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A new use for the ISS
Stu
post Jul 12 2008, 10:25 PM
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I know there's about as much chance of this happening as there is of Keira Knightley ringing me up and asking me to show her the stars on the next clear night, but what a wonderful, wonderful idea...

Moving the ISS


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jmjawors
post Jul 12 2008, 10:40 PM
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Hrm. Wow. I only made it through about half of that. He's fudging somewhat to get us to the conclusion that he has clearly reached (nothing more to learn in LEO) and that it would be "fairly easy" to retrofit it for interplanetary (!!!) travel.

It is an interesting idea, but I suspect that any engineers that read and post here would punch a million practical holes in it.

But aside from the engineering, I disagree with the premise that we have figured out how to combat the effects of weightlessness. He doesn't even mention radiation (unless he does on page 2... didn't get there). I also disagree that that is the ISS's sole function anyway, at least as it is ultimately envisioned. There's plenty of work to be done up there with materials and bio-medical science that benefit not just astronauts but the rest of us down here. We just have to get it up to that 6 person crew (next year).


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djellison
post Jul 12 2008, 11:07 PM
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"There are good answers to all these objections."

There are not.

"How likely is any of this to happen? Not very"

Thank god.

He doesn't understand one iota of the challenges involved.

419,000 kg when finished

Let's guess a conventional ( rather than months-in-the-van-allen-belts ion ) ISP - 390s

http://www.strout.net/info/science/delta-v/intro.html suggests 4.1km/sec required

You would need something like 16,000,000,000 kg of fuel. 16 MILLION tons.

A fully laden Saturn V rocket on the pad carried 2,708 tons of fuel. It had a max payload of 118 tons.

Let's go optimistic - lets say it's a 1600 ISP Ion engine.

The requirement then is just 5,000 tons. 42 Saturn V launched laden with Xenon.

Someone please check the numbers on that - they may well be orders of magnitude off - but they do, to me at least, seem to be in the right sort of 'bloody stupid idea' ball park.

The phrase ' hand waving over the details ' has never been more appropriate


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nprev
post Jul 12 2008, 11:07 PM
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Well, one hole to punch, anyhow (although I like the idea, too!) tongue.gif I guess that you could fly the ISS to the Moon pretty easily but not rapidly with an ion engine, and to Mars with much more difficulty from a logistics standpoint. I'm concerned about the crew's radiation exposure in either scenario, though. Right now, it's below the Van Allen belts and relatively protected. We'd need to add a pretty heavy radiation shelter for solar flares at the very least, and not at all sure how rad-hardened the rest of the station systems are for such events.

Another concern is how many of the extant station experiments are designed to examine the LEO environment for commercial applications? (Kibo springs to mind.) Going outside of the Van Allen regions would invalidate such results, and presumably tick off the investigators.

Other than that...Putting it around the Moon might be a good idea. It could serve as a gateway, a transfer point from an Orion transfer vehicle to a hopefully reusable ISS-to-ground shuttle (using LOX produced in situ at a base site). Sounds cost-effective to me, if practical: more hardware reuse, less overall boost mass from Earth to the Moon. Plus, of course, the right instruments could provide an extremely detailed survey of the Moon at any wavelength you want...


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djellison
post Jul 12 2008, 11:13 PM
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Incidentally - thermally, I would expect the environment at LEO compared to anywhere else, with half the 'sky' being full of a warm blue marble, to be significantly different requiring non-trival modifications to ISS. Power wise, you've going to need twice the solar arrays if you take it to Mars. We're 4 months from Zarya being 10 years old. Mir lasted 14 years as a crewed vehicle. The author of that article has written a book I once flicked through. I find it hard to believe it's the same guy.

Doug
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nprev
post Jul 12 2008, 11:21 PM
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Good point, and "non-trivial" might be an understatement, unless you put it in like an 80 km lunar orbit with attendant fuel requirements for orbit maintenance. Does the ISS even have heat pipes now, or is the sheer volume of the structure enough to dissipate the current thermal load each orbit?


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Stu
post Jul 12 2008, 11:23 PM
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Sigh... of course it's rubbish, but the image, people, the image!

I know that technically it's about as practical as using dog farts to propel a nuclear submarine into orbit, but as the Forum's lone Hopeless Romantic I have to say I find the image of the ISS sliping free of Earth orbit and setting sail for worlds beyond almost too beautiful for words... rolleyes.gif


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jmjawors
post Jul 12 2008, 11:26 PM
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I'm with you there.

The reactions here are more in response to the guy's article, not your romantic thoughts. smile.gif

Slight tangent, but I can't wait until the crew size doubles next year so that the station can get down to doing what it's supposed to be doing. Then everyone could be happy (unless you want a trip to the moon, of course).


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nprev
post Jul 12 2008, 11:27 PM
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Oh...I get the image, believe me (you know me that well, at least! smile.gif ) Just tryin' to think of a way to make it work, is all, and the first step is to ask really annoying 'what-if'-type questions. Got this stupid engineering degree, may as well try to use it a bit.


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cosmo
post Jul 12 2008, 11:33 PM
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QUOTE (djellison @ Jul 13 2008, 01:07 AM) *
Someone please check the numbers on that - they may well be orders of magnitude off - but they do, to me at least, seem to be in the right sort of 'bloody stupid idea' ball park.

Your fuel mass is by far too much. Using the rocket equation yields something different (maybe you mixed up v_ex with Isp? v_ex = Isp * g0). To achieve a delta-v of 4.1 km/s with chemical propulsion you would need ~3 times the mass of ISS of fuel, thus ~1,200 tons. With electric engines as supposed just around 550 tons. Quite alot, but feasible.
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siravan
post Jul 12 2008, 11:39 PM
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QUOTE (djellison @ Jul 12 2008, 07:07 PM) *
Someone please check the numbers on that - they may well be orders of magnitude off - but they do, to me at least, seem to be in the right sort of 'bloody stupid idea' ball park.


Given delta_v 4100 m/s, exhaust velocity of v_e=Isp*g=390*9.8=3800 m/s, the amount of propellant needed is m = m0*(exp(delta_v/v_e)-1)=814 tons. Ignoring the weight of the propellant tanks and rocket engines and millions other engineering problems, this is just 7 or 8 Saturn 5 launches!
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cosmo
post Jul 12 2008, 11:48 PM
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Siravan, youre right!

I confounded fuel with total mass, what a shame rolleyes.gif . Its ~800 tons of chemical fuel and ~125 tons of Xe.
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TheChemist
post Jul 13 2008, 02:06 AM
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I have a better idea. Let's fit an ion-thruster to this guy's car, and use it for MSR. smile.gif
And please spare me the technical difficulties. The car already has seat belts, we 'll use sun lotion and raybans for radiation protection, and there is plenty of space in the back for soil samples. We 're in business baby ! mars.gif
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Greg Hullender
post Jul 13 2008, 02:20 AM
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QUOTE (nprev @ Jul 12 2008, 03:21 PM) *
. . . unless you put it in like an 80 km lunar orbit with attendant fuel requirements for orbit maintenance.


As long as we're dreaming, :-) better would be to park it at the Earth-Moon L1 point and simply tether it to the Lunar surface with a cable.

But getting it through the Van Allen belts without wrecking it seems too hard. I could imagine clever engineering solutions to the other problems, but not to that one.

--Greg
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jmjawors
post Jul 13 2008, 04:50 AM
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QUOTE (TheChemist @ Jul 12 2008, 09:06 PM) *
I have a better idea. Let's fit an ion-thruster to this guy's car, and use it for MSR. smile.gif
And please spare me the technical difficulties. The car already has seat belts, we 'll use sun lotion and raybans for radiation protection, and there is plenty of space in the back for soil samples. We 're in business baby ! mars.gif


Of course you're right. It'd be "fairly easy."


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