Reasons against Mars Direct

Ad Astra · 2003-12-05 20:01:54

Yes, I am a heretic. I've lost my faith in Mars Direct.

I've wrestled with this for a while and whether a lot of Zubrin's assumptions and estimates were correct. But talk to the people working on the ERV design project and they will tell you that Zubrin's mass estimates were optimistic.

Rocky Persaud, president of Canada's Mars Society, spoke in favor of a crew of six or larger to accomplish all of the science for the 550 day stay at Mars. Adding two more humans increases the amount of mass you have to put into earth orbit, as NASA discovered in 1993.

Other Mars Direct critics have noted that the plan will lead to "flags and footprints" despite Zubrin's insistence otherwise. A big strike against the plan is that nothing is reused (except the habs, which could conceiveably be reused as surface shelters.) I happen to favor electrically-powered shuttles for transport between Earth and Mars.

In spite of its faults, Mars Direct is a commendable, paradigm-shifting effort. Although I don't believe the Mars Society should continue to support Mars Direct, many of its ideals and concepts (like maximizing the science return, utilization of Martian resources, artificial gravity, and minimizing orbital assembly) should continue to be central to the Mars Society philosophy.

RobS · 2003-12-05 23:08:08

The Mars Society has to think very carefully when to update Mars Direct. Any plan requires periodic updating, but if you update it too often, no one can remember what the latest version is and it gets harder to sell it. On the other hand, if you don't update it at all, it starts to look like a technological dinosaur.

Maybe their ERV contest is part of the plan to update the proposal.

It's also important to remember that masses that are optimistic or low now may be correct twenty or thirty years later. The ERV may be too light, but the Hab could now be replaced by an inflatable vehicle and would be lighter than originally planned.

Creating a reusable Mars Direct architecture is a great goal, but may be technologically or financially impractical right now. As we have seen with the Space Shuttle, overreaching can have bad consequences.

-- RobS

Ad Astra · 2003-12-06 00:29:37

It would be better if the Mars Society did not throw its weight behind any proposal, but instead supported any and all plans that follow Zubrin's basic ideas about living off the land, minimized orbital assembly, etc. NASA's refernce mission in its initial form was very close to Mars Direct, yet addressed many of the original MD shortcomings. Over the past decade, the NASA DRM has become quite complex. Only the future space policy of the United States will give NASA an impetus to restore some discipline to Mars mission design.

GCNRevenger · 2003-12-06 00:32:58

Mars Direct has always been right on the lower edge of sane mass estimates, putting four people in the tiny ERV or HAB for that long without nice radiation shielding and then there's that scarry artifical gravity spinning scheme. Some more modern MD variations rumored already cut out the pressurized Mars rover and drilling rig out to save on weight. However, the problem with MD is not so much that its too heavy, but rather it is designed to do the wrong thing...:

If we make it about science, Mars Direct (or somthing like it, such as Nasa DRM) is what we will end up with. Any Mars mission should be in the context of establishing a perminant base first, and science/exploration second, which would need a architecture much (MUCH) bigger and more reuseable than MD. Make no mistake, Dr. Zubrin is wrong, MD would become a "Martian Apollo" given its expendable, margin-less ultra-light design. You can't make a real base out of HAB modules, the occasional medium cargo lander, and having to build/launch a new HAB & ERV every time you need a crew rotation. Adding reuseability, heavy payloads, and larger crews to the Mars Direct plan will, well, eliminate the possibility of it being direct wouldn't it? That would essentially lead to having to scrap the architecture to a large degree and would be a little more than a "upgrade..."

The technology does exsist to build MD today and to do the limited, short lived flags/footprints trip MD would enable but does NOT readily exsist today to make a really robust, reuseable, space-only Mars ship (which seats six). For that, we will have to have engines with more thrust than Ion engines but much higher Isp, preferably more than solid-core NTR. A reliable, reuseable crew lander/acent vehicle, fueled by ISPP fed by Martian water+carbon dioxide ,would also be really nice for exploration hopping around Mars besides running crews to/from a perminant base to the Earth shuttle

The only real propulsion options are the nuclear rocket or the VaSIMR engine for manned ships, since Ion engines won't ever reach suitable thrust levels. A solid-core NTR is only a marginal improvement over regular cryogenic engines, and wouldn't make the trip much faster. A GCNR or Vasimr engine would also permit fast flight times with large payloads and radiation shields plus you wouldn't need a finicky and dangerous artifical gravity scheme. Since both of these engines would make travel to Mars easy enough to make a perminant base possible, and the Mars base hardware will take a while to develop to maturity anyway, the decision is easy to make...

Delay Mars

Wait until we are ready to go big, and go to stay. In the mean time, go back to the Moon, and get Nasa used to supporting humans on other worlds over the long term while building super-engines, inflatable modules, and Mars fuel factories. Mars Direct gets us there in a hurry, but gets us off just as fast... No flags and footprints!

Enyo · 2003-12-06 05:04:21

Delay Mars
Wait until we are ready to go big, and go to stay. In the mean time, go back to the Moon, and get Nasa used to supporting humans on other worlds over the long term while building super-engines, inflatable modules, and Mars fuel factories. Mars Direct gets us there in a hurry, but gets us off just as fast... No flags and footprints!

Delaying a trip to Mars isn't going to prevent it from being a one shot deal. I don't think anything done to prevent "Flags and Footprints" would be effective.

Without a drastic reduction in costs or a society interested in science for science's sake cost cutting will be inevitable.

I also don't think we should play into the hands of those trying to set the rules of engagement in their favor either. A 18 month stay on Mars is nothing like a few days on the Moon. I don't believe the "Flags and Footprints" term has meaning here.

Ad Astra · 2003-12-06 10:30:10

The only real propulsion options are the nuclear rocket or the VaSIMR engine for manned ships, since Ion engines won't ever reach suitable thrust levels.

I wholeheartedly agree that chemical rockets should not be used for transit to and from Mars. But I think that ion might be the engine that NASA chooses for the first missions, seeing as how it is being developed for JIMO. I'm a big fan of VASIMR, and it will hopefully be flightworthy by the 2020-2025 time period. Gas-Core NTR is going to be a long-term development, but even when it's done it will only provide thrust for a short duration.

On the question of science vs. colonization, I side with the scientists, particularly those who want to make Mars exploration about finding life. The mysteries of Mars's lost oceans and rivers are too tantalyzing a question to ignore much longer. If we search for life and find astonihing results, there will be justification to explore for a long time to come.

GCNRevenger · 2003-12-06 14:51:55

An ion engine would be fine for long-flight cargo shuttles, especially if it were not limited by power with the use of a reactor or large solar arrays, but the achillies heel of ion engines remains... low thrust. It would take many weeks to spiral out of the Earth's gravity well, and wouldn't be alot better if launched from Lagrange either, that your astronauts have to sit being baked in the Van Allen belts while becoming deconditioned. Plus, you must carry a large reactor to supply alot of power long-term, with the low thermal-to-electric efficency they have.

Vasimr suffers from this problem too, albeit to a smaller degree with its high-thrust setting. Just like ion engines, Vasimr would require gobs of electricity over a long term from a large nuclear reactor.

Solid core nuclear thermal engines offer only a marginal improvement over LOX/LH engines (9000-1000sec Isp) as far as trip time or payload masses, plus they have a signifigant mass penalty because of the weight of the reactor and the biosheild compared to chemical engines.

A Gas Core NTR though... it can create very high Isp, on the order of 3000-6000sec, so is competitive with VASIMR and Ion engines but cuts trip time substantially since there is no lengthy acceleration/deceleration. Plus it does not need a large nuclear reactor to power it. Plus, you won't need to take a month to leave Earth's high radiation environment.

GCNR would be difficult to develop, but the concept is simple, and with the time it will take to develop the other hardware to go to Mars, GCNR wouldn't be far behind. Think how nice it would be to be able to get from LEO to Mars orbit so quickly, you wouldn't have to worry too much about long-term weightlessness or psychological strain.

Gennaro · 2003-12-06 22:01:15

I've wrestled with this for a while and whether a lot of Zubrin's assumptions and estimates were correct. But talk to the people working on the ERV design project and they will tell you that Zubrin's mass estimates were optimistic.

- Maybe that depends on how you look at it. The Mars Direct plan as outlined in The Case for Mars only pointed out what could be accomplished with two Saturn V launches. A very conservative baseline in my opinion.

Replace the upper stage with a solid core NTR and total payload delivered to the Martian surface increases from 53.8 to 89.6 tonnes. (p.89)

GCNRevenger · 2003-12-07 00:45:40

Using an Nerva-style solid core NTR engine on MD to increase payload would be nice, but would still be a little low for my tastes and you would have to lug a fairly heavy nuclear engine and shielding on both launches, partially negating the Isp advantage. The production Nerva engine weighed 11 tons if memory serves, not counting any bioshield.

And it still does not solve MD's cheif failing: that it is too expendable. Only by removing the "direct" part will Mars Direct be able to really serve as a transportation method to Mars, instead of a Martian Apollo as its designed to be today.

Gennaro · 2003-12-07 02:00:34

Using an Nerva-style solid core NTR engine on MD to increase payload would be nice, but would still be a little low for my tastes and you would have to lug a fairly heavy nuclear engine and shielding on both launches, partially negating the Isp advantage. The production Nerva engine weighed 11 tons if memory serves, not counting any bioshield.

- Hm, you have such expensive tastes, GCN. Why not go with hands on, off the shelf technology that requires a minimum of preparation and development? Besides, Nerva (which Zubrin used in the example) isn't even state of the art solid core technology, it's the baseline. Particle Bed or Advanced Dumbo offers more interesting solutions for present day applications. There's another thing, but I'll admit it's a favourite subject of mine. If at all possible (it's a reactor shielding question), solid core probably offers the best solution, radiation risk wise, for reusable NTR surface to surface veichles. And I'm aiming for an eventual standardized model, so Mars Direct would make a great test bed.

GCNR would be a good orbit to orbit transfer vehicle, but it will take longer to develop than solid core and then you'll still have to find a way of getting off and on the ground (due to the potential effects of a catastrophic failure).
As for Isp in itself, at least in relation to a direct mission, I find it's a minor point. Going to Mars on a higher departure velocity than about 5 km/s and a 180 day trajectory would only make aero-breaking too risky and difficult. Payload capacity is the all important parameter when planning manned Mars missions, and according to Dr Zubrin, a simple NTR addition would increase payload in the range of 50%. I'm sure he's aware about the reactor weight and shielding needs.
That's not to say a gas core upper stage would not make performance even a whole lot better, only that solid core is good enough.

And it still does not solve MD's cheif failing: that it is too expendable. Only by removing the "direct" part will Mars Direct be able to really serve as a transportation method to Mars, instead of a Martian Apollo as its designed to be today.

- At large I agree with this sentiment as I do your basic principle that no mission should be planned for science alone, but on settlement first and science second, but I'm not sure scrapping Mars Direct and thinking out some new plan is the right way to go right here and right now. It's all too clear though that MD at some point needs to be replaced by a Mars Settlement plan, calling for a whole other range of transportation hardware. And of course, that's the golden opportunity for the mandarins to burn the fleet.

Bill White · 2003-12-10 11:52:36

First, I agree that a new heavy lift booster is more elegant, probably cheaper in the long run and may be the optimal solution overall. However, to avoid putting Mars "on hold" indefinitely while we figure out the politics of building new, better and cheaper heavy lift, I wish to ask about this idea:

= = =

Can the MarsDirect mission planning be modified to allow a brief stay in a stable orbit in LEO? Or MUST trans-Mars insertion occur immediately (or nearly immediately) after launch?

Why do I ask?

What is the cost per pound to lift with Ares?

What is the cost per pound to lift with Elon Musk's Falcon? (Or the Russian Dnepr for that matter)

Could a modified MarsDirect be designed to allow on orbit rendevouz with payloads launched at a much lower cost per pound?

Launch TransHab on Ares (or Energia) and then dock with a series of Falcons/Dneprs and unload water, food and other high mass bulk goods.

Does this help the MarsDirect mass ratios?

From the spacetoday article:

Another comparable vehicle to the Falcon 5 is the Dnepr, a converted Russian SS-18 ICBM. The Dnepr can place up to 3,700 kg into LEO for a price comparable to the Falcon 5: an estimated $10-15 million. The Dnepr, however, has seen little activity, with only three launches since its introduction in 1999 (a fourth is currently scheduled for the second quarter of 2004.)

Add $30 million to the cost of Mars Direct and gain 7600 kilograms of extra supplies (well not exactly as trans Mars injection remains necessary) but at least a substantial additional amount of mass can be brought along

With a $30 billion budget whats another $30 million?

Bill White · 2003-12-10 12:28:13

Mars Direct has always been right on the lower edge of sane mass estimates, putting four people in the tiny ERV or HAB for that long without nice radiation shielding and then there's that scarry artifical gravity spinning scheme. Some more modern MD variations rumored already cut out the pressurized Mars rover and drilling rig out to save on weight. However, the problem with MD is not so much that its too heavy, but rather it is designed to do the wrong thing...:
If we make it about science, Mars Direct (or somthing like it, such as Nasa DRM) is what we will end up with. Any Mars mission should be in the context of establishing a perminant base first, and science/exploration second, which would need a architecture much (MUCH) bigger and more reuseable than MD. Make no mistake, Dr. Zubrin is wrong, MD would become a "Martian Apollo" given its expendable, margin-less ultra-light design. You can't make a real base out of HAB modules, the occasional medium cargo lander, and having to build/launch a new HAB & ERV every time you need a crew rotation. Adding reuseability, heavy payloads, and larger crews to the Mars Direct plan will, well, eliminate the possibility of it being direct wouldn't it? That would essentially lead to having to scrap the architecture to a large degree and would be a little more than a "upgrade..."
. . .
Wait until we are ready to go big, and go to stay. In the mean time, go back to the Moon, and get Nasa used to supporting humans on other worlds over the long term while building super-engines, inflatable modules, and Mars fuel factories. Mars Direct gets us there in a hurry, but gets us off just as fast... No flags and footprints!

How can we establish a permanent base without scouting the ground first?

I might more easily agree that Mars Direct should be delayed until there is a commitment to a follow on settlement program, however, how can you select a site for your settlement without some on the ground surveys being done first?

Bigger better ships will naturally follow from a commitment to settle.

GCNRevenger · 2003-12-10 20:26:25

Don't take me too literally... *chuckle*

My theory is, that whatever system is designed to go to Mars is the one we will be stuck with for a long time, like we were stuck with Shuttle and getting ready to be stuck with OSP for some time. The idea is not to nessesarrily set up a perminant base on the first flight to Mars, but to not have to build a whole new means of getting there when we do want to set up shop. This way, Nasa simply has less of an excuse and an easier time convincing the gov't to go to stay fiscally speaking. I still think the first mission should be to lay groundwork for a perminant base (at least) primarily and to do science/exploration on the side.

Building a high-thrust/high-ISP engine is the way to go, hands down... the radiation and the zero-gravity issues simply aren't as big of an issue if you can get there in ~100 days. With a GCNR or VASIMR engine and their very high ISPs, you don't have to aerobrake at all (which remains a high-risk low-tollerance untested technique), propulsive capture would work just fine. An engine that has 3000Isp gives tremendous freedom compared to chemical or solid NTR engines... the extra fuel for propulsive capture might even be able to do a direct abort!

The problem with solid NTR engines is mainly the temperature: since Isp for a given fuel is directly related to temperature, the higher the better. Unfortunatly, it isn't practical to have a solid core nuclear reactor of any configuration operate signifigantly above 3000C or so, limiting the engine to ~1000Isp... They just melt. Also kind of nice about a GCNR engine that you dump the fuel after firing is that you don't have to shield against the long-lived isotopes, simply eject them out the nozzle and change course slightly.

I'm also not thrilled about the idea of surface-use of NTR engines, except maybe as a one-shot acent/ERV vehicle. The engine itself would be heavy, the tanks would be large (low density LH2 versus high density LOX/CH4) and have to withstand ground launch, the engine would have to have much higher thrust, the LH2 would be hard to bring/make and have to be kept cold, and the radiation... building a bioshield for the crew cabin isn't that bad, but you'd have to enclose the reactor almost entirely (Astronaut walks around the rocket to take a picture of a rock, gets a 500REM dose...), thats alot of kilograms. Oh! And you couldn't service the thing by hand for weeks or months (or years!) if you wanted it to be reuseable.

wgc · 2003-12-11 07:54:32

I thought the amount of thrust you get from an ion engine was dependent on the amount of power you put in , ie. you would get a greater ISP using a nuclear vs. solar array. Didn't deepspace one ion engine achieve a higher thrust than smart-1. Doesn't seem like that mission duration was that long.

GCNRevenger · 2003-12-11 10:39:29

Increasing the power supplied to an ion engine does increase its thrust, yes, but that still isn't much thrust, and a large (say, 400KWe) nuclear reactor is still pretty heavy. Without more thrust than ion engines can provide, it will still stretch transit time alot. This is okay for most cargo, and a ion powerd cargo tug would be a great idea, but its not fast enough for a manned mission.

wgc · 2003-12-11 10:56:57

But I thought the HIPEP NEP engine , one of the candidates for the JIMO mission was being touted as a "High Power" , "High Thrust" ion drive. The Nasa website says it could reduce transit times. Ok not to sound dumb, but what are we talking about in terms of transit time from earth orbit to mars overall vs. using chemical rockets for Mars Direct.

Rxke · 2003-12-11 13:46:49

Don't take me too literally... *chuckle*

Hey! That's copyrighted stuff, dude!

(Sorry, couldn't resist)

wgc · 2003-12-11 13:53:07

Ask an intelligent question , and get a stupid reply.
I thought we were talking Ion engines.

Rxke · 2003-12-11 14:00:54

GCNRevenger,

You're of course very right in pointing out that more research into GCNR and Vasimir would be the more logical thing to do, but... Long-term planning hasn't been any government's strongest point, ever... And business has this thing called fiscal quarter... "Yea, um... we spent another bunch of money on somethng you shareholders won't see the benefit...errr never mind, look at our new old reliable LOX stuff!":D

So we're stuck with what we have, basically, we can only hope there'll be more demand for high isp stuff in the fuure, so that there'll be more money invested into those fields. Now it's just 'a waste of money' becase no immediate payback.

wgc, ion engines are more propellant-efficient, but only get 'interesting' for longger-range missions. They accellerate *very* slowly, but for long times. They're cheaper to go to mars, but slower... For further-outlying targets, like neptune, pluto etc, they are both cheaper and faster than the 'traditional' stuff. Simply because they have 'more time' to keep accelerating towards their targets. Mars is simply a little bit too close...

Rxke · 2003-12-11 14:05:16

wgc, about the stupid reply... sorry, i was only fooling around a bit... Didn't think you'd be reading that before i posted my 'real' reply... Turns out i'm a slow one at the keyboard.

was in no way meant to digress from the subject.

(edited: wow, this thing got posted 3 times in a row... another mess-up. I'm having one of those days, i guess)

RobertDyck · 2003-12-11 15:57:59

Can the MarsDirect mission planning be modified to allow a brief stay in a stable orbit in LEO? Or MUST trans-Mars insertion occur immediately (or nearly immediately) after launch?

You can stay in LEO just as easily as ISS. You can't stay in medium orbit because that's where Earth's radiation belts are, but low or high orbit are fine. The issue is that circularising in Earth orbit takes fuel, a directly launch to escape Earth doesn't need that fuel. But if a smaller launch vehicle is significantly cheaper, then the additional fuel to circularise is worth it.

GCNRevenger · 2003-12-11 23:19:45

I really, really, really, really, really, REALLY doubt that there will be any money to be made outside satelite launches to Earth Orbit for a very long time... The Space Island Group people are nuts... So, any investment made in hardware for use beyond Earth Orbit is going to be government funded, without question, or at least heavily subsidised beyond recognition. And with alot of big, decade-sized multibilliondollar megaprojects, once started, are hard to stop with sufficent support.

The huge differences in performance for a GCNR or other >1000Isp high thrust engine is really an enabling technology; the size of payload and ease of transit afforded by such megaengines lets you do things that weaker engines simply can't. Chemical engines are simply not efficent enough to do much beyond a "Martian Apollo," though they are just fine for a Lunar base.

I don't have any estimates for how long a transit using a cluster of Nasa's HiPEP ion engines would take, but it would be a while. HiPEP style engines are a big step up from older DS1 types, but the DS1 engine could only produce the same thrust as the weight of a sheet of paper... even a several fold increase in thrust-per-weight would only be a marginal improvement. Its taking ESA's Smart-1 a whole year and a half just to get from Earth to Lunar orbit. Ion engines are ideal for JIMO because Nasa is in no rush to get to Jupiter, and they want JIMO to last for a long, long time, so fuel mass is paramount.

RobertDyck · 2003-12-12 04:16:01

I see you are a one issue guy, GCNRevenger. Tying yourself to a single particular technology ensures your obsolescence with that technology, and makes your arguments very tired. At one time I thought that Venus was much better than Mars because Venus has nearly the same gravity as Earth and plenty of atmosphere. But the only technology that could terraform it is biological and that would take decades before the planet could be colonized. No, I don't think centuries, I said decades. But I doubt Venus could be colonized in my lifetime even if serious genetic engineering to create the terraforming microbes started now. However, Mars can be colonized NOW. I had also advocating simply dropping the idea of any form of nuclear propulsion because it was politically impossible. However, Dubya has made it viable so I say lets take advantage of this opportunity while it exists.

The issue today is a renewed focus and direction for NASA. Let's use what can be developed quickly to get a permanent base on Mars. We had the technology to do it a decade ago; if congress approved Mars Direct in 1990 we would have had men on Mars in 1999. If Nixon hadn't cancelled Apollo in 1972 we would have had men on Mars some time in the 1980's. Now congress and the President's office want to give NASA a direction. Possibly because they have been blamed for all the project cancellations. Possibly because they want to see something accomplished with the $15 billion they give NASA every year. Whatever the reason, let's go with it, not hold NASA ransom to a single pet technology.

Getting space profitable in the short term is necessary if it is to develop. There can only be so many communication satellites, and technology is becoming obsolete so fast that it is hard to justify a commercial communication satellite. There are other means to make money from space, and one goal congress has is to see a new industry they can tax spawn from their investment. How is the government going to get financial return on investment? Pretty pictures are great for gaining votes, but the exploration probes require tax dollars to pay for them and higher taxes reduce votes. Serious astronomical observatories are needed for academic study, and universities and research institutions are willing to pay for them, but they only have so much money. Pictures from space telescopes can be sold for artistic profit, but that only gains so much money. Space tourism can happen, and will as someone develops a safe and economical transport to LEO.

The Space Island Group had a good idea. It would only require a few small solid rockets to boost empty Shuttle tanks into orbit, and improved thermal insulation that won't flake off. Don't give me any guff about internal furniture; that can be installed after it's in orbit.

There will never be a single magic solution that is the be-all and end-all for economic development. A healthy economy has diversity. That means Earth orbit tourism, and commercial satellite launches, and on-orbit satellite servicing, and asteroid mining, and lunar mining, and lunar telescopes, and science probes all over the solar system, and Mars colonization. This can all start now. The two things we need are reduced cost access to LEO, and a permanent outpost in space. ISS requires continual reboost just to keep it from falling out of the sky, so I wouldn't call it the permanent outpost. With no natural resources to harvest or territory to explore it isn't self-sustaining. We need to get a permanent base on Mars to act as a beach-head for colonization. Some argue the Moon can serve that function, but I'm still not convinced there is enough water ice to support a colony, not to mention carbon or nitrogen. We can go to Mars now, and we need to go to Mars now.

wgc · 2003-12-12 05:42:45

Well I suppose you could use a HIPEP engine in a form of cycler, than the most fuel expendeture is in catching up and docking with the fast moving cycler. It may take the cycler awhile to get up to a resonable velocity but who cares because there is no crew onboard.

Bill White · 2003-12-12 11:39:58

Reasons to oppose MarsDirect:

Radiation protection

(See the recent NY Times piece and Zubrin's e-mail response)

Anti - MD position: No Mars until AFTER lots and lots of additional research (which is not yet funded). Zubrins's reply, radiation calculations are wrong and additional shielding is available (water, new plastics like Demron).

IMHO water is the optimal radiation shield. No heavy elements to emit neutrons like lead. A too thin lead shield can be worse than nothing when showers of neutrons are released "shotgun like" from the nucleous of the atom as the fast moving cosmic rays strike the shielding.

Water is also dual use. The astronauts can always find a use for water once they get to Mars.

Lunar water or Terran water? If someone can deliver water to LEO from Luna for less than Elon Musk can lift water from Earth, use lunar water. Otherwise use Falcon. See below.

Micro-gravity

CNGR and others argue that centripetal force is unproven and unsafe.

Unproven? True.

Unsafe? Unknown unless/until we try. Am I right about this? ???

NO ONE has been willing to fund simple experiments to see if centripetal force can be used to simulate gravity. Why not?

Robot experiments have been proposed and I believe I may have been the first to propose using expended Soyuz / Progress tandems to "practice" tethered flight manuevers.

Mass ratios / Chemical vs Nuclear propulsion

No Mars UNTIL humanity deploys fast big nuclear rockets. For me this is a Catch-22. Do I want fast big nuclear rockets? Of course. Do I want Mars "held hostage" until funding initiatives are found to build fast big nuclear rockets. Less sure about that. Like I said, Catch - 22

Mars Direct mass budgets too tight? Stage in LEO. Not pieces of the primary vessel, but launch bulk supplies with low cost means. Buy 12 Dneprs from the Russians or 12 Falcons from Elon Musk. Ask for a quantity discount Rendevouz 2 or 3 with each MarsDirect transit hab and offload water.

Why water? Its heavy and its a great radiation shield. Rather than postpone Mars until we deploy (1) a big new booster and (2) nuclear engines, be frugal and creative with whats available off the shelf.

Dnper can deliver +/- 3500 kg of water to LEO for $10 - $15 million. Can Ares be re-designed to add 3500 kg of payload for $15 million? I don't think so.

Launch MarsOne to LEO after 7000 kg of water is waiting in a stable orbit. Dock. Inflate Transhab (collapsed to fit in the Ares fairing) and transfer the water to TransHab filling the radiation shields.

No room for a pressurized rover? Buy another Ares (or Energia) and direct throw to Mars a rover stockpiled wthe additional food, water, fuel, tools a drill rig and trenching tool. If we cannot soft land the pressurized rover by remote operation, we cannot soft land the ISSP unit anyways, right?

IF this is to be part of a settlement campaign, launch vehicles will need to roll off assembly lines like Dell computers. Buying one more once the R&D is finished should be only a small fraction of the total project cost.

Are there other objections to MarsDirect?

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