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Posted by: Stu Jul 12 2008, 10:25 PM

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...

http://www.washingtonpost.com/wp-dyn/content/article/2008/07/11/AR2008071102394.html

Posted by: jmjawors Jul 12 2008, 10:40 PM

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).

Posted by: djellison Jul 12 2008, 11:07 PM

"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

Posted by: nprev Jul 12 2008, 11:07 PM

Well, one hole to punch, anyhow (although I like the idea, too!) 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...

Posted by: djellison Jul 12 2008, 11:13 PM

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

Posted by: nprev Jul 12 2008, 11:21 PM

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?

Posted by: Stu Jul 12 2008, 11:23 PM

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...

Posted by: jmjawors Jul 12 2008, 11:26 PM

I'm with you there.

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

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).

Posted by: nprev Jul 12 2008, 11:27 PM

Oh...I get the image, believe me (you know me that well, at least! ) 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.

Posted by: cosmo Jul 12 2008, 11:33 PM

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.

Posted by: siravan Jul 12 2008, 11:39 PM

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!

Posted by: cosmo Jul 12 2008, 11:48 PM

Siravan, youre right!

I confounded fuel with total mass, what a shame . Its ~800 tons of chemical fuel and ~125 tons of Xe.

Posted by: TheChemist Jul 13 2008, 02:06 AM

I have a better idea. Let's fit an ion-thruster to this guy's car, and use it for MSR.
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 !

Posted by: Greg Hullender Jul 13 2008, 02:20 AM

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

Posted by: jmjawors Jul 13 2008, 04:50 AM

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

Posted by: Stu Jul 13 2008, 07:20 AM

Minor technical details all...

C'mon guys, think outside the box....

Posted by: TheChemist Jul 13 2008, 07:25 AM

Excuse the late night sarcasm, I am sure most can resonate with the visionary part.
But in the same article, I see that NASA " ...hasn't always been particularly welcoming to outside ideas."
That line kind of killed the romance for me ...

Posted by: Tesheiner Jul 13 2008, 09:32 AM

I think the chances of her asking you to see the stars, clear night or not, are higher … but still infinitesimal.

Posted by: djellison Jul 13 2008, 10:17 AM

OK - so several orders of magnitude out Infact, just about an order of magnitudes worth of orders of magnitude.

But still no in the realms of feasable.

A space station in orbit around the moon is a great idea ( although a romantic one - I can't actually imagine any usefull purpose for it - if you change your perspective, we're all just in a high lunar orbit right now ) - but the ISS has never, is not nor will ever be the right tool for any other job than the one it is doing.

Doug

Posted by: dvandorn Jul 13 2008, 04:28 PM

Yeah -- there are great challenges to getting ISS out of LEO, and while it could be made feasible with a huge amount of money, it will never be cost-effectively so.

Now, Skylab -- *that* would have been far more suited to lunar orbital use. Remove the ATM, use the EREP to study the lunar surface instead of the Earth's surface... that would have been useful. And far, far easier overall to get out of LEO.

-the other Doug

Posted by: AndyG Jul 14 2008, 10:54 AM

Ok. Since the article seemed to suggest that there's nothing more to study about weightlessness, and the ISS is modular - just like Lego - can I suggest the following re-engineering -





Andy

(Having seemingly awoken the spirit of Kenneth Gatland)

Posted by: Stu Jul 14 2008, 11:30 AM

Oooh, I like that!

I can almost hear "The Blue Danube" looking at that pic...

Posted by: tanjent Jul 14 2008, 01:15 PM

If you are going to start imagining different configurations into which to rearrange the ISS modules, you could also spin off one or two and send them to orbit the moon. I don't know exactly what the point would be, but it would establish a permanent base out there a lot sooner than we could build one on the surface. It would also facilitate the colonization of the surface. Then the space shuttle fleet, no longer safe for taking off and landing, could be boosted to orbit one last time, stripped of their no-longer-neeeded wings, and put to work shuttling back and forth between the ISS and the lunar station. I suspect the shuttles would be much easier to convert into long-distance craft than the ISS itself. The objective isn't really to save money, because these ideas presuppose a major scaleup in the whole space program. If that were to happen (for some still hard-to-imagine reason), then we might as well redeploy our existing resources before fabricating new ones. I wouldn't have put all the effort into the shuttle and ISS programs in the first place if I could have magically reallocated those resources to UMSF activities, but now it's a sunk cost and we should make darn sure not to throw these assets away. Right?

Posted by: AndyG Jul 14 2008, 01:47 PM

...and the real anorak will note that, with the radius defined by the array lengths, and a spin rate of 3rpm (i.e. the highest possible before the cusp of nausea) the onboard artificial gravity will be...

(sounds of scribbled calculations on the back of a golden envelope)

..."Martian".



Andy

Posted by: PhilCo126 Jul 24 2008, 12:13 PM

Talking about the ISS:
Astronauts onboard the ISS dumped the 600 Kg Early Ammonia Servicer (EAS) over board and the heavy payload is now visible as a star. Quiet bright but not as bright as the ISS itself. The Early Ammonia Servicer (EAS) was set over board because the remaining number of shuttle flights didn't foresee the return of the 600 Kg servicer. It will be visible the next week before it burns up in the atmosphere...

Posted by: imipak Jul 24 2008, 08:41 PM

There's a good piece on http://www.universetoday.com/2008/07/22/large-chunk-of-iss-space-junk-becomes-easy-to-observe-video/ on the EAS, with ground observation video and observing tips. As it's an uncontrolled re-entry it could come down anywhere along the ISS' orbit track... with luck it'll happened during local night, near a well-populated area, with enough advance warning for the TV news or weather* to mention it - "And finally, if you pop outside about 10pm, you'll see a great fireworks show!"

* http://www.richardangwin.com/5.html often works in a mention of interesting night sky sights (meteor showers, aurorae, oppositions and the like.) (Heh! When I googled "BBC West weather astronomy" the first result was: http://www.bbc.co.uk/cumbria/weather/sky_at_night/stuart_atkinson.shtml ]

Posted by: Stu Jul 24 2008, 09:25 PM

The horror! That's DONKEYS' years old!!! I'll have to get them to update that...