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I'm sure everyone is familiar with the SpaceX plan to create a 'Mars Colonial Transport' (MCT) with which they hope to create incredibly cheap access to the Martian surface with. Obviously the vehicle MUST be reusable to do this (and the rocket it is launched on too), and while their has been a lot of good discussion about how a reusable vehicle could be made, but I think their is a key piece missing, the need to amortize the vehicle over hundreds if not thousands of trips to bring costs down, that will require us to look at orbital trajectories that maximize reuse. I'll be assuming that their are HUGE quantities of cargo being moved to Mars such that vehicles never run out of stuff to move, and that inert time insensitive cargo (machinery, spare parts etc) so completely dominate the system that human transport will simply be done on different vehicles specialized for that purpose and which are not relevant here for the design of a cargo logistics train.
Most speculation so far is that the MCT will be placed on top of a very large reusable rocket with the MCT possibly acting as a 3rd stage to do TMI from LEO, it will then land on Mars offload cargo and be refueled for a trip back to earth and will finally land on Earth to be reused. All elements are thus fully reused and can potentially have their costs amortized over multiple uses. But I don't think this can work with that flight profile.
The biggest problem in Amortizing a Mars Transport is the long duration of the Heliocentric transfer orbit combined with the 26 month planetary alignment cycle. People love to talk about how a little extra DeltaV can make the transfer period shorter (essentially by flying an orbit with Aphelion beyond Mars orbit), but this is within the context of expendable assets launched at the narrow windows. A fully reusable architecture needs to consider the entire alignment cycle and to deliver as much cargo over the cycle as possible, using more propellent to go faster isn't doing any good if your stuck loitering at either Earth or Mars waiting for the next alignment window so the DeltaV drops to within the vehicles capability, and making more trips with low cargo mass fractions could we worse then making fewer higher cargo mass trips. The statistic of merit is cargo delivery mass per unit of time over vehicle dry mass, fuel is so cheap as to be ignored and vehicle cost to both build and develop generally scales with vehicle mass so to amortize each ton of vehicle over as rapid a rate of cargo delivery as possible should be the goal.
By my reckoning it should be possible to conduct at most 2 round trips per 26 month cycle by exploiting a conjunction AND opposition launch windows. We all know that conjunction launch windows are better for initial manned mission because we get a 500 day surface stay in which considerable surface activity can be conducted, where as an opposition mission has a mere 1 month stay at Mars before departing. But short stays are what we want when were just ferrying material as fast as possible, by departing Earth at conjunction and spending ~190 days in transit and then rather then staying the normal 500 days we immediately return to Earth on a comparable transfer orbit. We would then return to Earth just in time to again depart on the opposition trajectory which needs to again give a ~190 day transit time each way. I'm doubtful that anything better then that can be done until were using 'sci-fi' types of propulsion technology that can just ignore planetary alignment all together and just fly strait lines. But I certainly encourage anyone who has the initiative to look at these kinds of orbits and to find the most efficient long term orbital cycle or the exact DeltaV of what I'm proposing (if it's even possible), you can and should assume fuel available at Mars as well, I don't think anyone believes full reusability is possible without that.
Now assuming I'm right about 13 month round trip we have a big problem, that just too slow to get good amortization, in 40 years a vehicle would only make 37 round trips, that's about 1.5 orders of magnitude better then full expandability and that's before accounting for better cargo mass fraction of expendables or the higher development costs of reusables so it would probably be no better then 1/10th the cost of expendables. Musk's goal is a full 2 orders of magnitude reduction, and I'd argue he NEEDS 3+ to actually get Colonization to be possible. So something more needs to happen.
More reuse can be squeezed out by breaking up the Earth-2-Mars journey into multiple legs with cargo being passed from one vehicle to another. The near Earth and near Mars portions of the journey can be more rapid and more aggressively amortized, while the heliocentric transfer portion of the journey because it is the main time driver and can't be shortened needs to simple use an extremely cheap and efficient vehicle. Fortunately an in-space only vehicle should be a lot cheaper then one that needs to do both planetary assent, in-space transit and planetary decent. So were looking at a 3 leg mission, Earth Ascent/Decent done with a rapidly reused capsule remaining in the Earth gravity well, heliocentric transfer done with an in space only vehicle, and then Mars Decent/Ascent done with another capsule that remains in Mars gravity well. I'll ignore how any of these vehicles get initially launched, assembled or placed where they need to be, that will all amortize out over their lifetimes, so long as the most efficient life-long usage is made of each the setup costs will be well worth it. The two capsules could have significant commonality so development is really for 2.5 rather then 3 different vehicles. Both capsules should be able to do round trips of less then a week so working for 13 months a capsule can deliver a minimum 50 loads to the heliocentric vehicle this sets up a 50:1 ratio between the cargo mass of the heliocentric vehicle and the capsule vehicle, assuming 1 vehicle in each leg. Obviously using more heliocentric vehicles could push the size difference down, or a heliocentric vehicle could be even larger and need multiple capsules to load it, but to get optimum usage it would need to grow in 50 capsule load increments. I'm envisioning something like the relationship between Trucks and huge Container ships, many trucks operating continually are needed to fill one ship. The shipping industry clearly shows that BIGGER IS BETTER, with a relentless drive to larger container ships, so I suspect the same economics of scale will dominate in space where their are literally no barriers at all to assembling massive vehicles or massive cargo blocks.
To make this heliocentric vehicle as cheap as possible it should have the most minimal DeltaV mission profile as possible and thus the highest cargo mass fraction possible. Departure from the highest possible Earth orbit (which is higher then even L2) and arrival at the highest possible Mars orbit would be desirable and DeltaV for that can be very low in the 1 kms range, but will likely need to be higher to hit the 190 day transit goal. In addition the vehicle would be greatly simplified if it carried cargo externally rather then internally, just like a container ships I'm imagining standardized cargo containers that can bolted to each other and form a massive 'brick' that can simply be pushed by a propulsion buss. This also has the huge advantage of allowing the heliocentric vehicle to simply detach the whole cargo block in Mars orbit and turn around immediately, then the brick can be nibbled away on by the capsule for 13 months bringing it to the Martian surface, meanwhile the Earth side capsule/s will be building the next cargo brick in Earth orbit. All vehicles can operate continually without having to wait for each other to load or unload.
In fact given the estimated diameter of the Rockets SpaceX is working on for the MCT (10m) and the estimated capsule width such a rocket could accommodate (15m) I think 20ft or 40ft shipping containers would be an ideal container (same shape and size but built of Aluminum), the capsules once landed on Mars would simply roll them out horizontally directly onto truck beds. Their would be other advantages, much of our existing technology base is designed to be moved in or is even built into shipping containers too allowing easier off the shelf tech and easier logistics on Earth for transport to launch sites. And as an existing international standard it would be very easy to get other space-faring nations to adopt it's use in space as well. Assuming a capsule fully loaded weighing 100mt this would provide 20mt for cargo, 10mt for structure and 70mt for propellent which should be sufficient for the Mars Assent DeltaV, how much would need to be reserved for landing I don't know, the Martian EDL paradigm remains the tough nut to crack in any mission profile.
The only thing to decide now is the propulsion system for the heliocentric vehicle, capsules will certainly be Methane/Lox as SpaceX has committed to this as their propellent of choice because of its slightly higher ISP then RP-1 and it's ability to be made on Mars. Chemical propellant could be used and it would likely provide the necessary DeltaV at maybe a modest 20%-30% propellent mass, a big dumb tank and a small engine could do the job as theirs no need for high thrust. Just hauling a lot of propellent up from Earth/Mars at each end point would work, but it directly cuts into delivered cargo mass. Every fuel load could have been a cargo load. I'm inclined to think that Ion propulsion systems will dominate here as they can get propellent fractions down very low, provided of course that we can generate the electric power AND they can be made to operate on Argon as there's no way we can supply 100's of tons of Xenon economically ($120,000 per ton Xenon, vs $5,000 per ton Argon). Power consumption is so large that Nuclear reactors are not out of the question but I think that Solar will continue to outpace any in-space nuclear system within the inner solar system.
Say that we have 100 cargo containers massing 20 tons each (2000 mt total) assembled at the edge of Earths sphere of influence by a pair of capsules (that might actually require a LEO-ESOI leg to be inserted but so long as it's staying in the Earths gravity well is just functions as an extension of the capsules delivery leg as it is not constrained by launch windows), the SEP system would need to be quite impressive, probably >10 Megawatts electric and 100-200mt of propellent, but the craft it's self would be quite small, perhaps only 100mt itself and should thus be reasonable in development cost, it would probably consist of numerous smaller thrusters and panel assemblies so in reality it's even lower in development mass and is then just mass produced and stuck together which is SpaceX's MO, a measly 100mt of hardware that only needs to operate in space getting poor amortization will be vastly better then 100 capsules each massing 10mt suffering the same fate, the capsule fleet is massively reduced in size as well, the one heliocentric vehicle effectively replaces 96 capsules as you only need 2 Earth side capsules and 2 Mars side capsules and one heliocentric vehicle to do the work of 100 direct flight capsules, the faster the capsule can be relaunched the better, if it can get down to Daily it would start to approach Airline rates of amortization, the helio vehicle needs to grow larger in response so it will look more and more like a Cargo container ship, perhaps holding thousands of containers.
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I think something like you envision will emerge. In my Mars novel I used reusable shuttles between the planetary surfaces and orbit and an interplanetary vehicle in between. I started out with solar thermal propulsion, using hydrogen propellant, then later switched to solar sailers with huge gossamer sails that were extremely thin and massed very little. One advantage of solar sails: they take so long to go between planets, they can leave Earth just about any time. You adjust the transport time by sending more or less cargo. Eventually lunar and Phobosian propellant became so cheap, they just used chemical propulsion. One advantage of Space X's approach is that the same vehicle can be used on both planets, thanks to the vertical landing system. The second stage can put about as much int high Mars orbit as the first and second stages together can put into low Earth orbit,
The other factor to consider is LEO and lunar facilities. Anything that hauls cargo into orbit for Mars can haul cargo into orbit for them as well. The launch schedule can focus on Mars for six months out of 26 and on the other cargo destinations the rest of the time. Thus the cost of the surface-to-orbit vehicles can be amortized via other destinations as well.
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Thanks, Impaler! Your cogent argument makes the very same case I have been trying to make for a long time: separate the functions of Earth ascent, orbit-to-orbit transport, and Mars (or anywhere else) descent in to 3 very disparate vehicles (or more, I'm not convinced that only one type of vehicle is suited for Earth launch). Give up the Apollo-on-steroids approach in favor of something that makes both technical and financial sense. Then go about creating the technologies and infrastructures needed to accomplish this (something absolutely not happening right now, at least at NASA et al, because they're still driven by the Apollo-on-steroids notion, mostly driven so by politics of big money).
GW
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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the need to amortize the vehicle over hundreds if not thousands of trips to bring costs down
And some people criticised my mission architecture. My proposal was soundly rejected in 2002 when I first presented at a Mars Society convention. Many on this forum have since said they like it. But in 2002, the attitude was Mars Direct and only Mars Direct.
My proposal wasn't for a colonial transport, but initial missions. It's designed to carry 4 astronauts, and reuse as much as possible. It's intended for the initial science mission. Robert Zubrin and his partner David Baker argued that human exploration was better than robotic. A valid argument, but now moot. My argument is robotic exploration is now finished. Done, over, complete. So let's use it. That means start the permanent human base with the very first human mission. Furthermore, Robert Zubrin and David Baker argued that a Mars mission is better than a space station; rather than waste time and money on a station, design the mission to not use a station, and go directly to Mars. Again a valid argument, but again now moot. ISS is complete, so use it. And a third point: Robert Zubrin argued to use life support technology available at the time. NASA wanted a system that would recycle 95% of oxygen and water before going to Mars. Zubrin argued to use what existed, and just bring whole/wet food to replenish recycling losses. Instead of dehydrated food. Again, valid arguments, but again moot. The life support system on ISS is good for Mars. I would make a few small additions, and the issue of calcium deposits in the urine processing assembly has to be addressed. But again, I would use ISS as a testbed for life support for Mars. So again, I'm saying use what we have. By the way, Robert Zubrin and David Baker worked for Martin-Marietta in 1989. After the 90-Day Report was rejected by congress, Martin-Marietta started studies to find an affordable way to get to Mars. One of those plans was Mars Direct. That plan was finished in 1991.
And instead of a 500 day surface stay, reduce that to 425 days. Although a 500 day surface stay with 180 day transit each way is the best in terms of rocket fuel, it creates a problem. That adds up to 28.4 months. The planets align once every 26 months, so the crew for the second mission have to leave Earth more than 2 months before the first crew arrive home. Reducing surface stay to 425 days means the first crew arrives home just as the second crew is preparing to leave. It means the two crews can meet and exchange knowledge.
But the point I wanted to make is I expect the ship for my design to last 10 missions. One trip every 26 months, means 21 years and 8 months. Even though the design has the ability to replace key components with new ones as they're developed, eventually it will be obsolete. Most cruise ships last 30 years, although some have lasted longer. I'm a big one for maintaining what you have, not throwing stuff out, but there is a limit.
Last edited by RobertDyck (2014-11-09 14:05:49)
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RobertDyck:
I understand completely about mission architecture bias.
I'm not sure there will ever be more than one government-funded mission to Mars with men, though. Not the way any of the agencies have behaved in recent decades.
It would be nice if that one government exploration mission did things in a smarter way, so that private or public-private partnership follow-on missions to establish a permanent presence looked more feasible. You do that by leaving usable assets behind that others can use later. Like landers in orbit. Like a small base building of some kind on the surface. Like an operating ISRU facility. Etc.
I think once you have a reusable Mars lander worked out, a decent Earth ascent-to-orbit scheme worked out, and some kind of orbit-to-orbit reusable transport worked out, that will fill the bill for the necessary human transport system, which can also be the same fleet that does cargo transfers. I've seen elements of all three proposed for a long time now, just not seriously funded.
And yet, any orbit-to-orbit transport and Earth-ascent-to-orbit system suitable for Mars can be suitable for anywhere in the inner solar system, even with today's propulsion. Landers for the moon and Mercury will be different, and you don't need a big lander for Venus or the asteroids. But that's the smallest part of the mission. An orbit-to-orbit ship design capable of transferring men with good life support, or massive amounts of cargo, that's the "biggie".
I haven't seen one of those proposed since the 1950's. Not by anybody in any sort of government agency. And yet it is the key thing.
But no, we're spending virtually all our money on a shuttle-derived Saturn 5 moon rocket to launch a new Apollo-on-steroids capsule suitable only for cislunar-length journeys, and with very little radiation shielding ability. And we're still lying to the public about how that capsule is the vehicle that takes men to Mars, when it quite simply cannot.
GW
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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Thx for the replies, I should be clear that I am looking at FAR future here maybe >50 years from now in which the interplanetary transport of freight is literally just extension of our present intercontinental freight system and it has become a competition driven business. This is NOT going to be the system for first human landing on Mars (which will be exploration forays NOT colonization), and I can see several GENERATIONS of vehicles between what SpaceX is currently working on and the final achievement of the 3-leg architecture I've described.
Their would be some kind of evolution from current SpaceX hardware to the final 'optimum' architecture, their current rocket systems will clearly continue to evolve into a huge rocket, the Dragon capsule will evolve into a bigger capsule and they are most likely going to do inefficient direct injection to Mars initially and even go expendable for the initial landings on Mars. The customer NASA will likely insist on buying a newly built vehicle every time, just like they buy brand new Dragons every time now for ISS delivery. I'm not criticizing that, thouse intermediate vehicles and exploratory missions NEED TO HAPPEN.
I'm just saying If I was Musk I would plan each vehicle as a stepping stone to fulfill some part of the eventually 3-leg architecture. As RobS say, if you take the 3-leg architecture Earth->Heliocentric->Mars and you substitute Moon 4 Mars and remove the Heliocentric that looks VERY similar in DeltaV. So I would strongly suspect that were going to go Moon first and if SpaceX can create a fully reusable system to do that and can demonstrate reliable and consistent delivery, they will only need to insert that Heliocentric vehicle into the middle of the existing chain and modify the Moon lander for Martian EDL they will be done.
Also I would really like to see if anyone can find more data on DeltaV for low-thrust escape from Earth-Sphere-of-Influence (or some other orbit that will be Earth-fixed like Earth-Sun Lagrange 2). Any orbit that is Fixed relative to Earth will be a constant DeltaV to reach so it can be a marshaling point, you basically want to get your cargo delivered as 'high' as possible before you make the jump into a heliocentric orbit in which your subject to the 26 month planetary alignment cycle which has BRUTAL Time/DeltaV penalties for departing outside of a window. Perhaps an Earth-Sun-L2 <-> Mars-Sun-L1 transfer is what would be ideal (dose Mars's more elliptical orbit even have stable Lagrange points?).
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Falcon-9, Atlas-5, Delta-4, and (soon) Falcon-Heavy can launch modules to LEO in the 13-20 (soon 53) ton class, most of them around 10-15 tons right now. There's nothing about an orbit-to-orbit transport that cannot be assembled in LEO from modules like this. It's same as the way we built ISS, except the launchers far more-than-factor-10 cheaper than shuttle ever could be.
The problem is the Mars lander, which ought to look at least vaguely like a conical capsule, just a lot bigger. Perhaps 15-30 m diameter. That'd be too big even for the ridiculously-expensive SLS, so it'll need assembly from smaller components on orbit, which in turn eliminates the need for an SLS. That includes a sectionalized heat shield. Sounds risky, but we knew it worked in 1969 with the Gemini-B used on the one-and-only USAF-MOL flight. That was a reflown Gemini, by the way.
It'd be awfully nice if we had a supple spacesuit so astronauts in LEO could do small nut bolt and rivet work, as well as small wiring and plumbing connections. That makes assembling landers on-orbit in LEO much more feasible. We could have had one (a supple spacesuit) by now, the prototype tested OK in 1968.
GW
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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I'm quite doubtful of EVA based hand assembly in space, especially for a vehicle which is to undergo the rigors of EDL. Station took a lot of labor to assemble and it is is simple using CMBs to hold it together, those couplings are nothing compared to whats needed for holding a vehicle together in a planetary decent.
I think we will just launch large capsules that are empty of fuel (or reach LEO empty because they employ their engines to act as final stage of accent). Because our Mars Lander NEEDS to be a SSTO (Mars Only) that implies a minimum of ~70% fuel mass fraction when performing that assent. If the big rocket that SpaceX is working on can put 100mt into orbit then that could be 100mt of DRY vehicle, no fuel or cargo. If the vehicle is 10/20/70 in structure/cargo/propellent then that means an incredible 1000mt at Mars Atmospheric entry, that is 1/3 of a Saturn V. If that's not big enough I'll eat a bug.
Point is that launching a big dry vehicles and fueling it will subsequent launches is going to be cheaper then doing assembly in space. We get the biggest possible heat shield, rigid structure, engines, and propellent tanks possible, all things that would be horribly hard to actually assemble in Space. Hell it costs an arm and a leg to assemble these things on the ground in factories.
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Impaler:
What you describe (launching empty vehicles) is certainly an option. My figure-of-merit is shroud or payload diameter = 1.5 x first stage diameter for something that can fly stably out of the atmosphere. Bigger "hammerhead" configurations do not fly well.
I think small hand assembly has been deemed impossible up to now, precisely because of the idiotic spacesuit designs we have used since 1961. The gloves have gotten ever fatter and stiffer. They rip off fingernails now, quite frequently, as the shuttle and ISS astronauts describe it. So, it's far worse now than it was with the first spacewalks in 1964. At least in 1964 it was possible to pull the trigger on a small hand-held reaction pistol.
It is possible to think outside-the-box and do a mechanical counterpressure suit design, which is an evolved form of a partial pressure suit, adapted to long-term service in vacuum, instead of "just enough for a 10-minute descent". The test-proven successful elastic prototype of 1968 actually had thin, rather supple gloves, of about the same restriction as ordinary latex rubber surgical gloves. Small by-hand assembly would be easily possible with gloves like that.
If you pay careful attention to workpiece temperatures, there is no need for thermal insulation in the gloves, and you really can use thin, mechanical-compression gloves for vacuum protection. So, on-orbit fine hand assembly in LEO could be quite possible, and very soon, too. You do it inside a space frame covered with a bunch of sheets of aluminized Mylar. You hang a bunch of big electric lights inside, and use the lighting power that provides both (1) adequate visibility, and (2) radiation-equilibrium workpiece temperatures between about 0 C and 40 C.
For really fine work, mechanical compression gloves can be doffed for up to perhaps 30 minutes safely. This is based on a variety of experiments and experiences obtained over the decades. Barehanded work in vacuum for limited time exposures is entirely feasible, as long at thermal injury can be avoided.
I know nobody has already done this. But it could be done. And to do what we need to do for LEO vehicle assembly, it should be done, and soon, too.
GW
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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I have heard of the 1.5x ratio as well it seems to be the standard and I have no reason to disagree. Do you think this is not wide enough and thus we need to build something bigger. If MCT is launched on 10m core that gives 15m capsule, how much total volume can that hold? By my math if we have two cones, 30m and 5m at that diameter we have 2000 m^3, if my rocket fuel is Methane/LoX that will have a density near 1mt per 1m^3 so I should have no trouble fitting 700mt of propellents into the vehicle and still having lots of volume left for cargo.
I don't see this hitting volume limits on internal fuel/cargo here, are you concerned with heat-shield surface area? If mass of the launch vehicle is adequate what's your driver for in-space-hand-assembly, it needs to be VERY compelling, even if our engineers were working in a shirt-sleeve environment the logistics of transporting and supplying them (and probably bonus pay for making them work in space vs a factory in which they can go home to the wife and kids every day) would be enormous. What kind of man-hour estimates do you have for assembling a vehicle?
Oh and screw assembly in space-suits, I'd just get a huge Bigelow inflatable, bring my components in through a 4-5m airlock and assemble inside an huge undivided space, if I need to cut the thing apart like an insect cocoon to get the finished vehicle out it would well worth it. By using a rounded or even a pancaked shaped inflatable I could make an incredibly wide vehicle if heat-shield area is your desire. Still I would rather assemble a vehicle on the ground and launch dry if I possibly can.
P.S. I'd use the second stage as my propellent tanker, just stretch the tanks a wee bit from what we would need otherwise and omit a payload, the 2nd stage now reaches orbit with 100mt of excess propellent (above the reserve for landing cause this is a reusable 2nd stage) and this is offloaded to another vehicle or a depot. Total commonality and no wasted mass or development on a tanker vehicle. It would take 7 more launches to fill the proposed vehicle, but the point is that this 1000mt monolithic vehicle can be done without any in-space assembly.
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The problem is the Mars lander, which ought to look at least vaguely like a conical capsule, just a lot bigger. Perhaps 15-30 m diameter. That'd be too big even for the ridiculously-expensive SLS, so it'll need assembly from smaller components on orbit, which in turn eliminates the need for an SLS. That includes a sectionalized heat shield. Sounds risky, but we knew it worked in 1969 with the Gemini-B used on the one-and-only USAF-MOL flight. That was a reflown Gemini, by the way.
GW
Even without orbital construction capabilites, I think it's not impossible to build a 5 meters diameter cylindrical lander, with a foldable umbrella heat shield that can be lauched with Falcon H and conected to your modular spaceship.
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Lander size depends upon what you attempt to do with it. If you do a minimal sort of Apollo-like stay, a small lander is OK. 5-7 mm dia near-cylindrical shape. The more tumble-home the sides have, the less heat protection they need on Mars. Such things could likely fly on a Falcon-Heavy.
If on the other hand you try to leave a functioning base camp, running on automatic, for the next mission to use, then we're talking about real construction of real permanent buildings. You'll need bulldozers or front-end loaders, concrete-like mixers, and a whole host of other construction equipment, plus a variety of bulky materials shipped from earth. Landers like that fall in the 15-30 m diameter range, and 30-100 tons at the very least.
It's mission objectives that drive this. Everybody has a different mission they'd like to see done, which is why opinions about the landers vary all over the map.
GW
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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Lander size depends upon what you attempt to do with it. If you do a minimal sort of Apollo-like stay, a small lander is OK. 5-7 mm dia near-cylindrical shape. The more tumble-home the sides have, the less heat protection they need on Mars. Such things could likely fly on a Falcon-Heavy.
If on the other hand you try to leave a functioning base camp, running on automatic, for the next mission to use, then we're talking about real construction of real permanent buildings. You'll need bulldozers or front-end loaders, concrete-like mixers, and a whole host of other construction equipment, plus a variety of bulky materials shipped from earth. Landers like that fall in the 15-30 m diameter range, and 30-100 tons at the very least.
It's mission objectives that drive this. Everybody has a different mission they'd like to see done, which is why opinions about the landers vary all over the map.
GW
Can we use as a lander a cluster of five cylindrical modules (D=5m; h=10m), protected by a 30 meter diameter foldable umbrella heat shield?
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Hi Quaoar:
If a folding heat shield can successfully be made, yes, it could protect a cluster of objects behind it. The key notion is one heat shield to protect all the objects.
You cannot survive as a cluster of objects each with its own shield. Each object sheds a shock wave impinging upon adjacent objects or connecting structures. Shock-impingement heating is simply not survivable with any technologies or materials that we have. Almost caused a fatal crash with the X-15 rocket plane in the 1960's.
The folding heat shield is a new technology item. No one has done it yet at full entry heating. It'll take a lot of testing and experience before that approach can be "trusted", especially with lives. Sure would be a nice thing to have, though. I think it can be done.
GW
Last edited by GW Johnson (2014-11-15 08:59:25)
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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Well it seems we need some way to make a Heat shield both BIG and REUSABLE for Mars EDL in order to have the MCT itself be reusable. Inflatable heat-shields are getting developed now, but they do not strike me as very reusable in practice unless some mechanized means of stuffing them back into some kind of enclosure. I'm assuming a vehicle cant really take off again from Mars with a big wide shield giving it huge drag, but maybe Mars air is really thin enough to do that, someone with some math skills should examine this, if it is possible then it dose present a driver for LEO assembly, a vehicle would be launched narrow and then a rigid immovable shield for use on Mars would just be bolted on around it in wedge segments and off it would go.
Now assuming that you do in fact need to tuck-in the shield to ascend from Mars and that inflatables prove insufficiently reusable, then some kind of mechanical deploy-able/retractable shield is a must. Quaoar umbrella if take quite literally would be solid ribs that hold a fabric material between them, the ribs are presumably moved into position hydraulically and then locked and could even be jointed to allow them to be longer then the side of the vehicle they are stowed against. Some gap will need to exist though, for retro-rockets if they are Draco-like and deployed along the side of the craft, as well as a Hatch (which I'm thinking may need to be quite large to accommodate heavy machinery roll-out). If the engines are placed flanking the the hatch with another pair of engines on the opposite side balance them then the entire rest of the vehicles slopped sides can be used to deploy the heat-shield. So I'm imagining two symmetrical 'Ears' each 150 degrees wide, imagine taking an umbrella and cutting the fabric away from two opposite segments.
Assuming a capsule 15m wide, 30m tall and the ribs are triple jointed they could stretch 90m. That would give a shield 195m in diameter and ~25,000m^2 (cut outs as described above included) which is simply colossally large. Even a vehicle massing 1000mt would be at just 40 kg/m^2 which would let the vehicle become subsonic 10s of km in altitude, this will minimize propellent for propulsive landing which translates to less propellent needing to be lofted in SSTO reuse. It should also allow safe landing to the Southern highlands of Mars which have notoriously thin air.
This paper http://spacecraft.ssl.umd.edu/publicati … hieldx.pdf examines this umbrella configurations and even suggests flipping the thing around and using it as a parachute too, but this dose not seam practical for a vehicle that must have rockets for assent anyways and which would rather stay in one orientation through both assent and decent. They concluded that on Mars the peak heating is just a bit over the capability of existing ceramic fabric, though I assume they were looking at only single use, multiple use would need an even lower heating, so some improved material science is needed here.
Lastly their could be some potential to steer the vehicle by applying more/less extension on some ribs and deforming the heat-shield to create an asymmetrical force, this could be used for a significant portion of the mid-course guidance before terminal rocket guidance takes over.
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Ceramic fabrics can be used at heat shield components. I'm not at all sure about the effects of their porosity, though, in that application. These are largely alumino-silicate materials, with a solid phase change in the vicinity of 2350 F (1290 C). Take the material higher, and it embrittles and cracks apart upon cooldown. That's a lot lower than the typical meltpoint: 3200 F = 1760 C.
There's actually no reason that solid panels cannot be placed into contact as portions of a larger shield, almost regardless of the material used. All you have to do is stop the flow through the gap between the panels. You need some sort of gap-filler. Something like caulk would likely work.
Retro doesn't have to fire around the corner at the periphery. It can fire through ports in the shield, as long as the space behind is sealed, to stop gas throughflow. It does need to be multi-engine and canted a bit off-centerline. The cant angle stops the instability in the retro plumes.
GW
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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Hi Quaoar:
If a folding heat shield can successfully be made, yes, it could protect a cluster of objects behind it. The key notion is one heat shield to protect all the objects.
You cannot survive as a cluster of objects each with its own shield. Each object sheds a shock wave impinging upon adjacent objects or connecting structures. Shock-impingement heating is simply not survivable with any technologies or materials that we have. Almost caused a fatal crash with the X-15 rocket plane in the 1960's.
The folding heat shield is a new technology item. No one has done it yet at full entry heating. It'll take a lot of testing and experience before that approach can be "trusted", especially with lives. Sure would be a nice thing to have, though. I think it can be done.
GW
Hi, GW. Tanks for your reply.
So the possible solution without new launcher are:
1) recycle an old Shuttle, send in unmanned in LEO with Canadarm and use it as an orbital assembly facility to build a 15-20 meter diameter lander. Is the best solution and a very good long term investment, but it's expensive and we know politicians and bureaucrats are penny wise pound foolish.
2) build a 5 meter diameter 15 meters height slender body biconic lander and launch it with a Falcon H. Have we some experience on slender body biconic reenter?
3) Assemble a cluster of five 5x10 cylindrical modules on a foldable umbrella shield. Advantage: is simple. Disadvantage: never tested.
4) Use many 5 meters diameter Dragon shaped landers: one for habitat, one for cargo, one for ascender. Advantage: is simple. Disadvantage: risk of collision during EDL, the landing sites of lenders are too far.
Last edited by Quaoar (2014-11-17 05:56:06)
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From what I read on Spacex's website, the payload shroud diameter is the same for Falcon-9 and Falcon-Heavy. Only the payload mass (and presumably shroud length, but I am not sure about that) are different. Why not build landers in LEO from pre-fab components shipped up with these boosters. Plus, anything a Falcon-9 can fling, so can Atlas-5 and Delta-4. No need to suffer problems with flight rates of the companies supplying the services.
Make the lander chassis out of steel framing members (for strength to weight, plus absolute strength and toughness). Have it fold up like a trundle bed frame, so it can ride up inside a payload shroud.
Do the same thing with the heat shield panels: do them as separate segments, and fit these into a payload shroud or two. They unfold, and caulk together only once. Same for the outer aeroshell panels.
The cabin and propellant tankage items are pressure vessels. These can be shipped up in a series of payload shrouds limited more by thrown weight than by volume, as none of these need be anywhere near the heat shield diameter of the lander.
Fueling on orbit requires more "payload shrouds" as tankers. Or, these could be tanks that ride "naked" except for a streamlined nose cap, on the front of the rocket. Dock such tanks to your lander, and make the connections. The lander can push itself and a huge swarm of tanks to Mars one way, to support a bunch of landings, from low Mars orbit.
Another lander plus a swarm of tanks plus a human habitat could be the manned orbit-to-orbit transport, except that's a waste of a good lander. Just use the lander engines on a lander chassis as a propulsion module docked to your orbit-to-orbit transport.
The mass of your fleet times launch prices between $1000/lb and $2500/lb is your launch cost, which in a well-run project ought to be around 33% of your total program cost. We're talking at most a few thousand tons in LEO here. Depends upon how big an expedition you wish to mount. Closer to 0.5-to-1 $B than any of the other numbers I have seen (especially that notorious $450B NASA ran up the flagpole several years ago). But the key is on-orbit assembly using commercial rockets that already serve other purposes. That way, you don't have to spend all your money developing gigantic rockets that can only serve one purpose.
Sure would be nice if we had a supple spacesuit to do this kind of on-orbit assembly, wouldn't it?
Sure would be nice if NASA was doing these things instead of spending $T's on SLS/Orion, with no space hab and no landers.
GW
Last edited by GW Johnson (2014-11-17 09:59:09)
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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Why not build landers in LEO from pre-fab components shipped up with these boosters. Plus, anything a Falcon-9 can fling, so can Atlas-5 and Delta-4. No need to suffer problems with flight rates of the companies supplying the services.
Make the lander chassis out of steel framing members (for strength to weight, plus absolute strength and toughness). Have it fold up like a trundle bed frame, so it can ride up inside a payload shroud.
Do the same thing with the heat shield panels: do them as separate segments, and fit these into a payload shroud or two. They unfold, and caulk together only once. Same for the outer aeroshell panels.
The cabin and propellant tankage items are pressure vessels. These can be shipped up in a series of payload shrouds limited more by thrown weight than by volume, as none of these need be anywhere near the heat shield diameter of the lander.
Fueling on orbit requires more "payload shrouds" as tankers. Or, these could be tanks that ride "naked" except for a streamlined nose cap, on the front of the rocket. Dock such tanks to your lander, and make the connections. The lander can push itself and a huge swarm of tanks to Mars one way, to support a bunch of landings, from low Mars orbit.
Another lander plus a swarm of tanks plus a human habitat could be the manned orbit-to-orbit transport, except that's a waste of a good lander. Just use the lander engines on a lander chassis as a propulsion module docked to your orbit-to-orbit transport.
GW
Great GW!
Why not posting in your blog a Mars lander assembled in orbit from pre-fab components?
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Why are you doing ANY designs around Falcon family, it's not going to go to Mars (though Moon looks to be in reach of F9H)? SpaceX has basically decided to use the Falcon family to service the commercial Satellite market and ISS (or other LEO station) resupply, while pouring profits into development of vehicles they do intend to send to Mars.
While I fully agree that Congress is wasting a ton of money on SLS and THEY should be developing tech like EDL/longer term life-support/ISRU and leaving rocketry to the commercial market. Unfortunately the die is cast on SLS and it has a >90% chance of delivering a usable (all be it ludicrously expensive) vehicle. Then when you add in SpaceX intent to basically make an equally capable rocket at a fraction of the price and their high probability of delivering their rocket (~75% to be conservative) we can be very confident of that Super Heavy Lift capability will be available in the 2020's.
And when big and little rockets are both available and development costs are sunk (NASA gets to ignore it's development costs, Musk will just charge marginal costs for Mars Mission to further his own aims), Big will win out for conducting any given mission. Assembly, Depots, fuel transfer, orbital rendezvous, all these things allow us to get more done out of any particular rocket size, and If Musk wants to 'colonize' he will need both a huge rocket AND every 'force multiplier' he can muster. But a basic science/reconnaissance mission that NASA would want to run, they won't need been much beyond the Supper Heavy lift rocket, and the force-multipliers generally only make sense when flight rate is much higher.
That means 15m diameter heat-shields and 100mt masses are what we should be planning around, if that needs a bigger heat-shield then so be it we can figure out a means to make an expandable shield, but I don't see any point is trying to squeeze shields into Falcon class shrouds if they aren't going to be the Mars vehicles.
Another thought, the 'umbrella' concept as it only needs to be deployed when in decent perhaps it should fold up and detach from the vehicle and be stowed in the Cargo bay (which is now empty) for the assent phase. Then in orbit the shield is taken out, opened and attached externally and the cargo is loaded into the now empty cargo bay for delivery to the surface. This scenario keeps the collapsible heat-shield from consuming a dedicated portion of the capsules internal volume when stored, it also makes the shield monolithic rather then segmented. Attachment and detachment could be done by a robotic arm, which will be a necessity anyways for cargo loading/unloading in a zero-G. Alternatively the robotic arm could be holding the shield the whole time during descent which would allow shifting center of mass and steering, possibly even the upside-down quasi-parachute use of the shield after the vehicle goes subsonic, it's speculated that a vehicle so equipped would only need a brief terminal velocity canceling burn right at touchdown, but this would require a very robust hydraulic arm or pair of arms to do.
Last edited by Impaler (2014-11-17 22:06:05)
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The problem you face with launchers for stuff to be built in LEO is that not all the components are big and heavy. Especially if assembly is by docking stuff together, very little of it would be 100 ton class, only the finished, assembled, and fueled item. That means current launchers (all of them, Spacex and ULA) are appropriate for a lot of the stuff we would want to send to orbit, if not the entirety of it. Depends on how much docking assembly you end up doing in your design.
Launch is only "cheap" if the vehicle flies at full load. You pay the same launch cost for a given vehicle, regardless how light your payload might be. The current fleet is characterized as about $2500/lb, but that figure goes up by big factors if you fail to fly full load. That per unit payload figure is simply launch price divided by max load. If you fly at half load, your unit price is twice as high ($5000/lb).
Launcher selection is thus set by two things: (1) mass of payload vs launcher capacity, and (2) width of payload versus diameter limit for the launcher. That last is true whether you ride inside a shroud or "naked" on top of the rocket. It's an aerodynamic stability limit during ascent.
If NASA ever gets its act together and gets SLS flying, then we will have a launcher fleet that can carry 10-20 ton objects (the current ones from ULA and Spacex), 53 tons (Falcon Heavy), and 70-130 tons (SLS). I'm not sure SLS will ever be remotely affordable. The others already are.
GW
Last edited by GW Johnson (2014-11-19 10:03:13)
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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I have borrowed from your ideas and want to run what I am thinking here and see how bad a beating I get on it, perhaps learn something.
I like your umbrella idea, and it makes sense to me.
However at some later stage of development could it be possible to launch to orbit folded carbon mesh as a starter form.
https://www.google.com/search?q=carbon+ … d=0CE0QsAQ
And also material to apply to it by a process similar to vacuum deposition / electrostatic coating.
http://en.wikipedia.org/wiki/Vacuum_deposition
I am thinking 3D printer as well as the method of action. Noting that their are already robot arms in use in orbit.
If so, then I might think that many shapes not confined to the diameter of launch vehicles might be obtained. However, I might wonder about quality.
I am thinking heat shields, tanks, and spacecraft bodies among other things.
What do you think the chances are that this could be useful later on?
Done.
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First the 100 launchers to assemble any is foolish as each is customized to deliver its payload to orbit and each payload is by itself a new design element as well as process step in assembly, which with any failed launch can cause the total mission to be haulted never to be completed.
If we are going to use alot of launchers that have the protective payload shroud, why not reuse it as a building block to make the large folding heat shield as its already strong enough.
Last edited by SpaceNut (2014-11-19 21:57:05)
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Nobody ever said we need 100 launches to go to Mars! But, we might come close, if we mount a really ambitious mission. So what?
A fleet of three ships, one manned, two unmanned, each around 500 tons, might do the mission, in a very BIG way. That's 1500 tons total to assemble in LEO. And that's a REALLY BIG mission!
Say a quarter of it (around 375 tons) is Falcon-Heavy stuff at 50 tons a whack. That's about 9 Falcon Heavies. Say another quarter of it is Falcon-9 stuff at around 12.5 tons a whack. That's 30 Falcon-9 launches. The other half (750 tons) is launchable with Atlas-5 and Delta-4 at around 20 tons a whack. That's about 38 rockets from ULA.
That's a total of 77 launches to assemble a REALLY big Mars mission. And I do mean REALLY REALLY big! Figure launch costs at an average of 2500/lb ($5.5M/ton) for the ULA and Falcon-9 stuff, and nearer $1000/lb ($2.2M/ton) for the Falcon-Heavy stuff. You must fly near-capacity to get it that cheap. Even so, that's a launch price of $825M for the Falcon-Heavy launches, and about $6188M for the rest. Total launch price is $7013M = about $7B for direct launch costs, if you fly near-capacity on every rocket.
In a well-run program, launch costs OUGHT to be around 25% of your program cost. In a poorly-run program, maybe 10%. Use that 10%. On the $7B.
You get a price in the vicinity of $70B to put a wastefully-inefficient project in place, for a HUGE expedition to Mars. You really ought to be able to do it for something closer to $30B.
And I'm talking reusable orbit-to-orbit transports, reusable landers, and conducting around a dozen or so different landings at sites all over Mars, in the one single trip, plus establishing the core of a permanent base at the "best" site. And maybe even flying a lander to visit Phobos while we're there.
NASA estimated a far less ambitious trip (one site, "flag-and-footprints only) at $450B a few years ago. Bah, humbug, and what-a-load-of-BS that is/was.
It's the Spacex's and Virgin Galactic's of this world that will do this right. Not governments.
GW
PS: ANY rocket can send something to Mars, even the ancient original Atlas or Thor of 60 years ago. They did, in point of fact.
Last edited by GW Johnson (2014-11-20 16:54:31)
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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So for 30 Billion to pay for the design & launch of all payloads to assemble
three ships, one manned, two unmanned, each around 500 tons
what do we really get?
The one manned vehicle, is it left in Mars Orbit to become the ERV? Does it land and become the habitat instead?
Does the crew transfer in mars orbit to either of the unmanned vehicles to land on mars? Could this be the crews Habitat or does it play the role of ERV staying in orbit?
What is the second unmanned vehicles purpose? Is this an insitu refuelling unit that acts as the MAV?
Last edited by SpaceNut (2014-11-20 18:47:51)
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