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Careful guys, this has gotten a bit political. One of the moderators may step in. Although, some of the criticisms seem well-founded.
I saw a comment above about livestock being "inefficient". That's true, depending upon what you measure and how you measure it. Maybe not so true looking at a larger picture.
But, consider this: livestock are one proven way to get lots of what we might call "organic fertilizer", in simpler terms, manure with microbes in it. The so-called "sustainable agricultural practices" here on Earth depend upon that kind of fertilizer as a way not to turn real soil into just rock dust doped with chemicals. (Unfortunately, the output from that cannot sustain all 7 billion of us.)
It doesn't matter that there are vegetable means of producing calories and protein more efficiently, pound for pound. You still need the manure with all that microscopic ecosystem in it. It's just the way life evolved. Cannot fight it, seems silly to fight it, actually. Plus, we ourselves evolved as omnivores. Not carnivores-only. Not vegetarians-only. Omnivores. It takes that mix of foods to support the size of our brains. Unpleasant little evolutionary fact of life, I guess.
As far as transporting livestock to Mars (or anywhere else) goes, that is another big argument for artificial gravity. It'll just take a whopping big ship to send lots of supplies and livestock to start a real farm colony. Guys, that's where the old nuclear pulse propulsion comes into play. It's only high-performance if you build spaceships larger than current naval warships. The very sort of thing we would need.
We have the concepts and most of the means to do this right now. All that is lacking is the political and social will. In a world ravaged by a recession/depression where only the already-rich received any substantive relief aid, people like us wanting to colonize space are definitely in the minority, and by far. That means setting up big self-sustaining colonies on Mars is not a reasonable expectation for some decades yet.
But setting up small bases and experimenting with ways and means to live off the land is a reasonable expectation in the next few-to-several years. There's pressurized buildings for living spaces and dry-land agriculture, and there's ponds of water under ice-and-regolith cover, for aquaculture. The pressurized buildings are fundamentally scale-limited to relatively small sizes by the square-cube law. But, covered-pond aquaculture is not fundamentally-limited in that way. Fish, shellfish, crustaceans, and aquatic plants could have a really big role to play on Mars in the future.
The real trick is inducing a few visionary commercial entities to go try it. All the technologically-capable governments have proven rather feckless for over 40 years now. I wouldn't bother holding my breath waiting for one of them to mount a Mars expedition. Not even NASA. Almost none of the big, serious things they going on, have much to do with interplanetary-range human flight. Going to Mars ain't going to the moon. We're talking years, not a couple of weeks, in space.
GW
Hi Midoshi! That's good news about Maven. Keep us posted.
These forums have been awfully quiet lately. Have you noticed?
GW
The difficulty of the Mars lander problem depends upon whether you think one-shot or reusable.
It needs a heat shield because you must do hypersonic entry with severe friction heating on descent. It may not need parachutes, as it is likely that its entry ballistic coefficient will substantially exceed 100 kg/sq.m, and there's simply not time enough time to deploy a chute and have it do any deceleration with higher ballistic coefficients. Going straight from hypersonic entry to terminal rocket braking is the better, simpler, and more practical idea in that regime.
You can build a one-shot vehicle as two stages, to increase the delivered payload fraction substantially. With entry aero-deceleration doing the brunt of the work on descent, the terminal rocket braking requirements are actually quite modest at around 1.5 km/s delta-vee, versus nearly 4 to ascend. That means you do the descent and part of the ascent on stage 1, and finish the ascent and the rendezvous with stage 2.
On the other hand, with a lower payload fraction (and larger vehicle for the same delivered cargo), you can do the entire job on chemical propulsion in one stage, because the total delta-vee required of the rocket is only 5 to 5.5 km/s. It looks better with LOX-LH2, but can be done with the other propellant selections in the 300-350 Isp class. That's a lander you can refuel (at either end of the trip!) and fly again, And again, and again, etc. I typically get around 60-90 tons of loaded fueled Mars lander vehicle for a 3 ton cargo delivery. Closer to 30 tons with LOX-LH2.
Myself, I like that second choice (bigger but reusable) a lot better, because it lets you visit multiple sites in the one mission to Mars, in spite of the added tonnage you must send to Mars (landers plus lots of propellant for the multiple landings). That multiple landing sites capability makes a whopping lot more common sense to me than the Apollo model of one mission-one landing. If there's one thing we have learned all these decades with the probes and the Apollo landings, it's that no one site characterizes a planet (surprise, surprise!).
If you can build a thing like that for Mars (and we can, right now), you can build a similar reusable, one-stage chemical lander for the moon. There's less total delta-vee in spite of the all-powered descent, and no heat shield needed, so payload fraction can be quite attractive. I have no idea why NASA thinks they have to build a one-shot two-stage Apollo-LEM-on-steroids to go back to the moon. Except that it looks like they are still thinking Apollo-on-steroids with one mission-one landing. If we go back to the moon, that's not appropriate. We would be going to set up bases and commercial mining, etc.
One other point: reusable landers must have rocket engines capable of many, many restarts, and a long service life. You can use that propulsion to push said lander where you want to go (moon or Mars), drawing from added propellant tanks (not whole propulsive stages!!) for that purpose. If you choose to return the lander to Earth, it can push itself back and enter LEO. The lander's engine is the "service module" engine for a manned capsule. All it needs is refillable propellant tanks besides what it has internally. Reusability spread over multiple missions is a massive cost reducer.
That is a very beneficial fit with generalized modular design (assembly from docked modules) for all the vehicles. The right size of module is 10-25 tons right now, up to twice that when Falcon-Heavy starts flying (two 25 ton modules per Falcon-Heavy, say). Unit prices to low LEO are about $2500/pound right now, and should be near $1000/pound with Falcon Heavy. Unless SLS can get under that unit price (and it never, ever will), there's no point to use it for these missions. That's something NASA and Congress should have considered.
The modular concept leads one almost immediately to the orbital transport idea for Mars, equipped with landers. The landers might be flown there separately, or maybe not. The transport, if shaped as a long "baton" from docked modules, can be spun head-over-heels for artificial gravity. And that solves a whole host of life support issues for a 2.5 year mission to Mars.
There's real benefit available if one stirs up the guts to think outside the old Apollo box.
GW
I see by the news releases that Curiosity has reached the foothills of Mount Sharp. The wheel damage issue slowed them and modified their route, but they made it. I hope failed wheels don't "kill" the thing early. It's always quite rocky in mountainous areas here.
On the way, there was one striking photo they obtained that created something of a stir: an oddly shaped rock that looked like a thighbone. The soil colors and rock outlines in the dirt looked rather similar to the Mount Sharp foothills stuff, so it must be fairly close by where they are now. That odd rock was interesting enough that I hope they poked around a bit, investigating it, before resuming the trek. To me it looked there were cavities under some of those mostly-buried slabs. That's a rather nifty site.
But, I only ever saw the one photo of the "thighbone" site, and nothing about it since.
GW
I'm not sure an inflatable greenhouse brought from Earth will ever be practical, precisely because of the cold, the harsh UV, and the pressure differential effects. All the good plastics we have , have serious shortfalls for that environment. In the post just above, RobertDyck turns to advocating glass in a greenhouse built from in-situ materials. That's my favorite concept, too, and it has been for a while (see also post #51 above, from 2012).
I had sort-of fleshed this concept out in a posting on my "exrocketman" site, as a mushroom-shaped masonry building held in place against internal pressures by dead-load regolith on its roof. There is a multi-layer glass panel-between-columns ringwall around the perimeter that lets in light with reduced UV, and keeps the air and heat in. So you get the reduced UV necessary for agriculture inside, and the added benefit of radiation shielding from your roof. All we need is a concrete substitute that works in the cold near-vacuum that is the atmosphere of Mars, and we can build this thing out of mined local rock. Or send framing steel from Earth. Or both.
Y'all might enjoy looking at my old posting. It's something we could build with front-end loaders and a glass-making facility suitable for Mars. And it would work on the moon, too. http://exrocketman.blogspot.com. Use the navigation tool on the left. Go to "2013", then "January", then "Aboveground Mars Houses", posted 1-26-13.
GW
I think that was actually Bob Clark's blog. That's where I saw him post stuff about Maasten's lander ideas. Basically, they make a great deal of sense. More tonnage onto the moon with something no bigger than what we flew there before. Just done better.
I think Spacex's Falcon-Heavy will be the rocket-of-choice for going back to the moon, among other things. It can fling 53 tons to LEO, for a unit price currently projected to be about $1000/pound, under half what the current stable of commercial rockets can do in the 10-25 ton range. I think a really viable moon mission ship might be a Dragon v2, a big tank module or two of propellants for orbit-to-orbit departure and return (for reuse!!), and one of Maasten's landers (or something similar) and use its propulsion to fly you there and back, as well as landing on the moon as a single-stage vehicle. Why fly two sets of engines when one will do? (As long as it's a cluster for redundancy.)
One of the things we might ought to look seriously at is flinging hardened propellant tanks to LEO with a light gas gun for under $100/pound. It would require an LEO space taxi to retrieve them. You transfer the propellants to your vehicle, then send the gun launch hard tanks back for refill and reuse.
GW
I dunno, Tom. Failing some incredible breakthroughs in physics and propulsion technology, I don't see us building a practical starship any time soon. Flight times measured in centuries to millennia simply are not practical when compared to our lifetimes of just under a century.
That being said, when those breakthroughs have happened, and we are capable of interstellar travel with practical flight times, I also wonder why we would care about habitable planets. With technology like that available, would we not be building our own habitats in space? Why live at the bottom of a gravity well when you don't have to?
However, from a public motivational viewpoint, your interstellar planet-detecting space telescope idea has great merit. I like it. The Hubble did more than anything else in recent decades to stir support for some of the things NASA does. Kepler was another, just not as popular, because no images were returned. People understand pictures, not data. More are coming.
We don't need a gigantic rocket like SLS to launch such a thing, because it can be assembled in orbit from docked modules, flung up there with rockets we already have, like Falcon-9, Atlas-5, Delta-4, and (soon) Falcon-Heavy. Not to mention things like Ariane and Proton.
The giant rocket potentially makes it cheaper to fling the stuff up there, because there is a unit launch price break as "flingable" payload increases. But it's a rather small effect once you exceed around 10 tons. Using all of the above-named rockets to establish a unit price vs payload mass trend, one would predict that SLS at (70-140 tons) should fly for around $500 / pound maximum, and probably a lot less than that.
Trouble is, SLS won't ever be anywhere near that cheap (current projections look like $2000-2500 / pound), because it's being developed by NASA, not the commercially-competitive companies. That's no better unit price than where we are right now with 10-20 ton payloads. Even those numbers aren't reliable: NASA is infamous for under-estimating costs.
When there's a need for a giant rocket to launch 100+ ton payloads to orbit, the commercial companies will come up with one that really is inexpensive: under my $500 / pound figure. Unfortunately for us, the SLS will never be that rocket. NASA knows nothing about how to simplify logistics, which is where most of their super-high costs come from. The support tail for the commercial rockets is the population of a small city. For NASA, it's multiple megalopolises.
Meanwhile, just as for the telescope assembly process, any manned or unmanned mission we might like to accomplish can be assembled from docked modules in LEO with the rockets we already have. That includes men to Mars, asteroids, the moon, or anywhere else. But, that approach rules out Apollo-style one-rocket / one-mission designs.
In point of fact, NASA resisted doing a lunar lander until it was almost too late, because that idea came from an outsider to the agency. Until they decided to go with a lander instead of landing the entire Apollo cluster on the moon, the best they could do was two Saturn-5's per moon mission, with LEO rendezvous and some sort of on-orbit refueling. At the time, a lunar lander was actually less risky than on-orbit refueling with cryogenics. It forced them to accept the outsider's idea, which is how they got down to one Saturn-5 per flight to the moon.
In retrospect, had they done docking in LEO as well as at the moon (with the lander), they could have gone to the moon with perhaps 3 Saturn-1 shots per trip. And THAT is why I say the same processes, done correctly, would allow us to fly to Mars RIGHT NOW with the rockets we already have. That architecture leads one to a generalized orbit-to-orbit transport design, fitted with landers appropriate to the destination. Such designs inherently accommodate artificial gravity by spin, which has direct and indirect benefits to all aspects of crew life support.
Costs are reduced by making that rig reusable to the greatest possible extent, and then using it for multiple trips on a variety of missions. The very same ship could be used to visit Mars, the asteroids, Venus, and Mercury. Although, the moon is really too close by to benefit fully from its use. Build one or two, and use them to do all of those things.
What we did with Apollo only makes sense if you are racing hostile competition. We don't do that anymore. At least I hope not ever again. It's too wasteful.
As for future developments in propulsion technology, well, just keep retrofitting the one or two ships you built. Now there's more money to go around doing all the other things you really wanted to do. Someday, replace them, using the same basic ideas, just better components and technologies. Before too long has passed, you'll have bootstrapped your way into real starships.
GW Johnson
Dave Maasten might have an even better lander, which could still ride one of Spacex's big rockets. XCOR might even have a better engine than the RL-10 that is stock on Centaur, around which Maasten's lander is conceived.
GW
Parts of Antarctica are cold enough for this, and would be one hell of a lot easier to reach than Titan.
Parts of the Arctic used to be cold enough for this, but no more. Would have been even easier to reach. Don't count on Greenland's ice cap anymore. It'll work right now, but no one can say for how much longer.
GW
Eyeballs-back vs eyeballs-down makes a really big difference to high-gee tolerance. Fighter pilots are mostly eyeballs-down, although the seat in the F-16 is semi-reclining. F-16 pilots could therefore cope with 9 gees longer than the pilots of most other fighters. Still only times measured in 10's of seconds, though.
Centrifuge studies seem to indicate that 10-15 gees is feasible for times measured in minutes to hours for reclining humans. Maybe even more. The Apollo return from the moon was a 3-minute long pulse of deceleration that peaked for several seconds at 11 gees. What they contemplated for free returns from Mars missions was worse, perhaps 15 gees or so. Similar pulsed profile of gees vs time.
The brief pulses of gee in the rocket sled tests in the 1950's revealed a max level of tolerable gee for humans: about 40-to-45 gees. Exceed that, and your body is literally torn apart. The films from the animal experiments are quite gruesome. Paul Stapp endured about 40 gees on the sled, which nearly killed him. He was hospitalized for a long time, but recovered. We're talking exposures under 1 or 2 seconds at levels like that.
That level fed into ejection seat design: limiting ejection gees to under 40 gee, for the newer "zero-zero" seats introduced in the 1960's. You'll survive, but you will be injured, perhaps seriously. Usually spinal injuries. Which is why most test pilots refer to ejection seats as a means of committing suicide in order not to be killed (in the crash).
GW
Cephalods are jet propelled. Octopi, squids, etc. Water jets.
GW
Regarding post #7 above (5-30-2014): as I understand it, the fins on the trunk are for aerostability during ascent abort down in the atmosphere. Apparently it takes the trunk with it, and separates from it after getting clear of the booster rocket. I might be wrong, but that's what I heard.
As for not using a chute, it would be wise to swap out chutes between missions, even if unused. You just repack it and load it on the next mission. Same as what paratroopers do. Flying on a "stale" chute is asking for trouble.
GW
This sort of thing might work on Earth where the air is thick. Are you proposing this for Mars? The air there is too thin for a fixed-wing aircraft to be practical. Why would rotary-wing be any different?
GW
Well, 8 cables certainly has some redundancy. Am I correct in surmising that we start and stop the spin when pulled together, with the spin slowing to design values as you pay out to the design radius? Otherwise, I have no sense of how to spin this up and down without tumbling and tangling things. You can't push on a string, after all.
Between the structure of the habitat module, and whatever water and wastewater is on board, I don't see that solar flare shielding is that big a problem. Even if there's not 20 cm of water available. Sounds like there's probably not, especially for the smaller mission and vehicle designs. (GCR simply isn't a problem, as long as the crew doesn't do this trip twice.) Stored foodstuffs, stored clothing and bedding items, and stored equipment can also serve as shielding. As can any tanks of thruster or main-engine propellants. But, I think water supply estimates should expanded some: with spin gravity, you can do real cooking with real free-surface liquids in real pots and pans, and, you can use real frozen food (another potential radiation shield, and a very good one, too).
From a spacecraft designer's safety-first standpoint, I'd still recommend the flight control station be the radiation shelter for solar flares, not the sleeping quarters. That way, critical maneuvers can be conducted regardless of the solar "weather" outside. Those events are at most a handful of hours long. But at peak, the worst ones are every bit as lethal as the fallout right after a nuke weapon surface blast. Up to around 4000 rem/hour.
I would also recommend that habitat module interior layout be designed around the notion that access must be had to the pressure shell in seconds, in order to repair meteor/space junk punctures before the module can depressurize. It's another safety-first thing. That does not seem to be the custom yet, but that design practice is long overdue adoption. It means you do not mount any equipment at all, of any kind, on the pressure shell wall. Period. Everything needs to go on a central core structure. And you need a repair kit in every single compartment. No exceptions. The upside is more emotionally-spacious living spaces, and the opportunity to have lots of windows.
GW
Aw, it's not hard to figure out. With spin gravity, the centrepital acceleration is a force field dependent only on radius R from the spin center. What that means is there is a significant gee gradient with R, directly proportional to spin rate, which is the only difference between what happens in a smallish centrifuge versus what we experience down here. Down here, R is measured in 1000's of km and spin rate is a very, very small number, so we are unaware of the (otherwise inherent) gradient.
With small medical centrifuges, the gee gradient is considerable, so the fruit flies may well be confused by it. So would people, so the Kibo centrifuge module for ISS that was cancelled might not be the best design. At this point, who knows? There is precisely zero experience with it.
But! We know that untrained civilians can tolerate 3, at most 4, rpm for a spin rate. Using that 4 rpm figure, the radius R for 1 full gee is 56 m. That has a fairly-low gee gradient, too!
That's too big a radius to spin a ship about its long axis for anything but a gigantic nuclear explosion-propulsion colonization ship. But it is quite reasonable for a slender baton configuration spun end-over-end. That's a configuration seen as extremely stable in every Friday night football game all across America (baton twirlers throwing spinning batons high in the air), in spite of the fact that NASA has never looked at it.
That implies a ship design around 120 m long with a departure weight around 300 to 900 tons. Big, but definitely not "Battlestar Galactica".
Your habitat is at one end, your engines at the other, and the "structure" in between is your propellant tankage, which you have to carry anyway. How simple is that concept? Why in the hell would we ever need either a truss (massive inert weight gain) or a cable-connected structure (multiple single-point failure modes)? Those are all that NASA ever looked at.
GW
"Why wasn't that (a centrifuge at fractional gee) included?"
Because no one at NASA wants to, or will ever, admit that not doing fractional gee studies in LEO was a major mistake in judgement and management.
Further proof they really have no intentions (yet) of flying humans to Mars. Or anywhere else beyond cis-lunar space.
GW
Deep space mission design with people on board is a severely-constrained optimization problem. The best result is constraint-driven among several constraint-driven choices, somewhat like linear programming, except this is very non-linear. It will never be "truly optimal" in terms of weight or dollars. It may not resemble the expected notions going in, not at all.
With humans to support, these constraints are very severe, more so than any other kind of mission, and violating them risks the most expensive thing we know of: loss of a crew.
A lot of the vehicle and mission design concepts I have seen on these forums are quite innovative and interesting. Some include features I would never have thought of by myself. My trouble with most of them is that I cannot see how the microgravity disease and radiation-exposure risks can be addressed in vehicles that small. We can argue about living space requirements, another serious shortfall (in my opinion) with smallish vehicles. But the need for shielding and spin gravity looks to be fairly absolute.
This may just be me, but I also have a hard time with cable-connected spin designs. Not with steady-state spin, but with the transient dynamics of spin-up and spin-down, required for every maneuver and all dockings. Further, a cable seems to me susceptible to severing by meteor impact or other accident, admittedly low probability, but nonzero. There seems in most cable-connected designs no way to recover from a parted cable, which event then leads to loss-of-crew, unless you use multiple cables, which is heavier and risks entanglement.
Solid structures can be designed to be more failure-tolerant and simultaneously have fewer failure modes to begin with. That being said, I'm no fan of trusses either, that being a really fast way to gain inert weight that only serves a single purpose. I'd rather use my propellant tankage as my rigid spin structure, weight I have to carry anyway. At least it would serve two purposes.
Just food for thought in these discussions.
GW
A powered version of the "2001 A Space Odyssey" space station? No, something that big is not required to send 6-12 people to Mars. Not at all.
The orbit to orbit ship is a long skinny thing sort of like the "Discovery" from that same movie, except not as big, and except that you deliberately spin it nose-over-tail, the way it was found in the second movie "2010 Odyssey 2".
That means the habitat module at one end is not a sphere with a centrifuge inside, it's a simple cylinder (or cylinders) with decks perpendicular to the ship's long axis. You set the spin rate for 1 full gee on the deck furthest from the center of gravity. If the ship is 100 to 150 m long at 150 to 400 tons, it's really easy to get 1 full gee at 56 m radius, and a spin rate of 4 rpm, easily tolerable even by untrained civilians.
Most of the long journey is spent coasting. You spin for gravity during those phases, which greatly simplifies life support, waste control and processing, cooking, and a whole host of daily living needs. You de-spin for a few days only for major maneuvers, living on astronaut food and using zero-gee toilets only for those short periods.
Put your daily work shift stations on the far deck at 1 full gee. Put the sleeping quarters at the lowest-gee deck, because gravity provides little health benefit when prone while sleeping (otherwise bed rest studies would not be in least useful for understanding microgravity effects). Recreation and storage can be in-between.
You put your main engines at the other end of the baton-shaped ship, so that the center of gravity is nearer the geometric middle. The length in between is docked-together propellant tankage. You stage off empties and reconfigure to the same long baton shape after each burn, and then spin-up again for gravity. How easy is that? How reliable, too? No cables to break, causing loss of vehicle and crew.
Propellant is the cheapest of all commodities to be launched. I'd make the ship maximally reusable, meaning minimum number of empty tanks to be jettisoned, and reuse it for multiple missions. That just means a bit bigger departure mass.
I'd reuse it to visit any and all of several destinations. The same ship could take human crews anywhere from Mercury out to the main asteroid belt. It could serve for decades with periodic propulsion and subsystem upgrades, as they become available.
If you add electric propulsion mounted at the spin center 90 degrees to the spin plane, you could use that to cut travel time, without incurring the spiral-out/spiral-in time (and delta-vee) penalties associated with super low-thrust electric propulsion as we know it.
GW
Radiation from nuclear weapons is not the same as GCR or solar flare outbursts, but it is sort-of similar. My experiences working in the defense business told me that electronics and biology are susceptible to nuclear radiation, while basic electrical hardware and basic materials, not so very much. Oddly enough, the old-time vacuum-tube electronics were generally (not always) nuclear-hard, while the solid-state stuff was extremely susceptible. Terrestrial insects were more nuclear-hard than terrestrial reptiles and mammals, for reasons outlined in another post above somewhere.
Solid-state electronics can be made nuclear-hard by appropriate shielding. The same thing works for biology, you just need an even-better shield. It'll take either a Star Trek EM screen or else many meters of material to shield against GCR "effectively" (to levels like here at home) for men, women, and children in space. It takes more meters of material because of the secondary-shower effect, which you have to contain as well. But 20 cm of water works for solar flare outbursts, and (I suspect) the stuff circulating in the Van Allen belts (and their analogs at the other planets).
In the inner solar system, GCR cycles with the sun's activity between 24 Rem and 60 Rem (annual dosage), according to NASA's best data. It might be worse further out. NASA's annual limit for astronauts is 50 Rem, which is not very much different from that max value. This is complicated by a career limit (accumulated exposure over multiple years) that varies with age and gender. Astronauts currently are expected to accept a higher risk than us surface civilians (nearer or under 1 Rem). Under these rules with nominal 2.5-year missions, a crew can go to Mars once, but not twice, unshielded in any way from GCR. Two missions hits the career limits.
The 20 cm of water as a shield is too thin for there to be a secondary shower effect, but it does act to reduce GCR exposure slightly. I'm not sure, but I think it might actually reduce 60 Rem outside to right at 50 Rem inside the 20 cm water shield. In other words, we know enough RIGHT NOW to get a crew to Mars and back without overexposing them to GCR or solar flare outbursts. It's just that no one wants to bite the bullet and design-in that 20 cm water shield about a designated radiation shelter space. Why? Because that'll be too heavy to fly as a single launch of an SLS-type vehicle, and it'll be too heavy for a direct shot to Mars.
The problem isn't the shield, or its weight, it's the mission design.
You'll have to have that mass of water on board anyway in terms of life support and waste treatment for a long voyage. So, use it! For the radiation shield. The design decision regarding health protection is obvious to the casual observer! The smarter designer would wrap that water shield around the command flight deck, so that critical maneuvers could be made no matter the solar "weather" outside.
Designs like that will have to be assembled in LEO from multiple components docked together. You don't need an SLS to do that, but it might help if its launch cost were under $2500/pound delivered, where we are now with Atlas-5, Delta-4, Falcon-9, and several European and Russian rockets. These all exist in forms capable of delivering 10+tons to LEO, some up to 20 tons. I think there is a version of Atlas-5 capable of 25 tons, but I'm not sure it has ever flown. We built ISS with stuff up to 15 tons, we just did it with an idiotically-expensive launcher at $30,000+/pound. LEO assembly SIMPLY NEED NOT BE AS EXPENSIVE AS BUILDING THE ISS WAS!
This kind of design approach sort-of rules out Mars-direct type mission designs. Unfortunately. But, it was the original Apollo design, before they went with lunar orbit rendezvous, which got them down to one Saturn-5 launch per mission ("moon direct"?). We knew that long ago it (assembly in LEO) could be made to work, and we have since acquired most or all of the skills needed to make it work for Mars.
Doing both LEO-rendezvous/assembly and Mars orbit rendezvous (a lander like Apollo) pushes you right back to the 1950's concept of an orbit-to-orbit transport assembled in LEO, with landers to use at destination. That's the mission design with minimum launched mass that also meets what we now know we must have for life support and health protection. Sorry, that's just life. Not fair. Nobody ever said it was.
So, as it turns out, that orbit-to-orbit transport idea from over half a century ago always was the best idea. Plus, today, we already have the skills and technologies to make it work. We've known everything we need to know since about 1995-ish. The health protection requirements weren't really known until about then.
The kind of direct (minimalist) missions to Mars that have worked so well sending probes is just not the best choice for sending men. It is past time to face up to that unpleasant fact. The life support and health protection requirements simply point in a different direction. Microgravity diseases (plural) and radiation shielding requirements do dictate that different path, until and unless there are major technological breakthroughs in both propulsion and magnetic screens. Like "warp drive".
Don't hold your breath for those breakthroughs, I certainly won't. If you want to live long enough to see men on Mars, then we need to push for doing it with what we have right now. Very few technology-development programs ever actually fly anything in the way of useful vehicles. The ones that produce useful flying vehicles use off-the-shelf stuff. Another little unpleasant fact of life.
GW
Hi Josh:
I read them too, several years ago now. Thought it was very good. Would have to re-read before commenting, memory fades with time, especially for an old guy like me.
Technological progress is very non-uniform. It goes in spurts separated by stagnation. Like all the other forms of evolution.
Example: between 1903 and 1944 we went from the very first controllable powered airplane flights at all, to 500 mph combat jets (ME-262) that were very capable and effective doing their missions (shooting down bombers over Germany).
However, between 1970 and 2014, very little aviation progress has been made. Some of the very same planes (B-747's) are still flying, and the newer ones are but variations on that same 500 mph design. The few things of much greater capability that did fly (SR-71) fly no longer. The fighters might dash at Mach 2, but they cruise subsonic (500 mph).
I fear things like the Mars trilogy and Star Trek/Star Wars overestimate the actual advance of technology over long times. The example of 20th century aviation certainly suggests long periods of stagnation. Our very first 500 mph transports date to 1953 (DeHavilland Comet).
I was expecting back in 1970 to see most airline transport aircraft capable of flying single-stage to orbit by now, 40+ years later. Boy, was I ever disappointed.
GW
A cycler with an orbital period of 15 earth years means either (1) you only have travel opportunities every 15 years, or (2) you must have several of these vehicles out there, each in its own orbit with a 15 year period, just a different position along that orbit. For an equivalent every-opposition travel opportunity, you would have to have 7 or 8 cyclers out there, since oppositions occur roughly every 2 years. The actual possibilities are a digitized spectrum between those extremes, digitized by the number of cyclers actually deployed.
Such a cycler vehicle is at least ballpark-equivalent to building a more conventional orbit-to-orbit transport vehicle. We're talking about stuff assembled into a space station-like structure out of smaller components assembled together by docking. The effort and cost for the cycler could be a lot more, depending upon just how big a cycler you go for. But as a minimum, it ought to be comparable in size to the reusable transport ship.
If you opt for choice (2) and also opt for a minimum cycler size, then building 1 cycler would crudely cost about the same as building 1 reusable transport, building 6 cyclers would be 6 times as expensive as building 1 reusable transport, etc. Now, the transport might indeed have higher maintenance and refurbishment costs, which would reduce the contrast of the up front construction cost ratio some. But for more than 1 cycler, it's still factors > 1 , perhaps >> 1, never < 1.
So, assuming 15 years between trips is OK, costs are crudely comparable if you build only one cycler, but only with it further restricted to be of a size comparable in effort and outlay to your transport ship. If you build anything bigger for your cycler, the reusable transport is always the better deal financially. Remember, each would use "fairly comparable" infrastructure to effect flights up from Earth and the flights down to Mars. And return.
I say "fairly comparable", the infrastructure for the cycler is actually 40+% more demanding: escape versus orbit plus a tad more to reach the cycler transfer orbit, at each end of the journey. In contrast, the reusable orbit-to-orbit transport leaves from LEO, and parks in LMO, for minimal delta-vee demands on the infrastructure. What you save in Earth and Mars infrastructure costs with the orbit transport pays for the higher delta-vee demanded of the orbit-to-orbit transport. You'll pay that cost the same, one way or the other, anyway.
If 15 year travel opportunities are unacceptable, then you must have multiple cyclers out there, each of which is an investment comparable to (or more than) that of the reusable transport. There is no way around that dilemma, it must be faced immediately, up front, when you start the competing designs. In that case, the reusable transport is always the far-better deal financially, plus it has travel opportunities each-and-every opposition, which is roughly every 2 years. It takes 7 or 8 cyclers to match that, as I said before.
Bottom line: the cycler approach can never cost less-to-build than the reusable transport approach, but could cost many-factors-more to build, if multiple cyclers are required, or if very large cyclers are desired. Life cycle cost ratios are probably similar in direction but less contrasting in magnitude.
So, that explanation taken all together is why I think constructing a conventional but reusable orbit-to-orbit transport makes very much more common sense than constructing and riding a system of cyclers.
GW
Tom made my point with his statement "The Orion capsules are basically to return astronauts to Earth in the context of a Mars mission, the rest of the ship is to get the astronauts to and from Mars and to land and take off from Mars." He and I are saying the same thing about NASA and its Orion capsule, he just didn't think so when that issue first came up.
As for a "cycler", how is that different to any significant degree from using an orbit-to-orbit transport coupled with landers at destination and a return capsule at LEO?
I'll answer my own question: if you go orbit-to-orbit, you are less restricted in your choice of return date. It becomes only a matter of shipped propellant supply, or what you can make in-situ at Mars, or both.
So, I see little point to leaving hardware in the transfer orbit as a cycler, instead of parking it directly in the orbit about the destination.
You have to make those burns anyway, and with the majority of the mass, unless you attempt to build far-too-massive a cycler. Which would be too expensive. So, what's the point of the cycler, vs the orbit-to-orbit transport?
I'm coming around to the notion of having both conventional and electric engines on the manned orbit-to-orbit transport. I'd use the conventional engines for impulsive departures and arrivals to orbits, thus eliminating months of spiraling in and out with electric propulsion. Time is money you know, even for unmanned vehicles. But with men, low travel times are even more crucially important for interplanetary missions.
The electric propulsion I would use during the manned transfers, to cut down the time on the transfer trajectory between departure and arrival orbits by means of a higher mid-point velocity. However much solar electricity you can actually make, that's how much extra impulse you can add to the transfer trip. It's a win-win, no matter how crummy the electric propulsion thrust/weight is. And they are crummy. All of them.
My own choice would be LH2-LOX conventional, with an oxygen-based electric. The conventional uses LOX/LH2 at 6:1, with those being produced at 8:1 from water by solar-electric electrolysis and liquefaction. The excess O2 gets used for life support and the electric propulsion propellant. Propellant for "immediate use" is stored as cryogenic LOX and LH2. The rest gets shipped as super-easy-to-store water, and gets converted as needed "on the way".
There is water-as-ice all over Mars. In some few places the deposits are massive, and therefore easy-to-mine, which tells you where you really want to land. If you use the same LOX-LH2-from-water for your reusable (many multiple flights) lander as for your orbit-to-orbit transport, then in-situ propellant manufacture is more of a "sure thing", and will support additional suborbital missions using those landers. Cleaning local dirty water is easy: just filtering and gravitational separation of solids, and the local salt content just makes it more conductive for the electrolysis. The waste product is concentrated, dirty brine. So what?
All of this leads pretty quickly to the same overall mission design. It ain't minimalist. So why is there still debate about this?
GW
I'm sorry, but you are wrong about the Orion capsules, Tom.
Those will NEVER be adequate by themselves for any mission beyond cis-lunar space. I know the PR says "interplanetary missions", but that's a convenient lie.
Orion is way too small for long-duration flight beyond 2 or 3 (or at most 4) weeks. It has no radiation shielding for solar flares. And just where are you going to store the supplies for a crew on a 2.5 year mission? Not in that ESA service module, not by a long shot. How will you keep the crew healthy with 2.5 years' exposure to low-to-zero gravity? (We already know that about 450 days is the outer limit for that.)
All of this is apparent to any casual observer. But you do need to be aware of it, to see it. They are counting on you being unaware of it.
Orion was developed only for going back to the moon, nothing more. Nothing about that capsule development was changed, even when Constellation (to go back to the moon) was cancelled. It became a gravy train for favored contractors some years ago. I think it will eventually fly, but only to the moon's vicinity all by itself.
Going to Mars either requires super-fast travel (not yet possible), or it requires a big habitat space properly arranged, artificial gravity-by-spin, a proper radiation shelter (20 cm water will do), and plenty of space to store supplies. With artificial gravity, life support becomes a lot easier, too (you can do free-surface cooking with water, and simple toilets, among many other advantages).
A good lander is also required, plus its propellant supply. And, there's the surface supplies and equipment to investigate how to live-off-the-land while the crew is there. Why go if you're not landing? It's so hard to get there, what's the point of going and NOT landing?
Orion by itself has NONE of that. NASA isn't working on ANY of that, at least not seriously. And THAT is why I said what I said about NASA.
GW
NASA doesn't want to go to Mars. I thought that was obvious by now. Why is this still a question?
NASA does not want to send humans to Mars because (1) it is dangerous, and (2) it is difficult. They cannot make a big PR splash unless it is neither. It is not. It will still be difficult and dangerous for some time to come.
NASA has not wanted to go to Mars with humans since Nixon's executive order in 1972 that killed all human spaceflight outside LEO. When that order came down in the middle of the Apollo landings (planned all the way through Apollo 22, with hardware already built !!!!), they still had a mission on the books for humans to Mars in the 1980's, and they were testing the NERVA engine that was to take them there.
All of that was dead by 1974. "Why build the rocket if we're not going to go?" was the rationale for killing everything associated with human spaceflight outside LEO. The shuttle and the space station were "sops" to NASA to keep them busy. Nothing more. The "can-do" NASA of 1960 was dead by 1975. It is still dead. And the other countries' agencies are modeled on it. All dead. That's why nobody has gone.
Although, we learned an awful lot from both "sop" programs (shuttle and space station). Including the fact that a human crew in a tiny space capsule for months one way to Mars would have died on that Mars mission back in the 1980's. I repeat: they would have died. Even if the hardware had worked perfectly.
It would have been a race to see what actually killed them: (1) microgravity diseases (and I do mean plural !!!), (2) solar flare radiation, or (3) fatal insanity from too-tight confinement. But, we have known how to send a crew to Mars successfully and safely (!!!!!) since about the mid-1990's, mostly from knowledge gained off the ISS and some Russian stations.
We didn't send a crew to Mars, because NASA has not wanted to go, nor have any of the presidents since Kennedy. Nor has congress. The public excuse is that it's "too expensive". But that is a convenient lie maintained by a NASA who no longer wants to go, and by a whole swarm of space program opponents. Strange bedfellows, those are, don't you think?
It is simply not too expensive anymore. It has not been "too expensive" ever since the advent of commercial satellite launch at about $2500/pound, added to the on-orbit assembly by docking that we did for ISS. And that price should fall a little further (factor 2-ish or at most 3-ish) as available launcher payload sizes grow to the 100 ton class. Just DO NOT count on SLS to price-out that low! IT WILL NEVER BE THAT CHEAP!
Anymore, nobody wants to go, except visionaries like Musk, Branson, and some others. None are government employees. The long-established contractors (Boeing and Lock-Mart) make more money on dead-end gravy-train programs than they would ever make actually building the hardware to go to Mars. That's why THEY don't want to go, either. Together they're ULA, so ULA doesn't want to go.
I think we need some new contractors. It's way past time to break the monopolies.
Money has always talked far louder than the law, common sense, or any collective societal goals we have ever had. You all know that! So why is this (NASA wanting-or-not to go to Mars with humans) still a question?
GW
Hmmmm.
There is one other forgotten propulsion concept that might apply to interstellar travel. That would be the Bussard ramjet made famous in Larry Niven's book "Protector", part of his "Tales of Known Space" series. You would need fusion rocketry to get you up to ramjet takeover speed, which speculation has at somewhere near half lightspeed. But, since it scoops up interstellar matter (largely hydrogen), it is not limited by mass ratio. A gigantic strong properly-shaped magnetic field scoops up and compresses the hydrogen to the fusion point, then also controls the expansion of the helium product to achieve lots of thrust.
Theoretically, it can move at very close to lightspeed. Faster if you do not believe the "lightspeed limit" is real. The missing technologies are (1) control of very strong AC (oscillating polarity) magnetic bottles hundreds to thousands of miles in dimension, and (2) controlled magnetically-confined thermonuclear fusion of ordinary hydrogen w/o deuterium or tritium.
The other possibility is that somebody finally invents a Star Trek warp drive, and a way to navigate when moving faster-than-light.
GW