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The idea of a public-private venture of some sort to settle new places is a proven one. Besides the Hudson Bay Company, there were the British and the Dutch East India Companies. All of these were government-licensed monopolies. It worked then. Why not now?
GW
The really interesting thing about the curves I plotted for this is that tripling payload capability only cuts the unit price in half. Spacex and ULA are all showing the same trend at the same slope. For only factor 2-class benefit, it's hardly worth building bigger rockets by factor 3 payload-class. Unless you have a specific and compelling need.
The second interesting thing is where spaceplanes might actually fit into all this. Over at the left, where payloads are small, under 10 tons, a well-designed spaceplane might be cheaper, especially since the launch rocket curves seem to bend upward going that direction. Although, that remains to be seen. From that, I suggest that a successful spaceplane will look more like a Dream Chaser or an X-37 than our old shuttle. Self-launching Skylon is the dark horse there. There's a couple of others, too.
GW
Hmmm. Back in the 50's and 60's we were told a U233 bomb was not possible. It seems things have changed.
I like it. There's more thorium than uranium, just about everywhere we have looked, and by far. Sounds like a thorium breeder plant is needed somewhere "out there" to make the U-233 for reactor fuel and pulse propulsion devices. I'd put it on the close-by moon for now. That pretty well keeps it out of the hands of terrorists and other infantile idiots. Plus, it's way far easier to launch the charges into space for use by a pulse ship, too. Some sort of catapult could do it.
U-233 triggers on an ordinary lithium-hydride fusion, all configured as a shaped-charge for propulsion. I like it. Cleaner than straight fission, and easily scalable into the 1-50 megaton range for really big ships.
There's got to be at least some EMP from these things in vacuum, because of the expanding cloud of bomb debris. There's a lot more during surface launch in the atmosphere. You launch with very low-yield devices, since the shock wave assists thrust. As the air thins, you increase the yield. Out in space, you use much larger-yield devices.
I certainly wouldn't put the shipyard and launch site for these things anywhere near a populated zone with a power grid and electronics. But we really don't need to build very many of them. So the risk is low. Ships built like this could serve for centuries, periodically updated to the "latest and greatest".
Talking about propulsion like this is fun, because, for guys, there are few things more fun than converting perfectly good fuel into fire, smoke, noise, and thrust. There's drag racing.......
GW
Well, right after the initial "tin can" base setup, it might not be quite so confining if the folks there had supple, lightweight mechanical counterpressure suits, instead of the clumsy gas balloons we have been using. Think vacuum-proofing "underwear", and ordinary outer clothing suited to the weather and the job. We've known how to do this since 1969. Only inappropriate compression requirements are holding it back today.
Then there's habitats. Big open spaces inside, and good panoramic views outside, tend to support mental health. Sounds like the "tin can" approach is the wrong one, long term. The old science fiction transparent pressure domes concept points the right way, it just has to be done with regard to meteroid repair and radiation protection. Clear walls, solid roof.
The real problem is open-"air" agriculture on Mars. 7 mbar total P, 0 mbar water vapor partial-P. Ain't gonna happen until Mars gets terraformed some. That means dry-land plants and animals and soil organisms will need the same sort of clear-wall/solid roof dome that the folks live in, just whopping larger to cover the acreage. I dunno how to do that, but I bet we do know in less than 50 years.
Meanwhile, it might be possible to do aquaculture farming in ponds under an ice-plus-regolith cover. Done right, the water plus ice supplies the external pressure on the organisms. No spacesuit needed, just a wetsuit and oxygen scuba rig. No pressure dome. But because there is no pressure dome, this concept is scalable to very large acreages very easily. Underneath cover like that, we're talking artificial lights for the photosynthesis, whose waste heat keeps the water liquid.
There's clearly things we could do to keep folks on Mars sane and healthy and living productive lives. But it won't (and can't) look like Earth until the planet is terraformed.
I agree, living inside a tin can is definitely not the way to do it. Even nuclear sub crews need lots of time ashore.
GW
I put an illustrated article up over at "exrocketman" that explores aero decelerators on Mars, and their possible combination with simultaneous rocket braking. Also, rocket braking during entry hypersonics is there. Nothing really substantive, just the concepts.
GW
RobS was right about Viking somewhere above. I had completely forgotten the chutes it used. Sorry.
The trouble with Mars is there's not enough density for the chutes to decelerate you very much, before you're on the ground. But some combined scheme of aero decelerator-plus-rocket braking might be a possible answer. We've never really done those two together. And there are serious problems with that concept, I know.
The other problem with chutes is that there seems to be a limit to how big a payload can be practically supported by chutes, even here at home. I've never seen more than 3 chutes at once in a cluster, or a payload bigger than an Apollo or a Dragon. It's worse on Mars by the density ratio/0.38.
The Russians used a combination of chute plus last-second rocket braking to land army tanks (no persons aboard) dropped from airplanes, some time about 5 decades ago. I'm not sure the density on Mars would make that approach practical, given the dynamical troubles of chute plus rocket simultaneously, and the low density. Probably not worth the trouble. It barely worked for the Russians here. But it's an idea.
GW
"All of the above" is not limited to just NASA's budget. Funding can come from a variety of agencies, as it did decades ago. There are many paths here to explore. And they all need exploring. Not as a precursor for going to Mars, but for later on.
I for one would like to see a means be found to uprate the engine thrust/weight ratios for electric devices, out of the 10^-4 class. They have the Isp, it's just that vehicle accelerations that are ridiculously low. Until that changes, those are not a viable path for fast trips to Mars (it's too close for the buildup of speed to have much effect).
GW
I thought the old 1959 fission designs were remarkable in and of themselves. Their 10,000 tonner, surface-launched, was estimated to leave fallout in the atmosphere equivalent to the atmospheric test of one single 9 megaton bomb.
In the decades since, we have learned there is less fallout per unit yield (by far!!!) with thermonuclear devices. So a fusion update of pulse propulsion is radiologically intrinsically cleaner. The real side effect, unrecognized at the time, is EMP with each pulse. You don't start one of these in LEO. You could surface launch from out in mid-Pacific, I guess. Or maybe Antarctica.
I'm not sure U233 bred from Th232 can be made to explode. I was always told that a U233 bomb was not feasible. But it can be made into very good reactor fuel.
GW
I surely am glad to see that porn spammer gone. My sincere thanks to whoever did that.
Here's something to think about when looking at a 50-year interval into the future: we're going to have way-better traveling machines 5 decades from now. 50 years ago, the original Atlas was severely challenged to loft a 4000 lb Mercury capsule to LEO. Now, its descendant Atlas-V-HLV can fling 29 metric tons to 23 deg LEO out of Canaveral.
We will not be limited forever to minimum-energy transfers, although they do now (and always will) make economic sense with unmanned stuff. For manned stuff, there'll be much hotter propulsion available, for the fast trips that are nearly straight-line shots to Mars. We've been yakking about NERVA, gas core NTR, pulse propulsion, and a host of others. Some are electric, some even solar.
I dunno what we'll really have 5 decades from now, but it'll make high-pressure LH2-LOX shuttle technology look like a quaint rotary engine-propeller combination on a WW1 biplane, as compared to the air turboramjets of the SR-71 ca. 1960. About 5 decades separates those two, also.
Far sooner than 50 years from now, you will not be limited to "best launch windows" to Mars that are about 2 years apart.
That is, if somebody will actually get to work on it, instead of retreading old shuttle stuff. Damn Congress anyway.
There has to be a way to "up" the engine thrust/weight on the electric stuff above 10^-4. There's a few guys working this, but it's not big time stuff. VASIMR is one, but they don't have a (T/W)engine solution, either. They have the Isp at around 6000 sec, they just don't have any significant vehicle acceleration capability. Until they do, it's not a fast-trip system.
There has to be a way to quickly and safely revive the NERVA/Dumbo-type nuclear thermal stuff. It will involve telling the politicos to either get lost or else get on board and tell their constituents the real truth about this stuff. Same for pulse propulsion (for which the really serious side effect is not radiation, it's EMP, something not yet understood in 1959, but we got an inkling of, in 1962).
Microgravity illness is fought with one of 2 things based on current physics: (1) fast flight times, or (2) spin the ship. We pretty much know the spin rate limit for "typical civilians": under 4 rpm. We don't know what partial gee is sufficiently therapeutic, so until we do, use 1 gee. Simple enough. At 4 rpm, that's a 56 m spin radius.
Radiation is fought with shielding. Use the water and wastwewater tanks you already know you gotta have anyway. Smart designers would make the shelter the flight deck. The enemy is not so much cosmic rays as it is solar storms. About 20 cm thickness of water is enough, and not so much as to cause secondary shower effects with the cosmic rays.
It doesn't have to be Battlestar Galactica: imagine a long slender ship assembled from docked modules about 300-500 tons in mass and maybe 150-300 m long. Put the habitat at one end, engines at the other. Now spin it end over end whenever in coast, at pretty close to 1-2 rpm. That ought to work, and be both dynamically stable and very easy to do. That's smaller than the ISS, and we built that (at $27,000/lb delivered; now it's down to $2500/lb, and it's soon headed for $1000/lb).
50 years from now, folks will think an assembly like that is tiny. In 10 years, it will look "just about right" for going to Mars, Venus, and the NEO's. In about 25 years, and with hot-enough propulsion retrofitted to the same basic hardware, it'll look pretty good for visits to the main asteroid belt.
Leaving Earth orbit does not mean we go back to the Apollo model of [one launch-one-trip, one trip-one landing, “flag-and-footprints” plus some towsacks of surface rocks]. We should instead take advantage of the orbital assembly we have learned over the last decade or so. And start thinking like real explorers. It's not a race this time.
GW
We do need to eliminate the porn spammer.
I notice he's not gmail. Not everybody on gmail is a spammer. I'm certainly not.
GW
Viking was big and heavy and nothing but rocket braking to landing, all the way from the end of atmospheric entry. I don't see why that can't be scaled up to any size. Might not be the lowest propellant mass, but we already know it worked twice in a row back in 1976.
GW
Population growth has always been exponential, not linear, regardless of all known circumstances. The first trips to Mars will be small handfuls of people, even when we finally decide to establish our first (probably experimental) bases. Very late in the 50 year interval proposed in this thread will be actual colonization ships. There are pulse propulsion ships we can conceive right now that could carry 10's of thousands, or more, even 100’s of thousands, in a single trip. Typical exponential growth, just different circumstances than we have seen before.
The best near-term solution to finding out "how much gee is enough" is the proper experimental facility in LEO. It's a multi-level centrifuge, shaped like a frisbee disk, spinning. 1 gee at the rim, less (proportional to radius) at each deck closer to the center. It has to be large so the rotation rate can be slow enough not the bother the typical human middle ear. That's somewhere under 4 rpm.
Radius for 1 gee is 56 m at 4 rpm. We're not talking "Battlestar Galactica" here. How about several thin pie-slice sections launched separately by existing launchers, and just docked together in LEO the same way we built the ISS? What is so bloody hard to understand about that? Or to do?
I rather suspect that once we actually investigate this, we'll find 0.38 gee on Mars is more-or-less enough to maintain some acceptable level of health, just maybe not quite as good as we enjoy here at home. I'm not so very sure that 0.17 gee on the moon will be enough, but I know nothing for sure. If it is, fine. If not, then that conical centrifuge idea is something the base will need for long-term residents. Size it for a vector sum 1+ gee at its rim, at spin rates under 4 rpm. It's nothing but right triangle trig.
Perhaps 4 hrs per day exercise at 2 gee would be efficacious. Who knows? We need to run the damned experiments with that frisbee-shaped lab in LEO, that we have never had. We need to do it now! There is not much more important for NASA (and ESA and JAXA and Roscosmos and all the rest) to do, than that. Except maybe re-start nuclear propulsion of all kinds.
As for Deimos/Phobos first-or-not, it makes more sense to me to make one damned first trip, and visit the surface and one or both moons, all in the one trip. Just get it done. Since you don't really know what you'll really find as "ground truth" on any of those 3 locations, you have to carry the fuel and supplies to make the trip, regardless. Carry ISRU gear and try it out, but absolutely do not bet the crew's lives on it. Not that first trip.
Depending on what you actually find on those surfaces, subsequent-trip missions might look quite different. But the history of Mars exploration is that our picture radically changes each time we send a new probe. Each one's findings overturns some part (up to and including all) of all previously "thought-to-be-known" results. It won't be any different when we as a species finally summon-up the gumption to actually send men there.
Ground truth has always, always, always been at least 98% at variance with what we thought before we went there (robot or manned). And, no two sites have ever been the same anywhere, not here, not the moon, not Mars. (I predict not anywhere.)
You have to take that into account when planning a mission, manned or not. Most of the manned mission architectures I see proposed for the moon, Mars, or the NEO's, ignores that very inconvenient fact of life. As a species (or as any individual institution) we have not adequately learned that lesson yet. But we certainly need to. It would make life easier. And more certain.
Just some thoughts from an old guy. This stuff really is more art than science. (Something corporate managers desperately hate. Politicians and bureaucrats, too. )
GW
Launches of Falcon-Heavy from Vandenburg AFB in S California are more-or-less southward over the Pacific for more-or-less polar orbits. Very popular for military stuff, not useful at all commercially. Spacex's pad at Vandenburg will be mostly for USAF payloads as the customer on Falcon-Heavy. Those are typically 25+ ton payloads, what the shuttle bay was originally designed to carry.
Polar-only at Vandenburg is why Spacex trying to buy the old shuttle pad at Canaveral, to support eastward launches of Falcon-Heavy at about 23 degree inclination. That's what the LEO 23 deg 53 ton figure is for. That's for both NASA and commercial payloads. But, Canaveral is pretty much governed by NASA rules and bureaucracy. If they can obtain the pad, that'll be their first available eastward launch site for Falcon-Heavy.
They're also looking for a purely commercial launch site, where only FAA approval is required, unhampered by NASA bureaucracy, for purely commercial launch services. The candidates are all eastward launch for the more-or-less 23 degree inclination, supporting commercial needs. Far south Texas is the one I'm rooting for. Near Brownsville at the mouth of the Rio Grande. Out over the Gulf of Mexico into the mid-to-south Atlantic.
The cost per pound-or-kg delivered payload can be deceptive. They are usually calculated as launch cost divided by max payload capability. But, if the rocket doesn't fly fully loaded, launch cost is usually the same or not very much different, while payload weight can be very much smaller, leading to a very much higher unit cost. You get the full cost benefit only if you fly fully loaded.
I noticed a new, slight price break being projected for Falcon-Heavy on Spacex's website: below 6 tons, $85M, but from 6 tons to the max 53 tons, $124M. I might be off a trailing digit or so, but those figures are pretty close to what I read a couple of days ago. The unit cost at 6 tons is bunch higher. It really pays off to fly at or very near full load at 53 tons. Metric tons, that is. Right at $1000/lb.
Figured at launch cost divided by max payload, I had right at $2500/lb for Falcon-9 at its 10.45 tons. Shuttle was 1.5B per launch, 25 metric tons max, which was about $27,000/lb. Multiply those figures by 2.205 for $/kg. I can't remember what I had figured for some of the Atlas-V and Delta-IV configurations, but those data are posted over on "exrocketman" in the last few days.
If you want 1 G exposure on the surface of 0.38 gee Mars, then build a large conical merry-go-round type centrifuge, and spin it slowly (under 4 rpm). The vector sum of the centripetal acceleration and vertical acceleration of gravity need to add up to 1 gee. By then, we might actually know if less than 1 gee "is enough", and if so, precisely what fraction we need.
Of course, we ought to be working on that right now, but I see no one doing it except by very questionable surrogates, such as enforced bed rest at this or that angle. Bah, humbug! Where's the real data at real fractional gee? None of these space agencies have seen fit to tackle one of the fundamental design constraints for the first trip, much less a colony or base.
This next is really terraforming, but why not go find some really ice-rich bodies in the outer solar system, and deflect them to hit Mars. This is just a crude guess, but maybe half the ice vaporizes, and maybe half ionizes into oxygen and hydrogen. The hydrogen that doesn't recombine with oxygen gets lost to space rather quickly, leaving a net gain in oxygen. How much, I dunno. Just guessing here.
But, do that a lot for a while, to the tune of a handful of cubic miles of ice, and things really add up. Eventually you add many dozens of mbar O2 on top of the existing 7 mbar CO2, plus you start filling the northern lowlands back up as an ocean (probably ice-covered, but still a great heat reservoir and rain source).
Voila! Terraformed Mars! In years, not centuries. No p-suit or O2-mask required. Just add organic matter and appropriate organisms from Earth to the dirt and start farming. The climate should resemble that of south-central Canada. Or south central Siberia. And, aerobraking with parachutes is finally practical for landing stuff from space.
Pardon me, I probably got too wild here. But if you can deflect NEO's to save the Earth from a hit, you have the means to deflect icy bodies in the outer solar system to hit Mars. Only the travel times are longer. (But not with pulse propulsion.)
We are getting closer to actually having this deflection capability, especially if somebody works out a water-NERVA, a way to stick it securely to the icy body, and a way to use the engine waste heat to melt some ice and use it in that water-NERVA. A robot could do that deflection. You just need to transport a real mining crew out there to install the equipment. Every site is different. Needs adaptability to site conditions, and that's men.
GW
The old 1959-ish designs from the original Project Orion were smaller. If memory serves, their big one was a 10,000 tonner for going to Saturn and back in (only!!!) 3 years, stopping off at the moon and Mars along the way! It used shaped-charge fission devices, at about 1 per second.
You use low-yield fractional kiloton devices for surface launch, where the blast wave helps push you, then a few kilotons each, once out in space where it's pure radiation pressure. Again, if memory serves, that design was in the 2-to-4 gee range during the "burn". Then in coast, it just spun about its longitudinal axis for artificial gravity. A 2-to-4 gee "burn" measured in a day or two, is quite doable for some very high interplanetary travel speeds. Months instead of years to Saturn, for example.
Myself, I'd be afraid to try to land a thing like that directly upon a planetary surface. Launch, yes. Land? Jeez, how do you keep it controlled that fine? If it were me today, I'd have rocket landing craft aboard, to make the surface visits. Being nuke anyway, I'd just use a hell-for-stout-built single stage "boat" powered with a close variant of the old NERVA solid core nuke thermal rocket. That's good enough for single-stage two-way on Mars, Mercury, or any of the outer moons. At 10+% payloads.
GW
Last I heard, Spacex is building a pad at Vandenburg for Falcon-Heavy. Their first customer is supposed to be USAF for really big military payloads. The pad should be ready by 2013. First flight might be later that year. They gotta test the stages in Texas first. That test stand is being built right now.
They're trying to buy one of the shuttle pads at Canaveral to convert over for Falcon-Heavy. That might be for both NASA and civilian/commercial payloads. I'm not sure how that's going, haven't heard for a while, and NASA can be amazingly bureaucratic.
Which is probably why they are looking for other civilian/commercial launch sites where they need only deal with the FAA to launch. One of those is near Brownsville, Texas, near the Rio Grande delta. They would shoot out over the Gulf toward the mid-to-south Atlantic. I'm rooting for that one.
GW
Rune:
You did a really good job thinking about a lot of really tough issues on that one.
There's a lot of pulse propulsion information buried in George Dyson's book "Project Orion: The True Story of the Atomic Spaceship". George is the son of famous physicist Freeman Dyson (who did work on old USAF "Orion"). The "cover" to get funding as a USAF project was an "orbital bomber". But that team clearly had deep space exploration travel as their goal, the whole way.
There's a whole slew of famous folk who worked on that project who couldn't talk about it until recently. Who they were and what they did will really surprise you. What eventually happened to it will disgust you. As it did me.
You're exactly right about the nuclear "shaped charges", that's exactly how to get a spindle shape of EM radiation pulse from the explosion. In space there is no blast wave at all, just that pulse of intense EM radiation. If it's spindle-shaped, your pusher plate can be made to intercept one end (half) of it, at the design detonation distance. It's a diameter-at-range thing (constant angle).
Until one looks at actual nuclear test results from Nevada in the 50's, one would think this radiation pulse would vaporize the steel pusher plate, but it does not. If you grease the plate, the steel is completely un-eroded even for multiple explosions (sacrificial very thin layer of grease, replenished after the "burn" to be ready for the next one).
Your L/D proportions for spin about the longitudinal axis matches old Orion's typical ship shape and dimensions. It was my long Mars "stacked module" ship that spun the other way: end over end. Both are dynamically stable, and extremely simple. Short and fat works best with pulse propulsion.
I'm guessing that the shaped charge effect can be done with thermonuclear devices (all they did back then was fission). If so, then gigantic pulse ships like yours become easy to build. We already know it works. The old Orion guys flew a 1-meter model just fine with ordinary explosive charges long ago. Even though they weren't supposed to.
The only real problem would be EMP wave effects from the explosion damaging electrical stuff near enough by to be hurt (it is a 1/r^2 decrease with range, like ordinary radio). I doubt very seriously we would really want to start one of these from low Earth orbit routinely. But maybe a few thousand miles up would work fine. 10 times more r is 1/100 times the EMP intensity.
Even with fission devices, the fallout from surface-launching a fairly big ship is about like popping one typical ICBM weapon warhead in the atmosphere. Spread over a period of a few years, I think we could easily afford the radiation fallout from launching a half dozen of these. The real problem is EMP during the launch. The "shipyard" needs to be very isolated, like way out in the Pacific, maybe. I dunno.
Imagine what we could do with anywhere from 1 to 6 of these in the 10,000-100,000 ton range of size: plant major colonies anywhere in the solar system, in a single trip. And your 10,000,000-100,000,000 ton size range actually could be a slowboat multi-generational starship.
The hardest thing about your starship isn't the ship or its propulsion, it's the closed ecology life-support, and the organized "miniature industrial society" setup to maintain all the technologies and hardware and pulse "fuel" for centuries. We get those items down right, and multi-generational interstellar flight becomes a realistic thing to consider doing. We may even have some reliably-identified more-or-less-Earthlike target exoplanets to visit, by the time we get that support stuff "right", if we started right now and worked on it (but, we are not doing those things).
I think you're much younger than I am, being bothered by "exams". That's over 4 decades ago for me. You might actually live to see one of these pulse ships built, if the politics changes to support it. I probably won't. I'll be lucky to live to see a manned Mars mission of any sort. Maybe not, the way things are going right now.
But hope springs eternal....
GW
Louis:
What you say is probably true, although I haven't checked the numbers for chemical. In my calculations, I looked at substantially-higher delta-vee requirements to cover up to 30 degrees orbital plane change, each way. Without that, you are restricted to a very narrow track right under your orbit. I also looked at two-way self-supplied trips, no refueling on the ground. That's a much tougher problem. To do all of that single stage at 20% inert structure (for tough-as-an-old-boot reusability) and 10% dead-head payload required nuclear Isp. You could do it multi-stage chemical, but then it's a one-shot throwaway. I was going for a multiple-landing lander, refuelled in orbit between trips. I was also going for multiple landing sites in the one trip. Different mission objectives.
GW
All the Dragon data that I have seen says there is 1290 kg (1.29 metric tons) of hydrazine and NTO in the capsule itself, without the trunk. You have to shed the trunk to use the heat shield. No trunk during powered landing (but there are landing legs adding to the inert mass!!!).
Figure a capsule around 5 or 6 tons, with 1.29 tons of fuel. Use about 307 Isp for hydrazine/NTO in near-vacuum, but knock your theoretical delta-vee down by a multiplicative factor of 0.71 for the cant angle of the Super Dracos. Even with a parachute assisting during the last part of the descent, that's really pushing a successful landing.
That kind of delta-vee is entirely insufficient for an ascent, even if fully refueled on the surface somehow. You've got gravity and drag losses cutting it further (I'd hazard a guess of a 1.05 divide-by knockdown factor for 0.38 gee and very thin "air"). You still have the 0.71 cosine multiplicative knockdown factor for the cant of the nozzles.
Dragon might serve as the manned cabin on something much larger. It just can't do the two-way lander job all by itself. Rocket equation physics simply precludes that. If Musk is planning to use Dragon as part of a manned lander, then he has a big landing stage, or multiple stages more likely, up his sleeve that we haven't seen yet. (Or maybe he doesn't. Yet. But he will.)
There's another company out there that I personally know hasn't revealed everything they want to do just yet. I'm supposed to help them do it when the time comes. I suspect all the rest are similar in their secrecy about plans and schemes.
GW
I'm guessing there might be a way to land a man on Mars in something like a Dragon capsule, using a parachute and a lot of rocket braking with the Super Draco thrusters. But it's a one way trip.
So, how does he get back to orbit, to go home?
IMHO, it is a practical Mars lander that is the critical design lack that we have, as regards sending men to Mars. I don't see anybody working on one, either.
GW
Glad you liked the data, Louis. I worked hard on that, to make sure it was both usable and reliable.
As soon as there is a reliable lander, I'd bet Musk will scrape up the money and go to Mars, without NASA if he has to. But the lander is the missing tinkertoy in our toybox, as far as Mars is concerned.
Exactly what kind of a lander you build depends in great part upon your basic mission architecture. For first-visit explorations, I just don't see the sanity of sending the Earth return vehicle to the surface of Mars. That's the same weight penalty that almost forced Apollo into a two-launch-one mission architecture. Doing a lander ("lunar orbit rendezvous") made the moon shots do-able as one launch-one mission. That was fortunate, because back then, orbital assembly by docking was beyond our reach. Docking capsule with lander was a stretch, back then.
There are serious difficulties landing things over about half a ton on Mars. Aerobraking is not sufficient because the "air" is just too thin, yet thick enough for significant entry heating. It simply takes rocket braking, and that means propellants and stages if chemical. Yet, it has to be clean aerodynamically, and it has to have a heat shield. It cannot be built flimsy and light, like the Apollo LEM.
Unlike the moon, there's enough gravity on Mars to put a two-stage rocket-braker out of reach with chemical propellants. Three or more stages makes for a very large vehicle with a fixed payload mass and volume. Tiny things like a small sample return we can design, but how big a thing does it take to carry 1-6 men to Mars orbit? That's huge!
I think the lander is the critical design issue. Orbit-to-orbit ships we can build. It's that lander that drives things to distraction. That's the solution we lack.
I suspect you could do it single stage rocket burn descent and ascent with a NERVA-like solid core nuke and LH2. (I'd really like to see a water nuke, but nobody ever built one.) Single stage landers can be made refuellable and reusable. That opens up a whole new slew of mission design possibilities.
The government has a monopoly on things nuclear here in the USA. If ever there was a critical enabling technology needed to send men to Mars, it is a practical Mars lander. Single stage nuke is the practical one, or so it seems to me. So why is NASA screwing around with a gigantic shuttle-derived launch rocket, when a practical lander is what we really desperately need?
I hate how politics has killed what once was a shining example of a government agency.
GW
I suppose some sort of solar-thermal airplane could be built. NASA and others have already flown solar-photovoltaic aircraft, including that big one at about 70,000 feet. But, these have all been very slow, and very lightweight/flimsy things. None has been capable of significant payload.
That's not to say it couldn't get better over decades: compare a WW1 biplane observation plane with today's jet transports. It did take about a century of concerted effort to grow that capability.
If I was to do a solar-thermal engine for a slow craft, I'd be looking at solar-heated piston and turbine engines, all for driving airscrew propellers. Even after a century, the propeller is best suited for slow flight. The solar PV designs all do that, too.
As for ramjet, that's very high speed flight. Even the pitot-inlet stovepipe engines had to be moving just about transonic to do much good, and they'd peak out about Mach 2 or so. Below about 300 mph, engine Isp was lower than a plain old solid rocket (180-250 sec). You could get thrust > drag, but it just wasn't worth it.
The better ramjets are supersonic inlet types, with minimum takeover Mach numbers in the 1.5 to 2 range. That takes a big booster just to get moving that fast. These types of ramjet engines can peak out in the Mach 4 to 6 range. Airframes capable of these speeds are quite different from the slow fliers that solar power currently seems able to push.
GW
I doubt the wisdom of building something arbitrarily to the shape of a science fiction design. But, I like the idea of building an orbit-to-orbit transport of some kind. That idea makes a great deal of sense. You add a "landing boat" for visiting the surface, if needed.
Based on what we currently and demonstrably know how to do, I think that such a craft craft would be assembled from cylindrical docked modules, like the ISS. I also think that the habitable volume will be very small compared to the propellant volume, based on propulsion we know how to do and have done, at one time or another.
I rather think the ship we might build will be a slender linear stack of modules with habitat at one end and engines at the other, more like the "Discovery" in the movie "2001 A Space Odyssey". Except, rather than building a centrifuge inside the habitat, it would be easier just to spin the ship end-over-end, while in coast, to provide one full gee at the habitat module, at very low rpm, and with no bearings or anything else to worry about. Short term exposures to zero gee while de-spun for maneuvers should be no problem at all.
As for propulsion, with chemical rockets, the propellant volume is huge, and empty tanks will have to be staged off. The rocket equation evaluated at realistic mass ratios confirms this. It is even true for LH2-LOX, the very best we have. The trip is a "slowboat" minimum-energy orbit of 7-9 months one-way. That cannot be avoided. Given the wait for orbits to be right for return, this is about a 3 year mission.
4 decades ago we came within about a year of flying a solid-core nuclear thermal rocket engine called NERVA that used LH2 for propellant. It has been forgotten to death, and slandered with irrational fears, ever since. Using that technology, a modular Mars vessel is 3-4 times smaller. But it still must stage off empty tanks, and it must still fly by the "slowboat" min energy orbits. It's still about a 3 year mission.
The kind of propulsion we need for the fast trajectories does not yet quite exist in a usable form. Claims have been made about trips anywhere from 30 to 90 days one way using ion or VASIMR electric schemes. These have the specific impulse, but not the thrust per unit engine weight to pull that kind of a trip off. Basically you get a thrust measured in single-digit pounds for an engine system weighing tons, mounted in a vehicle weighing dozens to hundreds of tons. Just the getaway from LEO is months long. Whether you use nuclear or solar power, a MW-class electric generator is simply going to weigh many, many tons.
It might be wiser to put high-thrust chemical or nuke rockets for the getaway and arrival burns, and apply the electric stuff to speed up the coast in between. That might actually help. In that case, a slowboat mission might be done without staging empties off. Maybe even a bit faster.
There are some other concepts that might provide higher thrusts for the weight at high specific impulse. I am not familiar with them all. One I am familiar with is gas core nuclear thermal rocket. Some of the benchtop feasibility experiments were done 40 years ago. But no test devices were ever built. These are entirely "mythical" at this time, but the projected performance looked good enough back then to make one-way trip times to Mars in the 30-90 day range possible, all single-stage and completely re-usable. But until and unless someone actually builds one, these things remain speculations.
GW
I revisited launch unit cost to LEO with better source data than I had in January, and posted what I computed and plotted in a new article over at http://exrocketman.blogspot.com, dated 5-26-12. Right now, it's top-of-the-heap.
I also drew some very interesting interpretations and conclusions from that data. They have strong bearing on the various proposals for manned (or unmanned) Mars missions I see being discussed here.
Take a look, and let me know what you think, either here or there.
GW
Well, instead of a tow sack of surface dirt and rocks (Apollo), why not add a real drill rig to the back of the rover. Just about anybody can be trained to operate a drill rig. Get your samples meters to a km down, based on whatever you're seeing in the output cores. Just like the oil drillers here. Could do that pretty easily on Mars, the moon, or any other body with say 10% gee gravity.
Drilling deep for samples. Now there's a good reason to land men. How do you program a robot to do that? And with the time lag, it's impractical to do it by remote control.
Until that kind of thing is done, you cannot answer fully the two questions: "what all is there?", and "where exactly is it?". Until you answer them, you have not really explored.
Isn't exploration supposed to be the purpose in going there?
GW