system, and I don't think it has enough room to accomodate the inflatable habitat, powerplant for life suport, furniture, or equipment. But you could include the habitat with the cargo lander.

My thoughts were to design the mission as follows:

ERV/CRV - 1 Energia launch "direct throw" to Mars

Surface hab + some supplies - 1 Energia launch "direct throw" to Mars

Crew transit hab + X-38/additional supplies - 2 Energia launches, dock in LEO, ferry up crew via Soyuz after crew transit hab attains higher orbit etc. . .

After arrival in Mars low orbit ("LMO"?) crew transfers to X-38 and lands. Additional supplies dropped in low tech manner - ballutes and airbags to cushion landing. Higher tolerable impact speeds + the ability to bounce around, safely, ensconced in airbags may allow a much less expensive landing protocol for boxes of MREs and tools, compared with people.

Earth-Mars transit hab either returns to LEO via remote operation for re-use or docks with ERV/CRV after surface mission giving more spacious accomodations for Mars-Earth return trip.

Whether this works better is a matter of number crunching - we add 2 Energia launches over the original MarsDirect but we don't need a fancy new lifter, saving much R&D.

I had thought to use the X-38 to save development costs for a crewed lander but I suppose the R&D will be needed anyway to successfully land an ERV in a condition to successfully launch from Mars.

Whether an X-38 lander would be cheaper than buying a 2nd copy of the as of yet undesigned crewed lander? I don't know. The X-38 option would seem to leave more mass in LMO and perhaps save on heat shielding as compared with a lander derived from the ERV/CRV lander but it may be a close call.

Could an aeroshell accomplish Mars aerocapture and remain safe for a subsequent Earth aerocapture or is that asking too much?

Finally, my gut feeling is that leaving crew in LMO during a surface Mars mission is pretty pointless. What will they do - besides getting lonely, bored and jealous- that cannot be done by remote operation? Any ideas?

RobS · 2002-08-27 12:46:58

This is quite an interesting posting, Bill, but without masses I don't have a sense of whether it is feasible. With chemical propulsion, Mars Direct puts 28 tonnes out of 140 (28/140 = 20%) on the surface of Mars as soft-landed cargo. Solar thermal can raise the percentage from 20% to maybe 30%. Same with nuclear-thermal engines. Electric propulsion might raise the percentage even higher; maybe Robert has a sense for that. Smaller vehicles will send a smaller percentage of their total mass as cargo because of the efficiencies that larger vehicles produce. People have to be moved with chemical or nuclear-thermal.

Which Energia were you referring to, in terms of throw weight? What's the mass of the X-38; I don't think I've seen that.

Regarding aerobraking, certainly an aerobrake that works in both planets' atmospheres and can be used more than once can be developed. The shuttle's heat shield is an example of a multiple use heat shield. But the mass of the shield grows. The rule of thumb I have see is that for aerobraking into Mars orbit, the aeroshell/heat shield has to be about 15-20% of the total mass. That's still less than firing an engine, but it's a lot. I suspect a reusable heat shield for both planets (and Earth's would be the higher demand environment) has to be at least 20% of the total mass, maybe 25%. Again, maybe someone else has some details I am lacking.

-- RobS

RobertDyck · 2002-08-27 13:47:45

Remember the mass that Energia can "direct throw" into a trans-Mars trajectory is 29.3 metric tonnes, and that is C3=15 which is a Hohmann transfer orbit: 10 month trip. That mass must include navigation systems and maneuvering thrusters to adjust course to Mars, heatshield/aeroshell, parachute, and landing system. One reason I suggested keeping the CRV in Mars orbit as well as food, life support and crew accomodations, was to reduce the total mission mass. The other reason was to reduce the Mars Ascent Vehicle so it could be launched with a single Energia. If the MAV can be launched by "direct throw" instead of solar electric propulsion, then by all means do so. Mass for the Mars Direct ERV is 28.36t (Earth to Mars mass) according to the Earth Return Vehicle Definition Sheet, which does fit, but many people are skeptical. Remember, Mars Direct also stated an Ares rocket would be necessary to launch it.

RobertDyck · 2002-08-27 14:13:42

According to NASA's X-38 Fact Sheet (it's a glossy sales brochure) the mass is 25,000 pounds (11.3 metric tonnes). It can carry 7 astronauts in clothing, but I remember another announcement that it can carry 4 astronauts in spacesuits (I believe that's an ACES suit or equivalent, not an EMU).

Bill White · 2002-08-27 14:30:19

I fear I am "over my head" when handling these details, but here I go again. . .

I apparently mis-used the term "direct throw" as I do believe everything except the crew should go with solar ion assist.

Robert's post seems to suggest that by adding solar ion (thereby greatly reducing the mass of the rocket fuel needed for travel from LEO to Mars) a single Energia can place a sufficent MAV/ERV on Mars and a 2nd single Energia can place a sufficient surface hab on Mars as well. Thereafter, two Energias could launch hab components for docking in LEO with occupancy by 4 or 6 astronauts after successful hard docking.

By the way, per astronautix.com - the original X-38 weighs 8100 kilograms, a fraction of the Energia EUS launch capability. An X-38(m) would probably weigh more - but much more? I also believe the X-38 would fit inside a module that would fit inside the Energia - another show stopper to the idea of using the X-38 as a Mars lander - so if the X-38 module could be stowed inside part of 1/2 of the Earth-Mars crew vessel the rest could be filled with supplies and living space.

I recall reading that a Soyuz launch "costs" $20 million. Two Soyuz with 6 astronauts costs $40 million - peanuts to a $20 -$30 billion mission.

My main point, the one I most intended is:

*IF* an Energia launch "costs" between $150 - $200 million, using 4 Energias may well be cheaper than spending vast sums on research and development to design a mission which requires only 2 launches but uses Ares or some other yet to be built launch vehicle.

Is $1 billion a ballpark "upper limit" for all needed heavy lift for a Mars mission? Four Energia launches plus refurbished infrastruture.

Maybe $20 billion would buy more than a "bare-bones" mission after all. Even with the "wrong" red/white/blue flag. . .

A final point or question - How much of any of these Mars mission cost estimates are based on buying the 1st vehicle of a new design? In other words, once the first Mars MAV/ERV is designed and built, how much less would a 2nd or 3rd cost?

Bill White · 2002-08-27 14:35:12

A serious downside to the X-38 as a Mars lander is the lack of an abort to orbit option. Once you go in, you are going down.

RobertDyck · 2002-08-27 15:14:55

The descent module of the Soyuz-TM is only sized for 3 crew in Sokol spacesuits, but it masses 3 tonnes. Would a version designed for 4 astronauts plus samples and direct entry at interplanetary velocity mass 4 tonnes?

RobertDyck · 2002-08-27 16:20:13

I think the "commit" factor will be with any Mars mission. The "Mars Orbit Rendezvous" plan I described would have a similar one. The space hab / surface hab / Crew Return Vehicle assembly could fly by Mars and return using a free return trajectory. Once captured into Mars orbit, the MAV could be remotely launched and rendezvous with the space hab to propell it back to Earth. The surface hab could make a close fly by of Mars and abort back to the space hab. Once the surface hab enters Mars atmosphere, however, it is committed; once in it is going down. At that point it better land close to the MAV.

Thinking of backup modes, I had described both rovers on the cargo lander. Perhaps we could still put the pressurized rover there, but move the unpressurized 2-man rover to the surface hab. Then if the hab lands far away from the MAV they can use the unpressurized rover to go get the pressurized one. They could carry the inflatable hab on the rovers to the MAV location. Furniture, life support, and other equipment could be removed from the lander and driven over to base. This would dismantle the surface hab lander and carry everything useful to the MAV location.

Mars Direct has an even more dire commitment. Once you launch from Earth you had better land on Mars. There is no abort option. The only backup is to send another ERV. There is a free return option, but would the hab survive Earth reentry?

Bill White · 2002-08-27 16:44:18

As for back up/redundancy - if Energia EUS + solar ion can send an operational MAV to Mars for $150 million excluding payload cost - and if "most" of the MAV cost will be R&D - why not send 2 with the first mission?

Or send two MAVs 26 months early and a 3rd by separate launch, with the crew, to de-orbit from LMO only if MAV #1 and MAV #2 are both inspected and found to be flawed or damaged. If MAV #1 and/or #2 are OK - land MAV #3 at the landing site chosen for the 2nd crewed Mars mission.

If we exclude R&D - a fixed cost fully sunk once we build the 1st MAV - how much more can a 2nd MAV cost excluding all R&D?

RobertDyck · 2002-08-27 20:43:39

You know, this discussion that the majority of the cost is R&D makes me think of a radical redesign. How much more would it cost to make the MAV reusable? That is, give it a metallic heatshield similar to the one developed for X-33. That would be durable and reusable without maintenance. Put engines and empty propellant tanks on the space habitat. The MAV would transfer propellant to the space hab on-orbit, then park in Mars orbit. Permit the MAV to keep its landing legs and retain enough propellant to land again. The space hab would keep its aerocapture heatshield. This would turn the space hab into a lot more than a habitat; it would become the permanent shuttle. In fact, if we sent the MAV with the manned mission it could act as the crew lander. The inflatable surface hab would be sent with the cargo lander. An initial MAV would be sent first with ISPP plant and power plant. When the crew arrives they have 2 MAVs at the base. If the first MAV failed they could transfer propellant to the MAV used to land, or use the ISPP plant and power plant to produce new propellant.

The second mission would rendezvous with the orbiting MAV and use that to land. The second mission wouldn't carry an MAV, surface hab, or other crew lander to Mars at all. Reusability of the parachute becomes an issue.

The permanent shuttle would use the same heatshield it used to aerocapture into Mars orbit to aerocapture into Earth orbit. It would then be met by an enlarged Soyuz space taxi, or a pair of Soyuz spacecraft to carry astronauts back to Earth. This completely eliminates taking a Crew Return Vehicle (either capsule or X-38) to Mars at all. It does require bringing a heatshield for aerocapture and ruggedizing the permanent shuttle to survive the stress.

All this would require robust equipment to survive multiple missions. Once built, the Mars base can be visited by multiple crews simply by refuelling, resupplying and transferring new crew. Additional equipment for new experiments can be sent on cargo landers. Each new delivery of cargo would enlarge the Mars base.

Phobos · 2002-08-27 21:12:14

The MAV would transfer propellant to the space hab on-orbit, then park in Mars orbit. Permit the MAV to keep its landing legs and retain enough propellant to land again. The space hab would keep its aerocapture heatshield. This would turn the space hab into a lot more than a habitat; it would become the permanent shuttle. In fact, if we sent the MAV with the manned mission it could act as the crew lander.

The only aspect of making the hab a reusable space vehicle that I don't like is that it could prevent the clustering of habs into a something of a permanent Mars base. I like the idea of launching a new hab each time and parking it near the last hab that landed on Mars to build up something of a research station. Of course, I guess you could save costs by having a permanent space hab that would shuttle people back and forth between Mars and Earth once enough habs have been clustered together on the Martian surface.

RobertDyck · 2002-08-27 22:04:14

How is this for a plan: Use the Mars Orbit Rendezvous with unpressurized rover included with the surface hab. Have a second MAV complete with ISPP and power arrive at Mars shortly after the crew lands. If the crew lands too far from base the second MAV can rescue them. If not, it can land at base to supply the second mission.

After a few successful missions, replace the MAV with a reusable one, and the orbital hab with a permanent shuttle. This permits an initial low-mass mission to reduce cost, and equipment can be improved after field trials for the permanent shuttle. This permits precision landing on Mars to be proven before committing astronauts to it.

periscopeboy · 2002-08-28 16:11:59

Mars Direct has an even more dire commitment. Once you launch from Earth you had better land on Mars. There is no abort option. The only backup is to send another ERV. There is a free return option, but would the hab survive Earth reentry?

I may be completely out of my league in posting on this thread, as I didn't understand most of what y'all are talking about. But in answer to this question, the hab doesn't need to survive earth re-entry, it only needs to be able to dock with the ISS. I'm sure in the time it takes to make the round trip a re-entry vehicle or space shuttle could be sent to the ISS to return them to earth.

RobertDyck · 2002-08-28 17:04:02

Ooh! Someone thinks my messages are out of his league! I'm just a computer programmer and wannabe aerospace engineer. Ok, so I develop real-time software for embedded systems including flight systems using the same operating system as CanadArm2, but I don't have a degree in aerospace engineering. I learned much of what I know by chatting on the original Mars Society message board and researching the web, reading science and technical journals like Science and The Journal of Propulsion and Power, reviewing my college physics text book, Zubrin's books, a text book on Orbital Dynamics, and technical papers from NASA. Any member could do the same.

C.COMMARMOND (FR) · 2002-08-29 06:22:45

Hello everybody,

I see where you are now, you are far from a Mars direct Mission... And I agree with you.

1 why do we need to take a 3 ton Earth reentry vehicle when we can stop on orbit and rendez vous with ISS or a shuttle ?

2 Why do we need to use the Mars Hab as a space vehicle since their use is really different (environment, labs...).

3 When you spend $20 billion, you can hope that the technology was tested, what is a better test than to send a complete set of stuff to Mars, land the Hab, refuel the MAV...
So, when you send a second vehicle with a crew, you are sure that every thing should be OK (as said robertDick, it's a win or die gamble for the crew, the 'abort' scenario will always be to spend 2/3 years in the space vehicle)...

4 I personnaly think that we need at least 100 tons (for 20 people and all the needed toys) to Mars ground, so we should use 3 Energia and slow way (12 to 18 months) to send a maximum of stuff to Mars and then 1 energia to put the Earth-Mars transport vehicle on orbit and then use a fiable rocket to send the crew in it.
(for info: russians planned to launch 40 energia/year and to improve energia to energia-M for 150 tons on LEO, but they don't have funds).

5 I think it is a good idea to have a fully fueled (kerozene/H2O2, not cryogenic) 'return vehicle' sent from earth on Mars orbit as a test, because it at least garanties that if your fuel stock get lost between the time you go and the time you want to go back, you will always have a spare vehicle to do so...

6 General consideration about cost of the R&D: when I look to military stuff, it seems to me that design costs 3 to 10 'objects' ( e.g: planes ). So if the MAV design costs 100 M$, buy ten should cost only 200 to 400 M$. The price of the launches could be reduced if we were able to order 10/15 per year, because the people is the same if you do 1 or 10, the design is paid so at the ultimate end, you only pay the materials, the work made on them, transportation to launch site and fueling. And right now, I think that RKK Energia (the company which build energia rockets) would like to make a special price to someone who wants 10/15 launches/year...

And to finish, it is obvious that the Mars direct scenario was made for very low quality systems, where space rendez-vous are forbidden and i don't think even Zubrin would go in it (too dangerous).

CC.

RobertDyck · 2002-08-29 09:08:34

Thanks CC.

The point is to keep cost as low as possible while retaining safety. Use of Mars resources eliminates a lot of mass that must otherwise be brought from Earth. Bringing propellant from Earth not only increases launch weight by that mass, but also extra fuel to launch it from Earth surface to Mars. If you abandon ISPP that will greatly increase mission mass, and therefore mission cost. Another thing I tried to do is avoid duplicate hardware; to create backups with alternate use of existing hardware. For example, the laboratory would normally receive life support by air ducts from the habitat. If the habitat fails the laboratory can act as a habitat by using life support on the pressurized rover. Landing the MAV first and generating propellant guarantees it is ready for the return; the only reason for a backup is if the crew lands too far to reach it. The plan I described would have a smaller and less expensive MAV than the ERV of Mars Direct, therefore duplicate hardware is cheaper.

NASA DRM version 1 included 4 launches:
- MAV with ISPP, power system, pressurized rover, unpressurized rover, 3 teleoperated science rovers, science payload
- surface habitat, power system, unpresurized rover (launched unmanned)
- return habitat with fuel to return to Earth
- second surface habitat, power system, unpressurized rover (launched with crew)
Each of these would require a launch vehicle capable of lifting 200t to LEO. That is even larger than Ares; it would require a HLLV a large as Vulkan. NASA DRM version 3 reduced mass and repackaged the missions to launch the TMI stage separately. They replaced the unmanned hab with a cargo lander, and the second pressurized rover on the crewed hab with a TransHAB derived pressurized habitat. That would permit 8 Magnum or Energia launches instead. I'm trying to keep it down to 3 or 4 Energia launches per mission, and explore the option of Earth orbit assembly using existing launch vehicles: Proton M, Angara 5, Atlas V 551 or 552, or Delta IV Large.

If RSC Energia (in Russian, RKK Energia) wants to sell at least 10 launch vehicles, we can do that with multiple manned missions.

As for eliminating the Earth reentry vehicle, the alternatives are to aerocapture into Earth orbit and use a crew taxi to bring them back to Earth, or aerocapture and aerobrake into a circularized low Earth orbit to rendezvous with ISS or Shuttle. How much mass would that require and how much time spent in Earth's radiation belts? The plan I described would use the heatshield for Mars aerocapture to land the surface hab. Earth aerocapture requires bringing another heatshield. I believe lowering orbit to ISS or Shuttle range quickly enough to avoid crew radiation exposure would mass more than a reentry vehicle. The extra heatshield for aerocapture only may mass less.

Phobos · 2002-08-30 16:23:32

And to finish, it is obvious that the Mars direct scenario was made for very low quality systems, where space rendez-vous are forbidden and i don't think even Zubrin would go in it (too dangerous).
CC.

I think Zubrin was trying to keep down the complexity and thus the cost of a Mars mission by eliminating the need for orbital rendezvous. If we just build the Mars hab with a lot of care and forsight and make sure its got good redundancy and testing, I don't see why it can't work. Anyways, it's true that some of the ideas in Mars direct might be a little more dangerous since we're relying on our return vehicle to be fully operational and fueled up when we get to Mars but I don't think the danger is prohibitive.

John_Frazer · 2002-09-03 14:03:24

Didn't see some other bugs with Mars Direct.

1) no escape system on the crew launch. Better to wait an orbit or 2 for the crew to meet the hab in LEO from a Soyuz or 2, than risk the roman candles with absolutely no hope for survival.
Read here about the Shuttle's rotten safety.

In October 1999, former astronaut Michael Coats testified at congressional subcommittee that he personally experienced sitting on the pad during STS-41-D in 1984 while a hydrogen fire was burning below him and knowing he had no way to escape. Only one month after the release of the NASA safety report justifying not having a crew escape system, NASA had to scrub the launch of Space Shuttle Atlantis because of another hydrogen leak. This time there was no fire and no crew on the vehicle. The gambler was lucky this time... but what about next time..

So use Energia or something without roman candles as a first stage. Plenty of ways around it. (Sure, the crew acccepts the risks, but I doubt anybody is selfless enough to risk that, when there are ways around it)

2) No experience with long term exposure to low G. Much is made of Shannon Lucid walking off the Shuttle after a long time on Mir, and other cosmonauts surviving even longer durations. Yes, they made it, but a decade later, they still haven't completely recovered.

I suspect that .38G for 3.5 years will make the crew either permanently crippled or long-term debilitated after they get back. It'll take far more than mice in orbit for 50 days to settle it, and I suspect that it will prove that low G is almost as bad as zero G. (I've got a couple of long-term bets on it) Face it: people who don't get much exercise just aren't as healthy. They'll have to exercise strenuously for several hours every day of a Mars Direct mission, and they'll still have serious long-term health problems.

Not saying this is a mission killer. There may be other data out there, and you may find a crew willing to do the mission. It is a big unknown, though.

John_Frazer · 2002-09-03 14:45:30

We're getting pretty far out here. 3, or 8 HLLV launches to do a single mission? That's a lot of funding to get up front, before a single thing is actually done.
Part of why Mars Direct is small is to keep up-front costs down.

I have another controversial option, if we're thinking of a mission of this size.
Earlier here, the hysteria over launch of Cassini was mentioned, and the 100kw nuclear reactor mounted in a truck.
If you can get past the hysteria to launch the truck, if you can get past the horror stories to launch a nuclear thermal rocket upper stage, then why not go all the way, and use a real interplanetary rocket?
If you're tralking about launching more than a few hundred tons into LEO before the mission starts, and assembling the ship in space, then do it right.
For 500 tons in LEO, you can get over 200 tons of cargo to Mars, in a 6week trajectory! Forget about all the problems with long-term space travel. Forget about cutting safeties & redundant systems to shave off vehicle weight -build it like a Navy cruiser!
So, granted, we'll run into lots of trouble, trying to get variances to the treaties, and then getting the weapons grade fissionables, and setting off a few hundred atomic bombs. We are talking about an enterprise with enough clout to get private funding to do a manned Mars mission... Granted, some protestors will still complain about "polluting space" with the bomb fallout!

Orion at Mars, releasing lander

10 meter Orion upper stage module for S-1-C launch

configured as Mars expedition

Launch profile (if a single HLV-lifted mission is allowable, otherwise, lift separate ~100 ton lots.)

Another aspect of the political difficulties is presented here.
Note that the CDI is not hawkish. They aren't promoting the militarization of space, and certainly not relaxation of weapons-testing or development restrictions.

Orion will rise!
http://www.cdi.org/russia/johnson/5550-12.cfm
Orion Can Rise!
http://www.skali.com/index.p....n=print

...Orion spacecraft was never built. But it offers a radical solution now for using up the thousands of nuclear weapons Presidents Bush of the United States and Putin of Russia agreed to mutually destroy...
It would then be assembled (in orbit) outside an already-existing manned space station.
Such a project would achieve several major ends simultaneously.
First, it would remove from both the U.S. and Russian governments the nightmarish, literally never-ending task of guarding forever the nuclear raw material stockpiles from the bombs they had dismantled. And it would obviously also vastly lessen the risk terrorists like Osama bin Laden or the leaders of rogue states like Iraq or North Korea could steal such weapons or material.
Second, an Orion program would reassure both the Russian and American governments and their publics both sides were indeed handing over their nuclear weapons and eliminating them because those bombs would be needed to fuel Orion space ships.
And with each detonation to provide the kinetic energy to propel the Orion spacecraft further and faster on their voyages of exploration, it would be absolutely certain another genuine nuclear warhead had been destroyed. No huge and flawed program of mutual or international inspection would be required to ensure compliance.
Third, such a visionary program would truly bind the American and Russian peoples together in friendship and partnership. Former House of Representatives Speaker Newt Gingrich, one of the most visionary U.S. political leaders of the past decade, has envisaged a similar constructive unifying goal for the United States and the nations of Western Europe. He has advocated having them cooperate jointly on a manned mission to Mars over the next 20 years.
But Orion would be far cheaper in research, engineering and construction costs than a Mars project using vast numbers of far smaller and slower rockets with outmoded chemical fuel technology. Gingrich's Mars proposal would serve no strategic purpose such as the mutual destruction of U.S. and Russian nuclear weapons. And it would only serve to bind together U.S. and European nations which over the past half century have appeared far less likely to come in to conflict with each other than they all have with Russia.
Finally and fourth, the United States and Russia would prove natural partners in such a project. Both nations have enormous nuclear stockpiles. They have the longest traditions and experience of space flight, exploration and technology by far in the world. And their specializations in these fields complement each other.

We have all this Pu sitting around. What are we going to do with it?
Why not blow it off into the solar wind, once & for all?
Every aspect of this calls for international cooperation,from dismantling the warheads, to flying the Mars mission. Hey -if China gets manned spacecraft flying, the US and Russia might be scared enough to push for the treaty modifications and using Orion for a multinational Mars mission.

RobertDyck · 2002-09-03 15:57:40

Actually, the orginal Mars Direct plan called for 2 launches of Ares: 121.2t to 300km orbit, or 47.2t to trans-Mars trajectory. The solar-electric option of NASA DRM version 3 attempts to do the same with 3 launches of Magnum: 54.4-93.9t to 407km orbit (2 or 4 SRB's). I suggest 3 launches of Energia: 88t to 200km orbit, or 29.3t to trans-Mars trajectory.

If you want to look at high-performance systems without concern for public outcry, then I would look at NTR, not Orion. The Timberwind 75 engine had an Isp of 1,000 seconds (vacuum) and 890 seconds (sea level). As a launch vehicle, the Timberwind Titan was supposed to be able to lift 63.636t to 155km orbit. With a unit cost of $166.66 million in 1985 dollars, and a vehicle status of "development", I think the Russian Energia is a more cost effective option.

Orion Saturn V would have had a specific impulse between 1800-2500 seconds and able to launch 100t into trans-Mars trajectory in a single launch, but it was based on nuclear bombs. I don't think anyone would accept a vehicle that carries multiple nuclear bombs into space.

Phobos · 2002-09-03 18:24:17

John Frazer, I share your sentiments that the orion is hands down the most efficient and quickest way to go to Mars, but what about the radioactive fallout and the EMP problems that would be created from launching such vehicles? I personally have no problem with using them in space but launching them from the ground creates sticky problems that I'm not sure there are solutions to. However, that idea of an orion upperstage module is one I've never heard before. Such a module might create a good mixture of both environmental safety and efficiency.

RobertDyck · 2002-09-04 05:57:01

In another discission, C.COMMARMOND (FR) recommended sending a crew of 20-40 on the initial manned mission. Since that addresses mission design, I'll respond here.

Requiring a crew of 20-40 for the initial manned mission to Mars would require such a large spacecraft that no one could afford it. The point of Mars Direct is to make it affordable. The principle of "bootstrapping" means to start small, then build with each successive mission. Another point of Mars Direct I disagree with is manned missions to different locations, and only focusing on a single location after several missions. Unmanned probes (MGS, Pathfinder, Odyssey, Mars Exploration Rover, etc.) can do the scouting for us. An unmanned sample-return is the only addition needed to select a location for a permanent base. But the base must start small. Clustering habitats together is a simiple way to start a permanent base with an affordable initial manned mission.

For colonization, we will eventually need a permanent shuttle that can carry a significant number of colonists, say 100. But that will require infrastructure on Mars to refuel for the return to Earth. It will require ISPP on Mars or one of its moons, a fuel tanker, and a shuttle to carry colonists and their luggage from Mars orbit to the surface.

On-orbit fuel transfer has not been developed yet. Could freezing fuel lines block fuel transfer? Could pressure changes from the transfer cause thermal problems with the tanks? Could rapid fuel movement in zero-G of cryogenic fuel cause fluid flow problems? These issues can be worked out in Earth orbit before we go to Mars, but it hasn't been done yet.

C.COMMARMOND (FR) · 2002-09-04 06:15:41

Hi RobertDyck,

Just to say that I also said that before to send a crew, I will send 100 tons freight on Mars in automatic vehicles using a slow trajectory, a vehicle on Mars orbit for the descent/ascent... So the vehicle with 20 people in has just to carry people and food for 6+6 months.
Fuel to come back to Earth can come from in situ fuel synthesys.

For this, I think we could use a NTR or Solar thermal rocket with an Isp of 800/1000 so 100 tons fuel for 100 tons on mars orbit.

CC

periscopeboy · 2002-09-04 17:37:13

If the shuttle weighs about 100tons, and can get to 200 km, can't we just strap the marsbound craft onto the shuttle fuel tank and boosters, add a couple of engines to the mars-craft, and send it on it's way? How much would the engines weigh? more than the 12 ton difference? (I'm using 12 tons because RobertDyck says we need to get 88tons to 200km).

RobertDyck · 2002-09-04 20:41:52

The idea to replace the Shuttle orbiter with just engines is a good one, but not new. The Shuttle-C was supposed to be just that: replace the orbiter with engines surrounded by a heatshield and parachutes to recover the engines. Magnum is similar: mount the engines on the underside of the external tank, and reshape the oxygen tank to a cylinder instead of tear-drop. That permits mounting the hab or cargo on top of the tank. Shuttle-C or Magnum would have the lift you are talking about. Shuttle-C with 3 main engines (same as the current Shuttle) or Magnum would have equivalent lift to Energia.

The reason I mentioned 88t to 200km altitude, is that's the capacity of Energia and Robert Zubrin said we could do it with 3 Energias. I just tried to look at how to accomplish that goal.

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#51 2002-08-27 09:28:28

Re: Mars Direct Rethought - Fixing the potholes in Zubrin's plan

#52 2002-08-27 12:46:58

Re: Mars Direct Rethought - Fixing the potholes in Zubrin's plan

#53 2002-08-27 13:47:45

Re: Mars Direct Rethought - Fixing the potholes in Zubrin's plan

#54 2002-08-27 14:13:42

Re: Mars Direct Rethought - Fixing the potholes in Zubrin's plan

#55 2002-08-27 14:30:19

Re: Mars Direct Rethought - Fixing the potholes in Zubrin's plan

#56 2002-08-27 14:35:12

Re: Mars Direct Rethought - Fixing the potholes in Zubrin's plan

#57 2002-08-27 15:14:55

Re: Mars Direct Rethought - Fixing the potholes in Zubrin's plan

#58 2002-08-27 16:20:13

Re: Mars Direct Rethought - Fixing the potholes in Zubrin's plan

#59 2002-08-27 16:44:18

Re: Mars Direct Rethought - Fixing the potholes in Zubrin's plan

#60 2002-08-27 20:43:39

Re: Mars Direct Rethought - Fixing the potholes in Zubrin's plan

#61 2002-08-27 21:12:14

Re: Mars Direct Rethought - Fixing the potholes in Zubrin's plan

#62 2002-08-27 22:04:14

Re: Mars Direct Rethought - Fixing the potholes in Zubrin's plan

#63 2002-08-28 16:11:59

Re: Mars Direct Rethought - Fixing the potholes in Zubrin's plan

#64 2002-08-28 17:04:02

Re: Mars Direct Rethought - Fixing the potholes in Zubrin's plan

#65 2002-08-29 06:22:45

Re: Mars Direct Rethought - Fixing the potholes in Zubrin's plan

#66 2002-08-29 09:08:34

Re: Mars Direct Rethought - Fixing the potholes in Zubrin's plan

#67 2002-08-30 16:23:32

Re: Mars Direct Rethought - Fixing the potholes in Zubrin's plan

#68 2002-09-03 14:03:24

Re: Mars Direct Rethought - Fixing the potholes in Zubrin's plan

#69 2002-09-03 14:45:30

Re: Mars Direct Rethought - Fixing the potholes in Zubrin's plan

#70 2002-09-03 15:57:40

Re: Mars Direct Rethought - Fixing the potholes in Zubrin's plan

#71 2002-09-03 18:24:17

Re: Mars Direct Rethought - Fixing the potholes in Zubrin's plan

#72 2002-09-04 05:57:01

Re: Mars Direct Rethought - Fixing the potholes in Zubrin's plan

#73 2002-09-04 06:15:41

Re: Mars Direct Rethought - Fixing the potholes in Zubrin's plan

#74 2002-09-04 17:37:13

Re: Mars Direct Rethought - Fixing the potholes in Zubrin's plan

#75 2002-09-04 20:41:52

Re: Mars Direct Rethought - Fixing the potholes in Zubrin's plan

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