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#776 Re: Science, Technology, and Astronomy » Drill to crack earth’s crust » 2005-10-16 04:02:32
A Japanese drilling ship is targeting a depth of 6 miles. It will take them 12 months to go that deep. They hope to recover a sample of the mantel (the layer beneath the crust) by 2012. They also hope to find extremophiles living in temperatures over 500 F.
#777 Re: Science, Technology, and Astronomy » Stanford robotic SUV finishes $2 million race » 2005-10-16 03:50:09
Okay then, how long do you think before the first truck driver's strike demanding a ban on 18-wheeled robots?
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#778 Re: Civilization and Culture » A fully developed, mature, and sovereign Mars » 2005-10-16 03:37:31
Please add to, or comment on any of these subjects. ^_^
Wow, a thousand years post-terraforming - my crystal ball gets a little hazy that far out. By that time, every gravity well has its space elevators, but one of the things that space elevators do is make it easier to build biospheres at places like L5. Mars is of course, crucial in the "short" term, but I wonder if, in the long run, living at the top of a gravity well doesn't beat living at the bottom?
At L5, you've got no-cost access to minimum energy orbits to any solar system location, asteroids and comets can be delivered to your doorstep with their own volatiles, and kilometer-scale disks of solar cells and parabolic mirrors with minimal supporting structures provide you with no-fuel EM and thermal energy clear through a billion terrawatts.
In addition, as technology improves, any individual biosphere - including Earth's or Mars' - is vulnerable to destruction by smaller and smaller groups of angry people. Unless we reach a point where noone ever has reason to be angry again, multiple independent biospheres may just be flat-out safer.
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#779 Re: Human missions » Lunar Carbon? » 2005-10-16 00:56:41
How much energy does it take to heat 1 kg of dirt to 1700 K?
The AASM puts the specific heat of luna regolith at 840 J/kg, so that is something like 0.4 kWh/kg for dry roasting to 1700 K. They say that wet processes for extraction (i.e., heavy duty acids) require a lot less energy.
tSpace says 26 kWh/ton to mine lunar ice. You only need to heat the regolith to 150 K in vacuum to get the water ...
http://www.exploration.nasa.gov/documen … tSpace.pdf
The presentation above also includes a survey-backed forecast of a multi-billion dollar space tourism industry by 2025.
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#780 Re: Human missions » Lunar Carbon? » 2005-10-15 22:35:51
Extraction of volatiles. Lunar soil heated to 1300 K releases 0.1% by weight of the following trapped volatiles: CO, CO2, N2, H2, H2O, SO2, H2S, CH4, and inert gases (He, Ar, Ne, Kr, Xe). As much as 0.5-1.5% by weight may be released upon heating to 1700 K (Phinney et al., 1977).
This is from NASA's 1980 Advanced Automation for Space Missions study, which proposes self-replicating robot factories for Luna development.
#781 Re: Science, Technology, and Astronomy » cost of space elevator » 2005-10-13 21:07:53
A magnficient concept very poorly defended up to now, IMHO...
There is certainly lots of opportunity for invention before launch day
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#782 Re: Human missions » The Moon - A great place to build space ships » 2005-10-13 16:25:17
Proton is $1000 per pound to LEO today.
Which is $10000/lb to GEO, which is at least $30000/lb to lunar surface? Even then I'm giving you the next 5 years of tech. What estimates have you seen for reaching the lunar surface?
Besides, how do you supply power to that machine?
I like the Sterling engine idea.
#783 Re: Science, Technology, and Astronomy » Stanford robotic SUV finishes $2 million race » 2005-10-13 15:09:11
How long do you think before these things are street legal?
#784 Re: Human missions » No immune system....oh crap! » 2005-10-12 17:08:32
Well... I think that settles it. Some kind of artifical gravity system is an absolute nessesity if this can't be fixed with drugs.
They'd be some interesting drugs.
Why is there resistance to artificial gravity anyway? Just because it is another thing that can go wrong? Or does it make lots of things more difficult?
Are they sure that the immune system doesn't perk back up after exposure?
Everything I've read said that the only long term effect of low gravity was bone loss, which takes lots of work to reverse.
#785 Re: Science, Technology, and Astronomy » cost of space elevator » 2005-10-12 15:40:56
So, its mean that the space elevator isn't geostationnary, such as the SE earth station should be mobile
and abble to fly over mountains
I think you're joking, but just in case - no, it means that geostationary orbit for point masses is different from geostationary orbit for 35000km long cables. The strength of gravity varies over the length of the orbiting cable - this is something weird and new that you have to take into account.
A nuclear reactor ? That isn't simple nuke powered batteries.
Do you know how heavy is a "nuclear reactor" ? Is it included in the costs prevision ?
If it is necessary, I can't imagine it would be a show stopper. Maybe it could be something along these lines ...
#786 Re: Human missions » The Moon - A great place to build space ships » 2005-10-12 14:43:27
I am wondering if the samples which were at the temp to freeze Hydrogen and other gasses were part of the escape of it to the crews habitat or LM as the temperatures rose. Thus making it hard to find any.
I think orbiters can detect hydrogen in the soil. In fact, here is one of the images that make people think there is ice in enshadowed craters ...
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http://nssdc.gsfc.nasa.gov/planetary/ice/ice_moon.html
Hmmm, 6 billion tons with soil concentrations of up to 1%. That isn't too bad.
#787 Re: Human missions » The Moon - A great place to build space ships » 2005-10-12 14:32:26
I assert it will be far cheaper to import methane and extract LOX than dig water out of cold traps and crack into H2 & O2 (let alone process out the impurities)
At $30000/lb? If I can send a 2 ton machine that can extract 1000 tons of water, I've got a pretty big win.
Is the existence of lunar ice confirmed? I thought there was still some controversy.
#788 Re: Human missions » The Moon - A great place to build space ships » 2005-10-12 14:19:28
I believe a good solar alternative would be Stirling cycle engines that use supercritical CO2 as the working fluid (Argonne Nat'l Lab has done some work on supercrit CO2 turbines); deploys the "cold end" of the Stirling cycle engine in shaded regolith; and the "hot end" at the focal point of multiple inflatable mirrors.
This sounds like a great idea! My only concern would be the in-situ manufacture of Sterling engines. I know they can theoretically be of any size, but the ones I've seen are huge and complex machines. I wonder how simple they can be in practice?
#789 Re: Human missions » The Moon - A great place to build space ships » 2005-10-12 14:13:42
If there are going to be vast quantities of solar cells built, it would be awfully hard to import large quantities of dopant economically
You can use phosphorus for n-doping and aluminium for p-doping. Boron is usual for p-doping, but like you say it would be a hassle to have to import it. The vapor deposition process needs hydrogen, which would have to be imported. But only Si and Al would get used in great quantities, and there is plenty of both of those.
#790 Re: Martian Politics and Economy » Concern about the Government.Will they allow black to go » 2005-10-12 13:56:02
interpersonal relations of the crew, missing home and loved ones, conflict between the crew, dealing with stress issues
These people are going to be adventurers. The sort of people who answered Shackleton's ad:
"MEN WANTED FOR HAZARDOUS JOURNEY. SMALL WAGES, BITTER COLD, LONG
MONTHS OF COMPLETE DARKNESS, CONSTANT DANGER, SAFE RETURN DOUBTFUL.
HONOUR AND RECOGNITION IN CASE OF SUCCESS."
What drives such people crazy is exactly the mundane domesticity that others find so appealing. For them, the adventure is liberation.
#791 Re: Human missions » The Moon - A great place to build space ships » 2005-10-12 06:23:33
Try searching the page for the word "dopant"
#792 Re: Science, Technology, and Astronomy » cost of space elevator » 2005-10-12 03:15:08
Lets say 92000km ?
Oh I see what you want. Maybe this will put your mind at rest ...
http://www.mit.edu/people/gassend/space … r-of-mass/
The main thing being that you can't treat the space elevator as a point mass like normal satellites, so you have to take into account the gravity field - which varies by a factor of 300 over the length of the cable. The lower portion counts for much more than you might think.
Either an object is in balance at geo, then if you pull it with a traction motion, you disbalance it, or there is a traction force opposite to your traction to keep the balance, that's physical basic law, sir
Yes but you and I are also subject to lunar forces - magnitude matters. You're right - there is going to have to be active adjustment of the orbit. The question is the order of magnitude. Basically the question comes down to: can I use solar power, or do I have to put a nuclear reactor at GEO?
#793 Re: Human missions » The Moon - A great place to build space ships » 2005-10-11 21:54:32
here a web site you might be interested in.
Wow, thanks. It'll take me a while to go through that.
I also found this 1989 paper by Landis that takes about Lunar solar cell production ...
http://www.asi.org/adb/02/08/solar-cell-production.html
And it looks like you can make the process much simpler. These guys use only Si and Al, and their process is mostly automated ...
#794 Re: Science, Technology, and Astronomy » cost of space elevator » 2005-10-11 18:29:08
I see though, that Steindl and Troger have called the no-counterweight version of the elevator (they use the term sky hook) into question in a recent (2005) paper. Let me read their paper and I'll get back to you.
So it looks like you need some sort of counterweight at GEO just from a stability point of view. Interestingly, lighter cables need larger counterweights for this issue. However, for a 65 GPa cable, Steindl calculates a minimum 6000 kg counterweight - which isn't going to be a problem - we're not even talking asteroid. Papers addressing other orbital stability problems (like the ones caused by the Moon and the Sun) are also referenced.
Looks like a cable that goes further than GEO still needs more study though.
#795 Re: Science, Technology, and Astronomy » cost of space elevator » 2005-10-11 16:16:40
They say that a terminal counterweigh is tighted to SE terminal.
In your opinion, which is its orbital speed so that it would be in a straight line with the SE main station on Geo orbit ?
I guess that depends on how far the counterweight is from GEO?
I see though, that Steindl and Troger have called the no-counterweight version of the elevator (they use the term sky hook) into question in a recent (2005) paper. Let me read their paper and I'll get back to you.
#796 Re: Human missions » The Moon - A great place to build space ships » 2005-10-11 15:29:38
We can make solar cells reasonably easily from the common materials found on the Moon
Do you know of a detailed proposal for actually doing this? The solar cell manufacturing process seems fairly complex.
#797 Re: Science, Technology, and Astronomy » cost of space elevator » 2005-10-11 04:35:36
Carbon nanotubes can behave as semi conductor or metal, depending on their structure, and conductivity can be doped.
But still not a superconductor. Even if you can drop the resistivity to that of copper, you're losing 500 MW to provide 2 MW to the climber. The adaptive optics guys say they can get 3% efficiency to GEO, so to beat them you're going to need a resistivity 1/10th that of copper, with no added weight from the doping or no loss in effective strength. Good luck.
For Cnanotubes elasticity, Cnanotubes are much stronger than steel wires, but if traction force reaches to a high value, instead of breaking out, C nanotubes will behave elastically, inducing strong oscillations in the space elevator. Altitude oscillations also mean orbital speed variations
I hope you realise consequences for a space elevator to have an orbital period slightly different from geostationnary. Earth Spacelift Station will have to let ribbons free in order to avoid any Space Elevator start rolling up around the globe.
I scanned a half dozen papers on oscillations. As long as your length is not some integer multiple of the lunar or solar resonance periods, the oscillations are "tame." There are worries about the climbers inducing longitudinal oscillations, so that needs looking into, and twisting oscillations are harder to model. You're right, some active damping will be required, but it doesn't look like a show stopper. GEO is pretty stable.
#798 Re: Terraformation » Venus Terraforamation - Can we colonize the death furnace? » 2005-10-11 01:26:39
Floating cities with limitless thermal energy. Almost perfect. Now I just need wings 8)
#799 Re: Science, Technology, and Astronomy » cost of space elevator » 2005-10-10 17:45:55
http://www.pa.msu.edu/cmp/csc/ntproperties/ Then go to electrical properties
Later, Phaedon Avouris [12] suggested that stable current densities of nanotubes could be pushed as high as 10000000000000 A/cm2.
At http://www.pa.msu.edu/cmp/csc/ntpropert … facts.html it says its resistivity is 10e-4 ohm-cm. Not bad, but the resistivity of copper is 1/50th of that. It is a little higher than that of stainless steel. Transmission losses would kill your efficiency (you'd lose a MW per km at 100 amps) and heat the cable to 1000 degrees. Perhaps those laser power guys aren't such morons after all?
#800 Re: Science, Technology, and Astronomy » cost of space elevator » 2005-10-10 13:58:38
Space elevator terminal is summited to Eath-Moon tidal forces twisting the cables or ribbons which are flexibles and tends to exchange energy with Earth and Moon so that its position must be maintained by permanent energy supply by motors.
The ribbon is under a lot of tension - it isn't going to be bouncing around. There was some worry that tidal resonances could cause destructive failure, but I thought a study showed it wasn't going to be a problem. You still need some active damping for sub-harmonics, but I think they can be solar powered - not free, but minor in comparison to the total cost.
Laser beam energy supply to propell loads is a fantasy. When you know the % of laser energy conversion output, you realize that using doped carbon ribbons in order to make good electricity conductors is much more a cleaver option to supply energy to lift loads.
The ribbon is going to be between 35000 km and 100000 km long. Wouldn't it have to be a superconductor as well as the world's strongest material? I think you are asking a lot.