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Wow, that's some history. More than I understand, being a mechanical engineer, not a geologist or instrumentation scientist. Odd, how no one ever fixed a known problem, isn't it? The emperor runs around naked in a lot of organizations, and no one ever tells him.
I'd suspect that no two locales on Mars have the same regolith, myself. There's many, not one. At least, that's the way it is here. The dry salty dirts we've seen might resemble a sample from the Atacama desert, or maybe the lake bed in Death Valley. Not-so-salty dried up lake and stream beds might resemble something from the Owens Valley near China Lake. There's got to be lots of volcanic stuff resembling the lava flow terrains in New Mexico. Do any of those ideas have any merit?
I'd think there's sandstone-like rocks on Mars, not unlike the red-rock sandstones of places like Monument Valley, although perhaps a different mineral species than straight silica. What seems to be missing so far is anything resembling limestones. I was surprised and pleased when they announced they'd found clays. Although your proton-mode problem description could cast doubts on that.
GW
IC or turbine engines with fuel and oxygen are going to suffer really high combustion chamber gas temperatures. Here in the air, nitrogen is a huge dilution gas, limiting flame temperatures to about 4000 F max. Fuel-oxygen flame temperatures are usually in the 5000-6000 F range. It's a very difficult engine to build.
It was tried as diesel-hydrogen peroxide in submarines on multiple occasions, but never very successfully. Overheat problems and peroxide instability ended that stuff, more so the unstable peroxide explosions inside a pressure hull. But engine overheat was a very, very serious problem, even with massive amounts of seawater for cooling available.
I have no problem with LOX-LCH4 for some sort of engine, but you will have one huge (as yet unknown) cooling system, or you will have a huge supply of inert diluent gas, or both. You can't feed back the exhaust gases to use as diluent gases without cooling them first.
This is a fundamental area of new technology that is not developed yet. You should not make your mission contingent on developing new technologies, or you will not ever fly. That's been the experience history. The trick with really flying is to use existing technology, so that all you have to do is prove-out your specific hardware designs. That way, you already know that the technology underlying them already works. That's a huge, huge difference.
Liquifying hydrogen is now a very well-known technology here on Earth, unlike 1960. I suspect (engineering experience and intuition) that coming up with hydrogen-liquifying equipment suitable for robot operation on Mars would be easier, faster, and cheaper than coming up with a new IC or turbine engine technology capable of handling fuel-oxygen flame temperatures.
But at least folks are looking at these ideas. That's good.
The hydrogen-oxygen fuel cells used since Gemini in space are just that: bottled gas feeds to the unit. Those work fine in vacuum. You could just as easily use liquified gas sources, and they did on Apollo, at least for the oxygen.
I like the aluminized plastic film idea for hydrogen cryo-tanks. That should stop the gross leaks through porous composite materials. But, hydrogen percolates right through all materials at a slow rate. Even steel. It's a molecular-scale diffusion thing through the pore spaces between atoms. A welding gas bottle of hydrogen will lose around 30% of its pressure in a few weeks.
As for liquid versus compressed gas storage, it's a trade. Bottles are heavy. So is a liquifaction plant. Take your pick.
GW
We'll soon see. I think the launch is scheduled for March 16.
GW
In construction work here, temporary bracing and facilities are normal operating procedure. For construction "out there", it should be the same notion, just different details. The problem is water in vacuum with a lot of materials, so temporarily enclose that item in an inflatable at low pressure, just high enough to stop the boiloff. That would be 6 mbar of water vapor alone, in a bubble over water being used at 0 C. You could make "icecrete" on the moon or Mars or even an asteroid that way.
The nitrogen problem rules out Earthly cold-weather concrete techniques, as you say. But for structures that will stay cold and be protected from ice sublimation, "icecrete" is a real possibility, and very simple. It's not atmospheric pressure that prevents sublimation, it's water vapor partial pressure in the atmosphere that prevents sublimation. That's the kicker.
But, we already know buried ice seems to be stable on Mars, and maybe the moon. So, buried "icecrete" foundations look like a real application. And, we do need a solution to the concrete problem. This sort of thing can be researched in simulation chambers down here, and demonstrated to some extent in LEO, or even on the moon. These are activities that already should be going on, if we really intend to send men to Mars or back to the moon and create bases. They are not, and that disturbs me.
GW
Hi Bob:
My own opinion is that all three projects should get "crash" funding, so that we end up with three different working manned spacecraft for LEO operations, not obtained from Russia (or China). But there is a fourth item: we need a domestic engine for Atlas-V. The current Russian engine makes us susceptible to Russian blackmail over that launcher.
My own guess is that if money were no object, and the companies' criteria were used for readiness instead of NASA's, that manned Dragon could fly in 6 months to a year, Boeing's CST in not more than a year, and Dreamchaser in about 2 years. (Dreamchaser is a spaceplane, and they're still harder to do than a simple capsule.)
Given proper adapter hardware, either Atlas-V or Falcon-9 could launch any of the three. Actually, so could Delta-IV. So those sets of adapter hardware are a 5th item needed fast funding. That would give us any of 3 spacecraft atop any of 3 launchers. We're not currently headed there, but we should be.
I think the track record for Falcon-9 is pretty good so far. It does appear that they did a very good job designing-in both basic reliability and fault tolerance. I'm a lot less concerned about "Falcon-9 being too new to be considered safe", than I am Russian antagonism (Putin actually) screwing things up, now that Cold War 2 seems to be breaking out.
I am concerned about the breadth of our stable of commercial launch providers. There are really only two entities: ULA (Boeing + Lockheed-Martin) and Spacex. Orbital Sciences cannot yet routinely launch payloads of that size, although their Cygnus cargo vehicle may lead them to that capability. Until Spacex forced its way in, ULA was a monopoly, and acted and priced like it.
The government launch business is still biased toward ULA, the "favorite" contractor, really just because of how long the government has known and done business with those companies. All that needs to change to provide a level playing field and more competitors. Only two providers is too dangerous, for any of a number of very good reasons.
GW
I'm not up to date anymore on fuel cell technologies, but the ones they talked about for cars here were methanol-air fuel cells. There was a rectifier stage that converted methanol to hydrogen and CO2, releasing the CO2 to the air. The actual fuel cell was hydrogen-oxygen, just diluted with nitrogen. Methanol is made most cheaply here from natural gas.
I'd guess the methane-oxygen fuel cell would be similar, leading to the same basic hydrogen-oxygen reaction basis.
But if it was me, I'd just use hydrogen-oxygen as the type that has the most history behind it, for reliability's sake. That gets the technology development out of your program (if you do technology development instead of just basic shakedown of new hardware, you won't ever really fly).
I'd ship water and a solar electrolysis rig to Mars as a stationary plant, and I'd run the rover from stored compressed gaseous oxygen and hydrogen in ordinary bottles. Do the compression at the stationary plant, and just load bottles on the rover for the trips. You could have a solar panel and a battery on the rover as a low-power emergency back-up.
I'd restrict rover trips to a few 100's of km, and do the longer excursions as suborbital flights (with a reusable lander, naturally). You send enough water to supply your basic mission objectives. If you successfully find more water, just process it to supply more explorations beyond your basic objectives. If your lander uses hydrogen-oxygen engines, then so much the better. Add only a liquifaction plant, and you get to fly extra suborbital trips in it.
Basic water, solar electrolysis plant, compressed gas bottle-loading plant, gas liquifaction plant, cryo-tank storage vessels. A habitat building of some kind, plus space inside the landers to live. Rovers with drill rigs. Add a front end loader to experiment with construction techniques. Sounds like a first base to me, to be established on the first (and possibly only) government-sponsored manned mission to Mars.
GW
Hi Josh:
I looked at Spacex's site yesterday. It appears that the next Falcon-9/Dragon shot to ISS will be rigged with a working set of landing legs. I got the impression that they plan to try the legs out. They didn't hold out much hope for success, but at least it's a trial.
Not sure what landing legs get you, with an ocean landing, but the test is planned. Has anybody heard of which island they might eventually land these reusable stages upon?
GW
RobertDyck and I seem to argue a lot, but actually we think very much alike about a lot of things.
My opinion: what we are seeing with the Ukraine thing is the start of Cold War 2. I don't know how long this will last, but it won't be over quickly. Putin will last quite a while, and there are clones ready to step in when he is gone. Don't look for a fast resolution to any of this. The missile arms race could re-start, too.
One upside (small as it may be) to this trouble is that (once the politics-of-money gets ditched) manned Dragon could be greatly accelerated. Of the 3 contenders, I think it could fly first: 6 months to a year. Boeing's CST could follow shortly after, if both outfits get money thrown at them. Spaceplanes are a tougher proposition, still. I'd hazard the guess that Dreamchaser is still 1 to 2 years away, even accelerated.
GW
For bases off Earth (moon, Mars, etc), it's my understanding that about a meter or two of rocks and dirt over your head makes a pretty good shield against anything the sun can throw, and cuts down on cosmic ray threats, too.
All we need is a concrete substitute that works in vacuum and in intense cold, yet doesn't go away in the heat. Then ordinary construction of a dugout "house" becomes possible with the space equivalent of a front end loader.
You use gravity to offset internal pressurization forces, and line the thing with a multi-layer inflatable to hold the air.
Concrete substitutes could be developed down here and final-demonstration-tested at ISS. Makes you wonder why that hasn't been tried in all these years, doesn't it? Any outfit serious about going to Mars and/or back-to-the-moon should have been doing things like this.
GW
Musk is no fool. He won't fly a manned Dragon until he gets paid for all the work he has done, plus what there still is to do, plus a premium for being the only game in town ready-to-go. But once he gets paid, he will fly one manned so fast it will make your head spin.
The tough part of the engineering was done some time ago: figuring out how to actually do it as an integral part of the capsule's basic design. That was integral to Dragon's design from the beginning. He's been paid to scale up the Draco thrusters into the Super Dracos that provide abort thrust. That's now final shakedown work that has been proceeding for a while now, on the contract that he has.
There is only integration and demonstration of a Super Draco-equipped Dragon left to do, before flying manned. That's what NASA has scheduled to dribble-out funds for, until 2017, in order to protect Boeing (and by extension ULA), their favorite contractor these days. It's not about technological readiness, it's about super-high-dollar corporate political influence (something Musk does not yet have).
If the politics gets ditched, money thrown at Musk quickly could have Dragon flying manned in at most a year, perhaps as short as 6 months. Just an educated guess on my part, but I think he could do it. That's faster than Boeing can make its CST fly, and certainly faster than Dreamchaser could be ready. It was the same pattern with cargo to ISS: Musk could have had cargo Dragon working even earlier, but even limited by NASA's schedule as it was, he beat Orbital Sciences by a year.
What you are seeing over Ukraine is the start of Cold War 2, which will gradually end US-Russian cooperation on a lot of things, including space. It will take the idiot politicians a while to recognize that we cannot tolerate the post-shuttle gap any longer, and even longer for the bone-headed un-elected bureaucrats. But, eventually, this geopolitical problem will accelerate Musk's manned Dragon.
GW
Anyone who believes Putin will stop at annexing Crimea is living in a dream world. We've seen this before with Czechoslovakia in the 1930's. And many other smaller examples since.
Hillary Clinton was right to draw the comparison between Hitler and Putin, wrong to back down and "clarify" it. Damned politicians, that weasely behavior is why Hitler got away with what he did as long as he did, and why Putin is a problem today. Lots of people will die before this ends. The longer it goes on, the more will die.
I'm not sure that Energia is still a viable launcher. Haven't heard of any being launched in several years now. But, unopposed, Russia will annex the Ukrainian aerospace industry, and that includes Antonov in Kiev. Pretty much the entire Ukraine. And most of the rest of the breakaway ex-Soviet "republics", too.
Cassandra has spoken.
GW
Hmmmm. These hab modules y'all are discussing sound like landers to me, just once down and maybe once back up.
Whether you need the full space allottment per person would depend upon stay length on the surface. But, for around a year, I'd say yes, you need it.
If one uses 90 cu.m per person and a crew of 4, that's 360 cu.m of unobstructed pressurized space. Assuming such space is 25% obstructed with equipment or propellants, that's about 500 cu.m of vehicle. Assuming a cylinder of L/D=2, that's a vehicle 7 m in diameter and 14 m long. Plus its propulsion, or a separate ascent vehicle. That's awfully big.
What if you built a smaller lander and brought a big inflatable with you for surface use? I know multiple payloads might be landed at the same site, if you have working homing capability during the hypersonics, and during the descent after hypersonics are over (not really available with chutes, but these things are too big for chutes anyway). Missing the target, collisions, and rocket blast damage are all serious issues with multiple vehicles to be landed at a single site.
This notion of landing direct does put some serious constraints on what you design, if you intend to meet the living space criteria we were discussing here earlier. If you do not meet them, you have well-known health concerns to address. This can get quite serious.
GW
There is one other misconception creeping into a lot of news items: that Dragon can't be manned until it has an escape tower like everybody else (meaning Boeing capsule and NASA's Orion). I saw this hinted-at in an Oberg (edit: might have been Boyle, not sure) article a couple of days ago, and I have seen it before from several other sources. But, it's simply wrong.
Dragon will NEVER have an escape tower, it will have the large Super Draco thrusters in addition to the Draco attitude maneuvering thrusters. The Super Draco's are "thrusty" enough to provide abort from the pad to orbit insertion, something you lose before orbit insertion with tower jettison.
And another thing: escape towers are inherently one-shot throwaway devices. Propulsive thrusters on the capsule are not. Once you start reflying capsules, you are inherently reflying / reusing your crew escape system. I like that, it's simply a better idea.
They've been testing Super Draco's for some time now at the McGregor test facility. Technical issues are not holding this back, NASA over-bureaucracy is. Given the funding "now" instead of dribbled-out over time, I doubt it would take a year to install the Super Draco's, test them a couple of times in space, and fly a company astronaut or two. NASA's schedule stretches this out to 2017. Which is ridiculous.
GW
Quaoar:
Thanks, I had never seen that NASA report before. Amazing how they came to the same conclusions I did: 4 rpm, 1 full gee, and an end-over-end spinning baton as both stable and (at least a bit) maneuverable while spinning.
The truss they used is an artifact of the nuclear-electric propulsion they assumed. There's not a plethora of propellant tanks, but you need connecting structure to make the baton shape.
If instead you use chemical propulsion, then you have a plethora of propellant tanks, and that stack of tanks can serve the function of the truss, without a need for any truss at all. If you are clever with your stack-up of those tanks, you can stage-off empties and still maintain overall length, just at reduced mass and (to a much lesser extent) mass moment of inertia.
This kind of thing just does not integrate hardly at all with direct-landing or aerocapture designs. Unfortunately. But, I think it solves so many other problems, that it's worth the extra propellant. Just my opinion.
GW
I don't honestly know, Quaoar. I'm not sure a "magnetic confinement" nozzle would do any better than a physical one. I'm not sure how big this loss is. But I would think it might be possible to use MHD to extract some of the ionization energy out before the stream goes to nozzle expansion, and then feed that energy back in somewhere else, where it might do some good.
GW
You have to understand Putin and his ruling clique in Russia to understand the seemingly-strange things they do. Putin formerly was a high official in the old Soviet KGB, for which THE enemy was always first and foremost the US. He still thinks exactly like that today, people rarely change in any fundamental ways.
His dream is to restore the old Soviet empire to power and glory, and win (if he can) over the US in every way possible. Simple. Once you understand that, you understand why Putin's Russia does things in geopolitics to oppose the US, even when it hurts them. Ukraine is a "shooting war" example of opposing the US no matter how bad it will hurt Russia. And this will, long-term for sure.
From the US side of the fence, depending on Putin's Russia for manned access to space is beginning to look the the crazily-stoopid (stupid with two O's) idea that it always was. But when you are managed to optimize politics, instead of by common sense, the emperor can be quite naked, yet no one hears the few who stand up to say he's got no clothes on. That's how we got here, and there really isn't much of a way out.
There's the Boeing capsule, Spacex's Dragon, and Dreamchaser. Hard to pick a winner. You can crash all three projects at great expense, or just crash one at less expense and risk not picking a winner. Rock-and-a-hard place for "politics-as-management". Change that management style and we could probably fly either of the two capsules in a year, and maybe 2 years for Dreamchaser (capsules are simply easier to do than spaceplanes).
Don't forget something about Dragon: unlike the Boeing design, its heat shield was designed for a free return entry from Mars. You might risk two returns from the moon on a heat shield like that, and several flights back from LEO. Spacex hasn't done that yet, probably not to embarrass NASA over its overbureaucratized way of doing things.
Now, if they did start reflying capsules, it would be immediately apparent to the general public that there is no reason not to install the Super Draco thrusters and fly manned "right now". But, Musk will make more money doing it NASA's way. He's no fool, for sure.
As I said, there's no good way out of this. Not even the "status quo" is any good. In every organization I have ever seen, it is management style that resists change to-the-last-breath.
GW
NASA's 90 cu.m per person criterion comes from Skylab. If you take the propellant tank volume total for an S-IVB stage and divide it by crew size 3, you get pretty close to 100 cu.m. Skylab was basically a reworked S-IVB with the internal tank shells removed. As a space station, it was very wide open inside, as the old photos so clearly indicate. Obstruct about 10% of the volume with station equipment, and you get about 90 cu.m per person.
Not only is a volume allowance per person important, its distribution and arrangement for use are also important. These are harder to put numbers to, though, as it's more about psychology. People need big wide open spaces in which to come together and do communal things. They also need some private spaces where they can be alone. And an awful lot of us need contact with nature, which suggests some sort of garden or greenhouse space might be very important. Individuals differ, too.
350-400 cu.m of unobstructed-by-equipment space for a crew of 4, properly distributed among communal, private, and garden spaces, is not something you can design into a capsule, or even a big descent vehicle. People can "camp out" for a while in more cramped spaces, but eventually (weeks? months? depends on circumstances) they must return to a more normal environment to remain sane and healthy.
Sitting in a capsule at 5-10 cu.m 8 months to Mars is a recipe to arrive insane. Insanity is a recipe for a dead crew. That plus microgravity diseases and radiation exposure is why the old vintage 1969-designs for the planned-for-the-1980's manned Mars missions probably would have killed their crews. We didn't know about stuff like that back then, but we do now.
If the required space is too large to land and live in for a year on Mars waiting to return, then leave it in orbit, land in something smaller, and erect something bigger on the surface. Or base from orbit and take turns "camping out" on the surface in your lander for shorter stays. Or both.
This is the sort of thing that ought to set the mission architecture, not budgets. The real engineering here is to design mission architectures as a function of expedition size, and determine their cost. Your budget then determines big vs small crew size (expedition size).
But, my point is that there will be no solution space between designing properly versus budget available, as long as the current NASA management model is used: let congress dictate designs by politics-of-pork-in-districts, then expensively-overbureaucratize every item to maximize the corporate welfare for favored contractors. Don't kid yourself, all the government space agencies now do it like NASA. It's not just NASA.
The NASA of 1960 did not work that way so very much, and budgets weren't screwed-down so tight, which is why Apollo actually reached the moon.
GW
Found a news release on MSNBC confirming what RoberytDyck and I were saying in the two previous postings just above. Tito's Inspiration Mars is now "integrated" into NASA, in that the vehicle is now Orion plus Cygnus, to be launched by SLS. Now that Tito is "part of NASA", he cannot shame NASA into doing anything about Mars.
The whole point of the mission is now completely defeated.
The date has been pushed from 2018 to 2021, because Orion and SLS won't be ready before then (if ever). Had they stayed with Dragon and either a Bigelow or a Cygnus, plus a Falcon-Heavy, they could still have flown in 2018.
From there the discussion in the news release devolved into political wrangles over what NASA's long term plan ought to be: moon, asteroids, or Mars? The wording of the article definitely suggests this is more about what will be made in whose congressional district, not about anything that might make good common sense, without actually coming right out and saying that.
THAT is why I have little faith in government-run manned space programs.
Musk, are you paying attention to all this?
Your capsule, Bigelow's and / or Cygnus modules, a long-life smaller LH2-LOX engine like the XCOR replacement for Centaur engines, LH2-LOX tank modules that have powered cryocoolers to greatly reduce boiloff, a reusable lander, a supple space suit, and a rover car with a digging bucket and a drill rig on it, are all we really need to go to Mars. Now.
Stack them up as a modular ship with a spinning baton shape for spin gravity, and reconfigure the stack between burns to maintain "radius". You need the supple suit to build the landers from component in LEO, and you need it to explore on Mars. Everything else is just dock modules and connect them.
We already have everything we need except the tank module, the lander, the supple suit, and the rover car. None of those need to be a massive development spread out over the maximum number of congressional districts, either. (If that IS done, those things will NEVER be done in time to support going anywhere.)
It need not break the bank, either. Reduce scope a bit from my "Mars Mission 2013" proposal on "exrocketman", and I'd bet this could be done for $50B, make more than one landing, and leave behind an operating ISRU facility. With a "way out" designed-in at every mission phase.
Now, where does Musk get his $50B?
GW
Interesting concept! Thanks.
Just guessing here, but I'd guess not all the propellant can be arc-heated. If the ionization level is too high, a simple C-D nozzle expansion cannot convert that energy to kinetic energy. There might be some sort of MHD thing that might do it, though. Pretty far afield from what I do know.
GW
Inspiration Mars was supposed to be a privately-financed flyby that would shame NASA into actually doing something useful. Going for government money actually bollixes the basic concept up. Thus NASA still need not do anything useful. As long as they do nothing useful, the odds are they won't kill another entire crew. Just onesey's and twosey's on suit malfunctions and such like.
I have no real problem with the basic Inspiration Mars design concept, other than it is more likely to be a suicide mission than not. Regardless of the capsule chosen, that and a Bigelow inflatable as a habitat does not provide solar flare radiation protection. And 500 days' exposure to zero gee is an accident waiting to happen when you look at free-return-from-Mars entry gees. It was 11 gees with Apollo coming back from the moon at only 2/3 of Mars free return speed.
The design I posted could be done by somebody other than NASA. Or ESA. Or any of the government agencies. In the quarter century since the time of Bush 41, I think the trend is quite clear: NASA is unwilling to make the fundamental management changes necessary to go to Mars both safely and affordably. I have pretty much lost faith in government-run manned space programs, myself. The track record does not justify such faith.
So, I kinda doubt they'll be the ones to do it. Somebody like a Spacex might be. Tito might more likely shame Musk into doing it sooner, instead of screwing around waiting on NASA. That last is why manned Dragon is slated to fly no sooner than 3 years from now, instead of late this year or early the next.
GW
What RobertDyck says about budget constraints is quite true. Unfortunately, what I said about dead crews being supremely expensive is also true.
So, the real question is this: is there a solution space where we can insure crew survival and still meet a realistic budget?
That’s actually a very good question. In my opinion, the answer is “no” if we attempt to do this the same way we have done everything earlier.
But, the answer might be “yes” if we learn from those experiences what not to do, and do this a lot differently.
Solution space: what is the budget constraint, really?
We already know that numbers in the $500B to $1T range are politically infeasible, as RobertDyck pointed out just above. I’m going to guess that $200B might be feasible, $100B even better. Just pulling numbers “out of the air” here.
If you assume the project can be run more like the way the private launch business is run, not the way NASA does things, then your direct launch expenses might be around 20% of your overall budget. That means your sub-budget for direct launch expenses might be in the $20B-$40B range.
Atlas-5, Titan-4, and Falcon-9 all fly (fully loaded) for unit prices to LEO in the $2500/pound ($5500/kg, or $5.5M/metric ton) range. Atlas-5 and Delta-4 can handle payloads in the 15-20 ton range, and Falcon-9 13 tons. There will soon be Falcon-Heavy at about $1000/pound ($2200/kg, $2.2M/metric ton), but it will be a small fraction of the total launch rate achievable for some time to come.
But you need to fly fully loaded, or the unit price is far, far higher! That sets your payload masses discretely. Which in turn suggests a modular design for your mission vehicle(s).
OK, just use the current $5.5/m.ton price. For $20-40B, you can send about 3600 to 7300 metric tons of “stuff” to LEO to assemble whatever you need to pull off this trip. In any way that seems prudent, I might add. So far I have said ABSOLUTELY NOTHING about what that mission might look like, other than modular vehicles!
OK, call it a nominal 4000 metric tons of stuff in LEO, delivered in chunks between 13 and 20 metric tons, matched to the rockets they ride, with a few 53 ton items in the mix. What can you do with that?
Can you design-in “a way out” for the crew in every mission phase?
Can you design-in a way to cope in the field with whatever equipment items prove not to work, and still meet basic mission objectives (which require proper definition by the way)?
As a bonus, can you design-in ways to accomplish more than the basics if all your stuff actually works right, and can you make any of your equipment reusable for other missions?
You all can answer those questions in any way that you want to. Everybody gets a different set of answers. As they should.
But, simply by changing the way you manage the project (from the government model to a commercial model), you get 4000 (not just dozens or a hundred) metric tons in LEO, which is a quite generous allotment of launched mass.
But, remember, it’s based on nothing but a budget-bounding calculation, as described just above.
However, we should be able to accomplish one hell of a lot with that 4000 ton mass in LEO budget, actually. A whole lot more than most of what I’ve seen proposed.
The way I looked at it used an orbit-to-orbit manned transport (crew of 6) that goes both ways with spin gravity, and is recovered in LEO for reuse; and three reusable landers pushing a propellant supply dump one-way to Mars orbit.
The reusable landers and propellant supply dump were sufficient to enable 6 surface landings and one trip to Phobos. If propellant ISRU works well at any of the surface sites visited, that propellant enables other sites to be visited sub-orbitally by the same landers. That’s a lot of “bang” for the bucks spent on the one trip to Mars.
First 6 months, 3 do science from orbit and provide rescue capability for 3 on the surface at any one time. Surface stays are in the 2 weeks to 1 month range, until the “right” site is positively identified. Then everyone goes down to that site with all the landers.
Surface habitat IS the lander. Suborbital trips are flown one vehicle at a time, so the other vehicles provide rescue capability. I based it around 3 lander vehicles, so that if one “craps out”, you still have a rescue bird and need not abort any remaining planned trips.
Second 6 months is spent building a “base” at that site in the sense of a facility that does propellant and life support ISRU. That facility is left operating unmanned when the crew goes home, to serve the next mission. I personally would include road and building construction and materials processing experiments in that facility. The idea is to learn as much as possible about “living off the land” while the crew is there, and more yet after they go home.
This mission rough-out is posted over at “exrocketman” as “Mars Mission 2013”, dated 12-13-13. My fleet in LEO is 4 ships, one manned that is under 1000 tons assembled. The 3 unmanned ships are about 1000 tons each.
In my plan, I reused EVERYTHING. Not even one empty tank was staged-off into deep space. I left the landers and empty tanks in Mars orbit for future missions to utilize. If I had stage-off the empties, my fleet would have been lighter still. Or I could have baselined even more landings in the one mission to Mars.
This is almost all docked modules with quick-disconnects, just like ISS, except that there are only about 4 distinct types of modules, not a whole plethora. The exception is the landers, which have heat shield diameters around 10-12 meters diameter. Those have to be assembled from components small enough to fit the launch rocket payload shrouds.
That in turn requires astronauts with real dexterity and mobility, unlike today. But there is a way to do this, too, and it needn’t break the bank. Far from it, actually. See also “On-Orbit Repair and Assembly Facility”, posted 2-11-14 on “exrocketman”. That article describes a free-flyer, but one of these could easily be added to the ISS, where we could test out the suits and the assembly techniques.
All of this is a house of cards that tumbles down, if you don’t radically change the management approach.
Do this the traditional NASA way, and all you can afford is 2 guys in a two-module rig that might have to forgo spin gravity, and has single-point failure modes at every single mission phase. They’ll likely die from mishap, radiation exposure, or the effects of microgravity exposure. That expensive outcome will end the possibility of any other people ever going to Mars on any tax dollars at all.
So, it’s all in the assumptions, including the ones you may not even know you are making. Gotta think WAY outside the box, if there is to be a solution space here!
GW
Nothing is as expensive as a dead crew. NASA has proved that beyond any shadow of a doubt.
GW
The only real problem with manufacturing and reusing plastics on Mars is the energy. You'll need a significant nuke power plant or else one whopping lot of PV panels. Same for steel. Same for aluminum. Same for making water, oxygen, and hydrogen out of local ice, especially if you have to desalinate the water. Etc.
That kind of setup is not something you land in one or two small landers. The capable your ISRU is to be, the more mass you had better be prepared to land. (Sorry, that's just a restatement of Murphy's Law, I suppose, but then we engineers are paid to be professional pessimists.)
GW
Spinning rigid structures work very well, actually. One sees them at Friday night football games all over the US, in season. The baton twirlers throw their batons spinning end-over-end high into the air. They are extremely stable, and easily controlled. Basic spinning dynamics says so, too.
Most of the missions that actually address maximized crew health maintenance and survivability are not like Mars Direct (a really minimalist approach). For survivability, health, and "a way out" at every mission phase, you must have at least a habitat, a bunch of propellant, and some engines, both ways. And on the way there, maybe landers plus their propellants, too, unless they go separately. It's just not two simple modules you can cable connect.
Having a bunch of modules is really easy to rig as a spinning baton, just like at the football games.
GW
7 km/s entry at Mars seems high. Isn't 5 km/s closer to the "typical" direct interplanetary transfer entry?
If you can guess a hypersonic drag coefficient for the inflatable-or-extendable fabric heat shield shape (somewhere in the 1.4 to 1.7 range), and you have accurate figures for both entry speed and entry trajectory angle below horizontal, the old Julian Allen warhead entry analysis I use does a decent ballpark job telling you peak gees, peak heating, and end-of-hypersonics (about local Mach 3). You'll have those quantities plus the altitudes and speeds at which they occur.
Peak decel gees and heat shield diameter, coupled with density at peak gee altitude, give you the average pressure exerted over the heat shield. You can figure stagnation pressure pretty easily, and your average ought to be between stagnation and nothing, probably about half stagnation as a ballpark guess. You can even guess a pressure distribution from that.
The pressure distribution and geometry lead you to structural stress/strain analysis. The pressure distribution and geometry also lead you to a ballpark estimate of gas leakage due to porosity. That and the old rule of thumb that gas temperature in deg K is speed in m/s divided by 10, gives you a shot at a ballpark heat transfer analysis.
I'd be very wary of impregnating the fabric heat shield with any resins. You lose flexibility and impact damage resistance that way. If you need to impregnate it, use an elastomer. I'd go with a hard char-forming solids-doped silicone, myself. Probably not exactly DC-93-104, but something like it.
None of that takes any account of factor-2+ variability in the high altitude density profile at Mars, something that does not happen here. Your end of hypersonics point will vary exponentially with things like that.
Most of the ballistic coefficient stuff I have done recently suggests that ballistic coefficients are larger at larger vehicle masses, shapes and proportions being otherwise unchanged. It's a square-cube law thing. When those get too big, on Mars chutes get to be quite useless post-hypersonics. The way out of that dilemma is supersonic retropropulsion technology. There'll be a point where square-cube scaling won't let you build a survivable inflatable/extendable heat shield for vehicles that large.
My own studies are not for a minimalist mission, but more like a mission with an orbital transport and multiple landers. Those landers typically exceed 30 tons, and approach 100 tons, depending upon propulsion choice and payload size. Their ballistic coefficients typically fall in the 300-500 kg/sq.m range. The probe folks at JPL seem to need Rube Goldberg stuff above about 100 kg/sq.m. So, that's the "breakpoint" where you start needing to use supersonic retropropulsion instead of chutes.
The inflatable/extendable heat shield is a way to reduce ballistic coefficients at larger vehicle mass. But, you will hit that 100 kg/sq.m limit rather quickly, even with heat shields like that. I rather doubt a 5 ton lander would be very useful.
GW