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Ballutes are very interesting stabilizers and decelerators. For use at high-subsonic and low-supersonic speeds, I found round ribbon chutes superior in stability. But chutes cannot be used successfully during re-entry. There is the possibility that ballutes can.
If some sort of ablative coating could be added to the ballute, a gas-inflated conical ballute could be used as a decelerator and stabilizer drogue during re-entry. On the end of a long ablative-protected line, it could add deceleration capability over and above what the basic object's heat shield does. How much, I dunno. Up close, none.
If the ballute is really big, part of it will protrude outside the object's wake into freestream flow, even up close. Then it could really produce a lot of decelerator effect, at the cost of very high surface pressures on the freestream-exposed surfaces. It just needs a high-enough inflation pressure. Don't count on ram effect for that, you won't get it.
GW
GW
RobertDyck:
Bad memory goes with the gray/white hair. Mine is getting pretty bad. I have to write everything down or it's lost.
I quite agree about absolutely idiotic, wasteful spending. Politicians ought to be the targets of the missiles that cannot hit the other missiles. Stationary targets, easier to hit. Their political window-dressing projects are just wasteful crap.
I cannot think of any politicians since JFK and LBJ that were actually really serious about any sort of space projects. JFK was just sort-of, he did the moon thing as a race with the Russians. It wasn't about the moon, it was about just beating the Russians at something big. Going to the moon was just a convenient "big" thing. But, I give him credit: once he decided, he stuck with it.
LBJ was actually a spaceflight hobbyist. By chance, we got him as VP, then Pres. He was in there just long enough to get done the follow-through necessary to actually carry out the plan, and thus actually go to moon. The next one, Nixon, killed it before we could make all the planned landings (all the way to Apollo-22 not just Apollo-17). Nixon thought spaceflight was useless.
All the ones since have been window-dressing projects, not properly formulated or funded. Botching the shuttle into a dangerous side-mounted cluster, just to hold down some yearly budgets, is really why two crews died. Nixon was part and parcel of that. His executive order didn't just kill Apollo, he killed all spaceflight outside LEO.
And NASA responded by killing the nuclear rocket program, which was just ready to fly. The official thinking was "why build the rocket if we aren't going to go?" How short-sighted and idiotically-foolish was that?
And, where is the medical centrifuge on the ISS that determines how much gee is enough to stave off microgravity illness? They had a module for that, but cancelled it! ISS as it is, will never give us that absolutely crucial answer for long space voyages. Very expensive window-dressing, as it is.
Reagan's X-30 scramjet in the 1980's had no hope of being feasible, even if scramjet had been ready for application (it still is not): airbreathers alone do not have the frontal thrust density to climb that steeply in air that impossibly-thin (at 100,000+ feet, the Mach-15+ compression of near vacuum is still near-vacuum). Several $B got spent to find out what we already knew. No craft ever flew, of course. Political window-dressing (it was never really intended to fly). Expensive. But just crap.
The smarts isn't in the government labs, and most certainly not the politicians themselves. The real smarts is out in the contractors, and the breakthroughs will not come from the long-time favorites that have been on the payroll so long. Example: The real breakthroughs in LEO access are coming from Spacex, not ULA.
Problem is, this is government-led stuff, because exploration and blue-sky R&D is generally not what business CEO's invest in. They do it only when paid to do it. If the government lab is too hide-bound to foster some new contractors for the breakthroughs, they won't happen. And the smarts that was in the unfunded contractors is lost: they die/retire/go elsewhere and do something completely different.
That third outcome is what happened to me personally. I was once one of about a dozen or so all-around experts in ramjet propulsion, in the whole US. Most of us are dead now. I haven't done ramjet since 1994. Now I teach math in a 2-year tech school.
Not very smart of the government. Penny-wise, pound-foolish, as the adage has it.
GW
I don't know a lot about the details of nuclear reactors, but I have heard of the U-233/Thorium-232 breeder cycle. The Indians are actually trying to do this. You have to use a normal enriched-uranium reactor (involves U-235 fission and the inevitable U-238 breeding to Pu-239) with Th-232 also inserted, to be bred into U-233. You do this until you accumulate enough U-233 to shut down the uranium plant and just go with a straight U-233 reactor, breeding its own fuel from Th-232. This may take a small number of years (I dunno exactly). The waste products of U-233/Th-232 are much more benign than the U-235/238-Pu-239 cycle.
I kinda think that's something we ought to bootstrap into operation down here right now, and just ship U-233 product to space settlements, for direct breeding of local thorium into U-233 fuel. It saves having to ship two breeder reactors, if we could just get it started here first. Thorium is a lot more plentiful here on Earth than uranium, and I rather suspect that's true elsewhere, too.
Also, a U-233 reactor could also be a nuclear rocket. Even in open-cycle gas core designs, the radioactive plume is a lot less objectionable than a uranium or mixed-oxide reactor basis.
Just a thought.
There's a a natural timing here. If we could get the technology started now, it would be ready as we plant settlements soon, and they need atomic power for whatever the local industries might prove to be, not long after.
After all, you simply cannot make steel powered by solar energy.
GW
About the only three things I can think of RE: "ice concrete" are:
1. Boiloff of water into the near-vacuum that is the Martian atmosphere. It'll be in a stout form. I guess lay some relatively impermeable tarps over the freshly-poured material's free surface, and quickly bury that with local dirt several inches to a couple of feet deep (that's just a wild guess). The overburden pressure should stop most of the boiloff until the thing can freeze solid.
Fixing the wild guess: Somebody with a steam table handy could find the vapor pressure of water at 32 F (0 C), and convert that to dirt depth at a typical loose dirt effective specific gravity of 1.68 and 0.38 gee on Mars. I don't have one here.
2. What do we use for forms? No lumber on Mars. Old spacecraft shell plating?
3. Exposed ice concrete structures will be subject to slow sublimation into the near vacuum, reduced somewhat by the aggregate. Dirt cover should stop that. Based on the probe and rover results to date, maybe 3 inches (7-8 cm) of dirt will do. Maybe even less.
I'd use this stuff for in-ground foundations and building structures that get buried or built underground and buried.
For roadway-trackway uses, it'll need a few inches of the dirt cover on top of exposed surfaces. But it should be the same hell-for-stout heavy structural material that concrete is here at home.
Makes me wonder if there is a coating we could apply that would stop the sublimation? Ideas? That would make exposed bridge beams possible. Sort of important.
For rocket landing pads, in some locations just grade off the dirt to expose bedrock. Land directly on that.
Other places where the bedrock is irregular or too deep, that's where the mortared basalt blocks come in real handy. If you find an old lava flow, just saw them out quarry-style. Why waste the energy to melt basalt you already have to cut? It doesn't even need to be basalt. Actually, almost any rock will do.
GW
The way I had in mind to make the suggested martian "ice" concrete would be to mix liquid water, local sand, and local rounded rocks (yep, rounded, no sharp edges or corners), and pour that into a form the same we do ordinary concrete here. Then just let it freeze solid. The liquid water would freeze to the aggregate and stick there, just like the little boy's tongue on the subzero light pole.
In such a formulation, the water ice takes the place of the Portland cement in concrete here. The other two components (sand and rocks) are the same. Here, concrete has both the sand and the rocks, and tests in compression as much stronger than mortar mix, which is just Portland cement and sand. Both are way stronger than Portland cement alone without the sand. There's something about a particulate embedded in a matrix that is far stronger than the matrix alone, even without any fibers.
As for reinforced martian "ice" concrete, you rig the basalt fiber braided ropes, or the steel rebar, inside the empty forms, then pour the concrete in to fill the forms. This embeds the reinforcement inside the structure.
To do pre-stressed beams, rig the forms and reinforcement, plus the empty pipes or tubes from one end to the other. Then pour your concrete mixture. Once fully hard, slip the pre-stress rods through the tubes, add thrust washers on each end, add the nuts, and tighten savagely, but to an engineered torque (so that the tensions in the rods are what was intended).
I see very little difference between doing this with Portland cement here and water ice there. Except that it takes about 30 days for Portland cement to reach full cure strength here. I doubt it takes that long to freeze the water and lower the ice temperature to below -20 or -30 C there. Once that cold, the stuff should be very stout.
Plus, ice composites are harder to melt than straight ice. The dirty snowbanks of plowed snow beside the road are the last to melt.
Rounding sharp edged rocks merely requires tumbling them in a drum with some steel hammer shot.
GW
I had the weight statements and delta-vee figures worked out for Dragon with a "modest dumb tank" inside the unpressurized cargo space. I had 2.3 km/sec total delta-vee that way. You could do a bigger tank, it just needs to dock somehow to the rear. These would be minor mods to the existing design.
The figures I caloculated are in figure 11 of the posting-version of my convention paper. It's over at http://exrocketman.blogspot.com, dated 7-25-11. The by-date navigation tool on the left can take you right to it. This stuff was reverse-engineered from the data posted on Spacex's website.
I haven't done anything for Falcon-Heavy yet, but Falcon-9 I reverse-engineered into a weight statement and some delta-vee estimates in the posting on "exrocketman" dated 12-14-11. It's the first figure in the article. That's the posting on re-usability in launch rockets. Falcon-Heavy is a Falcon-9 with two extra first stages strapped on. The key to their design is propellant cross-feeding among the three 9-engine units. The center one is still nearly full when they drop the outer two off, yet all 27 engines have been burning.
The data I calculated for Dragon should be pretty realistic, unless what I found does not take into account the cosine correction for the canted Draco thrusters. I'm not sure on that one.
What I did for Falcon-9 should be really close.
GW
I remember two Project Plowshare shots named gasbuggy1 and 2, if memory serves. I thought it was natural gas they were after. But you're right, it was too radioactive to use. Those underground shots all have the total mass of the bomb fragments (and the weapons guys SOOOOO love to go with plutonium), plus all the induced secondary radioactivity in all the debris and surrounding rocks. It stays lethal down there for many many, years.
There are a couple of caves that might contain the volume of a test or two, pressurized. But you can't leave it that way, you have to depressurize the cave or it'll leak. That still means cleaning the gas of radioactive debris. Might as well just build the rig to do it on-site as an artificial structure.
By the time you pay for building such a facility, you could have sent the whole kit and kaboodle to the moon. It's pretty expensive stuff. After about the first test or so, it'll begin to pay for itself in spite of the space travel costs, seeing as how with open-plume tests, you get to concentrate your funds on the testing, not the cleanup operation. On the moon, those plumes shoot straight out into space, never to return. The exhaust velocities are way far beyond lunar escape.
GW
Now you're thinking outside the box. Good show, Rune.
GW
I agree with Rune that the sooner we get over our irrationality and apply nuclear propulsion, the sooner things will get affordable, no matter the destination. Don't forget, NERVA-type nuclear is not the best that could be done, it was just the only thing that actually ever got done. Big distinction there.
I disagree that the way to test a nuclear engine is flying somewhere out in space. Nope, chemical or nuclear, you start testing on a stable thrust stand somewhere. If every test has to be a flight test, nothing will ever be done. Because it simply cannot be done that way. Engineering reality.
I suggest we start testing nuclear stuff in a deep crater on the moon. Safe place to do it, and close enough to be reached without nuclear power or gigantic rockets. We can do it with what we already have going. Flying to the moon will prove cheaper than building a facility on Earth that can capture and clean the plume from a nuclear rocket engine that leaks radioactivity. Open plume nuclear tests on Earth are no longer allowed.
GW
Back to using Falcons and Dragons to go to the moon. You will need a lander of some tonnage, probably not unlike the old Apollo lander. You might even build it out of a Dragon with extra tanks, or maybe a from-scratch design. Whatever.
But, I don't see why you need a Centaur or any other departure stage. You don't need any more engines, you just need delta-vee. The Dragon will have the new Super-Draco thrusters on it with 120,000 lb of axial thrust, according to their website. There's eight of them, plenty of redundancy there. Just add a big dumb propellant tank, and plumb it up to the Dragon's system. Use the Dracos for all the delta-vee from LEO to lunar orbit, and back, sucking from the big dumb tank.
Launch the lander on one Falcon-Heavy, launch the Dragon and the big dumb tank on the other. Rendezvous in LEO, and dock the big dumb tank to the rear end of the Dragon, and the lander to its nose. Make up your plumbing connections. Then go to the moon.
Lots of minor details to work out, but I don't see any show stoppers here.
GW
If you are building colonies, build more than one. I'd put them in the northern lowlands, which were once ocean beds. There will be whopping amounts of water ice buried deep. That's ice mining. Put one colony much nearer the north pole for dry-ice mining, and build a railroad between them. Use local ice/basalt fiber/local rock aggregate to form the concrete track for the rail line. Use rubber tires on the train cars. If you can ensure by careful design that the tracks never see much bending or tension, then plain ice-aggregate unreinforced "concrete" will do. (Basalt fiber manufacture is likely to be rather energy-intensive, unless you can find a local active volcano with a basaltic type of lava, not the silicic type.)
To quickly and easily get CO2 gas at 1-10 atm, haul in mined dry ice by rail to your processing plant, and put it in a pressurizable space of limited volume, then apply solar heat, and vaporize the dry ice. It will pressurize the closed space quite easily, no machinery required! Use that pressure to transport the gas down a pipe to where you do whatever you want to do with it.
If you just want raw solid carbon, I've heard tell that Phobos is a carbonaceous chondrite. There's a carbon mine. But you do have to fly it down to the surface to use it.
It's some kind of iron ore, plus a massive energy source, that will be needed longer-term. I'm thinking steel-making, which is extremely energy-intensive. But steel is the key to the future of any viable technologically-based society. Steel and concrete. We've already seen it here.
GW
In the other conversation under "3D Printers", I just today described an ice-matrix Mars concrete, including how to form the basalt fiber rebar, and how to pre-stress beams for bending resistance, the same way we do here. That conversation had veered into concrete, too.
GW
Cold ice absent any liquid phase seems to stick to things pretty good, essentially being its own glue. That's why little boys who stick out their tongues and touch them to light poles on sub-zero days (that's under 0 F, = to temps under about -15 C for you metric types) get stuck there until someone frees them by melting the ice bond with a warm liquid. My frozen dishrag bat was pretty stout, too.
Concrete's matrix, Portland cement, actually has rather poor bonding to its aggregate or to its rebar. That's why the rebar is not smooth bar stock, it has formed circumferential ribs that protrude into the concrete, for a simple mechanical lock against actually sliding through the concrete. Check out the broken surface of concrete rubble some time. It's not very hard to pry out some of the aggregate rocks, if about half of the rock protrudes, so that it is not mechanically locked.
Designing experience with concrete suggests that simple rebar reinforced concrete is capable of some fairly-limited but non-zero tensile and bending resistance. Concrete highway bridge beams have a different reinforcement: a tensile steel rod (or rods) protruding out both ends, onto which nuts and thrust washers are added at each end. These tensile rods ride loose inside tubes embedded in the beam. These rods are really savagely torqued down, pulling very heavy tension on the steel rod(s). This force's static reaction exerts a compression load on the ends of the concrete beam, by means of bearing forces under the washers at each end. By substantially pre-loading the entire concrete beam in compression this way, a much larger bending stress can be endured without exceeding the concrete's limited tensile strength on the tensile side of the beam's stress distribution. This is called a pre-stressed beam.
I rather think that ice could replace Portland cement, local rocks on Mars can be the aggregate (as long as you tumble them to be rounded of shape), and thick braided ropes of basalt fiber could serve as a sort of rebar, since the surface of the rope has enough porosity plus the braided texture to mechanically lock it into the ice, if nothing else. Light duty plastic pipe and steel rods could serve as pre-stressing members, the same way they do here, for substantial beam bending resistance as standard pre-stressed beams.
If energy is too dear to expend on melting basalt to process the fiber, then we have to bite the bullet and import steel rebar from Earth.
Finding iron ore on Mars will be very important. A source of carbon for the refining and alloying processes is required. If Phobos is a carbonaceous chondrite, then there's a carbon mine. A source of copious energy will be required: steel-making is extremely energy intensive. But in the longer term, cheap steel is utterly essential to the viability of any industrial/technological society. Unpleasant fact of life, but there it is.
GW
Bob:
Yes, I found it on the internet at one of the watchdog sites. ULA does not post costs the way Spacex does on their site. I don't have the data here at work, but I did record where I found it, at home, I think.
Falcon-9 has a 10 metric ton payload to LEO from Canaveral, for what I figured as $2400/lb. It could carry things in the 2-10 class fairly easily, although the payload shroud might or might not fit.
I found launch costs (as $/max payload weight) to scale down non-linearly with max payload size. It's really only fair to compare at comparable max payload weights.
GW
I really am getting old. Divided when I should have multiplied! Sorry.
Falcon Heavy: $800-1000/lb = $1760-2200/kg for 53 metric tons
Atlas-5 5xx series: about $2500/lb = $5510/kg
Still about factor 2.5 apart. Same basic message. The size of the logistical tail (which reflects the simplicity-complexity issue) is crucial to low-cost LEO access.
GW
No one yet has any idea of the cost ($/kg) of payload to orbit with the new heavy lifter. We do know what ULA can do with its Atlas 5 series. It's around $2500/pound=$1135/kg for a 20 metric ton payload to LEO. Doesn't vary a lot amongst the different versions. It's the cheapest one in their stable, the Delta's are a lot more expensive.
Falcon-Heavy is about to fly this year or next, from Vandenburg AFB, last I heard. Their website projects 53 metric tons to LEOP at $800-1000/pound= $363-454/kg. Two of these could put 106 tons up for about $48 million.
The new heavy lifter is supposed to be able to loft 130 metric tons to LEO, roughly what two Falcon Heavies could loft. To do it competitively, their one launch price needs to be under $48 million, and their per kg price needs to be under about $370/kg. That's about factor 2.5 cheaper than the cheapest ULA launcher currently flying: Atlas 5.
In other words, they need to be as lean and productive as Spacex. The logistical tail to support each launch of the heavy lifter needs to be the size of a village (like Spacex), not a major city (as is usual with NASA). The chosen heavy lifter design (thank you Congress!) being recycled shuttle hardware and technology, I have zero confidence NASA and its favorite ULA contractor could ever pull that off. They have zero history of doing it. And things get especially dicey when Congress dictates the design- we saw that with Shuttle.
So, the smart way is to buy Spacex Falcon-Heavy launches and do a little orbital assembly (something already demonstrated with ISS). You can build on-orbit vehicles of any size and any complexity desired. That opens up any destination you want: Moon, Mercury, Venus, NEO's, and Mars. All are within reach.
Even closer if you ressurrect NERVA nuclear rocket technology.
GW
Terraformer:
I, too, looked at adding extra fuel to the Dragon in the unpressurized module, for a different reason. Go look at the 7-25-11 posting over at http://exrocketman.blogspot.com, and scroll down to figure 11. It summarizes what I got after a bit of reverse-engineering the data Spacex had posted on their website back then.
I was calculating 0.9 km/sec max delta vee for the basic Dragon with 1290 kg propellants, with another 1.4 km/sec possible from propellant tanks at 10% inert in the unpressurized cargo space. That's about 2.3 km/sec total, but, some of that must be used for attitude control.
There's one other thing to consider. Dragon cannot land with the unpressurized module. You have to stage it off.
GW
Here on earth the aggregate in concrete is small stones. Dirt as we know it here does not work. Too fine-grained, and the organics decompose, leaving behind voids. The key to concrete as a building material is the sand and stones: two widely disparate particle size distributions as reinforcement.
Here, concrete is cement plus sand (around 0.5 mm diameter) plus gravel/small stones (around 50 mm diameter). And, both the sand and the stones are washed very clean, and thoroughly dried. Not only that, they are carefully sieved for their size distributions. The chemistry that sets the cement is a hydration reaction of the calcium oxide with water. It is slightly exothermic, and requires the water to be in the liquid phase.
Any concrete variant on Mars will require a source of calcium oxide (unslaked lime) for the cement. Sand and stones should be no problem, but the lime is a problem. That means we need something widely available that is peculiar to the physical chemistry of Mars, to serve as the source material for cement.
I suggested ice because it is widely available there and here, and because the same sort of particle reinforcement would provide similar properties. Plus, on Mars, temperatures are well below the freezepoint of water.
There are fiber-reinforced versions of concrete in use here. So a basalt fiber reinforced material would make a lot of sense there. With ice there is no chemical reaction, only a phase change. But, the result is a strong composite material anyway.
Building materials (like concrete) are generally particle-reinforced composites, and they have to be very inexpensive, and widely available. We may not be able to identify viable candidates until men have actually landed on Mars and played with the local materials. It is difficult in the extreme to program a robot to look for stuff like this, precisely because you won't know it until you see it.
That's why I keep saying don't plan on successful ISRU on the first mission. Do the detailed exploration and the ISRU experiments on the first mission, and use that new knowledge to plan an ISRU scheme that actually will work, on the second and subsequent missions.
GW
I sure hope this pans out. We've been 20 years away from practical fusion for about 60 years now.
GW
To reinforce something with basalt fibers means you can't heat to basalt meltpoint, or the fibers melt. Use those fibers as the reinforcement in some other matrix instead.
How about ice? I once froze a wet dishrag, and used it as a bat to hit a ball a very long way indeed. Mars is a cold place. Basalt fiber-reinforced ice might be a pretty good building material. Bricks and panels.
Or a blend of materials:
Compression members could be ice with a regolith aggregate in it, analogous to concrete. For bending and tension situations, imbed some ropes made of basalt fiber to act as the rebar.
Ice and basalt seem plentiful on Mars, although individual sites most likely vary a lot. There just might be a real future for ice-regolith-basalt fiber as the analog to reinforced concrete.
Toughest part is melting the basalt. It would be nice if someone spotted an active volcano with basaltic lava.
GW
Rune:
I looked at Spacex's web page yesterday. You are right, the Super-Draco is a much more powerful MMH-NTO thruster system. What I saw indicated 8 units, angled though they are, sum up to 120,000 pounds of axial thrust.
It's a tad unclear, but I'd hazard a guess they will keep the little Draco's for attitude control, and use the big Dracos as a launch escape system, a delta-vee maneuver source, and as a landing system.
As a landing system, I'd bet it's combined chute and final-seconds thrusters.
GW
RobertDyck:
Is Nextel 440 the replacement for the older Nextel 312? Silicate fire curtain cloth. Your parasol idea is intriguing.
Given a low enough ballistic coefficient, I think it might work for aerocapture, or possibly even re-entry to a landing.
GW
Myself, I would not count on ISRU from the first landing anywhere. Chances are it won't work the way you want, because what resources are actually at the site are not quite what you expected (and assumed in your design).
First trip (moon, Mars, just about anywhere), you bring the propellant with you to go home. You try some ISRU experiments while you're there. Maybe they work, maybe they don't. But the data and experience you gain will make the second trip's ISRU far more likely to work. Maybe even enough to count on, if the first experiments turn out fairly well.
It's all about suspenders-and-belt, and learning-as-you-go. That's how you get the crew home safe. Killing a crew can get your program killed. NASA has 3 dead crews so far, and look what has happened to them.
GW
I have my doubts that concrete as we know it would ever cure in intense cold, unless the water in it remained liquid. The hydration reaction requires liquid water.
I could cast slabs down to about 29 F (-2 C), but only because the cure is very slightly exothermic, and the slab never cooled below 32 F (0 C) until the "cure" was finished.
And, that only gets it to "walk-on-it" strength. Typically, concrete slowly cures further over about 30 days to its full strength. It's not exothermic enough to get a difference from ambient during this period.
I rather suspect we'd need a new kind of concrete on Mars. Something will work, just not what we do here.
GW
Hi Rune:
I took a look at the NASA report that you sent as a link. The "fire baton" idea is exactly what I was talking about, and I noticed they were using the very same 1 gee and 4 rpm max figures that I use. The transhab looks great except that it is way too small for 6 people -2 years. On a per person basis, Skylab was around 5-6 times the volume in transhab. So, I disagree with their criterion of 25-30 m^3 actually habitable volume per person. It needs to be much closer to 100+ m^3 person to stay sane and fit cooped up like that, the more the better. If one assumes Skylab had half its gross volume habitable, that's 165 m^3 habitable volume for each of the 3 on board. Transhab is just plain too small for a Mars trip.
GW