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I just started reading The Case for Mars and it's gotten me very excited. The question is where exactly is NASA on adopting this plan? Is this going to be a congresional decision only or what? In the book it says Zubrin met with top level NASA people about the plan and they liked it. If it's just a question of re-schuffling current NASA money could't Sean O'Keefe make this decision himself?
Danny------> MontrealRacing.com
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The short answer is "no"
O'Keefe would have to do away with Shuttle and the ISS programs to have enough money to fund MarsDirect or NASA's similar DRM-III plan, and he really can't do that without congressional authorization, especially since the ISS and Shuttle construction of it is a matter of international agreement and not an internal NASA or even US decision.
NASA has a plan called the Design Reference Mission, which is vaugely similar to MarsDirect: Three large launches, each equiped with a modest nuclear upper stage and aerobrake shields are sent to Mars.
Flight #1 puts a fully fueled Earth Return Vehicle powerd by storable propellants into Mars Orbit
Flight #2 is the MAV/Surface Payload, a small rocket to get from the surface to the ERV, the nuclear power plant, and surface vehicles & miscelleous stuff. Different versions call for the MAV to be sent fueled and some call for fuel to be made on Mars ala MarsDirect.
Flight #3, the HAB, launched manned from Earth and lands on Mars near Flight #2. The crew of 6 does Mars for 500 days or so, then pile into the MAV and head home.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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I just started reading The Case for Mars and it's gotten me very excited. The question is where exactly is NASA on adopting this plan? Is this going to be a congresional decision only or what? In the book it says Zubrin met with top level NASA people about the plan and they liked it. If it's just a question of re-schuffling current NASA money could't Sean O'Keefe make this decision himself?
You have several question in there and I have been follow it loosely, so I will see if I can answer your question and other people on this board will give you there answer.
Your question are:
1. The question is where exactly is NASA on adopting this plan? How is NASA in regard to Zubrin and his Mars Direct?
They are on friendly terms, but NASA is cold to the idea of a Mars Direct plan. Now NASA did a study with the European space agency to go to Mars using the Mars Direct floormat to be use for illustration purposes and not to be use as a serious effort for going to Mars. The only reason they used it was that it was the cheapest way to get to Mars and it was more or less laid out as to what you need to do to get to Mars. So that was there primary reason for using the Mars Direct Model.
2. Is this going to be a congresional decision only or what?
Yes, this decision has to be make on either a congressional or by a President and generally they have to work together to make something like this happen.
3. In the book it says Zubrin met with top level NASA people about the plan and they liked it. If it's just a question of re-schuffling current NASA money could't Sean O'Keefe make this decision himself?
There are some people in NASA that like plan and there are some people in NASA that don't like the plan.
No!
Sean O'Keefe can not reorder the NASA budget to do the Mars direct mission even if he wanted to. The money in NASA budget is dedicated to individual programs within NASA and Sean O'Keefe does not have the authority to move the money around where he would want to put it. So any shifting of the budgets is going to be very limited by Sean O'Keefe and as he has no control over it.
Larry,
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For an apollo style direct mission is a great idea, it is designed on apollo, but because of the distance a few things needed to be changed , but this is a scout mission onto Mars , nothing else.
Scout missions can happen, when we have the start of the infrastructure necessary to back it up with a colonization approach for permanent settlement. By the time the first and posible second scout missions are over, then we move into colonization mode. The scout missions have as one priority to survey the proposed sites for large scale settlement.
It Dosn't matter if we go now or in the future but , what matters is the scout missions must be part of a large and more complex strategy that under implementation.
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I've been trying to get a sense of the NASA objections to Mars Direct, and so far I have found two:
1. They're concerned that in situ resource utilization won't work. In other words, no one knows how easy it is in practice to build the couple tonnes of equipment (reactor, sabatier) fly them to Mars, and have them work reliably enough to refuel a rocket with no one around to repair them. Zubrin feels a robust system can be built that will work, but remember any complex system can break if one little thing fails. For that reason, NASA seems to be more comfortable with using a Mars Ascent Vehicle small enough so that if ISRU doesn't work, it can be sent to Mars with a full load of fuel. That's the reason they favored what Zubrin calls "Mars Semi-Direct" with three vehicles instead of two. The complicating factor: one has to leave an untended vehicle in Mars orbit for years and rendezvous with it in order to fly home. Which is safer, a complex ISRU system, or a complex earth return vehicle, both of which have to sit untended for years and work fine?
2. The NASA-ESA joint study of Mars Direct noted that it had rather thin safety margins. This probably refers to the lack of intermediate steps; no Mars flyby mission is proposed, no near-Earth asteroid visit to test out the equipment, etc. But those steps could be added. Some Mars exploration plans propose a first mission to Phobos and Deimos. This allows the Mars orbital vehicles to be tested in actual use separately from a landing; rather like Apollo 10 tested out systems without an actual landing on the moon.
The thin safety margins may also be a reference to the tight mass budget of the proposal. Mars Direct does include a "spares and margin" in all of its calculations, but mass creep could seriously threaten the mission, since the booster would be developed to throw a vehicle of a specific mass.
3. The other safety issue that occurs to me is that if one flew the hab and ERV to Mars together, the ERV could serve as a lifeboat if the hab got crippled. This is the Apollo-13 scenario when the astronauts had to rely on the lunar module's systems to get them home safely. Mars Direct is not set up to do this, but presumably could be.
-- RobS
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In reference to NASA's problems with Mars Direct:
I don't think NASA is concerned that Martian resource utilization won't work. Instead, there is a concensus that you could land a lighter ascent vehicle (instead of Zubrin's ERV) on the Martian surface, and still get the vast majority of your delta-V for earth return by producing propellant for the flight from Mars' s surface to Mars orbit. The overall result is less spacecraft and fuel mass being sent to Mars.
NASA has other problems with Mars Direct. They want a crew of six, Zubrin thinks you can get away with a crew of four. Rocky Persaud, president of Canada's Mars Society, did some time at a Mars analogue station and remarked that even six might be too few for a Mars mission.
I've also spoken with some people who did the ERV design contest (Kepler Prize) and they feel that Mars Direct, in its purest form, is unrealistic and unworkable. Granted, I saw some significant problems in their proposal, but I feel that these would not have affected their overall conclusion.
Personally, I prefer the Stanley Borowski (et. al) version of NASA's DRM. It retains Zubrin's ideas like artificial gravity and Martian resource utilization (at least for the flight to Mars orbit,) introduces nuclear-thermal propulsion, and incorporates some reusability. Check it out and tell me what you think.
"I'm not much of a 'hands-on' evil scientist."--Dr. Evil, "Goldmember"
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We must remember no matter how we get there to Mars we must stay on its surface for the approximate 2 years cycle before the window to return can be made.
Now that said, That makes for a pretty big Mars lander for supplies for the crew to survive on, Another one just as big for all equipment to mine, process and refuel return vehicle. Lets not forget in addition science equipment, other habitat modules and or green houses.
Also if the plan leaves the return vehicle in orbit for that long what could or might happen will happen to it, so where is the back up if only one set of them are sent.
As you can see it is a fleet of ships just to support a minimal crew safely.
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Well SpaceNut, the solution to that problem is simply not to have a backup plan... somewhere along the line, you have to trust in the hardware, and the less trust you afford the system(s) it gets exponentially more expensive. There will be no fleet of ships either which way.
For the Semi-Direct arcitecture, you just have to trust that the ERV will be good for three years on orbit, which is not that unreasonable since it will just be in storage... the LSS will be shut down, the engines will not have been fired once yet, and so on. The ISRU is obviously the less reliable solution, but the fuel plant and vehicle will land and generate the required return fuel on Mars before the human crew is sent, so if the plant were to break down that wouldn't be such an issue, and so the only trouble is keeping the fuel stored and the ERV/MAV storage on Mars.
MarsDirect does two things, it illustrates the smallest theoreticly workable Mars mission arcitecture, and showcases some ideas to make the trip a little more comfortable... That said, artifical gravity is not really nessesarry, the crew size is obviously too small to accomplish mutch, and the arcitectures' reliance on the Ares rocket is questionable.
It is simply not practical to build a shuttle-derived vehicle of any sort with a LEO payload much higher than 120MT, which makes the MarsDirect mass margins pretty small. Dangerously small. If somthing turns out to be heavier then the plan calls for, and Ares can't handle it, the whole idea is sunk. MarsDirect ought to call for a 150MT minimum launch vehicle, which would make for a very comfortable margin. For instance, the ERV vehicle is probobly much too small for four people to live for 6-9mo without going bonkers, and it is questionable if a large rover can be included at all.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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The beauty of Mars Direct is that it shows us how a single mission can be done. You solve all of its problems if you think in terms of a sustained program. Any serious mission to Mars should spend five years launching equipment to Mars before anyone arrives.
We live in a time when robots can do much of the work once invisioned needed by human labor. Let's assume that any mission to Mars is preceeded by a pair of rovers.
The rovers could do some site exploration and shake out any bugs before equipment arrives.
Then our pair of rovers can move delivered hardware from where it actually landed to where our crew is going to land.
Many people want you to think that going to Mars is a challenge for the next generation, but it is not. We have the technology to do it today, but not the will. Sending humans to Mars is a challenge yes, but not one that need costs trillions or even hundreds of billions of dollars. All the problems can be worked out by a serious and dedicated plan to do such.
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The journey to Mars in months forces us to think about crew health.
Mars astronauts will hibernate for a 50 million-mile journey in space
http://www.belfasttelegraph.co.uk/news/ … ory=563721
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Mars direct of some variation very doable but where are the funds?
It Isn't Mars, but It'll Do for Now
Mars and the Moon can be tough on spacesuits. So can Arizona's high desert, and it's a lot easier to get to.
That's why a NASA-led team is at sites near Flagstaff, Ariz., this month to try out equipment -- spacesuits, rovers and science gear. The tests could help America pursue the Vision for Space Exploration to return to the Moon and travel to Mars.
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The in-situ propellant creation idea proposed in Mars Direct will be tested with the Mars Sample Return Mission. Also no matter how much you test a technology it can still fail. I think the original Mars Direct idea was the best. The on site propellant production unit for the Mars Sample Return Mission should have sensors and camera's or whatever necessary so that if it fails NASA can learn exactly what happened and fix it. Actually I believe two Mars Sample Return Missions should be sent before we ever launch the first large craft for on site creation of return fuel for humans. This would provide an acceptable level of testing of the technology.
Also NASA can afford Mars Direct now without taking anything from ISS. NASA's budget is what? $15 billion a year? Take $7 billion a year from it and put it towards Mars Direct and you will have it paid for in seven or eight years. Many of the little projects would have to be shelved and possibly the space shuttle as well but it's for the better.
Spacenut: 2 years on mars before we can return? That's not correct. And there is no way anyone is going to take a greenhouse with them on the first, second, or even third flight. Your fleet of ships idea is way out of line with the Mars Direct idea. Did you read the book? Astronauts hibernating? I sure hope we are not going to wait for that to be figured out.
Six astronauts to mars is too many. That's a lot of extra food, air, and water that must be taken. Four is the perfect number. Two to go out in the pressurized rover and two to stay back with the ship.
Deagleninja: We already have rovers on mars. They've been there for years. Why would you want to go to all the trouble to build a robot and send it to mars just to move some equipment to another place when you can simply land the humans next to it? Put it where you want it in the first place and leave the robots at home.
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Actually it says 1.5 in the Esa to Mars society comparison document.
http://www.marssociety.org/docs/MDCost.pdf
As for the green house sure would be cheaper than the extra rockets for supplies.
In-situ propelent is the solid rocket or is the gases filtered and seperated to get what is needed from what might be frost or under ground water.
This also means skipping the moon as a proving ground as well as other things.
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It is simply not practical to build a shuttle-derived vehicle of any sort with a LEO payload much higher than 120MT, which makes the MarsDirect mass margins pretty small. Dangerously small. If somthing turns out to be heavier then the plan calls for, and Ares can't handle it, the whole idea is sunk. MarsDirect ought to call for a 150MT minimum launch vehicle, which would make for a very comfortable margin.
Hear, hear!
I tend to think that launching it all in one shot is not a very good idea to begin with. As Dr. Benton Clark of Lockheed Martin's Mars group points out, it's good to have time in low earth orbit to check out all of the systems before you launch to Mars.
Right now I favor building a minimally-modified Shuttle C that can put 80 tonnes in LEO. Two launches would put up an 80 tonne spacecraft and an 80 tonne Mars injection stage. A third launch, this time with an EELV, can put up a Crew Exploration Vehicle that can take the astronauts to their waiting ship (as the Shuttle C would not have an escape tower.)
For the other elements in the plan (Mars Ascent Vehicle and the orbiting ERV,) two Shuttle C launches will be needed for each element. The pieces would be docked with their Mars injection staged under remote control from earth, just as the pieces of Mir were.
Assembly in space doesn't have to be painful as long as it's kept to a minimum and the shuttle is left out of it.
"I'm not much of a 'hands-on' evil scientist."--Dr. Evil, "Goldmember"
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Actually it says 1.5 in the Esa to Mars society comparison document.
http://www.marssociety.org/docs/MDCost. … MDCost.pdfAs for the green house sure would be cheaper than the extra rockets for supplies.
In-situ propelent is the solid rocket or is the gases filtered and seperated to get what is needed from what might be frost or under ground water.
This also means skipping the moon as a proving ground as well as other things.
The trip to mars will take 180 days with a 2 year, coasting, free return trajectory in case of engine malfunction. Now assuming everything goes well with the launch from mars the return will be less than 2 years.
Your posts are short and lack detail so I'm assuming in your comment about bringing a greenhouse and growing food rather than launching an extra rocket with food supplies would be cheaper. Where in the mars direct idea is there anything about launching a rocket with supplies? There isn't because it's not necessary. Also there is no guarantee we can grow food on mars. That would be a huge risk to take.
I don't understand your comment about the in-situ propellant. The fuel made on mars is not solid propellant (chemical gasses) and nothing is taken from the ground. All of the propellant needed comes from the hydrogen brought and the carbon dioxide gas taken from the mars atmosphere.
I would be for a moon landing only if it tested a lander that would then be used on mars.
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I am told in another thread that Hydrogen boils off due to the need for super cooling so the concept of taking it with you on the 180 day journey plus the 1.5 years on the surface would probably mean that by time you get to use it on the way back it would be gone.
Sorry if the insitu fuel did not come across, There are two forms of fuel deriving approaches one is to mining and seperated out of the Mars soils the minerals to make solid propelent and the other is the mining the soil and recapture the water contained within it to make hydrogen based fuels. A third would be to collect atmospheric gasses to refine the fuel type to be used. In all cases a large amount of equipment is needed just to provide for a return trip. some of which can double in use for survival for producing oxygen.
On the side of bringing the needed supplies with you or sending an advance ship ahead of the explorers that will be staying for quite a long time, how big do you really want the ships to be or of how many will you be willing to send is the question. The problem I see is for either approach is what if we can not leave Mars for what ever reason how would we survive, that is why I suggested the green house, you would get a two fold objective from exploring the science of plant growth on mars, one if food and the other is extra oxygen.
If no plans are to stay for any period of time then all we are doing is just another flag and foot prints to which I am not in favor of. Lets go to stay for long periods of time and to keep going.
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Lockheed Martin engineers believe transporting 6 tonnes of hydrogen to mars would not be a problem as long as you started out with an extra 15% to cover boil off-page 61 in The Case for Mars.
The book is not that expensive. You can order it from Amazon.com.
In the Mars Direct idea there are two earth return vehicles on mars before humans get there. If for some incredible reason neither of these work we can send another one from the earth. That is triple redundancy. It doesn't get much better than that for space work.
Your dome idea is full of risk and uncertainty. It's weight is not accounted for in Mars Direct and would likely require a launch just for it. Also, mars regolith has dangerous oxides that would almost instantly kill any plant. Where are you going to get the water from for the plants? You would need an acre per person for the plants to supply enough food or oxygen for a stranded crew.
There is no way any space agency would attempt to create a permanent settlement on mars on the first landing. It's not going to happen because that would be incredibly risky and for absolutely NO BENEFIT at all. Don't be a moononite.
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So if I am reading your blog correctly, there are three different ships with only the mars lander stage being the same for each aside from the possible return to Earth vehicle.
Each rocket center section between the return and lander portions are then comprised of a crew habitat, cargo ( water, Food) and equipment.
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Here's the Mars Direct plan:
Year 1: Send an "Earth Return Vehicle." This has largely empty tanks, six tonnes of liquid hydrogen, a 3.5 tonne 100-kilowatt nuclear reactor on an 0.5 tonne light truck, and an 0.5 tonne sabatier reactor/electrolysis/cryogenic refrigerator unit to make and store fuel. The "ERV" also has a 50 square meter crew cabin and the six months of supplies needed to fly back to Earth. But it has no people.
Once it arrives, one drives the reactor out of the cargo bay telerobotically on the truck. It goes out about 100 meters, unreeling a power cord as it goes. Then the reactor is activated and it starts to make 100 kilowatt of power, which is sent back to the ERV. The ERV sends the liquid hydrogen through the sabatier to make water and methane, then electrolyzes the water to hydrogen and oxygen. The methane and oxygen are liquified and stored. It actually isn't hard to liquify them because the liquid hydrogen is just about cold enough to liquify them both while the hydrogen is being heated up for use in the Sabatier.
The ERV also converts carbon dioxide into carbon monoxide and oxygen, stores the latter, and throws away the CO. The result, after about 10 months, is enough methane and oxygen to fly the ERV back to Earth, with enough water, oxygen, and methane left over for the crew to breathe and wash with and fuel their vehicles for 18 months.
2. Year 3. A hab with four crew flies to Mars and lands near the ERV. The hab stays on Mars and becomes the base. They can put sandbags on the roof to reduce radiation exposure.
3. Year 3 also, another ERV flies to Mars. If the hab does not land near the first ERV, the second one can land near it. The second ERV also has hydrogen, a reactor, a truck, and fuel making equipment. It serves as a backup launcher for the crew in hab one, and as the primary ERV for the second crew that follows two years later.
The cycle is then repeated every two years. If one were to create a central base at one place on Mars, ERVs could be sent without reactors or hydrogen, as there would already be reactors there and probably a water well. Then the ERV could carry ten tonnes of cargo.
It's a very clever, simple, system. The more I study Mars, the more I like it.
-- RobS
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"Also NASA can afford Mars Direct now without taking anything from ISS. NASA's budget is what? $15 billion a year? Take $7 billion a year from it and put it towards Mars Direct and you will have it paid for in seven or eight years. Many of the little projects would have to be shelved and possibly the space shuttle as well but it's for the better.
Spacenut: 2 years on mars before we can return? That's not correct... Did you read the book?...
Six astronauts to Mars is too many. That's a lot of extra food, air, and water that must be taken. Four is the perfect number. Two to go out in the pressurized rover and two to stay back with the ship."
First off, I don't think its nessesarry to read Zubrin's book to be able to discuss the basic tenants of MarsDirect, and being that you apparently have Dook, then i'm sure you are well versed enough to fill us in on any missing details...
A good chunk of the ~$14.5Bn that NASA has goes to the administration of the agency and into basic aerospace research, with a billion or so going to robotics and ~$8-9Bn going to manned spaceflight. About $3.0-3.5Bn goes to the ISS program, and $4.5Bn to the Shuttle program, with pieces of that and the rest of the budget for manned flight infrastructure (astronaut training etc)... As Shuttle and the ISS are inseperably joined at the hip, you can't really run one program without the other.
So, with about $10Bn out of the budget spoken for, and a good chunk of that $4.5Bn spent on administration, field labs, and basic research (which is one of NASA's primary missions) etc it is not at all credible to suggest that NASA suddenly cough up $7Bn a year. Even cutting Shuttle entirely and sending up $500M worth of CEV flights a year, slicing an additional $3Bn out of NASA's budget isn't happening... Particularly since you need Shuttle infrastructure to build/fly Ares, which will doubtless be overpriced... This is considering that the optimistic MarsDirect pricetag range can be attained at all through some competition/prize nonsense...
For the mission arcitecture that either MarsDirect or NASA's DRM-III use, the crew must stay on Mars 500-600 days for the planets to allign, in order to minimize travel time back to Earth. A shorter stay means a longer flight back, and more than 6mo is pushing it, artifical gravity or no.
Four people is not really that many when you consider all the science that should be done and the nominal cost of sending a slightly larger vehicle. I believe that even Doc Zubrin's Mars analouge station has suggested as much, and NASA (which has a bit more knowhow in planning these things) wants to send six. If MarsDirect with inflatable modules can't handle six people because it would weigh too much, then it is quite obvious that MD is too small, not that six people is too many, and that MD cannot scale at all. Again, MD is badly limtied by its launch vehicle, either launch it with a clean-sheet >150MT class HLLV or do it in 2-3 launches of Shuttle-C, well within KSC's ability to accomplish with an SDV.
For my part, MarsDirect is too small and places too much emphasis on being small and cheap rather than being effective and robust; if there are misgivings about the MD mass margins before the thing even leaves the "pretty picture phase" that should be some indication of trouble!
Some have a silly notion that a group of warn-out hab modules constitutes a "base" or somthing, and generally place far too much faith in the arcitecture being useful for anything other then sending and retreiving too-small numbers of people.
Mars Semi-Direct, aka NASA's DRM-III mission, ought to be considerd the minimum baseline mission, with MarsDirect being an interesting thought experiment/engineering excercise... I prefer the idea of building larger vehicles in 2-3 pieces in orbit, as you are simply not so chained to the limits of the launch vehicle, which would limit the options for future growth.
Edit: Shuttle-C class "MLLV" Mars mission breakdown:
Launch #1: TMI stage with two or three RL-60 engines and their liquid Oxygen
Launch #2: Mars lander, some surface payload, and TMI liquid Hydrogen, Earth/Mars transit hardware (solar, comm, etc)
Launch #3: TransHab based HAB module that seats up to 8, more surface payload, and the aerobrake shield
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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2 things
1) Great to have you back GCNRevenger
2) NASA has its own Mars semi direct plan which insists on a minimum of 6 crew and maybe this is too small. The problem is that as a social group it is too small and as a team it is maybe too big. But it is safety we should look at and sending 6 people is better than 4. A larger crew is better for group dynamics as we are going to send these people away for a long time and the more the people the more the chance for different interaction.
Chan eil mi aig a bheil ùidh ann an gleidheadh an status quo; Tha mi airson cur às e.
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I can say that I have never read the mars direct book and have only read what is in multiple versions of these or simular programs posted on the web. They all seem to place any stay on mars as more than the time to get there at a minimum, to the journey time plus one Earth year as a mid point and at the far end of the scale is the 2 year plus period. It does not matter to me how long so long as enough of the job of construction of a more permanent base can occur.
Also we are sending probes every 2 years to explore mars, due to orbital machanics so how could we send them every year and if so why is not Nasa on that time line instead for missions to Mars.
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On the topic of crew size:
Has anybody considered the prospect that some of the astronauts may not becoming back from Mars? There are a good number of chances that an individual astronaut could be killed, particularly on the rugged surface of Mars, or from cancer or another disease while on the ship. If you lose a person or two, will the Mars Direct crew be able to make it back? It takes two people to run the ISS as it is, so this seems unlikely.
It's like the Apollo 18 scenario in James Michener's fictional book "Space." I won't ruin it for you, so I highly recommend you read it for yourselves.
"I'm not much of a 'hands-on' evil scientist."--Dr. Evil, "Goldmember"
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Any concieveable Mars ship built with circa-2010 technology will probobly be very automated compared to anything now, plus the ISS was never designed to be low-maintenance, since you would have loads of manpower with the big crew and easy up/down transport with Shuttle's big MPLM modules. I bet it is possible to build the ship so only one crewman could probobly handle maintenance tasks, and you really don't need people to guide the ship other then landing.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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I think a six-person crew is better, if at all possible. Yes, the two functioning habs at Devon Island and in Utah both have a third story and a crew of six.
According to The Case for Mars, cosmic radiation and solar radiation exposure on a typical trip to Mars and back (30 months) raises the chance of death from cancer from about 20% to about 21% (maybe it was 22% to 23%; I can't remember the exact numbers). In other words, smoking, drinking, and obesity are all more dangerous to health. And the cancer most likely would develop some time over the next 30 or 40 years, not immediately. So the chance of astronauts developing cancer on the trip itself is pretty low.
I have no idea what the chances of dying on Mars are. Space suits should be safer to operate than scuba diving equipment (the latter involves big pressure changes). Most professional divers manage an entire lifetime without dying. I don't think life support systems are all that fragile. If a fan breaks in the life support system, you shut the system down and let CO2 accumulate a few hours while you fix the fan (assuming there's no backup system, which there would be). I think the experience with Mir shows that a very cranky, old, accident-prone system can be kept operating a long time, especially when you have redundancy. The same is true of automobiles; most people toss theirs after six or eight years because the repair bills get too high, but on Cuba, where no cars are rarely imported, there are a fair number of 50 year old American cars still running. I suspect the same is true of life support systems if you have smart repair men and a modest ability to make parts.
The most dangerous phases in spaceflight will always be launch and landing. In between it's relatively safe.
-- RobS
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