You are not logged in.
I would think he was referring to cooking inside a habitat at lower "air" pressure. However, for colonists having babies, I think you will find (if you research it) that something resembling Earth air at near 1 full atmosphere is required for successful pregnancies. This has a major impact on building pressurized structures in which to live.
Whether 0.38 gee is therapeutic enough to stave off microgravity diseases is still an open question, and will be for some time to come, since we did not put a medical centrifuge on ISS. (That seems rather stupid in hindsight, doesn't it?) There is some reason to worry about pregnancies in reduced gee, too, although personally I am less concerned about that risk, than I am having the correct atmosphere to breathe.
Backpacker foods are certainly an improvement upon what NASA has been feeding its astronauts in space, in terms of storage lifetime and palatability. The difference is also the downside: a lot more water is needed for backpacker foods. Once you grit your teeth and do water for life support in sufficient quantities, then better, longer-life food becomes feasible. But, water being very heavy, you don't get to fly a minimalist habitat design off of one big SLS shot.
GW
We're talking about travel between Mars's surface and orbit about Mars, or at least I thought we were. If you do not have to surround your tanks with structure, and you don't have to fit them inside any particular shape, I think your hard vehicle structure will be smaller and lighter than it otherwise would be. Your tanks are basically very lightweight inflatables, with a tad of tie-together hardware. I don't see why such tanks wouldn't fit in a very small mass budget, like 5-7%.
I was showing about 3.7 to 3.8 km/s for getting from the surface to orbit. Your figure of 4 is about right, and covers a de-orbit burn, and more. Once you stow the empty inflatable tanks inside, you have a small capsule shape with a heat shield, which can slow aerodynamically to about M3 at low altitude (5-10 km), which is about 0.7 km/s. Then just do retro thrust to landing. No more than about a km/s worth of delta-vee should cover that.
So we're talking about something on the order of 4.5 to 5 km/s total velocity increment for the round trip, a low-density ablative or refractory heat shield, landing legs, and inflatable tankage for most (but not all) of the propellant. For methlox, I can easily have a Vex near 3.1 km/s. At 5 required, I get a mass ratio of about 5. That's 80% propellant. If the inerts are around 10-15% (and with inflatables, this might be possible), you have 5-10% payload.
With LOX-LH2 it is even easier. Vex = 4.4 km/s is easy. MR= 3.1, which is 68% propellant. For 15% inerts, that's 17% payload. And I'm not at all sure that LOX-LH2 might not be the better choice, if a suitable inflatable can be devised. It's made from nothing but ice. All you need is a buried glacier and some solar electricity to make the gases. LH2 is tougher to liquify, though. And that super-cryo inflatable will be very tough to devise.
Just some random, not-very-sane thoughts.
GW
Here's a weird notion. I'm not at sure this is possible, but it might be.
Most plastics and elastomers are flexible at room temperature, but stiff when very cold. Make the tankage out of it, since we're talking methlox here, it's not extreme cryo like LH2. Warm up the empty tanks after the burn, fold them up, and stow them inside for the return in what is effectively a much smaller vehicle, for reuse.
You have to carry the mass of the "inflatable" tankage, yes, but you don't have to deal with a clumsy or vulnerable shape during entry.
Think a small capsule shape with the crew, cargo, some landing legs, and engines. Couple a bunch of these "inflatable" tanks to its "nose" for the ascent, and stow them inside for the descent. Some sort of rubberized canvas, multiple layered, perhaps?
GW
I to have heard there are 3-D printers that print metal. As best I know, it's basically a sintered-metal part. Mechanical properties of sintered parts are far inferior to castings, much less forged parts. We're not ready to print whatever we need. Still gonna need steel/aluminum/titanium mills for a while yet, I'm afraid.
GW
Here's a silly idea: put the dirty ice cube on the tail of the vehicle. Then just keep shooting it with the laser cannon pulses. It ought to fly by pretty much the same physics as pulse propulsion. But without nukes.
GW
Hi Bob:
I rather like the idea of flying faster myself. There are two things that could make it possible that I am familiar with, one speculative, one very sure. Those are open-cycle gas core nuclear thermal rockets (speculative), and nuclear pulse propulsion (a sure thing). I'm not so familiar with propellants made on the moon, though it seems like it could be done, so I put that somewhere in between speculative and a sure thing.
Failing faster trips, you avoid the microgravity diseases with spin gravity. So months in space need not be a health problem. Doesn't take building Battlestar Galacticas, doesn't take building Rube Goldberg cable contraptions. It does require on-orbit assembly from docked modules of a baton-shaped vehicle of significant dimensions. This is not something even SLS could fling up there, even if it ever does fly. At 4 rpm, for one full gee you only need a 56 m radius from the center of gravity to the habitat module. It's simply not outlandish to contemplate building a thing like that.
Imaging and remote sensing often get it right, sometimes get it wrong. It's a lot better now than when we first started using these technologies, when our results were most often quite wrong. Even so, there is still nothing like ground truth. That's the gold standard upon which you can ethically bet lives. To this day I'm not very confident that high hydrogen content should equate to abundant water. Lots of minerals have hydrogen in them, and not just hydrates. We are talking an alien world here, after all.
I really do worry about a radiation shelter. Not enough folks do, yet. The GCR issue doesn't worry me, a 2.5 year mission would only violate the astronaut annual exposure limits in a solar max year, and then not by very much at all, even if the vehicle had zero shielding effect. It's solar flares that worry me. But, 20 cm of water works even for the worst of those. Any life support system we build will have water and wastewater tanks. Just wrap them around your designated shelter.
I have seen no showstoppers for going to Mars since the 1990's, when we got the microgravity disease results from ISS, Mir, and Salyut all digested. We've known what to do about radiation even longer than that. And ever since Atlas-5 and Delta-4 became inexpensive commercial launchers capable of flinging 15+ tons to LEO, we've had the means to go, a whole lot more cheaply than we could have done in the 1990's.
The problems are not technical, they are idiotic politics (especially politics-of-money), and a lack of demand from a public swamped with economic troubles and wars, focused everywhere else but space. As I said in another thread, I think the Tito fly-by stunt is meant to shame NASA, ESA, and the rest into actually doing something. I dunno whether that stunt will actually accomplish that result. But at least he is trying.
GW
Midoshi:
Any news yet?
GW
The real point of the Tito mission is to shame NASA, ESA, and the rest, into actually doing something. I heard him and Zubrin say so at the convention in Boulder.
This is a fast loop-around of Mars, not an orbital stay. They will be close enough to Mars to do some photography and maybe some small science, for about a day or two. Nothing more. It would be hard to successfully fling a small lander from a fast flyby like that, but I think it might make sense to try one or two. Very tiny ones.
What's really to be demonstrated is a capability of voyaging for 500 days. My biggest reservations: (1) microgravity diseases will proceed to the fatality point without artificial gravity by spin, and (2) I've seen little or no radiation protection, leading to a lost crew if there is a solar flare/mass ejection event during the mission that hits them. The odds are significant because the window is 500 days long. The minimalist plan does not address these critical issues.
Enough living space for two is questionable, and I'd bet they have to rely on real canned and frozen foods, which will complicate their weight problems (the plastic bagged "canned" stuff only lasts about 12 to 18 months). But I think they will address these issues OK.
Propulsion: they don't need to wait around for SLS. Falcon-Heavy should fly out of Vandenburg pretty soon. If it takes two heavies and docking in LEO to pull this off, then so be it. Even if it takes three, so be it. That's something we know how to do.
I just pray they address spin gravity and a radiation shelter in the design.
GW
Bob:
I do think a mission not depending upon ISRU is possible, although it is inherently more expensive. You have to send the return propellant, as we all know, which makes your vehicle or vehicles much larger. We now know how to do this with on-orbit assembly, and our commercial rockets are big enough to do it, and 10 times cheaper than the shuttle was. ISS taught us a lot about this.
I think Josh is correct, we can test ISRU and ISPP equipment in chambers here on Earth, and to a point, we can send small versions on landers to Mars between now and the time the men go. It may prove reliable enough to bet lives on it, and it may not. My money is on "not", especially if the government does it. It takes them 25 years to build a jet fighter now. There's only 15-20 years left to get this job done on NASA's schedule, shorter yet if commercial entities take the lead.
There's a reason for that very first expedition to bring their return propellant: exploration. Which is answering the deceptively-simple questions (1) what all is there? and (2) where exactly is it? Robots can only partially answer these, remote sensing the same. Until men can react to what the robots were not programmed for, and until men can drill a km or two down, you simply cannot answer those questions.
Because every site is different in what it offers, and what it conceals (just like here), you have to explore at more than one site. As many as possible makes a great deal of basic common sense. To incorporate multiple landing sites into one mission requires on-orbit basing with multiple (or better yet reusable) landers, and also perhaps with pre-landed supplies at those sites. It makes sense because it is (and will be for some time yet) so difficult to safely make a manned trip that far and that long. Why go to all that trouble and just land at one (likely unrepresentative) place? That's flag-and-footprints nonsense. We've been there.
What you do is test out all that ISRU and ISPP stuff "for real" as you explore. If it works, and you have reusable landers, use the propellants you made to explore more sites yet. More bang for the buck. An even better chance of finding what is needed for a base.
Pick the most promising site while you're there for such a base, and put it together, operating robotically, and ready for the second mission, which will base there, not in orbit. Once you have that target base, the commercial folks will likely mount that second mission. That is the seed from which a colony grows.
I dunno what combination of resources and profit opportunities will justify that base. No one knew details like that when they started sailing from Europe to the Americas. They just knew they would find something, and that they would know it when they saw it. So will we.
GW
I know you can send encoded data over radio like that. I just don't have a clue how. But I've heard the varying hum of a carrier with data encoded on it, for decades on short wave radio. I know they have done it, as far back as the 1960's, and likely a decade or so before then.
GW
I've seen the Zubrin paper with the freezer and the sabatier (sp?) reactor. It's a nice device. It's also a laboratory environment device. Not yet ready for prime time on Mars. But it could be made ready.
The point I am trying to make is that one test on one probe mission (and it doesn't need to be a sample return, any of the landers we have sent could have served) is not enough experience with it to justify betting lives on this technology. You need at least about half a dozen to a dozen such tests, all at different sites. Dozens (plural) would be better, but not practical to accomplish. One or two? Nowhere near enough.
Weather is different at every site every day all around the calendar and the globe, and varies strongly on short time scales with the passage of weather systems. The device will respond differently as weather changes. Saying the atmosphere is the same might be technically true in the sense of its chemical composition, but that ignores the very important fact that the climate and weather is always different and always changing.
GW
Ignoring the drag/heating problem (a mistake, I might add), look at the velocity distribution of the "connected-particles" around your orbiting loop. If the orbit is circular, they all have the same speed, and thus want to stay the same distances from each other.
If your orbit is elliptical, and it has to be to function as a launch device, then at perigee the velocities are large while at apogee they are lower. The particles will want to be a lot farther apart at perigee, and a whole closer together at apogee.
Since the velocities and their differences are measured in km/s, I suggest that we are looking at compressions and extensions measured in km, relative to gage lengths (typical construction dimensions) measured in perhaps 100's of m. I don't know how to figure the numbers for stress-strain in this orbit situation, but this m vs km disparity suggests we would have to have a material that is elastic over strains measured in the hundreds to thousands of percent. That's not a material available to humankind at the present time in history.
I've worked with polyether polyurethane (PEPU) which was 800% elongation at failure, but only the first dozen-or-so percent was at all elastic. That's the biggest stretchiness I have ever heard of. I used it as a one-shot shock cord in a parachute rig. Its normal use is absorbing the shock of fins opening on bombs. This is all one-shot stuff, the elongation is almost entirely inelastic. And the stuff was a molten mess at only 300 F. Metals, rock fiber, carbon fiber, all have single digit elastic elongation numbers, and small digits at that.
You can work around elongation to provide stretchier spring constants in non-trivial shapes, like a coil spring. Geometries like this would have even more drag and heating as they dipped through the air at orbital speeds. There's a very good reason we have to use sacrificial ablatives at the stagnation zones of entry heat shields.
GW
Josh:
Relative to your point 1 in the last post, what happens when the pre-landed ISPP device fails to produce enough propellant (or even any at all) by the time the launch window rolls around to send the men? This is a nonzero probability, after all is said and done. At least there will be months of warning, as the device falls further and further behind its quota. So, what's the backup plan? Carry return propellant, or don't go? That's one of a zillion failures we have to be prepared to deal with.
As for what the failure-to-produce might trace to, without men there to observe and diagnose what the robots were not programmed to recognize, it could be difficult (or even impossible) to figure out whether the fault lies somewhere in the machine, or with something peculiar about the site. That's why I keep saying the first manned trip ought to try this stuff out, but not bet lives on it. To check it out properly in time for a manned mission in the 2030's, we ought to have experiments like this already on Mars. We need at the very least a decade's experience (preferably more) with these devices, in multiple sites, before betting lives on them. There's very little time left to get that job done. And I don't see any credible efforts started yet.
Relative to point 2, I quite agree that the freeze-out and sublimation-compression scheme offers lighter weight and simpler machinery for the same massflow throughput, even if it's an average for batch production. That's definitely the way to go. It's not that piston or turbine pumps won't work, it's just that they'll be heavy and consume a lot of power for the same massflow throughput. And, it's mass that we must accumulate to return.
Conventional compression machines' mass, and to some extent power requirement, are more or less proportional to their volume throughput (piston machines are absolutely constant volume per cycle of rotation, and most turbomachines are close to that), while the mass throughput is directly proportional to inlet density. That's why looking at them on the internet, as designed for 1 atm ambient here, is quite misleading regarding their sizing for 0.007 atm ambient there.
To zeroth order, you're factor 140 down in massflow for the same volume, same machine mass, and some intermediate level of power. You can cut machine mass by a factor of 2 to 5 for flightweight vs commercial/industrial, but you'll never cut it by anything close to that factor of 140 imposed by low inlet density. I dunno what the factor on power will be, but it's likely bigger than the 2-5 factor for flightweight machine mass.
GW
I quite agree that conventional compression makes no sense on Mars. The compression scheme you describe is pretty much the only practical thing we could do. What I question is throughput per unit mass for the combined compression and reactor machine you describe. And, throughput per unit electrical power that must be supplied.
This thing you describe has to be big enough to make dozens to hundreds of tons of propellant in only a year (less per year if pre-positioned years ahead, but it has to run unattended by men in that case). Between it and its power supply, we might has well have shipped a bulldozer and an electrolysis plant, I fear.
I've seen some lab experiment results, including Zubrin's. But those are not prototypes of realistic equipment, not yet. Has anybody built a real prototype of what we might send to Mars? Tested it at simulated Martian conditions? Not to my knowledge, they haven't.
It better be much further along in the development and test process, than a prototype tested a few times at simulated conditions, before we bet lives on it. I would not yet risk my life on it, which is a powerful statement, when you consider my first career choices in the 1960's were aimed at being an astronaut for the then-planned Mars mission of 1983. That was long before we understood all the risks of 2.5 years in space.
GW
Your effective range depends upon your frequency, and upon atmospherics. Sometimes 10 to 80 m FM ham radio reached several dozen miles, sometimes it would bounce intercontinental. It's inherently iffy.
AM broadcast is fairly reliable for dozens to hundreds of miles at several KW transmitted power. But it's low-quality, noisy, and subject to easy disruption.
GW
My gut feel is that the atmospheric drag forces and friction heating will be catastrophic, no matter whether the loop moves streamline to the air or not. Any off-angle just makes things worse.
Plus, Josh is right about vibrations induced by vehicles using this thing. There's as yet no "unbelievium", "unobtainium", or "manurium" from which to make this thing. Same basic problem as the space elevator, which at least hangs static in the air.
GW
An older pressurant scheme is just a solid propellant gas generator. All sorts of weapons used this. Some still do. Maybe not something a colony might manufacture, but certainly something you could easily bring along from Earth on an exploratory mission. Very simple, very reliable.
GW
I have to question ISPP schemes based on the atmosphere due to the compression problem: 6-7 mbar is next-of-kin to vacuum. You only have a 1 year stay on Mars to make the 100's of tons of propellant required to return. And you need some hydrogen.
It can come from soil ice, but you have to process millions of tons to get hundreds or thousands of tons of water, unless you just happen (I repeat JUST HAPPEN) to land almost on top of a huge near-surface buried glacier, and not a bunch of small scattered lenses plus interstitial ice. And, Mars Direct-style minimalist mission plans don't call for landing the equivalent of a D-8 or D-9 Caterpillar bulldozer to dig it out. Those weigh dozens of tons, and they're not the only heavy equipment you are going to need.
If you have massive ice available, and you have a mining machinery (in the dozens of tons class), then you can make LOX-LH2, with all the evaporative problems involved with LH2, and also providing our solutions here for the para vs ortho form also work on Mars (NOT a foregone conclusion).
If you add in a workable compression scheme, then you can use local atmosphere to make LOX and LCH4, instead of LOX-LH2. That combo will store easier and longer with lower losses. Bit lower Isp, but OK.
That's a lot of if's, either way. Which is why I hold the unpopular opinions that I hold.
GW "dead crew" Johnson
I had two friends in college who were "hams" (amateur radio operators). One is long dead, the other spent his engineering career in avionics. For them ham radio was a hobby, and they enjoyed talking to other operators all over. Just fun.
There is another aspect to it that I know of. In times of disasters, often normal communications are knocked out. Some of the hams with their own power supplies can still provide the emergency communications pathway that sets up disaster relief.
Never was a ham myself. I did some CB radio long ago, but that's about all. CB was 11 m, close enough to my friend's 10 m ham rig that he and I could CB over longer ranges when he used his big 10 m antenna coupled to a CB radio.
GW
The main advantages of hydrocarbon-acid are (1) a long history of reliability, and (2) hypergolic ignition. This can still be done with solid hydrocarbon, that being the motor in Spaceship Two.
In small sizes, it is about as easy to to use a heavy pressure tank for the acid and dispense with propellant pumping in favor of direct pressure feed. In larger sizes, the heavier tank becomes too much of an inert weight problem.
The tank will never be light: you have to protect it from being eaten away by the acid. Injector plates are a short-life part for that reason.
Just some practical stuff. I dunno whether hydrogen peroxide is reliably hypergolic with hydrocarbons, liquid or solid. It is with hydrazines.
GW
NASA will never subsidize anything they do not (over-) control. What's required is a plan based on tinkertoys that NASA can be convinced to subsidize, and which will not be killed by NASA over-control. Schedule is far slower that way, but the job gets done. Example: manned Dragon, for which there is no logical reason it could not fly in a year, instead of waiting till 2017.
Commercial guys are better off with private financing, except that the price tags are generally too high for private financing. It's a price tag vs how-fast-can-we-do-this question. There are not sufficient billionaires with vision. I'm surprised there are as many as there are.
Governments (at all levels and in all places) drag things out by worrying way too much about yearly budgets, all the while increasing total integrated program costs just to hold down peak cost in any given year. This generally causes technical problems as well as high integrated costs. Example: space shuttle's vulnerable cluster vehicle. Another example: that's why the typical highway construction job takes 2-5 years per mile of freeway, when concrete cures in 30 days. Ridiculous.
GW
I agree with Josh in post 150, although Mars Direct might not in itself be the best way, but something relatively-small sort of like it might be.
I am unconvinced that betting lives on in-situ propellant production is consistent with a decent chance of returning the crew safely. Every site is different, what if the site you choose turns out to be unsuitable for unforseen reasons, and you cannot make your return propellant? Until you do know, it's a very bad bet on that very first trip.
One of the things NASA has learned to its chagrin is that there is nothing as expensive as a dead crew. Space travel has extreme dangers, they've learned that lesson 3 times now. And it applies to the commercial folks, too. No one is immune to that fact of life.
That first trip needs to explore deeply enough to find that now-unknown "thing" that provides us a compelling reason to return. Period.
The best way to do that is make multiple landings, once you have gone to all the trouble to send men all that way. That's how you play the odds: no one site is likely to provide that compelling discovery. But out of many, the odds are much better that one will.
Lesson: maximize the number of landings at different sites all over the planet in that first trip. You are looking for stuff the robots cannot find.
Myself, I don't think we ought to bet lives with in-situ return propellant, which will still be "experimental" on that very first trip. You experiment with it (and all the other in-situ technologies) on that trip, yes, but you have to assure the return, even if all your in-situ experiments fail.
Just my opinions, and they would apply to both government or commercial missions.
GW
Josh:
Relative to your question in post 142 above, there are multiple points in a trip where a spinning vehicle must be stopped in order to maneuver effectively. Every arrival and any any dockings, for example. Plus any mid-course corrections. With a spinning baton, this is simple thrusters (or even just reaction wheels) acting upon a semi-rigid body structurally sized for the loads. Because there are many thrusters, an accidental single "stuck" thruster can be managed (Armstrong's Gemini-Agena near-disaster is the first example of such an incident).
A cable-connected assembly is dynamically very "soft", and limited in its structural strength to the cable tensile strength, and to the strength of the attach fittings. It's a lot more cumbersome to spin up and down with thrusters (you have to coordinate at least pairs of thrusters, assuming two modules), and I cannot even imagine how to do that with reaction wheels. One stuck thruster, and this thing starts bouncing around like one of those paddle things with the ball on a rubber band. That's a recipe for an unrecoverable disaster, and it's a single-point failure mode that the baton doesn't have.
The baton is bigger and heavier, but simply easier and safer. IMHO.
GW
Re post 134 above: I'm sorry, NASA is just wrong about how difficult artificial gravity might be. If you are afraid to go, you have a vested interest in playing up how difficult something is. That's what's going on with NASA regarding both artificial gravity and radiation protection. Neither is very difficult.
They (NASA) have evolved toward a no-risk posture. Which means they really do not want to go to Mars, since that is always high risk, as was Apollo in the 1960's.
I've posted here before on both artificial gravity and radiation protection. No need to belabor those points again. Suffice it to say that cable-connected spinning modules have way too many failure modes to suit my taste. I favor the slender baton spinning end-over-end. 56 m at 4 rpm seems eminently doable, just not something you can fling t orbit with a single SLS launch.
Brings up another point. Having 100 ton payload capability with SLS is nice, but not required, to go to Mars. We built ISS out of 15 ton modules. Atlas 5 and Delta-4 (in their respective "heavy" configurations) can fling modules 15 to 20 tons. They are far cheaper than shuttle was, and far cheaper than SLS will ever be! If we had to do it again, we could build ISS for about 10 times less, counting prices and learning-curve effects. That's the price of a proper Mars manned vehicle.
GW
A unified guide? Aw, you didn't expect things to make sense, did you?
You can use regolith as a GCR shield even in space, if you make it thick enough to capture the secondary showers. That's several meters thick. On a surface, that's just bulldozer work, it can be done. So, there's no reason you have to settle only at lower elevations on Mars. A roof of regolith several meters thick would be effective even atop Olympus Mons. Although, for the life of me, I don't see that as a particularly attractive place to settle.
On the blueberries as an iron source, aren't those about as high-grade an ore as some types we mine here? Their presence on an eroded surface suggests that the rocks in that vicinity might be full of them, just not eroded yet. You could bulldoze up the loose surface and sieve it for blueberry ore particles. Whether digging up the rocks would be practical would depend upon whether the blueberries were harder or softer than the rocks in which they formed. If harder, release them by crushing, and then sieve. If softer, probably not practical.
GW