FYI,

It's All Decked Out. Give It Somewhere to Go
Washington Post
http://www.washingtonpost.com/wp-
dyn/content/article/2008/07/11/AR2008071102394.html

: Consider the International Space Station, that marvel of
: incremental engineering. It has close to 15,000 cubic feet of
: livable space; 10 modules, or living and working areas; a Canadian
: robot arm that can repair the station from outside; and the
: capacity to keep five astronauts (including the occasional wealthy
: rubbernecking space tourist) in good health for long periods. It
: has gleaming, underused laboratories; its bathroom is fully
: repaired; and its exercycle is ready for vigorous mandatory
: workouts.

: The only problem with this $156 billion manifestation of human
: genius -- a project as large as a football field that has been
: called the single most expensive thing ever built -- is that it's
: still going nowhere at a very high rate of speed. And as a
: scientific research platform, it still has virtually no purpose and
: is accomplishing nothing.

: I try not to write this cavalierly. But if the station's goal is to
: conduct yet more research into the effects of zero gravity on human
: beings, well, there's more than enough of that already salted away
: in Russian archives, based on the many years of weightlessness that
: cosmonauts heroically logged in a series of space stations
: throughout the 1970s, '80s and '90s. By now, ISS crews have also
: spent serious time in zero gravity. We know exactly what
: weightlessness does and how to counter some of its atrophying
: effects. (Cue shot of exercycle.)

: And if the station's purpose is to act as a "stepping stone" to
: places beyond -- well, that metaphor, most recently used by NASA
: Administrator Michael Griffin is pure propaganda. As any student of
: celestial mechanics can tell you, if you want to go somewhere in
: space, the best policy is to go directly there and not stop along
: the way, because stopping is a waste of precious fuel, time and
: treasure. Which is a pretty good description of the ISS, parked as
: it is in constant low Earth orbit.

: This is no doubt why, after the horrifying disintegration of the
: space shuttle Columbia in 2003, the Bush administration belatedly
: recognized that, if we're going to spend all that money on manned
: spaceflight, we should justify the risks by actually sending our
: astronauts somewhere. So NASA is now developing a new generation of
: rockets and manned spacecraft. By 2020, the Constellation program
: is supposed to take astronauts beyond low Earth orbit for the first
: time since Apollo 17 returned from the moon in 1972. Yes, that'll
: be almost 50 years. Where will they go? To the moon -- the only
: place humans have already visited.

: Which leads us right back to the expensively orbiting ISS. It
: hasn't a fig-leaf's role left. The moon is the new "stepping
: stone," with Mars bruited as a next destination. Although NASA
: officials will never quite say so, their current attitude seems to
: be that the station is essentially a high-maintenance distraction,
: even a mistake. Their plan is to finish assembling the thing ASAP
: and hand the keys over to the Russians, Canadians, Europeans and
: Japanese, with minimal continuing U.S. involvement. This should
: happen by the shuttle's mandatory retirement in 2010. Meanwhile,
: we're still writing a lot of high-denomination checks and preparing
: the two remaining shuttles for risky flights to finish something we
: then plan to be largely rid of. This seems absurd. I have an
: alternative proposal:

: Send the ISS somewhere.

: The ISS, you see, is already an interplanetary spacecraft -- at
: least potentially. It's missing a drive system and a steerage
: module, but those are technicalities. Although it's ungainly in
: appearance, it's designed to be boosted periodically to a higher
: altitude by a shuttle, a Russian Soyuz or one of the upcoming new
: Constellation program Orion spacecraft. It could fairly easily be
: retrofitted for operations beyond low-Earth orbit. In principle, we
: could fly it almost anywhere within the inner solar system -- to
: any place where it could still receive enough solar power to keep
: all its systems running.

: It's easy to predict what skeptics both inside and outside NASA
: will say to this idea. They'll point out that the new Constellation
: program is already supposed to have at least the beginnings of
: interplanetary ability. They'll say that the ISS needs to be
: resupplied too frequently for long missions. They'll worry about
: the amount of propellant needed to push the ISS's 1,040,000 pounds
: anywhere -- not to mention bringing them all back.

: There are good answers to all these objections. We'll still need
: the new Constellation Ares boosters and Orion capsules
: -- fortuitously, they can easily be adapted to a scenario in which
: the ISS becomes the living-area and lab core of an interplanetary
: spacecraft. The Ares V heavy-lift booster could easily send aloft
: the additional supplies and storage and drive modules necessary to
: make the ISS truly deep-space-worthy.

: The Orion crew exploration module is designed to be ISS-compatible.
: It could serve as a guidance system and also use its own rocket
: engine to help boost and orient the interplanetary ISS. After
: remaining dormant for much of the one-year journey to, say, Mars,
: it could then be available to conduct independent operations while
: the ISS core orbited the Red Planet, or to investigate an asteroid
: near Earth, for instance.

: But, the skeptics will say, the new Orion capsule's engines
: wouldn't be nearly enough; a spacecraft as large as the ISS would
: need its own drive system. Here, too, we're in surprisingly good
: shape. The ISS is already in space; the amount of thrust it needs
: to go farther is a lot less than you might think. Moreover, a drive
: system doesn't have to be based on chemical rockets. Over the past
: two decades, both the U.S. and Japanese programs have conducted
: highly successful tests in space of ion-drive systems. Unlike the
: necessarily impatient rockets we use to escape Earth's gravity and
: reach orbit, these long-duration, low-thrust engines produce the
: kind of methodical acceleration (and deceleration) appropriate for
: travel once a spacecraft is already floating in zero gravity. They
: would be a perfect way to send the ISS on its way and bring it back
: to Earth again.

: This leaves a lander. A lunar lander substantially larger than the
: spidery Apollo-era LEMs is currently on the drawing board. It's not
: nearly as far along in development as the Ares booster and Orion
: spacecraft components of the Constellation program -- which is a
: good thing. While I question the need to return to the moon in the
: first place, I wouldn't exclude it as a possible destination, so I
: think we should modify the lander's design to make it capable of
: touching down on either the moon or Mars and then returning to the
: ISS with samples for study in its laboratories. Such landers could
: also investigate the moon's poles, where we think water may be
: present, or one of the near-Earth asteroids -- which may have raw
: materials suitable for use by future generations of space
: explorers.

: But, our skeptics will sputter, this will all cost far more money
: than the Constellation program. Who'll pay for it?

: Actually, it will in effect save all the money we've already spent
: on the ISS. And the station is already an international project,
: with substantial financial and technological input from the
: Russians, Canadians, Europeans and Japanese. In recent years, the
: Chinese, who have developed their own human spaceflight
: capabilities, have made repeated overtures to NASA, hoping to be
: let in on the ISS project. They've been unceremoniously rebuffed by
: the Bush administration, but a new administration may be more
: welcoming. An interplanetary ISS -- the acronym now standing for
: International Space Ship -- would be a truly international
: endeavor, with expenses shared among all participating nations.

: How likely is any of this to happen? Not very. A lot depends on the
: flexibility of a NASA that hasn't always been particularly
: welcoming to outside ideas. On the other hand, the agency also
: collaborates with outsiders all the time. So it's not impossible.
: The reason the ISS went from being a purely American, Reagan-era
: project ("Space Station Freedom") to one including the Russians and
: many other nations was a political decision by the Clinton
: administration. A similar political vision will be necessary here.

: All the billions already spent on the space station would pay off
: -- spectacularly -- if this product of human ingenuity actually
: went somewhere and did something. But it would also serve as a
: compelling demonstration that we're one species, living on one
: planet, and that we're as capable of cooperating peacefully as we
: are at competing militaristically. Let's begin the process of
: turning the ISS from an Earth-orbiting caterpillar into an
: interplanetary butterfly.

: michael.benson@...

: Michael Benson, the author of "Beyond: Visions of the
: Interplanetary Probes," writes frequently on space science issues.

Mark Reiff

While a good idea in principle there is one HUGE problem. In LEO,
that station is shielded by the Van Allen Belts. Once you move above
the belts, there is nothing to protect you from cosmic radiation,
solar flares and other radiation storms. The added mass and
structure needed to shield the entire station would astronomical,
both in cost and in mass. But if that can be overcome, this is a
great idea. Park the ISS at L-4 or -5 and use it as a true way
station

>
> FYI,
>
> It's All Decked Out. Give It Somewhere to Go
> Washington Post
> http://www.washingtonpost.com/wp-
> dyn/content/article/2008/07/11/AR2008071102394.html
>
> : Consider the International Space Station, that marvel of
> : incremental engineering. It has close to 15,000 cubic feet of
> : livable space; 10 modules, or living and working areas; a Canadian
> : robot arm that can repair the station from outside; and the
> : capacity to keep five astronauts (including the occasional wealthy
> : rubbernecking space tourist) in good health for long periods. It
> : has gleaming, underused laboratories; its bathroom is fully
> : repaired; and its exercycle is ready for vigorous mandatory
> : workouts.
>
> : The only problem with this $156 billion manifestation of human
> : genius -- a project as large as a football field that has been
> : called the single most expensive thing ever built -- is that it's
> : still going nowhere at a very high rate of speed. And as a
> : scientific research platform, it still has virtually no purpose
and
> : is accomplishing nothing.
>
> : I try not to write this cavalierly. But if the station's goal is
to
> : conduct yet more research into the effects of zero gravity on
human
> : beings, well, there's more than enough of that already salted away
> : in Russian archives, based on the many years of weightlessness
that
> : cosmonauts heroically logged in a series of space stations
> : throughout the 1970s, '80s and '90s. By now, ISS crews have also
> : spent serious time in zero gravity. We know exactly what
> : weightlessness does and how to counter some of its atrophying
> : effects. (Cue shot of exercycle.)
>
> : And if the station's purpose is to act as a "stepping stone" to
> : places beyond -- well, that metaphor, most recently used by NASA
> : Administrator Michael Griffin is pure propaganda. As any student
of
> : celestial mechanics can tell you, if you want to go somewhere in
> : space, the best policy is to go directly there and not stop along
> : the way, because stopping is a waste of precious fuel, time and
> : treasure. Which is a pretty good description of the ISS, parked as
> : it is in constant low Earth orbit.
>
> : This is no doubt why, after the horrifying disintegration of the
> : space shuttle Columbia in 2003, the Bush administration belatedly
> : recognized that, if we're going to spend all that money on manned
> : spaceflight, we should justify the risks by actually sending our
> : astronauts somewhere. So NASA is now developing a new generation
of
> : rockets and manned spacecraft. By 2020, the Constellation program
> : is supposed to take astronauts beyond low Earth orbit for the
first
> : time since Apollo 17 returned from the moon in 1972. Yes, that'll
> : be almost 50 years. Where will they go? To the moon -- the only
> : place humans have already visited.
>
> : Which leads us right back to the expensively orbiting ISS. It
> : hasn't a fig-leaf's role left. The moon is the new "stepping
> : stone," with Mars bruited as a next destination. Although NASA
> : officials will never quite say so, their current attitude seems to
> : be that the station is essentially a high-maintenance distraction,
> : even a mistake. Their plan is to finish assembling the thing ASAP
> : and hand the keys over to the Russians, Canadians, Europeans and
> : Japanese, with minimal continuing U.S. involvement. This should
> : happen by the shuttle's mandatory retirement in 2010. Meanwhile,
> : we're still writing a lot of high-denomination checks and
preparing
> : the two remaining shuttles for risky flights to finish something
we
> : then plan to be largely rid of. This seems absurd. I have an
> : alternative proposal:
>
> : Send the ISS somewhere.
>
> : The ISS, you see, is already an interplanetary spacecraft -- at
> : least potentially. It's missing a drive system and a steerage
> : module, but those are technicalities. Although it's ungainly in
> : appearance, it's designed to be boosted periodically to a higher
> : altitude by a shuttle, a Russian Soyuz or one of the upcoming new
> : Constellation program Orion spacecraft. It could fairly easily be
> : retrofitted for operations beyond low-Earth orbit. In principle,
we
> : could fly it almost anywhere within the inner solar system -- to
> : any place where it could still receive enough solar power to keep
> : all its systems running.
>
> : It's easy to predict what skeptics both inside and outside NASA
> : will say to this idea. They'll point out that the new
Constellation
> : program is already supposed to have at least the beginnings of
> : interplanetary ability. They'll say that the ISS needs to be
> : resupplied too frequently for long missions. They'll worry about
> : the amount of propellant needed to push the ISS's 1,040,000 pounds
> : anywhere -- not to mention bringing them all back.
>
> : There are good answers to all these objections. We'll still need
> : the new Constellation Ares boosters and Orion capsules
> : -- fortuitously, they can easily be adapted to a scenario in which
> : the ISS becomes the living-area and lab core of an interplanetary
> : spacecraft. The Ares V heavy-lift booster could easily send aloft
> : the additional supplies and storage and drive modules necessary to
> : make the ISS truly deep-space-worthy.
>
> : The Orion crew exploration module is designed to be ISS-
compatible.
> : It could serve as a guidance system and also use its own rocket
> : engine to help boost and orient the interplanetary ISS. After
> : remaining dormant for much of the one-year journey to, say, Mars,
> : it could then be available to conduct independent operations while
> : the ISS core orbited the Red Planet, or to investigate an asteroid
> : near Earth, for instance.
>
> : But, the skeptics will say, the new Orion capsule's engines
> : wouldn't be nearly enough; a spacecraft as large as the ISS would
> : need its own drive system. Here, too, we're in surprisingly good
> : shape. The ISS is already in space; the amount of thrust it needs
> : to go farther is a lot less than you might think. Moreover, a
drive
> : system doesn't have to be based on chemical rockets. Over the past
> : two decades, both the U.S. and Japanese programs have conducted
> : highly successful tests in space of ion-drive systems. Unlike the
> : necessarily impatient rockets we use to escape Earth's gravity and
> : reach orbit, these long-duration, low-thrust engines produce the
> : kind of methodical acceleration (and deceleration) appropriate for
> : travel once a spacecraft is already floating in zero gravity. They
> : would be a perfect way to send the ISS on its way and bring it
back
> : to Earth again.
>
> : This leaves a lander. A lunar lander substantially larger than the
> : spidery Apollo-era LEMs is currently on the drawing board. It's
not
> : nearly as far along in development as the Ares booster and Orion
> : spacecraft components of the Constellation program -- which is a
> : good thing. While I question the need to return to the moon in the
> : first place, I wouldn't exclude it as a possible destination, so I
> : think we should modify the lander's design to make it capable of
> : touching down on either the moon or Mars and then returning to the
> : ISS with samples for study in its laboratories. Such landers could
> : also investigate the moon's poles, where we think water may be
> : present, or one of the near-Earth asteroids -- which may have raw
> : materials suitable for use by future generations of space
> : explorers.
>
> : But, our skeptics will sputter, this will all cost far more money
> : than the Constellation program. Who'll pay for it?
>
> : Actually, it will in effect save all the money we've already spent
> : on the ISS. And the station is already an international project,
> : with substantial financial and technological input from the
> : Russians, Canadians, Europeans and Japanese. In recent years, the
> : Chinese, who have developed their own human spaceflight
> : capabilities, have made repeated overtures to NASA, hoping to be
> : let in on the ISS project. They've been unceremoniously rebuffed
by
> : the Bush administration, but a new administration may be more
> : welcoming. An interplanetary ISS -- the acronym now standing for
> : International Space Ship -- would be a truly international
> : endeavor, with expenses shared among all participating nations.
>
> : How likely is any of this to happen? Not very. A lot depends on
the
> : flexibility of a NASA that hasn't always been particularly
> : welcoming to outside ideas. On the other hand, the agency also
> : collaborates with outsiders all the time. So it's not impossible.
> : The reason the ISS went from being a purely American, Reagan-era
> : project ("Space Station Freedom") to one including the Russians
and
> : many other nations was a political decision by the Clinton
> : administration. A similar political vision will be necessary
here.
>
> : All the billions already spent on the space station would pay off
> : -- spectacularly -- if this product of human ingenuity actually
> : went somewhere and did something. But it would also serve as a
> : compelling demonstration that we're one species, living on one
> : planet, and that we're as capable of cooperating peacefully as we
> : are at competing militaristically. Let's begin the process of
> : turning the ISS from an Earth-orbiting caterpillar into an
> : interplanetary butterfly.
>
> : michael.benson@...
>
> : Michael Benson, the author of "Beyond: Visions of the
> : Interplanetary Probes," writes frequently on space science
issues.

I would make a far more modest proposal. Use ion engines to gradually adjust the orbit of ISS to something a lot closer to equatorial orbit, and then equip it as a fuel manufacturing and storage depot. The Russians would object to this. The reason why ISS is in the relatively high-inclination orbit it's in is because it's easier to reach that orbit from the latitude of the launch site Russia uses. But if the ISS were in an equatorial orbit, that would make it a better launching point for expeditions to the moon (or GEO, or Lagrange points)as it would eliminate a plane-change maneuver. But stopping at LEO just to stop really makes no sense. It only makes sense ifwe're gassing upthere. I'd propose a system where water could be delivered to ISS (it's safer, and requires smaller tanks). Power from the solar cell array could be used to electrolysize the water to hydrogen and oxygen. Some supplemental heat radiators could function in a cooling and liquefaction system to make fuel and oxidizer which would be stored in shaded and well-insulated tanks. Vehicles bound for higher orbits, the moon, NEAs, or maybe even Mars could dock at ISS with nearly empty tanks, refuel, and continue their journey. It's a bit tempting to propose parking the ISS at the Earth-moon L-1 point, to serve as both a way station to the Moon, and a staging point for departures beyond. But the radiation problem negmarron_99 mentioned would apply here. Manned stations at the L-1 point might have to wait on use of space materials, so that radiation shields of suitable thickness could be implemented in an economical fashion.

Regards,
Mike Combs

> I would make a far more modest proposal. Use ion engines to
> gradually adjust the orbit of ISS to something a lot closer to
> equatorial orbit, and then equip it as a fuel manufacturing and
> storage depot.

I have to agree with Mike; this would make a lot more sense. An
orbital transfer/assembly station and fuel (and other supplies) depot
can be extremely useful, provided it's in a sensible orbit, which ISS
currently is not. But its orbit could be changed -- with much
difficulty, but with far less difficulty than trying to turn it into
an interplanetary craft.

> The Russians would object to this. The reason why ISS is in the
> relatively high-inclination orbit it's in is because it's easier to
> reach that orbit from the latitude of the launch site Russia uses.
> But if the ISS were in an equatorial orbit, that would make it a
> better launching point for expeditions to the moon (or GEO, or
> Lagrange points) as it would eliminate a plane-change maneuver.

Yes, and the Russians recently struck a deal to launch from somewhere
in South America (does anyone happen to recall the details?), so maybe
they wouldn't mind as much as they used to.

Best,
- Joe

ISS: It's All Decked Out. Give It Somewhere to Go
ISS: It's All Decked Out. Give It Something to Do!

Ion drives would be an excellent way for the ISS to get around. As for shielding beyond the Van Allen Belt, large water tanks would work.

From what I remember of the last NSS convention the European Space port in South America were building launch facilities for Russian Rockets. I don't recall what the agreements were between Europe and Russia.

Just as somewhere to go, how about something to do. Here is a list right off the top of my head.

Have rockets send up parts for the ISS to build.
* A prototype SPS, you build it and test it at the ISS. Slap an Ion drive on it and send it off.
* A prototype microgravity manufacturing facility.
* A small habitat, farming and aqua-farming could be started in space.
* A load of standardized parts to build standardized cheaper space probes.
* A prototype solar sail.
* A very large Space Telescope. Start looking for Earthlike planets with O2 atmospheres.

The ISS should be a beehive of expansion and activity. A fuel depot, a facility for creating technology for manned space construction a jumping off point to other parts of the solar system. This is a simple no brainer of manned expansion into the solar system.

You know just as a thought we could always expand the ISS with a large rotating space station like 2001 and create the technology for simulating gravity.

BestRegards,
Pete

From time to time, one reads of plans to use the Space
Shuttle's external fuel tank as a space station module.
Any reason that couldn't still be done? Any reason they
couldn't be docked to the ISS as easily as to each other?
Indeed, that could be a use for ISS: it can already have
eight or so people ready to work on the next ET sent up.

The proposed Ares V launch vehicle is expected to use a
similar ET.

External tanks would make a great temporary shelter for a lunar base. How much extra delta v would it require to get one to the moon?

From time to time, one reads of plans to use the Space
Shuttle's external fuel tank as a space station module.
Any reason that couldn't still be done? Any reason they
couldn't be docked to the ISS as easily as to each other?
Indeed, that could be a use for ISS: it can already have
eight or so people ready to work on the next ET sent up.

The proposed Ares V launch vehicle is expected to use a
similar ET.

> Have rockets send up parts for the ISS to build.
> * A prototype SPS, you build it and test it at the ISS. Slap an Ion
> drive on it and send it off.
> * A prototype microgravity manufacturing facility.
> * A small habitat, farming and aqua-farming could be started in space.
> * A load of standardized parts to build standardized cheaper space probes.
> * A prototype solar sail.
> * A very large Space Telescope. Start looking for Earthlike planets
> with O2 atmospheres.
>
The ISS could also be a station which services and upgrades returning
spacecraft after space missions.
For instance changing low thrust thruster units, fuel tanks and solar
sail foil rolls.

One more job could be to test asteroidal materials coming from asteroid
prospector missions under space conditions.

Also processing asteroidal slag to radiation shielding.

Does concreting work in free space?
(How is water behaving if we pump it through free space into concrete
mixer units; does it freeze, does it boil or is space just a thermos,
does the water volatilize quickly, can we stop that through vapor tight
casting foils?
Can we mix the slag with water into rotating mixer units for concreting?)
Could we fabricate concrete rings in free space and put them together to
form a spacecraft hull which provides shielding for humans?

Humanity has assembled huge Buildings like the pyramides under the
difficult conditions of Earth's gravitation well.

Shouldn't it be a lot easier to construct a gravitation hardened hull
out of tens of concrete rings which are hardened in space
(even if it has a mass of thousands of tons in space) under microgravity
space conditions and with robotic crafts?

If so, the spacecraft hull would be provided by cheap asteroidal
materials which could be extracted with comparatively small robotic
probes using low thrust propulsion like ion drives and solar sails.

They would bank on the possibility to avoid the steep gravitational well
of planets and moons to decrease the costs of material collection and
transportation into space by orders of magnitude.
A comparatively small probe could gain tons of materials in one single
mission and bring it back to the ISS where humans are able to.

If the first of such probe missions would be a success, this probe could
be used again and again for further prospecting missions (just by
changing the thruster units or their fuel tanks).

The same type (or a improved one) could be mass fabricated and launched,
making it easy to get a fleet of prospecting units into space which
deliver a stream of returning asteroid material cargos to build concrete
spacecraft hulls which enable radiation hardened human missions to Mars
or asteroids.

For a complete mission you would need a mothership spacecraft which
delivers daughter units like landers to the asteroids, also observation
and communication satellites are needed to enable remote controlling of
those missions. While at the asteroid the mothership serves as
communication relay. After material collection the mothership returns
the prospector lander units with their materials back to the ISS.

For a design of such a low thrust mothership spacecraft take a look at
http://solar-thruster-sailor.info/figs/fig19-21d.html .
(I hold already a UK patent on this spacecraft, US and German patent
applications are pending too, so wish me luck :-) )

The mothership spacecraft is direct launchable from Earth with already
docked in daugher units. So a complete (comparatively low cost) asteroid
material return mission could be enabled with just one launch.

Besides daughter units the mothership carries ion thruster units, ample
solar cell arrays to power the electric thrusters and the spacecraft and
also solar sails with "roller reefing" for fuel less station keeping and
attitude control at the asteroid.

For more on the "Roller Reefing" technic look at
http://solar-thruster-sailor.info/figs/fig18.html
and
http://www.solar-thruster-sailor.info/PosterSSS.pdf

The mothership carries also winches which would enable to pull a
"lander" back into it's docking and payload station after the lander did
accelerate toward the asteroid and "smashes" (though with situation
adapted speed) onto the ground of the asteroid to "scoop" materials from
there.
This possibility would be used, if the asteroid has a layer of dust and
sand which could be scooped.

Other landers for instance with arms to collect stoney materials or
drilling devices would be also thinkable.

Best wishes

Frank

No fundamental reason one could not, but here's one reason it should not be done: How much mass would need to be launched from Earth to make the interior habitable? If the interior is fitted with any where near the equipment density of ground-prepared stations, it could easily exceed one hundred tonnes launched to an already orbiting ET to make it habitable. With all the construction work being done on orbit, where it costs $20 million to get each worker into space (which could be slightly offset by getting the ISS crew to work on it, but still) how would this actually be cheaper than just making a custom module on Earth? An ET does provide a tantalizingly large hull which could be pressurized on orbit, but I'm not so sure it would be cheap.

"It is better to fail in originality than to succeed in imitation."
-Herman Melville

Received: Wednesday, July 16, 2008, 8:59 PM

From time to time, one reads of plans to use the Space
Shuttle's external fuel tank as a space station module.
Any reason that couldn't still be done? Any reason they
couldn't be docked to the ISS as easily as to each other?
Indeed, that could be a use for ISS: it can already have
eight or so people ready to work on the next ET sent up.

The proposed Ares V launch vehicle is expected to use a
similar ET.

> No fundamental reason one could not, but here's
> one reason it should not be done: How much mass
> would need to be launched from Earth to make the
> interior habitable? If the interior is fitted
> with any where near the equipment density of
> ground-prepared stations, it could easily exceed
> one hundred tonnes launched to an already
> orbiting ET to make it habitable. With all the
> construction work being done on orbit, where it
> costs $20 million to get each worker into space
> (which could be slightly offset by getting the
> ISS crew to work on it, but still) how would
> this actually be cheaper than just making a
> custom module on Earth? An ET does provide a
> tantalizingly large hull which could be
> pressurized on orbit, but I'm not so sure it
> would be cheap.

These are actually some pretty solid concerns.
I'll give my opinion (because that's what I have
to give) on them.

The Shuttle is being retired, but the Ares V launch
vehicle is expected to use a similar ET. It is
also expected to launch 130 tons to LEO. There's
your equipment density.

Actually, though, I'd suggest less equipment density.
In fact, the first couple of ET's should be outfitted
as living quarters. One could be (tiny) private
sleeping quarters. Could have enough for twenty people.
The next could have a galley and a clinic. The next
could be set aside for exercise, recreation, and showers.
Toilets too. This wouldn't require much more tonnage of
equipment per ET than the smaller modules used now,
would free up a lot of space in the rest of the ISS,
let it carry more people, and YES the crew should do
the assembly. And besides, you're going to be launching
those ET's anyway.

So perhaps you'd only need 50 tons per, and the other
80 tons could be the solar panels, air, water, and such
that there's no getting around having to have.

And the tourists would like it. ^_^