|
|
Thread Tools | Display Modes |
#261
|
|||
|
|||
Questions about "The High Frontier"
On Oct 21, 1:12 am, Hop David wrote:
Mike Combs wrote: "Troy" wrote in message roups.com... Try telling that to politicians and hysterical anti-asteroid campaign groups! I'd have to allow that public education would be a hurtle to overcome. Similarly, I think SBSP is the best long-term energy solution (and might lead to space settlement), but that will require extensive public education that no, there's no cause for concern from the microwave beams. I think what we might call "Deep Impact hysteria" might rule out aerobraking asteroids through Earth's atmosphere, but I would hope we won't be prevented from depositing a fragment of an asteroid perhaps the size of an apartment building into either L-4 or L-5. It's desirable to have a near earth perigee not only for aerobraking but to exploit the Oberth effect. I don't think hysteria is the right word. Large payloads would be harder to control and a tiny error could change aerobraking to lithobraking. I would call it "Deep Impact sensible fear". Again, I advocate payload mass ceilings well below Tunguska size. I'm still curious whether there might be a way to increase payload mass and reduce terrestrial hazards by delivering asteroid-derived payloads to Earth orbit in the form of large spherical shells of material. As I've probably mentioned in this forum before, I was once asked to look at an RFP for "demisable tanks" -- i.e., satellite fuel tanks guaranteed to burn up on reentry. That inquiry went nowhere, AFAIK. Which underscores a point: maybe you don't need ablative shielding or heat-soaking tiles to bring stuff down intact. After all, LEO satellite fuel tanks have been found in desert regions with little more than scorch marks and dents from hitting the ground (at a relatively low terminal velocity, obviously.) Maybe that's a bug for satellite fuel tanks, but it's arguably a feature if you're interested in aerobraking or aerocapture of resources delivered from cislunar or interplanetary space. Now let's say you want to deliver a lot of asteroid-mined metal to an L-point, using aerobraking in the Earth's atmosphere. Blow the metal up into a big, relatively thin-walled sphere. Maybe store some asteroid-derived volatiles inside, which would coat the interior as they freeze down to the point where you get into equilibrium with sublimation losses. Then push it off toward Earth. Now let's look at the shipment failure modes. CLOSE, BUT NO CIGAR There's a navigation error: it misses aerobraking, and you lose a shipment. You've blown a lot of capital, but not much life/limb risk here. (Except crew loss if manned; see below.) TOO CLOSE There's a navigation error: it flies past Earth at or somewhat below its aerocapture threshold. Well, then, maybe it makes it all the way down. BUT, if it has a very low mass/volume ration, maybe it just falls to a certain altitude in the atmosphere and ... floats. Even with all the volatiles inside, boiled off, it might enclose a lot of relative vacuum compared to some point in the atmosphere. And a thin IR-reflective coating on the exterior of the sphere might give it more thermal load toleration during atmospheric entry, as the radiative heat losses during the long transit would reduce the temperature of the internal volatiles to some very low equilibrium point. If the volatiles mix is mostly H2O, so much the better: H2O has a lot of heat capacity. DIRECT HIT There's a navigation error: it enters the Earth's atmosphere at a high angle. This is by far the most worrisome scenario, and I would only hope that a large, thin-walled sphere would simply vaporize much more easily, at much higher altitudes, than any chunk of rock of the same mass. Some things I like about this idea, if it could be made to work: (1) Gradually scalable. Relatively small spheres might be returned to Earth just for starters, with relatively high value payloads (e.g., those platinum-group metals some talk about.) You could get people used to the idea that stuff can arrive ballistically from space without serious hazard to people on Earth. (2) Testable elsewhe one initial use for a Venus cycler might be to perform small-scale experiments on the idea, prototyping it by watching what happens in the TOO CLOSE and DIRECT HIT modes. Likewise for a Mars cycler. The results might have some scientific value for studying upper atmosphere composition on those planets -- assuming much more work needs to be done in that area (I wouldn't know.) (3) Putting terrestrial uses first: building a space economy might depend on first exploiting space material resources for use on Earth. And there might be a case for that. Digging up ore from the Earth's crust, transporting it by ship, processing it into steel -- these are all energy-intensive, with all the environmental issues that are raised by generating the required energy on Earth. A big ball of mostly-pure iron appearing in the atmosphere, ready to be aerially towed to steel mills with an assist from prevailing winds, might offer all kinds of financial and environmental economies, maybe enough to offset the costs of making it possible. (4) Water, water, water: if H2O proves to be the most valuable of volatiles for improving the heat load tolerance of such spheres, you might end up with a net surplus of water for use in space. As I've conjectured elsewhere, how we do things in space might change a lot if assume a relative abundance of water. Even payloads slated for delivery to Earth might offer a way to deliver water to cislunar space -- initial aerobraking passes might require the most water, and if so, you might jettison the vapor into balloons at the perigee after each pass, and use a little more vented vapor to propel the balloons to highly elliptical orbits that don't graze the upper atmosphere, or that aerobrake them more gently for delivery to LEO. (5) Human return vehicle: while I lean toward unmanned, automated/ teleoperated asteroid mining operations to keep costs down, human presence might turn out to be necessary for a while, and those people will probably want to come back. A big metal sphere would have obvious debris-strike protection value; one with lots of frozen volatiles inside might provide the foundation for a reasonable cosmic- ray-shield habitat as well. Well, it would be hellishly cold in there, though, right? But perhaps the process of applying a uniform, highly IR-reflective coating to the exterior could wait until late in the return journey. Do I know what I'm talking about? No. Is anybody else talking about this? Not that I've heard. If nobody else is talking about it, maybe it hasn't been shot down yet. My clay pigeon for the day, the product of little more than an afternoon's idle thought. -michael turner |
#262
|
|||
|
|||
Questions about "The High Frontier"
John Schilling wrote:
On Fri, 19 Oct 2007 13:10:07 -0500, "Mike Combs" wrote: "John Schilling" wrote in message . .. But it's probably going to be a *lot* less expensive if you allow for the inhabitants to build, provision, and resupply their habitat using local resources. And there's every reason in the world to expect an asteroidal settlement to be doing this. Except for the critical shortage of local resources that aren't steel or coal or glass. And Mars has a much broader range of useful resources than any NEO. Than all NEOs combined, probably. I'm not sure why you would say this. What resources would be available on the surface of Mars that you couldn't find in a well-selected CC-type asteroid? "CC" meaning "Carbonaceous Chondrite" generally? OK, let's see: How about useful concentrations of Helium, Lithium, Beryllium, Boron, Nitrogen, Fluorine, Neon, Sodium, Aluminum, Chlorine, Argon, Potassium, Titanium, Chromium, Manganese, Copper, Zinc, Arsenic, Bromine, Krypton, Strontium, Zirconium, Niobium, Molybdenum, Silver, Tin, Antimony, Iodine, Xenon, Barium, Hafnium, Tantalum, Tungsten, Gold, Mercury, Lead, Bismuth, Thorium, and Uranium. While CCs may be poor in some those materials, there are other asteroids that aren't. I acknowledge that one asteroid containing all these resources would be rare. It would be hard for colonists on a metallic asteroid to use nitrogen from an NEO on a different orbit. On the other hand, there's no superhighways, oceans or rivers that can be used for transportation on Mars. Transportation will be a substantial barrier to self sufficiency on Mars as well as among the NEOs. Mars definitely has some of those in abundance , and almost certainly has useful ores of the rest on account of having experienced the same geologic processes that produced such ores on Earth. I seem to recall Peter Tillman saying uranium ore was concentrated via biological processes. There's certainly some ore concentrating processes on Mars, but I don't regard it as a given Mars would have all the same ores earth does. Carbonaceous chondrites, based on the meteoric evidence, do not. Meteoric evidence is biased. Some meteorites are much more perishable than others. If they're not discovered within hours or days of impact, they're gone. More durable objects are more likely to reach the earth's surface and become meteorites. They're just raw primordial dust, slightly baked. Some carbonaceous chondrites may be homogenous aggregates that haven't experienced any ore concentrating processes. But this isn't the case for all asteroids. Metallic asteroids are believed to come from the interior of large asteroids that were massive enough to have differentiated layers. I also believe there can be ore concentrating processes going on in objects that outgas when they're closer to the sun. Asteroids, are where you get steel and coal and glass, and maybe magnesium and platinum for the export markets, and that's really about it. I believe water, ammonia and other volatiles not at the bottom of a steep gravity well and not far from the earth would be valuable. On http://clowder.net/hop/railroad/asteroidresources.html I give a list of reasons (with some web cites) why I believe volatile rich NEOs exist. Mars also has gravity, which is quite useful if you want your inhabitants to remain, like, alive and stuff. Providing gravity on or near an NEO is rather hard, especially at small scales. I wouldn't so much say "hard" as "requiring a certain minimal scale". If one has two counter-rotating structures of equal mass, nothing is required to spin them up and keep them spinning other than an electric motor between them. Making them useful requires more than just keeping them spinning, as you ought to know by now. Could you elaborate? And the minimal scale issue is critical, because the first outposts are going to be small and the first big colonies are going to be where the outposts already are. Minimum gravity to maintain health is still unknown. Human tolerance to angular velocity given a gradual transition is still unknown. So minimal scale is still unknown. Hop |
#263
|
|||
|
|||
Questions about "The High Frontier"
Damien Valentine wrote:
On Oct 20, 11:08 am, Hop David wrote: This is like saying if modest log cabins were good enough for the pioneers then why should their descendants bother with high rise buildings. Because building things in space (whatever those things may be) doesn't automatically lead to either log cabins or high rises. Someone mentioned oil rigs a few posts back; we may have 24-hour crews on them, but the crews don't stay on the rig for their whole lives and raise kids. There are no "oil rig cities", so far as I know. Many cities have sprung up around oil fields in formerly desolate, hard to reach areas. Same with mining towns. So far as I know, most long duration off shore drilling rigs aren't far from land and it's not a major investment for a worker to make a trip to a coastal settlement. But if it's very hard to access coastal settlements, I believe service industries would grow around a long duration rig. Eventually there'd be schools, churches, etc. Hop |
#264
|
|||
|
|||
Questions about "The High Frontier"
On Oct 23, 2:36 am, Damien Valentine wrote:
On Oct 20, 11:08 am, Hop David wrote: This is like saying if modest log cabins were good enough for the pioneers then why should their descendants bother with high rise buildings. Because building things in space (whatever those things may be) doesn't automatically lead to either log cabins or high rises. Someone mentioned oil rigs a few posts back; we may have 24-hour crews on them, but the crews don't stay on the rig for their whole lives and raise kids. There are no "oil rig cities", so far as I know. But there are such things as mining towns. Oil rigs are extremely dangerous and rather unpleasant places, plus they run out of resource eventually. They also have to be towed out in one piece. Johannesburg was once a mine, now it's South Africa's largest city. As Dr. Schilling pointed out when he kindly took the time to rip my argument to shreds, a bunch of small scattered habs is not going to make a decent permanent settlement. Mars does lend itself to permanent settlement because of the availability of resources and infrastructure concentration of a base of operations. If you have a single large base of operations which processes towed-in asteroids, support infrastructure will spring up around it, requiring more and more human presence. Trips back Earthside may happen every 6 months or so, but if you close your resource loop, it's effectively a permanent settlement. As the habitat becomes more... habitable, people may stay longer. |
#265
|
|||
|
|||
Questions about "The High Frontier"
Michael Turner wrote:
I don't think hysteria is the right word. Large payloads would be harder to control and a tiny error could change aerobraking to lithobraking. I would call it "Deep Impact sensible fear". Again, I advocate payload mass ceilings well below Tunguska size. I'm still curious whether there might be a way to increase payload mass and reduce terrestrial hazards by delivering asteroid-derived payloads to Earth orbit in the form of large spherical shells of material. As I've probably mentioned in this forum before, I was once asked to look at an RFP for "demisable tanks" -- i.e., satellite fuel tanks guaranteed to burn up on reentry. That inquiry went nowhere, AFAIK. Which underscores a point: maybe you don't need ablative shielding or heat-soaking tiles to bring stuff down intact. After all, LEO satellite fuel tanks have been found in desert regions with little more than scorch marks and dents from hitting the ground (at a relatively low terminal velocity, obviously.) Maybe that's a bug for satellite fuel tanks, but it's arguably a feature if you're interested in aerobraking or aerocapture of resources delivered from cislunar or interplanetary space. Now let's say you want to deliver a lot of asteroid-mined metal to an L-point, using aerobraking in the Earth's atmosphere. Blow the metal up into a big, relatively thin-walled sphere. Maybe store some asteroid-derived volatiles inside, which would coat the interior as they freeze down to the point where you get into equilibrium with sublimation losses. Asteroid mined metal would come from a metallic asteroid which is unlikely to have volatiles. There may be exceptions to this. One scenario I can think is an object from Jupiters' Trojans. Objects drift in, stay awhile and then drift out (I believe). See the NEC apohelion graphic on http://clowder.net/hop/railroad/asteroidresources.html) While milling about in the Trojan cluster it might be possible for two asteroids from very different orgins to collide at low velocity and form a "peanut". Then the asteroid drifts out to become a Near Earth Comet and then a later earth approach alters its orbit, dropping its aphelion. Even later, happy investors discover this peanut with metals in one lobe and volatile ices in the other. Then push it off toward Earth. Now let's look at the shipment failure modes. CLOSE, BUT NO CIGAR There's a navigation error: it misses aerobraking, and you lose a shipment. You've blown a lot of capital, but not much life/limb risk here. (Except crew loss if manned; see below.) TOO CLOSE There's a navigation error: it flies past Earth at or somewhat below its aerocapture threshold. Well, then, maybe it makes it all the way down. BUT, if it has a very low mass/volume ration, maybe it just falls to a certain altitude in the atmosphere and ... floats. It depends on duration of transit through the atmosphere. If its passage lasts long enough for heat to be conducted through the metal shell, the volatiles will turn to gas and provide supporting pressure. But if the volatiles don't vaporize fast enough, I'd expect the metal ball to crumple. Is it possible to have a metal shell strong enough to keep its shape while enclosing vacuum but light enough to float? I don't know. Given your conditions above, the object has a low flight path angle so it might have a long enough trip for heat to conduct through the shell. Even with all the volatiles inside, boiled off, it might enclose a lot of relative vacuum compared to some point in the atmosphere. And a thin IR-reflective coating on the exterior of the sphere might give it more thermal load toleration during atmospheric entry, as the radiative heat losses during the long transit would reduce the temperature of the internal volatiles to some very low equilibrium point. If the volatiles mix is mostly H2O, so much the better: H2O has a lot of heat capacity. DIRECT HIT There's a navigation error: it enters the Earth's atmosphere at a high angle. This is by far the most worrisome scenario, and I would only hope that a large, thin-walled sphere would simply vaporize much more easily, at much higher altitudes, than any chunk of rock of the same mass. Some things I like about this idea, if it could be made to work: (1) Gradually scalable. Relatively small spheres might be returned to Earth just for starters, with relatively high value payloads (e.g., those platinum-group metals some talk about.) You could get people used to the idea that stuff can arrive ballistically from space without serious hazard to people on Earth. (2) Testable elsewhe one initial use for a Venus cycler might be to perform small-scale experiments on the idea, prototyping it by watching what happens in the TOO CLOSE and DIRECT HIT modes. Likewise for a Mars cycler. The results might have some scientific value for studying upper atmosphere composition on those planets -- assuming much more work needs to be done in that area (I wouldn't know.) (3) Putting terrestrial uses first: building a space economy might depend on first exploiting space material resources for use on Earth. And there might be a case for that. Digging up ore from the Earth's crust, transporting it by ship, processing it into steel -- these are all energy-intensive, with all the environmental issues that are raised by generating the required energy on Earth. A big ball of mostly-pure iron appearing in the atmosphere, ready to be aerially towed to steel mills with an assist from prevailing winds, might offer all kinds of financial and environmental economies, maybe enough to offset the costs of making it possible. (4) Water, water, water: if H2O proves to be the most valuable of volatiles for improving the heat load tolerance of such spheres, you might end up with a net surplus of water for use in space. As I've conjectured elsewhere, how we do things in space might change a lot if assume a relative abundance of water. Even payloads slated for delivery to Earth might offer a way to deliver water to cislunar space -- initial aerobraking passes might require the most water, and if so, you might jettison the vapor into balloons at the perigee after each pass, and use a little more vented vapor to propel the balloons to highly elliptical orbits that don't graze the upper atmosphere, or that aerobrake them more gently for delivery to LEO. (5) Human return vehicle: while I lean toward unmanned, automated/ teleoperated asteroid mining operations to keep costs down, human presence might turn out to be necessary for a while, and those people will probably want to come back. A big metal sphere would have obvious debris-strike protection value; one with lots of frozen volatiles inside might provide the foundation for a reasonable cosmic- ray-shield habitat as well. Well, it would be hellishly cold in there, though, right? But perhaps the process of applying a uniform, highly IR-reflective coating to the exterior could wait until late in the return journey. Do I know what I'm talking about? No. Is anybody else talking about this? Not that I've heard. If nobody else is talking about it, maybe it hasn't been shot down yet. My clay pigeon for the day, the product of little more than an afternoon's idle thought. I took a few pot shots, more with a .22 than a 12 gauge though. I agree density should be considered when establishing payload ceilings. Hollow payloads may well be more amenable to aerobraking. Hop |
#266
|
|||
|
|||
Questions about "The High Frontier"
Troy wrote:
On Oct 23, 2:36 am, Damien Valentine wrote: On Oct 20, 11:08 am, Hop David wrote: This is like saying if modest log cabins were good enough for the pioneers then why should their descendants bother with high rise buildings. Because building things in space (whatever those things may be) doesn't automatically lead to either log cabins or high rises. Someone mentioned oil rigs a few posts back; we may have 24-hour crews on them, but the crews don't stay on the rig for their whole lives and raise kids. There are no "oil rig cities", so far as I know. But there are such things as mining towns. Oil rigs are extremely dangerous and rather unpleasant places, plus they run out of resource eventually. They also have to be towed out in one piece. Johannesburg was once a mine, now it's South Africa's largest city. As Dr. Schilling pointed out when he kindly took the time to rip my argument to shreds, a bunch of small scattered habs is not going to make a decent permanent settlement. True, supplying habs scattered thoughout the solar system is more difficult than supplying habs all in the same neighborhood. This is one of the reasons I advocate placing asteroidal payloads in orbits about Earth, Venus and Mars. Habs orbiting on the slopes of gravity wells are also more accessible in terms of delta vee (For example it takes less delta vee to land on Phobos or Deimos than it does a Mars Trojan). Mars does lend itself to permanent settlement because of the availability of resources and infrastructure concentration of a base of operations. If you have a single large base of operations which processes towed-in asteroids, support infrastructure will spring up around it, requiring more and more human presence. Trips back Earthside may happen every 6 months or so, but if you close your resource loop, it's effectively a permanent settlement. As the habitat becomes more... habitable, people may stay longer. |
#267
|
|||
|
|||
Questions about "The High Frontier"
On Oct 23, 10:46 am, Hop David wrote:
Damien Valentine wrote: On Oct 20, 11:08 am, Hop David wrote: This is like saying if modest log cabins were good enough for the pioneers then why should their descendants bother with high rise buildings. Because building things in space (whatever those things may be) doesn't automatically lead to either log cabins or high rises. Someone mentioned oil rigs a few posts back; we may have 24-hour crews on them, but the crews don't stay on the rig for their whole lives and raise kids. There are no "oil rig cities", so far as I know. Many cities have sprung up around oil fields in formerly desolate, hard to reach areas. Same with mining towns. So far as I know, most long duration off shore drilling rigs aren't far from land and it's not a major investment for a worker to make a trip to a coastal settlement. But if it's very hard to access coastal settlements, I believe service industries would grow around a long duration rig. Eventually there'd be schools, churches, etc. Sounds like what Halliburton sets up in Iraq for the war effort. Hop |
#268
|
|||
|
|||
Questions about "The High Frontier"
"Hop David" wrote in message
... On the other hand, there's no superhighways, oceans or rivers that can be used for transportation on Mars. Transportation will be a substantial barrier to self sufficiency on Mars as well as among the NEOs. There seems to be an assumption that overland travel on Mars has got to be easier than moving between asteroids because the latter is space travel and the former isn't, and as everybody knows, space travel is difficult, dangerous, and hideously expensive. I think this notion overlooks two points: 1. Overland travel on Mars, unlike same on Earth, will have pressurization and other life-support requirements little different from space travel. 2. Our notions of space travel are influenced by our most common experience of it, which is to say, travel from the surface of the Earth into orbit. Such travel requires large amounts of thrust (greatly in excess of vehicle weight in 1-G) quickly achieved, and an aerodynamic shape. None of these will be requirements for systems traveling from one asteroid to another. There's certainly some ore concentrating processes on Mars, but I don't regard it as a given Mars would have all the same ores earth does. And we cannot until we go there and obtain ground truth. Making them useful requires more than just keeping them spinning, as you ought to know by now. Could you elaborate? My point was that saying Mars provides us with free gravity may not be saying a lot if there's no large additional cost associated with spinning. John seems to be pretending he thinks my point is that having a space settlement is as easy as making something spin. -- Regards, Mike Combs ---------------------------------------------------------------------- By all that you hold dear on this good Earth I bid you stand, Men of the West! Aragorn |
#269
|
|||
|
|||
Questions about "The High Frontier"
"Troy" wrote in message
oups.com... If you have a single large base of operations which processes towed-in asteroids, support infrastructure will spring up around it, requiring more and more human presence. And I think there will be a single large base of operations. This might be where Hop parts company with me, but I really don't expect this process to start out at distant asteroids. I expect it to start out in HEO, close to the only servable market currently in existence, which is Earth. I expect the initial major product to be solar power satellites. Entire asteroids may or may not get towed into this orbital base of operations, but even if not, I'm sure that loads of ore pulled from some NEO will be getting towed in. -- Regards, Mike Combs ---------------------------------------------------------------------- By all that you hold dear on this good Earth I bid you stand, Men of the West! Aragorn |
#270
|
|||
|
|||
Questions about "The High Frontier"
Mike Combs wrote:
On the other hand, one might note that with the SMF with the spartan living conditions one sees quick turnover in skilled workers. People sign-on for 2 year tours (or whatever), fill up their bank accounts, and then come back to Earth to spend their money, because what are they going to spend it on living in an aluminum can in HEO? Then you might note that since you've got mining facilities on the moon and/or a NEA, a means of transporting ore to HEO, ore refineries and parts fabrication facilities in that same orbit, most of what you need to build a Bernal Sphere or Stanford Torus is already in place (and perhaps already paid for by SPS profits). So it might be worth a bit of investment for your workers to be able to live under natural sunlight surrounded by greenery, and able to do ordinary things like fish in a pond or walk in a park. Perhaps highly-trained and skilled workers might be more apt to spend their entire careers with you if they can look at their apartment or house in Bernal Alpha as "home" rather than some place on Earth. Families might be more apt to form in such a place than in a place which more resembled an off-shore oil rig. Mike, you're a good guy and everything, but the above is a textbook example of thinking with your heart instead of your head. In any other context except space (you yourself bring up oil rigs) you would quickly recognize the absurdities. But since this is space we're talking about...well, things are different in space, right? Jim Davis |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
The "experts" strike again... :) :) :) "Direct" version of my "open Service Module" on NSF | gaetanomarano | Policy | 0 | August 17th 07 02:19 PM |
Great News! Boulder High School CWA "panelists" could be infor it! | Starlord | Amateur Astronomy | 0 | June 2nd 07 09:43 PM |
"VideO Madness" "Pulp FictiOn!!!," ...., and "Kill Bill!!!..." | Colonel Jake TM | Misc | 0 | August 26th 06 09:24 PM |
why no true high resolution systems for "jetstream" seeing? | Frank Johnson | Amateur Astronomy | 11 | January 9th 06 05:21 PM |