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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
Long-duration LH2 storage can be problematical because of leakage, and because of boil-off. I know gaseous hydrogen will leak right through the steel welding gas bottle over time. Not so bad in liquid phase, but still, we're looking at about 2 years for a round trip, unless one bites the bullet and finds some way to fly much faster.
Here's a really nutty idea: for hydrogen that won't be used until many months later, why not ship it as ice? On-orbit solar thermal to melt, on-orbit solar PV to electrolyze. So it takes a while with a low-powered system. It'll be a while before you need it. It's a very damage-tolerant and minimal-maintenance way to ship your NERVA propellant and your oxygen supply.
I do like the idea of reusable tankage on the nuke ship. Throw nothing away. It can fly many missions, and not just to Mars. Pretty much any design capable of ferrying men from LEO to Mars orbit can be used to visit Venus, Mercury, and some of the NEO's. Refitted with a more powerful engine, it might take men to the main asteroid belt. You need a habitat module big enough for comfy living on 3-year time horizons. I'd suggest a solar flare radiation shelter that is also the flight control deck.
Here's another nutty idea: build the vehicle as a long train of modules. Put the habitat on the end away from the NERVA, and spin it slowly end over end for artificial gravity. That solves a whole host of life support issues associated with zero-gee. 56 m radius at 4 rpm is pretty close to the 1 gee we evolved with.
GW
Hi Rune:
Yep, compared to rocket, ramjet has a low frontal thrust density, due in part to the lower chamber pressure, and in part due to ingested airflow ram drag. Unless the core rocket accelerates like a bandit, the ramjet will be incapable of accelerating like that, especially vertically.
Besides, most existing launch vehicles accelerate off the pad very gradually. T/W just barely > 1. I'd add strapons with integral boosters to help it do the same thing at higher payload weight, and then save on a little of rocket propellant by shouldering a piece of the load between about M0.7 low and M2 about 60,000 feet.
That low down, the trajectory is still essentially vertical, so it would be easy to recover the strap-on ramjet pods at the launch site. I kind of like the scissor-wing idea the Russians put on their "Baikal" proposed strap-on booster idea. Add a nosewheel and two tail skids, and land on a runway.
But, you're right. Most missiles need no wings at all to pull lots of lifting gees at M3+.
GW
Louis:
I went and looked at the link. Very intriguing. Cold structural blocks and tiles I can see us mining from basalt provinces. But for fiber, why go to the trouble of melting it? Why not catch it liquid coming out at the mid-ocean ridges, and use the sea to chill the filaments solid as you extrude them? Sounds like some sort of undersea robot materials-harvesting plant to me. Probably self-transportable as a submarine vehicle.
The active lava flows hitting the sea from Hawaii I think are basaltic, too. There ought to be a lot of volcanic basaltic lava harvestable all over, already liquified by mother nature here on Earth. Not all volcanoes are basaltic, but many are. On Mars, that's another problem. I don't recall any reports of active volcanism reported there.
Intriguing idea, though. If it can be used as a glass fiber replacement, then cloth can be woven from it.
GW
Terraformer:
As near as I can tell, reusing upper stages would be very difficult. It would be easier and more practical to orbit the stage fully, and then de-orbit later to a place of your choosing.
I think an ablative heat shield on the front end, plus some ablative inflatables around the rockets engine(s) at the rear, would do nicely. The inflatables also protect the engines during ocean impact. It'll need a series of chutes deployed out the rear to slow it to under 100 mph at impact, and it'll need to be tougher than an old boot to survive 100-gee-class impact forces.
You just don't do that with any known materials at 5-8% inert fractions. But you might get it done at 15-20% inert fractions. To keep the same payload fraction overall, you'll need three stages instead of two.
GW
UV-protected polymer-insulated electric cables: Sorry, I was thinking more of modified supplies brought from Earth to make the initial installation.
Basalt fiber? Can you weave this into a cloth? If so, it might be possible to sleeve metal wire with it as an insulation, resembling the really-old fabric insulated wires no one sees anymore, except in older-model electric stovetop cookers. Those are asbestos-fiber fabrics. Would basalt be an insulator, or is it too conductive to serve? I honestly don't know.
Also, would basalt fiber pose the same inhalation hazard that asbestos fiber and fiberglass pose? Does anyone know?
GW