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Ahhh okay, thats a little different then. I still think that we will just see bigger versions of the smaller, faster space liners rather then such a luxury cruise ship. The trick is to get there FASTER, not bigger... A smaller ship powerd by a high-Isp/high-thrust engine could make two trips in the same time as the big chemical liner could make one.
My issue with aerobraking such a ship isn't the size of the Delta or the shield itself, but the ratio of vehicle mass to heat shield cross-section area, which needs to be kept under control for effective aerobraking. A ship neither too heavy for a little shield or too light for a big one.
"they will blow nuclear engines out of the water in terms of transport cost, unless such engines come down in price A LOT"
No they won't, since mining will never be as easy as simply shipping up extra loads of H2 and the occasional container of Uranium. Its just EASIER, and thats why nuclear will win. Design, operate, tend, and shuttle fuels back and forth between z zero-G asteroid mine, or just send up another few flights of Shuttle-II/III with Hydrogen? Its not even a question... mature GCNR engines or NSWR & VASIMR could reach 5,000 and 10,000sec Isp respectively...
Everything you know about the economics of rocketry in the face of such performance is... obsolete. I mean, come on, chemical engines will never even top 470sec!
And since the engines will be reuseable, the cost to build them really - and when I say "build" I mean alot of them - won't be a big deal compared to the bennefits of massively reduced trip times, wider departure windows, more abort options, or HUGE payload fractions.
"cheap nuclear engines are quite unlikely because of the near-paranoia guaranteed to exist about their safety"
What? The colonists will literally be placing their lives in the reliability of nuclear power plants on Mars, are you kidding? Heck, if >60% of Californians want more nuclear energy, then I am sure that this won't be an issue. You would need nuclear power to operate your asteroid mines too anyway.
Not meaning to pick on you about mass estimates, but not having to lug along the lander for each parcel sent to Mars makes a big difference.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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Might I ask why solar sailing isn't even considered here? Material sciences will make it the true reality for the vast majority of people. No requirement to mine and process lots of ore, no requirement for sheilding, and complex systems to keep failures from occuring. Perfectly viable in the inner solar system (and most likely the only way to efficiently exit the solar system and travel to other stars). It'll be chosen simply because it's the most economical and logical means of travel.
edit: oh, you did mention solar sails, and claimed they were slow, I've read some magic numbers for a one month Mars trip using Dusty-M2P2...
Some useful links while MER are active. [url=http://marsrovers.jpl.nasa.gov/home/index.html]Offical site[/url] [url=http://www.nasa.gov/multimedia/nasatv/MM_NTV_Web.html]NASA TV[/url] [url=http://www.jpl.nasa.gov/mer2004/]JPL MER2004[/url] [url=http://www.spaceflightnow.com/mars/mera/statustextonly.html]Text feed[/url]
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The amount of solar radiation reaching the surface of the earth totals some 3.9 million exajoules a year.
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What? The colonists will literally be placing their lives in the reliability of nuclear power plants on Mars, are you kidding? Heck, if >60% of Californians want more nuclear energy, then I am sure that this won't be an issue. You would need nuclear power to operate your asteroid mines too anyway.
Doubt pebblebed reactors work in zero G...
PS that asteroid is mine. If i want to build a nuclear propulsion system on it and slam it in to Washington, thats My regime changing right!
As for Phobosian fuel, again I'm talking about farther into the future, and I am frankly not quite as pessimistic as you about operating in zero-g. Yes, I have already heard your lecture on the subject several times. If lunar and Phobosian fuel are available at a reasonable price, they will blow nuclear engines out of the water in terms of transport cost, unless such engines come down in price A LOT. I think cheap nuclear engines are quite unlikely because of the near-paranoia guaranteed to exist about their safety, and colonization of Mars will depend on cheap transport.
Who says you need a nuclear drive for every ship? A nuclear propelled space Tug designed to push out to Mars your colony vessel, and return for next bunch who are ready to go is financially superior to go out, return, and wait for two years before the next crew is ready. it will cut costs by half.
If we went the space tug route, we could simply build habitats in space, push them out to PHOBOS, and anchor them to the orbiting Moon. Colonists could make their way down to Mars from there.
No risky aerobraking required.
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Might I ask why solar sailing isn't even considered here? Material sciences will make it the true reality for the vast majority of people. No requirement to mine and process lots of ore, no requirement for sheilding, and complex systems to keep failures from occuring. Perfectly viable in the inner solar system (and most likely the only way to efficiently exit the solar system and travel to other stars). It'll be chosen simply because it's the most economical and logical means of travel.
edit: oh, you did mention solar sails, and claimed they were slow, I've read some magic numbers for a one month Mars trip using Dusty-M2P2...
Feh, the M2P2 gizmo is just another one of those hair-brained "...if NASA would just send us a few million" ideas that physics buffs parade to the media as the best thing since sliced bread in the hope of generating outcry from ignorant people when their "revolutionary" work gets passed over. They need to do some SERIOUS theoretical studies and come up with a plausable outline for a mission including mass estimates. This will be the eleventeenth idea thats "Mars in a Month!"
"...no requirement for sheilding, and complex systems to keep failures from occuring. Perfectly viable in the inner solar system..."
No, no and no.
Thanks to the VERY long travel time (years), whatever payload you are carrying will need shielding to protect it from long-term soak in cosmic & solar radiation, plus probobly protection from the cold too... most sensitive electrons can't handle the cold soak.
It will also be quite complex. Its going to need some serious gyros for attitude control, solar arrays for power, and whatnot that have to last for decades to make a ten-trip design life practical to mitigate development/construction costs. This alone is not going to be easy.
And what cargo would you want to send this way anyway? You would obviously want the construction equipment or reactor parts or smelting furnace or whatever rather soon so that you don't slow down colony construction, and this nonsense idea about "just cue your shipments six or seven years in advance" is crazy with respect to actual construction. For use as a bulk (grain, water, ammonia, etc) hauler, we don't need any of those, and in fact we HAVE to avoid them... all - all - bulk materials HAVE to be made on Mars to make it economically viable.
I want to invoke the Nike rule again here: forget the sails, forget the asteroid mines, forget all that - just send up a few more RLV loads worth of H2/H2O/U-235 - just do it! Simplicity, speed, economies of scale, far superior mass ratios, more sorties per year, superior abort options. I mean, is it not obvious that high-energy nuclear propulsion is clearly the best choice? Just develop a powerful, reuseable GCNR or NSWR engine one time and be done with it!
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SRmeaney:
Actually PBR reactors do work in space, they were contemplated by the USAF for their Timberwind engine and space weapons reactors for their superior (for a solid-core) specific power, specific impulse and operating temperatures versus older NERVA-type cores.
"A nuclear propelled space Tug designed to push out to Mars your colony vessel, and return for next bunch who are ready to go is financially superior to go out, return, and wait for two years before the next crew is ready."
No. In order to get to Mars faster then six months every two years, you have to push the payload/ship faster then an aerobrake maneuver can handle. Plus, when your payload/ship does get to Mars, it still needs a way to slow down, which it can't if the tug and the engines are at Earth... which leaves aerobraking. You would have to slow down to enter Mars orbit to get to Phobos too, if you didn't, you would go sailing right past Mars completly. Going to Phobos does not eliminate the need to slow down.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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Feh, the M2P2 gizmo is just another one of those hair-brained "...if NASA would just send us a few million" ideas that physics buffs parade to the media as the best thing since sliced bread in the hope of generating outcry from ignorant people when their "revolutionary" work gets passed over. They need to do some SERIOUS theoretical studies and come up with a plausable outline for a mission including mass estimates. This will be the eleventeenth idea thats "Mars in a Month!"
I'm convinced Rob Sheldan's idea will work, and one day we're going to get the thing off the ground, once cheap access to orbit is obtained, I'll be personally behind the experimentation. Most of the components can be brought for under a few hundred dollars, believe it or not, it's quite an elegant and simple design. His proposal was denied, much to my dismay, while other totally http://www.niac.usra.edu/studies/studies.jsp]insane ideas (go to that link and count the ones you personally think were worth giving grants to, let me say that we'd probably be in agreement; btw, M2P2 is on that page, Rob's advancement to it, however, did not get accepted), with no actual science or realistic technology to back them were allowed grants. I think it's sad really. You can be dismissive all you want, but as far as I see, there are no major catches, at least none that nuclear wouldn't have to deal with. But it is admittedly too early to tell, we need to do some studies. Certainly there's room for our studies next to your nuclear research?
Thanks to the VERY long travel time (years), whatever payload you are carrying will need shielding to protect it from long-term soak in cosmic & solar radiation, plus probobly protection from the cold too... most sensitive electrons can't handle the cold soak.
Dusty-M2P2 has a magnetosphere that can be tens if not hundreds of kilometers across, if, and yes, I do admit it's an if (but the science is at least sound) it can scale, there is no way in hell anything can beat it. It's like blowing up balloons inside of a big wind tunnel, as soon as it gets blown up it quickly reaches the velocity of the wind. The first week might be spent within a million or two miles of earth, while the last three will be one hell of a ride.
By dismissing it off hand, though, I don't think you understand or care about the science behind it. I have no reason to dismiss nuclear, though when I say things like "if it works it's going to require such and such infrastructure" you can't really deny it. DM2P2 is simple. I say put some small pennies into research that at least has the prospect of simple, fast, space travel, before looking at the more understood alternatives that will undoubtedly cost a shitload of money to maintain.
Even if M2P2 can't scale to ships that can carry a few dozen people, a fleet of chepa one shot M2P2 ships that carry tens of tons would make colonization extremely viable.
Some useful links while MER are active. [url=http://marsrovers.jpl.nasa.gov/home/index.html]Offical site[/url] [url=http://www.nasa.gov/multimedia/nasatv/MM_NTV_Web.html]NASA TV[/url] [url=http://www.jpl.nasa.gov/mer2004/]JPL MER2004[/url] [url=http://www.spaceflightnow.com/mars/mera/statustextonly.html]Text feed[/url]
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The amount of solar radiation reaching the surface of the earth totals some 3.9 million exajoules a year.
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I remain quite unconvinced with the whole concept which, I think, is much too good to be true and so it probobly isn't. Particularly this business about it not having any signifigant snags or hurdles, which all such projects inevitibly do, is a red-flag to me that either the physics & engineering behind the idea haven't been properly developed to warrent spending big money on them, or worse somebody is trying to sell NASA a lemon. There are no refunds for research grants...
...More specifically, I am unconvinced that the vehicle can attain as high an acceleration and that the HTS magnets of sufficent specific field density could be produced. I find it odd that the need for a new breed of super-cryomagnet isn't mentioned as a signifiant issue with the technology, nor the issue of keeping the things below critical temperature and that systems' mass... Overall, the performance of such a system (payload masses?) is way, way too speculative to be throwing away claims about "Mars in the Month" typical of many other crackpot ideas.
Also, what constraints does the M2P2 magnetic coil place on the dimensions of the ship that it propells? Unless they were truely huge, that rules out zero-G spinning sections, and a magnetic field will also pass through the walls of inflatable modules to affect the passengers. Since the coil is directional and acceleration slow, that also rules out spinning the whole ship versus a counterweight for artifical gravity.
There will always be the "next neat idea!" that just needs a few million for development to get "results," and in aggregate that realy adds up... one thing that will need to happen for regular, inexpensive Mars travel is to take advantage of economies of scale; for that to happen, then the means of getting to Mars need to be as uniform and common as possible, such as passenger ships, heavy cargo, and fast cargo all sharing the same GCNR or NSWR engine. Also considering that developing only one technology to maturity, either of the nuclear engines or M2P2 gizmo, will be a fantastically expensive enterprise, we need to pick ONE and only one method of propulsion. High-energy nuclear engines will most likly work and do not impose limitations on the payload like the still-nebulous M2P2 concepts, so one of them are the natural choice... Room for M2P2 for manned applications? Not really.
I am not dismissing it out of hand, I know of the concept and it is interesting, but I think that it is pretty clear that the performance is quite speculative (magnetic field diameter estimates vary by an order of magnetude?) and the concept overall is still very speculative plus NASA really needs to pick one idea and bring it to maturity rather then a whole gaggle of outlandish ideas where none are really employed to their full potential.
"DM2PS is simple"
No it isn't. Certainly not simpler then a GCNR engine. New magnetic materials will have to be developed, huge coils larger and far more powerful then anything ever before fabricated and somehow deployed (how are you going to get the thing up there?), and I am sure that there are many unknowns about its behavior versus theoretical. Oh no, it will not come cheap either.
"a fleet of chepa one shot M2P2 ships that carry tens of tons would make colonization extremely viable."
No they wouldn't. The whole M2P2 device surely won't be "dirt cheap" to make, and at an incredibly puny 10MT each that really isn't a plausable way to move stuff to Mars. Payloads to Mars will need to really be starting in the 50MT region for colonization.
Further thoughts: my biggest question is though, if the total non-propulsive mass of the vehicle increases in a similar or somewhat slower fashion to its volume, but the magnetic field's area doesn't increase similarly with the diameter of a practical coil array, then it surely won't scale. It won't scale well at all.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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(double post)
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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Perhaps I should add, about the interplanetary passenger transporter I described, that it was not meant to sound like "luxury" accommodations. The volume per passenger--90 cubic meters--I think is the same as the design reference mission. Mars Direct's hab offers about 60 cubic meters per person and half that for the return mission. My reference to an orchesta and a theater company was a reference to the talents of the passengers being organized during their six month voyage to perform in the cafeteria occasionally, not to a professional team on board to provide entertainment!
Regarding the question of the relative cost of chemical versus nuclear propulsion, sometimes scenarios help explore the matter. Let's consider something like this:
1. A 100-tonne interplanetary transit vehicle capable of transporting 100 people from Earth to Mars in six months. The same vehicle, if it could make faster round trips, might be able to transport 150, because the life support system could be lighter and the shorter transit allows a higher passenger density. Let's assume the vehicle costs $1 billion to build (that's half the cost of the shuttle's orbiter). I am not worring about its shape right now.
2. Let's say we have a $1 billion dollar gas core engine capable of twenty reuses, or ten round trips. That gas core engine will cost $100 million per round trip.
3. Let's say the gas core engine can get the 100-tonne ITV to Mars fast enough so that it can make two round trips near Earth-Mars opposition. That kind of quick trip requires a delta-v of about 15 km/sec, with a Mars orbit injection of about the same (total delta-v, 30 km/sec). If we have a specific impulse of 5,000 seconds, the vehicle will need about 100 tonnes of propellant (liquid hydrogen).
4. On the other hand, if the vehicle is pushed to Mars using chemical engines with a delta-v from low earth orbit of 4.3 km/sec and it aerobrakes at the other end, it will need about 150 tonnes of liquid hydrogen and oxygen. I apologize that my wristwatch calculator is broken and my solar-powered calculator with natural log function is also broken, so these are approximate numbers, but they are about right.
5. With the gas-core engine and rapid transport, the ITV can move 300 people to Mars per opposition (two trips, 150 each) as opposed to 100 in the chemical option. This will reduce the cost of the ITV per passenger. If you assume the ITV can be reused over a ten-year period, it will transport 1,000 passengers in the chemical option (at a cost of $1 million each, in terms of equipment) versus 3,000 passengers with the nuclear option and a cost of closer to $300,000 each.
6. But what about the cost of fuel plus engine? Chemical engines will cost maybe $25 million, versus a billion for gas core. Each trip will cost $100 million in terms of the nuclear engine cost, versus $2.5 million for the chemical engine. So the big question is, is the extra fifty tonnes of fuel needed for the chemical engines worth more than $97.5 million (the difference in the costs of the engines), or less? Right now fifty tonnes of fuel cost about $250 million to put in low earth orbit. But if we get reusable shuttles able to launch things into orbit for $1,000 per kilogram, the fifty extra tonnes of fuel would cost $50 million. That's less than $97 million, but one might still want to use the gas-core engine because of the rapid transport, which reduces exposure to solar and cosmic radiation (at the cost of exposure to the gas core engines radiation, of course!).
7. If the gas-core engine is used for more leisurely round trips--say, four months to Mars and a long trip back to Earth--the total delta-v may come down quite a bit, to maybe 10 km/sec. Then the 100-tonne spacecraft might need only 25 tonnes of fuel, versus 150 for the chemical option. But if one can obtain fuel in low Earth orbit for $500 per kilogram--half a million bucks per tonne--the chemical option would still be cheaper ($77.5 million for fuel plus chemical engines, versus $112.5 million for gas core engine plus fuel). The big question is, how expensive will the fuel be? Will lunar or Phobosian fuel change things? Bulk transport of Phobosian water to earth via solar sailer might.
8. All these calculations have made two assumptions that unfairly favor gas core: (1) that the mass of tanks can be ignored (in fact, liquid hydrogen is about five times less dense than the liquid hydrogen/oxygen needed for chemical engines, hence needs heavier tanks); and (2) the mass of the chemical engine and gas core engine can be ignored (the former will mass maybe one tonne at most, whereas the latter will probably mass a lot; 10, 20, 50 tonnes).
9. Safety is a huge unknown. Chemical engines can be restarted reliably, but with aerobraking they don't have to be (assuming we can make aerobraking safe; that's not proved yet). Gas core, however, may not be a reliable propulsion technology for a long time. We would not want a passenger vehicle approaching Mars to discover its engine can't be fired. Aerobraking would not be an option--the decelleration would crush the ship or it would not slow down enough. A vehicle passing Mars at 15 kilometer per second would make a very big orbit before returning to the inner solar system; say, it would fly as far out as Saturn or Uranus, taking three to ten years, then return a ghost ship full of dead bodies whose last days were documented in detail by television cameras. Rescue would be immensely difficult. The alternative--two gas core engines--would double their likely huge expense. Perhaps the best compromise would be to fly two passenger ships with a gas core engine each, and if one engine failed the passengers would transfer to the other ship, possibly transferring some of their ship's propellant as well.
10. The calculation, as we see, has to make A LOT of assumptions about the mass of vehicles, tanks, and engines, their relative costs, their reuse, and the amortization schedule. This renders a precise answer almost impossible at this stage in our technology. Does that sound right?
-- RobS
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Regarding solar sailers:
Thanks to the VERY long travel time (years), whatever payload you are carrying will need shielding to protect it from long-term soak in cosmic & solar radiation, plus probobly protection from the cold too... most sensitive electrons can't handle the cold soak.
The travel times I've heard proposed are 12 to 18 months; about double a hohmann trajectory, and thus not that much worse in terms of cosmic ray exposure. As for cold, it will be a problem with a regular unmanned frieghters as well; couldn't it be handled more or less the same way, i.e., judicious exposure of the cargo pod to sunlight?
It will also be quite complex. Its going to need some serious gyros for attitude control, solar arrays for power, and whatnot that have to last for decades to make a ten-trip design life practical to mitigate development/construction costs. This alone is not going to be easy.
Granted, but this isn't a show stopper; this is an issue of investing in technology and figuring out ways to use light pressure to steer the sails.
And what cargo would you want to send this way anyway? You would obviously want the construction equipment or reactor parts or smelting furnace or whatever rather soon so that you don't slow down colony construction, and this nonsense idea about "just cue your shipments six or seven years in advance" is crazy with respect to actual construction. For use as a bulk (grain, water, ammonia, etc) hauler, we don't need any of those, and in fact we HAVE to avoid them... all - all - bulk materials
If the travel time is less than 18 months, you could use solar sailers to carry construction equipment (possibly minus their electronics and other sensitive parts like fuel cells), lathes, other metal cutting tools, surface vehicles, plastic extrusion equipment, some chemical manufacturing equipment, reactor parts, computers (minus the mother boards; the fans and plastic box could be shipped this way), hospital beds, lab equipment, etc. In short, you'll have to take out some sensitive parts and ship them separately and then assemble things on Mars. If Martian apartments need refrigerators, washing machines, microwaves, etc., it may be cheaper to haul the bulk of the parts from Earth by solar sailer. And I've mentioned luxury goods like barbie dolls, French champagne, and antiques; I doubt the champagne could go by sailer, but the Barbie dolls and antiques could. Sailers might not be practical for a Mars with 100 people, but they will be for a Mars with 10,000. Solar sails could play a major role in hauling heavy industrial equipment to Mars.
The sailers could haul bulk cargos back to Earth, too; gold, platinum group metals, light manufactures (plastic furniture for use at the Low Earth Orbit Hilton?), Phobosian water, Martian nitrogen for use on the moon, Martian argon for ion engine propellant, etc. If Phobos really gets going as a manufacturing center (when Mars itself gets big), solar sailers could be a key transportation option. Items could be transported to earth-moon L1 and stored until purchased either by lunar surface or low earth orbit operations.
-- RobS
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1. A 100-tonne interplanetary transit vehicle capable of transporting 100 people from Earth to Mars in six months. The same vehicle, if it could make faster round trips, might be able to transport 150, because the life support system could be lighter and the shorter transit allows a higher passenger density. Let's assume the vehicle costs $1 billion to build (that's half the cost of the shuttle's orbiter). I am not worring about its shape right now.
2. Let's say we have a $1 billion dollar gas core engine capable of twenty reuses, or ten round trips. That gas core engine will cost $100 million per round trip.
3. Let's say the gas core engine can get the 100-tonne ITV to Mars fast enough so that it can make two round trips near Earth-Mars opposition. That kind of quick trip requires a delta-v of about 15 km/sec, with a Mars orbit injection of about the same (total delta-v, 30 km/sec). If we have a specific impulse of 5,000 seconds, the vehicle will need about 100 tonnes of propellant (liquid hydrogen).
4. On the other hand, if the vehicle is pushed to Mars using chemical engines with a delta-v from low earth orbit of 4.3 km/sec and it aerobrakes at the other end, it will need about 150 tonnes of liquid hydrogen and oxygen. I apologize that my wristwatch calculator is broken and my solar-powered calculator with natural log function is also broken, so these are approximate numbers, but they are about right.
5. With the gas-core engine and rapid transport, the ITV can move 300 people to Mars per opposition (two trips, 150 each) as opposed to 100 in the chemical option. This will reduce the cost of the ITV per passenger. If you assume the ITV can be reused over a ten-year period, it will transport 1,000 passengers in the chemical option (at a cost of $1 million each, in terms of equipment) versus 3,000 passengers with the nuclear option and a cost of closer to $300,000 each.
6. But what about the cost of fuel plus engine? Chemical engines will cost maybe $25 million, versus a billion for gas core. Each trip will cost $100 million in terms of the nuclear engine cost, versus $2.5 million for the chemical engine. So the big question is, is the extra fifty tonnes of fuel needed for the chemical engines worth more than $97.5 million (the difference in the costs of the engines), or less? Right now fifty tonnes of fuel cost about $250 million to put in low earth orbit. But if we get reusable shuttles able to launch things into orbit for $1,000 per kilogram, the fifty extra tonnes of fuel would cost $50 million. That's less than $97 million, but one might still want to use the gas-core engine because of the rapid transport, which reduces exposure to solar and cosmic radiation (at the cost of exposure to the gas core engines radiation, of course!).
7. If the gas-core engine is used for more leisurely round trips--say, four months to Mars and a long trip back to Earth--the total delta-v may come down quite a bit, to maybe 10 km/sec. Then the 100-tonne spacecraft might need only 25 tonnes of fuel, versus 150 for the chemical option. But if one can obtain fuel in low Earth orbit for $500 per kilogram--half a million bucks per tonne--the chemical option would still be cheaper ($77.5 million for fuel plus chemical engines, versus $112.5 million for gas core engine plus fuel). The big question is, how expensive will the fuel be? Will lunar or Phobosian fuel change things? Bulk transport of Phobosian water to earth via solar sailer might.
8. All these calculations have made two assumptions that unfairly favor gas core: (1) that the mass of tanks can be ignored (in fact, liquid hydrogen is about five times less dense than the liquid hydrogen/oxygen needed for chemical engines, hence needs heavier tanks); and (2) the mass of the chemical engine and gas core engine can be ignored (the former will mass maybe one tonne at most, whereas the latter will probably mass a lot; 10, 20, 50 tonnes).
9. Safety is a huge unknown. Chemical engines can be restarted reliably, but with aerobraking they don't have to be (assuming we can make aerobraking safe; that's not proved yet). Gas core, however, may not be a reliable propulsion technology for a long time. We would not want a passenger vehicle approaching Mars to discover its engine can't be fired. Aerobraking would not be an option--the decelleration would crush the ship or it would not slow down enough. A vehicle passing Mars at 15 kilometer per second would make a very big orbit before returning to the inner solar system; say, it would fly as far out as Saturn or Uranus, taking three to ten years, then return a ghost ship full of dead bodies whose last days were documented in detail by television cameras. Rescue would be immensely difficult. The alternative--two gas core engines--would double their likely huge expense. Perhaps the best compromise would be to fly two passenger ships with a gas core engine each, and if one engine failed the passengers would transfer to the other ship, possibly transferring some of their ship's propellant as well.
Does that sound right?
-- RobS
No, no it doesn't sound right. A billion dollars to build a single copy of a GCNR engine is absurd! It hardly costs that much money to build an entire nuclear submarine for goodness sakes! You just came up with that number as a slant to make chemical look good.
A GCNR engine is not infinitely more complex then, say, the SSME: at its heart, it is not that far removed from it, it still uses a regenerative turbopump to push Hydrogen into the core, which will have no internal moving parts being only a carefully shaped metal vessel lined with heat-resisting/reflecting material, and injectors for UF6 gas. Its not a huge engineering nightmare, and the only big hurdles are what to build it out of. The Russians even contemplated building a lower performance one in the 70's with current day materials and without CFD technology.
Each copy of the SSME (or a gaggle of RL-60's) costs about $40M (plus weighs eight tonnes) and something like it to push a large vehicle for the desired number of sorties would probobly have a similar cost. A GCNR engine will not have radically higher complexity, as the engine itself is pretty simple once you get the materials and development done with, I can't imagine that it would cost more then like ~$200M a copy.
If the engine is developed properly, like just as well or better then SSME, then it should be quite safe since the engine is fairly simple. The sucessor to the SSME is going to have reliability on the order of >99.99%, which should be more then sufficent to prevent the engine from being much of a risk compared to other systems failing. The solution to the issue about breaking burn failing is pretty simple: have a rescue ship in a storage orbit in the unlikly event it would ever be needed, outfitted without creature comforts in favor of extra delta... there will be an awful lot of these ships, one spare won't be a big deal. Certainly better then relying on the firey plunge working with near-perfect precision every time. No self-correcting aerodynamics to help out here... And if you have trouble? GCNR-equipped ships would have the ability to abort, a chemical ship wouldn't.
You come up with a really big number for GCNR engine production, but assume really low operating costs of an asteroid water mine. I think that its very likly that it would be extremely difficult to produce tonne quantities of propellant on an asteroid, and that will destroy the economics of the proposition. Practical drills just aren't going to be coming up with tonne quantities of water from these rocks because there isn't that much water in the volume of the drill shafts... which you will be unable to make many of without gravity and if you have to line each one of them.
And what happens to the surface stability of a rocky asteorid, barely held together by its gravity, when you start turning it into swiss cheese?... The fuel (not oxidizer) required to launch Lunar propellant is also a huge cost problem. And shipping it to Earth via solar sail? Nonsense, the boiloff problem and rendezvous would be show-stoppers.
Then there are the non-tangible bennefits, like not having to subject your crew to lengthy trips. Six months is near the limit of human mental endurance for average people with signifigant training... for colonists, you get a nice shorter trip with GCNR which just isn't happening with chemical engines.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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RobS has hit on most of my points, so I'll just elaborate.
#1. Travel time limiting cargo choices for solar sails.
I don't see why this should be true. While a person probably isn't going to be to happy sitting in space for 16 months+ a bulldozer isn't going to care. I don't see why the duration of the trip would prevent Mars colonisation plans either. It isn't unheard of or even unusual for a buisness (esp. one involving some sort of heavy industry) to wait such a length of time for some new process or peice of machinery to come online.
The development times for new peices of equipment are still likely to be as long or longer than even the solar sail transit times. So you realy aren't able to avoid these sorts of issues. So you better have figured out when you are going to need some new peice of equipment much earlier than 6 months before hand. Not to mention their construction and the construction of the launch and transit vehicle. All space programs are going to involve alot of planning of when we are going to need new equipment/supplys and coping with the plans when/if these needs can't be met. Planning out years in advance is not a silly as it might appear. In any case these issues are only going to get worse as we go farther out, so we might as well learn to deal with them now.
And since solar sails are the only option that allows year round launching without a payload penalty use of a solar sails could mean cargo delivery happening all year round instead of bunched up at once.
#2. Radiation/cold/vacume limiting cargo choices for solar sails.
I also don't see why this is true. The extension of transit time from ~6 months to over a year doesn't realy change the dangers the cargo faces. Electronics may require some protection from the cold and radition, but they are going to have to be hardened to face such hazards on Mars as well. It isn't going to make much diffrence to the majority to the mass of any cargo. As RobS pointed out it's going to be just as cold for the cargo on a 6 month transit as it is for a longer one.
Radiation exposure is greater, but I always understood this to be an issue of magnitude of exposure, not duration. Either the radiation is strong enough to fry the chip, or it isn't. In this case a longer mission runs an increased risk of exposure to solar flares, but no more so to background radiation. Even if the hardened electronics are vunerable, some shielding and proper packing (ie putting the vunerable parts in the middle) should help eliminate this issue.
#3. Solar sails being tricky to design.
No doubt their are some serious challanges in designing a solar sail, much less one intended for re-use. But of course challanges exists in designing ANY interplanetary vessel, especialy one for re-use. However the problems a solar sail vehicle faces apear to be much simpler than those faced by virtualy any other propulsion technology, especialy those reliant upon nuclear power.
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GCRN, I was wondering if you had read this paper http://www.lascruces.com/~mrpbar/staifpaper.html] here: it lists delta-V requirments for a conjuction class fast mission at ~25Km/s one way when you include the breaking requirments. This sort of mission has a mass fraction of 20% about double that of a tradional hohmann chemicaly fueld transit. Very good, but if that same 3000 isp engine was used on a more conventional mission the mass fraction might be over 90%!
He who refuses to do arithmetic is doomed to talk nonsense.
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I think that short 18mo figure for a solar sail is being really optimistic for a practical payload, these things have always been talked about for light-weight things like probes and such, not 50-100-200+ tonnes of cargo. I doubt that anything less then three or four years is actually practical.
Slowing down base construction to wait for several years (time needed to build, integrate, and launch/land too) between when an item is specifically orderd and the time that it arrives is way way too long, that faster transit is absolutely nessesarry because it is too hard to plan base items that far in advance. And even if you could, the cost bennefit of solar sailing versus the severe inefficency of such long lead times will never be worth it given the impact and cost of delayed construction.
"It looks like our greenhouses will need more heat then we estimated, so we'll need another reactor - oops! we can't have one for another four years if we order it tomorrow from Earth though, guess we'll be eating canned rations for a few years longer, I hope we have enough to last before the next batch arrives by sail two years from now." Or "our bulldozer for buyring HABs is stuck, so we will need a crane to get it loose, guess we better order a crane from Earth so we can get started building again in a few years."
You get the picture... even a one-year lead time (construction, packaging, transit, landing) for a regular six month transit during the best departure times with chemical engines isn't good enough. We aren't going to know precisely what and when we will need most things until we are actually there, in which case waiting for half a decade for it to arrive is right out.
"this is an issue of investing in technology and figuring out ways to use light pressure to steer the sails"
$$$... and all that cost to develop the solar sail will be in addition to the "faster" means (chemical?) of getting to Mars to haul passengers and sensitive goods.
Phobos is NEVER going to be a manufacturing center of any sort, because gravity is absolutely nessesarry to simplify operations. Doing anything in zero-g on any scale is too hard, and notions contrary are ignoring the reality of this situation.
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"And since solar sails are the only option that allows year round launching without a payload penalty use of a solar sails could mean cargo delivery happening all year round instead of bunched up at once. "
Irrelivent, because depending on the location of Earth and Mars, the total time between launch from Earth's surface to Mars orbit varies widely. So what if a payload ship needs to park in orbit for a few months? It will take alot less time to transit.
A GCNR engine is actually far, far superior in this respect, because it has such high performance that it can leave at almost any time during the two-year window cycles without too big a fuel penalty... Say a GCNR ship needs a massive 70km/sec Delta-V for such a mission... with a 5,000sec Isp (50km/sec exhaust velocity) you are still talking about having a ~20-25% dry mass fraction. Or suppose a 3,000sec engine with a 60km/sec round trip, thats still a 13% fraction. Or a nice liesurely 15km/sec Hohmann trajectory at 5,000sec would give you a 75% fraction.
High Isp propulsion makes all the difference, I think that you underestimate just how powerful it is... With a 5,000sec Isp engine, we could be talking about missions to Jupiter for the same difficulty today of just getting to Mars.
(delta-V (km/s) = exhaust velocity (km/s) x Ln(wet mass/dry mass) )
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I am surprised and relieved you don't think gas core engines will be that expensive. I was surprised you described them as "simple" though, considering we don't know how to build them. (Admittedly, you used the term only once). I quite agree that gas core is the way to go for Jupiter and beyond; the ONLY reasonable way to send humans to those worlds (and I am sure we will send people to the Jupiter and Saturn systems, probably in this century).
Regarding solar sailers, the travel time will be a function of their size and that will be a function of investment in technology (assuming the technology will work, of course; we still haven't demonstrated that). You need about a square kilometer of sail to send five tonnes to Mars in one year, and that five tonnes is the mass of EVERYTHING, sail and gyros included. If you want to send twenty tonnes of CARGO, that may very well require ten or more tonnes of sail, and the resulting vessel will have a six square kilometer sail. That's a pretty big vessel. At the earth's distance, a one square kilometer sail experiences a "push" from sunlight of nine newtons (about 2 pounds). The delta-v from low Earth orbit to Mars is 14 km/sec. But very thin sails can mass less than a tonne per square kilometer, maybe much less. So I wouldn't rule out this technology, but it strikes me as something for the latter part of this century. I am not as pessimistic as you about the time delay because it is common now to plan Mars missions five years in advance. There will be big objects and manufacturing system parts that can sail to Mars at a leisurely pace. But there will certainly be a need for fast cargo (6-9 months) and even very fast cargo (1-2 months; chemotherapy drugs). It isn't a question of ridiculing solar sails as next to useless, but evaluating when it might be useful. That will also be a function of the cost of competing transportation systems, which we can't predict very well right now.
-- RobS
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I am surprised and relieved you don't think gas core engines will be that expensive. I was surprised you described them as "simple" though, considering we don't know how to build them. (Admittedly, you used the term only once). I quite agree that gas core is the way to go for Jupiter and beyond; the ONLY reasonable way to send humans to those worlds (and I am sure we will send people to the Jupiter and Saturn systems, probably in this century).
Regarding solar sailers, the travel time will be a function of their size and that will be a function of investment in technology (assuming the technology will work, of course; we still haven't demonstrated that). You need about a square kilometer of sail to send five tonnes to Mars in one year, and that five tonnes is the mass of EVERYTHING, sail and gyros included. If you want to send twenty tonnes of CARGO, that may very well require ten or more tonnes of sail, and the resulting vessel will have a six square kilometer sail. That's a pretty big vessel. At the earth's distance, a one square kilometer sail experiences a "push" from sunlight of nine newtons (about 2 pounds). The delta-v from low Earth orbit to Mars is 14 km/sec. But very thin sails can mass less than a tonne per square kilometer, maybe much less. So I wouldn't rule out this technology, but it strikes me as something for the latter part of this century. I am not as pessimistic as you about the time delay because it is common now to plan Mars missions five years in advance. There will be big objects and manufacturing system parts that can sail to Mars at a leisurely pace. But there will certainly be a need for fast cargo (6-9 months) and even very fast cargo (1-2 months; chemotherapy drugs). It isn't a question of ridiculing solar sails as next to useless, but evaluating when it might be useful. That will also be a function of the cost of competing transportation systems, which we can't predict very well right now.
-- RobS
6 ton's of sail to get 1 tone to mars, that is only about the same mass fraction as chemical propulsion except the kilometre square solar sail would be much more complex and therefore much more expensive.
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Not six tonnes of sail per tonne of cargo; more likely 1 tonne or 1.5 tonnes of sail per square kilometer, the rest of the mass (3 or 3.5 tonnes) being cargo. If we can ever make sails in space, they can be even thinner, too (you can't launch really thin sails because electrostatic forces can make them cling together and you can't unfurl them).
The mass fraction comparison is not useful because the sail will carry cargo over and over, with no new material needed. They should be inherently cheap vehicles from the point of view of the sails, which are basically aluminized garbage bag material (well, thinner than a garbage bag). Adding gyros and solar arrays for power will add to the cost (would on a rocket, too).
-- RobS
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Not six tonnes of sail per tonne of cargo; more likely 1 tonne or 1.5 tonnes of sail per square kilometer, the rest of the mass (3 or 3.5 tonnes) being cargo. If we can ever make sails in space, they can be even thinner, too (you can't launch really thin sails because electrostatic forces can make them cling together and you can't unfurl them).
The mass fraction comparison is not useful because the sail will carry cargo over and over, with no new material needed. They should be inherently cheap vehicles from the point of view of the sails, which are basically aluminized garbage bag material (well, thinner than a garbage bag). Adding gyros and solar arrays for power will add to the cost (would on a rocket, too).
-- RobS
Sorry I got your mass fraction numbers wrong. Anyway the mass fraction is a perfectly valid way to compare vehicles to chemical rockets provided you consider the time value of money. I further discuss this here (need to do some editing though)
http://www.newmars.com/forums/viewtopic … 7679#77679
I conclude that a sail that can make the round trip in 2 years and does not degrade in value is 3 times as valuable as a non reusable vehicle that can deliver the same mass fraction. A reduction of the cost of cargo delivery by three times is nothing to laugh at but I don't know if it is paradigm shifting. If the mass of the solar sail is around the mass of the cargo, you suggested it would be 1.5 times the mass of the cargo and can be built for the same cost as a chemical rocket that can deliverer the same payload, this will give about a 15 times reduction in the cost of shipping cargo from to mars. While it is too slow for human travel, in terms of one way mars mission this means that if similar cost reductions could be made in getting mass to LEO you could support a science base 15 times as big for the same price. Thus you science base of 12 becomes a science base of 180. I can only begin to image the work that 180 people can accomplish living and working on the Martian surface.
Now less optimistic is if no cost savings are made on getting stuff to LEO, the cost of shipping it from earth to mars is about 4/5ths of the total cost. So the new cost is (1/5+4/5*(1/15))=19/5/15=0.253. So a solar sale would reduce the total cost of shipping stuff to mars from earth by 75% and the base of 12 becomes a base of 48 which is quite a bit bigger the small crew imagined by mars direct.
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They wont go with Solar Sails. It will be with Reusable Nulear Propulsion Tugs (Fully Automated) They will dock with what is essentialy a space station of Mars Habitat landers every two years and push the two hundred thousand passengers out to Mars for their colonization wave.
It leaves in Mars orbit a torus of nodes (a kind of spacewheel) which are then anchored to a Martian Moon for Use as a Framework of Industrialization.
Lander Habs descend to Mars en mass.
The Tug returns for the next two hundred thousand passengers and does the same to them.
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They wont go with Solar Sails. It will be with Reusable Nulear Propulsion Tugs (Fully Automated) They will dock with what is essentialy a space station of Mars Habitat landers every two years and push the two hundred thousand passengers out to Mars for their colonization wave.
It leaves in Mars orbit a torus of nodes (a kind of spacewheel) which are then anchored to a Martian Moon for Use as a Framework of Industrialization.
Lander Habs descend to Mars en mass.
The Tug returns for the next two hundred thousand passengers and does the same to them.
Who is they?
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I dont know John, Who do you think "They" are? I was speaking broadly about a general group...Based on What China Said about Space being the Commonwealth of the human race, I think it will be Space Commonwealth.
Space Commonwealth:1 Corporate Space Warlords:0
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Why spend a foirtune to ship them there? I can't imagine any cheaper way to populate mars than to grow your own colonists.
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Of course Tholzel,
Send ten million people to Mars, let them have children and reach the billion humans capacity of a Terraformed Mars in their own time. Considering population quotas representative of the many earth nations, 1/24 colonists will be from the USA, 4/24 from China, 4/24 from India...Less than five hundred thousand US citizens will ever get to be Mars Colonists. Its going to be unpopular, but it gets an equal spread of earthlings.
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I think you are not looking at the colonization and cost of colonization in the correct framework. The colonization of other planetary ( both natural and artifical bodies ) means the growth for the human race and the expansion of knowledge, and understanding at a scientific and social aspects.
The costs must be worked on the benefits returned in all forms to the human race. The assets needed to move large volumes of people into space and sustain them in these places will be large, but it will move the human race forward to a closer society and moving the human race to the next level of social evolution.
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On the contrary Martin_tristar,
Every thing we do in space must be based solely on its ability to support human life. The Ability of Mars to support human life is defined by its absolute cost. That is 20 Billion per person x 1 Billion people = 20 Billion-Billion dollars.
It is a price that must be paid by the nation that it will become.
I simply reached a conclusion that a Space Commonwealth (an entirely new and independent nation whose territories expand ever outwards) would be best because it can begin as a nation from the very first colonist. More importantly, it can confine the Human problem to earth.
It requires an across the board selection of humans for genetic stock. People who will be educated and trained at it's expense in Astronautics, and Colonization. People who will rightfully be the Citizens of a new civilization and not just the self serving representatives of the old civilization.
The economy of it is established. A nation of near infinite wealth, recruiting citizens who unlike the rest of the world, will be working for an equal share of the resources.
It requires tool up of space industry capacity to a hundred thousand times its current level of industry.
This must support the movement of a hundred thousand a year to the Moon freely as citizens of the Space Commonwealth (contracted to provide free movement of tourists and lunar industries moving to the Moon). Ultimately a ten million-billion dollar contract to provide human movement to the Moon for a hundred years.
It gives the private sector of earth an opportunity to grow beyond what it will ever achieve, brings social and economic benifits to the Earth.
This will shift the profit from "Suborbital space providers" to Companies interested in Lunar and Lunar Space Tourism. The Space Commonwealth will pay to put it on the Moon, That will ensure that even the smallest business opportunity (whether it is either a brick making machine for dome shielding or a guy renting out lunar space suits for a few hours on the surface) is open to expansion. The Space Commonwealth will make it so freely available to the individual because even space tourism is going to be of benifit to its economy. There is nothing like brainwashing tourists to sign on as citizens. Do you think the Virgin group would support Sub orbital tourism when can offer around the moon racing to tourists or six months on a space station in space.
It requires a city on the moon with a population support capacity of one million people and the industry to employ them whether space industries or tourism at a cost of 20 million-billion dollars. Non Citizens will never go beyond the Moon.
Somewhere this leads to going to Mars and constructing real space settlements for Space Commonwealth Citizens alone. Only by leaving behind the past can you move forward.
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Old article but this should cleat up some rumors about the Trillion number
Note that according to Recer, the trillion-dollar figure is only for a single Mars expedition, not for both the Moon and Mars, which the UPI story stated were part of the new plan.
http://www.thespacereview.com/article/119/1
Recer stated that he had gotten the information from “industry sources and people I talked to.” He said that none of the information was provided by government sources. He said that his sources told him that in 1989 Congress—not NASA—had produced an estimate of $400-$500 billion for a mission to Mars as proposed by President George H.W. Bush. Recer had adjusted for inflation, which would have produced a range of $640-$800 billion. He had then rounded up by at least $200 billion to produce the estimate of “nearly $1 trillion.”
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Yep, a nice example of the power of the media to defame, distort and destroy whoever and whatever they choose, without any responsibility.
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