Realistic, near-term, rotating Space Station

[JohnFornaro]

So I put preserving ISS for the future as high priority,

That is waste of resources and is not viable to save it for future generations.  It does not have an infinite life.  Once it has served its purpose, it will be disposed of, much like old plane, ships and automobiles.  The ISS can not be preserved like museum or collector plane ships and automobiles.  They can be maintained in a static state, unlike the ISS which will require propulsion and attitude control systems that are operational, which in turn, necessitates power and a control system.  And the ISS can't be just left alone, it must be tracked so that other objects don't hit it, creating a debris problem.  Which, it will still create debris problem from impacts of items too small to track.

Here, I think Jim makes a valid point, but at the expense of preserving a historical artifact. There is certainly an argument that maintaining the Air and Space Museum is a waste of resources, as is maintaining the Acropolis, Chartres, Jamestown and so forth.

It is easy to imagine the ISS being preserved for historical purposes; parked in a much higher orbit.  True, it would be an energy intensive museum, and the ticket price for admission would have to reflect that.

Sadly, the way things are going here on the surface, one gets the impression that the government is  governments are [Edit:  We're pretty much ok for the moment, but a good bit of the rest of the world sure suffers at the hands of their governments] deliberately trying to make the planet a less viable environment, which would suggest that the ISS has a very finite lifetime.

[gbaikie]

So I put preserving ISS for the future as high priority,

That is waste of resources and is not viable to save it for future generations.  It does not have an infinite life.  Once it has served its purpose, it will be disposed of, much like old plane, ships and automobiles.  The ISS can not be preserved like museum or collector plane ships and automobiles.  They can be maintained in a static state, unlike the ISS which will require propulsion and attitude control systems that are operational, which in turn, necessitates power and a control system.  And the ISS can't be just left alone, it must be tracked so that other objects don't hit it, creating a debris problem.  Which, it will still create debris problem from impacts of items too small to track.

I have not said ISS should just be left alone.  I said in this thread that it could operated at low cost- 50 million [or less]. But I will amend this to, about same cost as Hubble costs per year.
Hubble was launched in 1990.
"Mission length    23 years, 9 months, and 24 days elapsed
Deorbited    estimated 2014–2021"
http://en.wikipedia.org/wiki/Hubble_Space_Telescope

My point is at some point if NASA continues to spend 2-3 billion dollars per year on ISS, more people
will come to conclusion of "That is waste of resources.."
My suggestion of 500 by 500 km or 500 by 1000 km orbit was something which could done within 5 years.
And that is still LEO.
And I would regard it as one step towards getting ISS to point of having low cost operation and the from 500 km orbit, at later point ISS could put in a more stable orbit- high earth orbit.
And once in a high earth orbit, is what meant by costing 50 million [or less] per year to simply keep in orbit.
And once in high earth orbit, ISS could be "viable to save it for future generations".
So near term plan would be to add radiation shielding so crew got same or less radiation as crew get now and have ISS in higher orbit [500 by 500 km would be only slightly higher- and 500 by 1000 being more "extreme"]. And the more mass plus being higher will require less re-boost and will be a step towards ISS going to much higher orbit.
If part of additional shielding can arranged so allow crew operate in limited manner in "solar flare type shelter" then crew could fly ISS when going thru Van Allen belts. Giving option of having crew remain on ISS when getting ISS to high earth. Though one also do this having ISS unmanned.

So 500 by 500 or 500 by 1000 km is something which could be done within 5 years, and putting ISS in high earth orbit could done within say, 10 years

[Jim]

Bottom line: There is plenty for it to do, but the government ain't interested.

And so are most of the governed, hence there is no need for such a station paid for by taxes.

[scienceguy]

Really, an artificial gravity space station will not be cost effective until we have cheaper access to space from a space elevator or  high temperature superconductors or antigravity or something.

[Jim]

1.  Here, I think Jim makes a valid point, but at the expense of preserving a historical artifact. There is certainly an argument that maintaining the Air and Space Museum is a waste of resources, as is maintaining the Acropolis, Chartres, Jamestown and so forth.

2. It is easy to imagine the ISS being preserved for historical purposes; parked in a much higher orbit.  True, it would be an energy intensive museum, and the ticket price for admission would have to reflect that.

3. Sadly, the way things are going here on the surface, one gets the impression that the government is deliberately trying to make the planet a less viable environment, which would suggest that the ISS has a very finite lifetime.

1.  ISS is not on the level of those historic artifacts and preserving the ISS require more resources than all of those used to to preserve the items you listed.

2.  To the uniformed it is, much like scifi fantasy.

3.  Quit the grandstanding  It isn't that bad.  You could be in another country such a North Korea or one of the many 3rd world countries in Africa.

[Jim]

I have not said ISS should just be left alone.  I said in this thread that it could operated at low cost- 50 million [or less].

You have no data to support that amount

[Jim]

My suggestion of 500 by 500 km or 500 by 1000 km orbit was something which could done within 5 years.

Still not viable.   What good is it at that altitude and  cost.  Too expensive for a museum piece.

[Roy_H]

See Attachment,
My silly modular space station concept using inflatable modules.
Center modules do not rotate.
Outer modules rotate about the center to simulate gravity.

What did you use to draw that?

[hop]

In my design, I provide the non-rotating hub for this purpose. It is just the living quarters that rotate.

Note that the transition to and from zero G is reportedly the most unpleasant part of the experience by far. It takes days to adapt, and many people are quite ill and in significant pain during that period. Once they are adapted, pretty much everyone says zero G is wonderful, despite the inconveniences. So if your plan is to have the crew commute between the spun and de-spun sections on a daily or even weekly basis, there is a very high chance they would be much worse off than just doing a 3-6 month tour in zero G.

Now it's possible if you did it every day, things would get easier but considering the significant physiological changes involved it's not a given.

[cuddihy]

2. It is easy to imagine the ISS being preserved for historical purposes; parked in a much higher orbit.  True, it would be an energy intensive museum, and the ticket price for admission would have to reflect that.

1.  ISS is not on the level of those historic artifacts and preserving the ISS require more resources than all of those used to to preserve the items you listed.

Let's put some numbers to Jim's point here. Let's just consider the cost to raise ISS to a stable orbit:
1. ISS weighs around 420 metric tons.

2. A FH if it existed could nominally deliver 50 mt to ISS orbit. If that's all in a large US, that's all fuel. But since we're talking about ISS orbit boost here, that has to be rendezvous-able with ISS. So lets's assume some kind of storable MMH / NTO propellant system on say a Dragon extended trunk. Let's assume 40 mt of fuel delivered to orbit for the purpose of boost. And 335s is pretty generous for ISP.

Using the old Joe Strout delta v calc, our hypothetical FH ISS orbit booster can add an impressive 290 m/s of delta V.

3. What's that cost? Well since we're spitballing here, let's assume our ISS booster costs about as much as a Dragon. So since SpaceX is getting approx $133M for each of 12 CRS flights, and at the time F9 cost just under $60M to launch, and the 53mt FH is about $125M now, it's probably on safe ground to say FH ISS booster would run about $190-$220M per. Let's call it $200M. (That's $690k per m/s of delta v.)

4. What's a stable orbit? Well, 2 that have been suggested are GSO (~3400 m/s) and EML2 (~3700 m/s). I believe those are good numbers, but not sure. So for GSO you're looking at 12 ISS Booster flights and for EML2 you're looking at 13. So $2.4Bil for one and $2.6 Bil for the other. Not impossible... But then you have to factor in resupply, etc at the new altitudes.

The numbers are also useful for comparison of cost to place a rotating station in one of those spots to get back on topic...

[Roy_H]

In my design, I provide the non-rotating hub for this purpose. It is just the living quarters that rotate.

Note that the transition to and from zero G is reportedly the most unpleasant part of the experience by far. It takes days to adapt, and many people are quite ill and in significant pain during that period. Once they are adapted, pretty much everyone says zero G is wonderful, despite the inconveniences. So if your plan is to have the crew commute between the spun and de-spun sections on a daily or even weekly basis, there is a very high chance they would be much worse off than just doing a 3-6 month tour in zero G.

Now it's possible if you did it every day, things would get easier but considering the significant physiological changes involved it's not a given.

Good point. I wonder if there is any way to test that. I imagine it is like getting sea-sick. Do people who get sea-sick find transitions from boat to land and back makes it worse or last longer?

[cordwainer]

Personally, I think we need to baby-step things. ISS is an antique but a useful antique.

1. We should lower the costs by automating more of the hardware on the ISS and using it as a test-bed for the maintenance and development of orbital tugs and OTV's(essentially writing off some of ISS costs and useful commercial R&D).
2. We should invest in building a public/private space station to replace the ISS utilizing SpiderFab and Bigelow style inflatable habitat technologies. I would suggest distributing mass by simply spinning a very large and long inflatable habitat over the length of a large central spar with docks and propulsion at either end.
3. Concentrate on developing ISRU refueling technology from the Moon and NEO's to further NASA's deep space mission capabilities.

Then we can start talking about developing the propulsion and artificial gravity technologies needed for long duration manned space flight. Let's not put the cart before the horse. Developing an artificial gravity space station actually seems to me an easy and not particularly costly venture if you keep the engineering simple, it's developing artificial gravity for a vehicle during long distance flight that is an issue due to the delicate balancing of counterweights or maintaining a steady direction while tumbling that is the harder engineering problem. Station keeping a stable orbit does not often require high sheer forces to be experienced. Raising an orbit in some cases only requires continuous low-thrust electrical propulsion or relatively low-thrust kick motors. Taking a spaceship out of Earth's gravity and inserting it into the orbit around Mars while maintaining comfortable gravity is more difficult from an engineering standpoint. A tumbling vessel would have to stop tumbling well before it gets to Mars for it accurately insert itself and would have difficulty tumbling to produce gravity while in orbit.(although this might not be impossible, particularly in a large gravity well like Jupiters) Using the various types of spin-habs, hamster wheels and other centrifuge based AG systems makes for a complicated design that has to properly balanced. Otherwise you run into increased structural bracing that is weight prohibitive or a very large spin-hab that is also weight prohibitive. Such systems could and probably would be stopped from spinning during high acceleration  maneuvers, since otherwise you would need to spend more money on unnecessary structural bracing as well as more fuel to the RCS systems to maintain a steady and precise flight path for orbital insertion.

As to the idea of counter balancing an inflatable habitat at the bow of the vessel with the weight of the propulsion systems I think it would be better to place an inflatable spin-hab near the center of the mast and place the landing craft, communication and scientific instrumentation at the front. Use two inflatable habs one inside of the other. The smaller internal hab would be used to provide mild micro-gravity for the crew during their waking hours. During sleep hours the internal hab would be spun down and mated with sleeping quarters in the located on the outer hab. The outer hab would spin faster and have a larger arc of momentum so would provide heavier more comfortable gravity while sleeping. I think a good gauge of what is the right minimal amount of gravity for astronauts is the amount of gravity needed for proper function of the prostrate and kidneys. Bone loss can be prevented through exercise, diet and hyper-centrifuges.

[Roy_H]

Taking a spaceship out of Earth's gravity and inserting it into the orbit around Mars while maintaining comfortable gravity is more difficult from an engineering standpoint. A tumbling vessel would have to stop tumbling well before it gets to Mars for it accurately insert itself and would have difficulty tumbling to produce gravity while in orbit.(although this might not be impossible, particularly in a large gravity well like Jupiters)

Could you elaborate on this. It is not obvious to me that there would be any difficulty, and I do not see the need to stop spinning to achieve Mars orbit. Is it because you envision high acceleration forces to leave Earth and stop at Mars? Even with chemical rockets, I don't think the acceleration would be much, in the order of 1/10g. This would be almost totally eliminated if a VASIMR drive was used which would provide near continuous low acceleration. Only issue would be the mid-point turn around, but even that shouldn't be too difficult.

[gbaikie]

2. It is easy to imagine the ISS being preserved for historical purposes; parked in a much higher orbit.  True, it would be an energy intensive museum, and the ticket price for admission would have to reflect that.

1.  ISS is not on the level of those historic artifacts and preserving the ISS require more resources than all of those used to to preserve the items you listed.

Let's put some numbers to Jim's point here. Let's just consider the cost to raise ISS to a stable orbit:
1. ISS weighs around 420 metric tons.

2. A FH if it existed could nominally deliver 50 mt to ISS orbit. If that's all in a large US, that's all fuel. But since we're talking about ISS orbit boost here, that has to be rendezvous-able with ISS. So lets's assume some kind of storable MMH / NTO propellant system on say a Dragon extended trunk. Let's assume 40 mt of fuel delivered to orbit for the purpose of boost. And 335s is pretty generous for ISP.

Using the old Joe Strout delta v calc, our hypothetical FH ISS orbit booster can add an impressive 290 m/s of delta V.

3. What's that cost? Well since we're spitballing here, let's assume our ISS booster costs about as much as a Dragon. So since SpaceX is getting approx $133M for each of 12 CRS flights, and at the time F9 cost just under $60M to launch, and the 53mt FH is about $125M now, it's probably on safe ground to say FH ISS booster would run about $190-$220M per. Let's call it $200M. (That's $690k per m/s of delta v.)

Ok, but let's try something different.
Let's use Centaur stages with their very costly engines. But we want these engines to burn longer
then they normally do. Because we want to reuse them.
So need adapter which fit with ISS, and docks 4 Centaur stages, but only 2 Centaur have engines and two other centaur stages are just tanks. And while boosting [and making about 1/25th of gee] the tanks will feed rocket fuel into the two stages which have engines.
So addition to having longer burning engines the centaurs also have be able to be cross feed at low gravity.  Wiki, Centaur (rocket stage):
Source: Atlas V551 Specifications.[19]

    Diameter: 3.05 m (10 ft)
    Length: 12.68 m (42 ft)
    Inert mass: 2,247 kg (4,954 lb)
    Propellant: Liquid hydrogen
    Oxidizer: Liquid oxygen
    Fuel & oxidizer mass: 20,830 kg (45,922 lb)
So adapter could include the pumps needed, but stages will need to modified to be able dock and allow
this refueling.
This could be made to allow also any rocket lift the centaur stage and tanks- neither have to be full
of propellent. So Falcon 9 could do this. But need a lot launches- and Falcon 9 has just one launch pad
which reaches ISS. But FH could do almost do one cycle in one launch- assuming tanks also have 20,830 kg
of Fuel & oxidizer: it's 60 tons plus for fuel- plus engine, tankage and the one adapter. Though the tanks
could hold less or more than 20,830 kg of Fuel & oxidizer.
So about 60,000 kg of fuel and 10,000 kg of everything else, but we get a Isp of 451

But I going to add 200 tons of water, so station is 620 tons.
So: Full Mass: 690,000 kg and Dry Mass: 630000 and 451 Isp
402 m/s
Centaur engines are expensive. But in this case the actual costs will depend upon how long they can safely
have total burn time. Though perhaps cheaper engines- which means longer duration of burn
time could be found for LH&LOX.
Considering one might spend 1/2 billion to 1 billion on engines it could prompt such development.
And ability of restart engines could be something ISS gives the kick needed or possibly other boosters [say solids] could also attached to adapter [and discarded and replaced for each boost].
And to launch tanks they could launched from KSC, Russia, Japan, and Guiana.

But if assume Falcon 9 could somehow launch enough in short enough time, it could launch 
2 1/2 filled Centaur stages, and 2 centaur like tanks filled with 11,000 kg of fuel.
So need four launches within days of each other.
So Centaur with 9000 kg and 11,000 kg for tanks giving 40,000 kg of propellent
So that's 272 m/s and excluding costs of Centaur stage: 4 times 60 million- 240 million.
So that does not require longer burn time- 20,000 kg fuel used by each of them.
If Centuar could do this twice it halves their cost, if only once, then I would guess they are
about 200 million. So having them be able to burn 40,000 or 60,000 kg of fuel could make a big
difference.
And not sure how long they could be made to burn for.
But XCOR might manage to get cheaper engines with longer burn time, which could also could do this:
http://www.xcor.com/press/2013/13-11-19_XCOR_ULA_announce_hydrogen_milestone.html

But say engines cost 200 million and rocket fuel 240 million. And adapter say 200 million.
And lifting 200 tons of water. It's 272 m/s
And not including the 200 tons of water: 393 m/s
http://www.strout.net/info/science/delta-v/intro.html

4. What's a stable orbit? Well, 2 that have been suggested are GSO (~3400 m/s) and EML2 (~3700 m/s). I believe those are good numbers, but not sure. So for GSO you're looking at 12 ISS Booster flights and for EML2 you're looking at 13. So $2.4Bil for one and $2.6 Bil for the other. Not impossible... But then you have to factor in resupply, etc at the new altitudes.

You could go 1/2 way.
GTO and with perigee of say 5-6000 km. If going higher than LEO, you need shielding, and mainly you need shielding vs solar flare. And such shielding would shield you from the Van Allen belts.
Or in LEO you largely sheilded from solar flares. Van Allen belts, wiki:
"While protons form one radiation belt, trapped electrons present two distinct structures, the inner and outer belt. The inner electron Van Allen Belt extends typically from an altitude of 0.2 to 2 Earth radii (L values of 1 to 3) or 600 miles (1,000 km) to 3,700 miles (6,000 km) above the Earth. "
And:
"Missions beyond low Earth orbit leave the protection of the geomagnetic field, and transit the Van Allen belts. Thus they may need to be shielded against exposure to cosmic rays, Van Allen radiation, or solar flares. The region between two to four earth radii lies between the two radiation belts and is sometimes referred to as the "safe zone."
12,000 km to 25,000 km above Earth?
So if you had in orbit of 6000 to 25,000, you would spend a lot time in "safe zone". And crew would dock with it at apogee- and getting there could quickly go thru lower belt.
Though, wiki:
"Regardless of the differences of the flux levels in the Inner and Outer Van Allen belts, the beta radiation levels would be dangerous to humans if they were exposed for an extended period of time."

So "safe zone" is safer for satellites- and *not* saying don't need to be shielded from beta radiation. And other radiation. But in regards to Beta:   
"BETA – can only be stopped after traveling through 3 meters (about 10 feet) of air, a few centimeters (less than 2 inches) of water, or a thin layer of glass or metal. Additional covering, for example heavy clothing, is necessary to protect against beta- emitters. Some beta particles can penetrate and burn the skin." - See more at: http://www.nuclearconnect.org/know-nuclear/science/protecting#sthash.n5IeqvyQ.dpuf

"Alpha particles can be shielded by a sheet of paper or by human skin. But if materials that emit alpha particles are inhaled, ingested or enter your body through a cut in your skin, they can be very harmful.

Beta particles cannot be stopped by a sheet of paper. Some beta particles can be stopped by human skin, but some need a thicker shield (like wood) to stop them. Just like alpha particles, beta particles can also cause serious damage to your health if they are inhaled or swallowed. For example, some materials that emit beta particles might be absorbed into your bones and cause damage if ingested."
http://www.kingcounty.gov/healthservices/health/preparedness/radiation/facts.aspx

It seems the problem beta particles is:
" the bremsstrahlung produced by shielding the beta radiation with the normally used dense materials (e.g. lead) is itself dangerous; in such cases, shielding must be accomplished with low density materials, e.g. Plexiglass (Lucite), plastic, wood, or water "
http://en.wikipedia.org/wiki/Bremsstrahlung
So water stops beta radiation fairly easily, but beta hitting a metal first will it cause bremsstrahlung and that is harder to shield against.
So generally plastic and water would appear work best on outside, rather than the inside of ISS.
But something like 2 feet of water seems it would should stop a lot resulting bremsstrahlung. And it seems the more energetic radiation will more easily pass thru the thin metal resulting less bremsstrahlung.

So, not saying between the belts is safe, but rather, what saying is you need good shielding if going to staying out LEO, anywhere, for any length of time. And between the belts is less radiation compared to either of the belts and one need enough shielding to be safe from solar flares and GCR.
And also, if current spacesuits are not sufficient, it seems they could be designed so they would to allow space walks while in this orbit.

[Jim]

Let's use Centaur stages with their very costly engines

Too much thrust for ISS

[mmeijeri]

Too much thrust for ISS

Because the structure can't handle it I assume, not because it would result in impractically high acceleration? Looks as if you might want considerably higher acceleration if the structure could withstand the loads.

[john smith 19]

Wrong.  There is no need for that and it is unrealistic.  A zero g work/experiment environment with zero g habitation meets is more than adequate.  Any health issues can be alleviated by crew rotation rate.

Depends what your future view of humans is in space.

If you think its government crews rotating to a govt funded and built space station until it gets too old to work and then gets dumped then yes there is no need for this. 

OTOH if you think the human race should expand off Earth then actually knowing the limits of long term exposure to low gravity environments is pretty important. 

For example what if it turned out that 1/10g was enough to preserve muscle tone and eliminate the need for exercise sessions? I think the only way to resolve the long term issues will need primate tests 

The need is there because there are in fact, several important things which could be done on a ring station.  There could be a hotel for paying visitors; research on lunar and martian gravity at intervening rings; plant growth experiments; a prop depot.

Bottom line: There is plenty for it to do, but the government ain't interested.

That sounds about right. 

[Roy_H]

I have updated my sketch as a result of some valuable comments. It now shows small station keeping thrusters. Although I have shown groups, it would probably be better to have one or two articulated to point in almost any direction. I would expect these to be used sparingly like 1 minute per week or less.

There was a comment about curved floors in the living quarters. I did a calculation and if the cables were 223m long the center of the floor in a BA330 would be about 5.6cm lower than the ends and if the cables were 890m it would be about 1.4cm.

[john smith 19]

I have updated my sketch as a result of some valuable comments. It now shows small station keeping thrusters. Although I have shown groups, it would probably be better to have one or two articulated to point in almost any direction. I would expect these to be used sparingly like 1 minute per week or less.

There was a comment about curved floors in the living quarters. I did a calculation and if the cables were 223m long the center of the floor in a BA330 would be about 5.6cm lower than the ends and if the cables were 890m it would be about 1.4cm.

This is actually quit a large station and I think it'd take quite a lot of funding.   

I'd I'm reading your diagram right you've got at least 6 Bigelow modules on there and a pair of capsules. While having spare docking ports is usually a good idea (especially if they mate to both capsules and modules) I think it's pretty big.

I'll also note you could go for a more asymmetric design with the modules on each end of the tether doing different things and the tether incorporating pipes for fluid movement and cables for power and/or data transfer.

I think the other issue would be this is good for one g level at a time, whereas I'd say there are several g levels you'd like to test.

Realistic & near term? I'd say 1 modules each side of a central core module. but without some kind of pressurized tunnel how will crew transfer to the g loaded modules? Otherwise de-spin the moduels and reel them in on their tethers to berth with the core module?

BTW do the "arrays" you show include heat radiators? ISS has a pretty big one and you'll need one anyway.

[Roy_H]

This is actually quit a large station and I think it'd take quite a lot of funding.   

I'd I'm reading your diagram right you've got at least 6 Bigelow modules on there and a pair of capsules. While having spare docking ports is usually a good idea (especially if they mate to both capsules and modules) I think it's pretty big.

I'll also note you could go for a more asymmetric design with the modules on each end of the tether doing different things and the tether incorporating pipes for fluid movement and cables for power and/or data transfer.

I think the other issue would be this is good for one g level at a time, whereas I'd say there are several g levels you'd like to test.

Realistic & near term? I'd say 1 modules each side of a central core module. but without some kind of pressurized tunnel how will crew transfer to the g loaded modules? Otherwise de-spin the moduels and reel them in on their tethers to berth with the core module?

BTW do the "arrays" you show include heat radiators? ISS has a pretty big one and you'll need one anyway.

This is a simple sketch to show general arrangement. It should not be taken as a final design for manufacturing. Numbers of modules, and functions can change according to design requirements. As stated before there could be other modules on shorter cables for fractional g testing.

There are thousands of details not shown, including solar radiators, pipes and wiring attached to various cables, even the number of cables per module would likely be more in final design if for no other reason than backup cables. I consider all of these simple engineering details that have fairly obvious solutions and would prefer to discuss any that would be difficult or not obvious.

I did say that one pair of rotating modules is for living quarters, and the opposite for farming. But that is not cast in stone either. Apparently you have not read all of this thread, so you did not understand that the Sundancer modules are elevators to transfer people and materials from the non-spinning hub to the rotating modules. Robotic arms would pluck the elevator off the rotating cable and bring it to the port on the hub.

One requirement is that the mass/momentum of opposite module pairs must be exactly equal at all times. This means that if a person travels down the elevator to the living module, and equal mass must move down the other side to the farm. This might be best done with liquids, where there is a tank in each side and pipes going from one end through the center to the other end. A pump would move the liquid from one side to the other as required to maintain balance. Obviously this would have limits, so careful attention must be made during engineering and upgrades to keep the modules at equal mass.

Yes, funding is the major issue. Initial version could have just one module at each end for the rotating part, to reduce cost. A spare docking port is a safety issue, as would be having a spare elevator. I am thinking this is more likely to be funded privately than by government. Bigelow is looking for customers, and envisions two customers/module. If he gets 6 corporations to sign up that would be 3 modules, half way to this design. Now if the existing Bigelow 330 uses 1/3 space for 2 people to eat, sleep, and operate their test/manufacturing equipment, could 12 people stay in a rotating module as living space only? Actually I don't think so, and yes this design will be more expensive. But if you could squeeze 12 in, then the cost would be pretty close to the same. Some have pointed out that devoting 2 modules for farming is extravagant and it would be cheaper to just ship the food up. Probably true. Although aiming for self-sufficiency is a worthy goal in itself. People want to go to Mars and be self-sufficient, and I think that is a long way to go for this experiment. Prove a completely space environment self-sufficient habitat can function for years near earth before doing it millions of miles away.