Speculation: Segmented Spin gravity habitat sized for launch in 2017 BFR Cargos

[rakaydos]

So the BFR will offer a whole new level of payload to orbit. Is it enough to build a pre-assembled Oneill Colony? Spin gravity and all?


Assuming the framework can be made light enough that lift mass isnt an issue... By eyeball, the BFR Cargo's potetial cargo area is  a cone just under 9m wide (that skin is ridiculusly thin) and possily as much as 1/3 the ship's total 48m length, or 16m long... but that's a cone, and you need pie pieces to build a cylender. So cut the length short to fit 4m square at the narrow end, and 4m by 8m at the wide end... Aim for 8 segments per ring, 1 segment per launch.

At those dimentions, with 8 segments, the hollow donuthole is just over 9.5m at the narrowest according to my calculations (octogon with 4m sides, 4 meters + 2 x(2 meters x sqrt(2) )= 9.657 meters) allowing a BFR to dock at the center of the ring, 2001 Space Oddessy style. The outside of the ring is twice that at 18m, which can generate a mars gravity (.3g) at just under 4 RPM.

Is this concept more than just a pie on the sky?

[QuantumG]

http://www.nss.org/settlement/space/GlobusEasierSettlement.pdf

Worth reading.

[docmordrid]

I would think that this would be a project for Teathers Unlimited's SpiderFab.

https://www.nasa.gov/directorates/spacetech/niac/2012_phase_I_fellows_hoyt_spiderfab.html

http://www.tethers.com/SpiderFab.html

[KelvinZero]

So you are talking about a toroid, not one of those big cylinder things? What constraints are you aiming for? 2rpm or better? Full earth gravity or only Mars gravity?

(Elon has discussed a much more far fetched proposal: massive geodesic domes on mars made from components transported in BFS cargo. I vaguely recall glass panes. Anyway, if you can do an arbitrary sized dome then you can do an arbitrary sized sphere for example.)

We could just ask what you could assemble with Bigelow components just as examples, just to constrain it further.

[rakaydos]

http://www.nss.org/settlement/space/GlobusEasierSettlement.pdf

Worth reading.

Indeed, though it seems focused on 1g long term habitats, which I suppose was impled by my "oneill cylender" comment.

The design I put forth, though, is an ISS-level space habitat intended for up to 1/3g for human physioligy testing, with a discreet number of segmets constructed before launch and docked together in orbit before spinning up.

Spiderfab looks interesting, but I hope to invalidate it with pre-assembily.

[rakaydos]

So you are talking about a toroid, not one of those big cylinder things? What constraints are you aiming for? 2rpm or better? Full earth gravity or only Mars gravity?

(Elon has discussed a much more far fetched proposal: massive geodesic domes on mars made from components transported in BFS cargo. I vaguely recall glass panes. Anyway, if you can do an arbitrary sized dome then you can do an arbitrary sized sphere for example.)

We could just ask what you could assemble with Bigelow components just as examples, just to constrain it further.

The contraints I'm looking at is how shallow a pie-slice will fit in the BFR cargo. The shallower the angle, the more segments per ring and so the bigger the assemled ring is when it's spun up, allowing higher g/lower RPM, as well as more habitable area.

[speedevil]

The cylindrical part of BFS, around the airlock can carry a cylinder 9m diameter, by 8m long.
It can lift around 150 tons.
This is 75m^3 of aluminium or so.
If we assume flat 8*8m plates with minimum curvature, that is 1*8*8m or so overall.
For no particularly good reason, imagine they are 25mm thick.
We can carry 40 of them.

Assume working load is 150MPa, and that internal pressure is the same as Flagstaff Az (75KPa), that means that the workable diameter is 100m.

Let us ignore that for the moment, and assume we want to make a section of cylinder about the same diameter it is long.

For 40 panels, you can make a cylinder 30m in diameter, and 24m long.

The structural loading on this is about 15% of yield, meaning the joining can have quite large stress concentrations without issue.
Ten launches get you the shell of a large toroidal station with the outside diameter 80m, with a cylinder diameter of 30m.
Or a cylinder 200m or so long by 30.

It would need a whole full load of liquid air to fill it to STP, around 150 tons.

You then begin to outfit the inside, once in STP.

(toroidal station of course would not have the segments quite square, and they would be individual.)

Joins would be handled with two million five hundred thousand M8 bolts, all alone in the night.

[rakaydos]

The cylindrical part of BFS, around the airlock can carry a cylinder 9m diameter, by 8m long.
It can lift around 150 tons.
This is 75m^3 of aluminium or so.
If we assume flat 8*8m plates with minimum curvature, that is 1*8*8m or so overall.
For no particularly good reason, imagine they are 25mm thick.
We can carry 40 of them.

Assume working load is 150MPa, and that internal pressure is the same as Flagstaff Az (75KPa), that means that the workable diameter is 100m.

Let us ignore that for the moment, and assume we want to make a section of cylinder about the same diameter it is long.

For 40 panels, you can make a cylinder 30m in diameter, and 24m long.

The structural loading on this is about 15% of yield, meaning the joining can have quite large stress concentrations without issue.
Ten launches get you the shell of a large toroidal station with the outside diameter 80m, with a cylinder diameter of 30m.
Or a cylinder 200m or so long by 30.

It would need a whole full load of liquid air to fill it to STP, around 150 tons.

You then begin to outfit the inside, once in STP.

(toroidal station of course would not have the segments quite square, and they would be individual.)

Joins would be handled with two million five hundred thousand M8 bolts, all alone in the night.

In-space construction is low TRL.
I'm trying to keep the design to ISS-level module-docking type construction, hence the 8 pie-wedge payloads design.

[MikeAtkinson]

Another way would be to use inflatable structures. Central core + inflatable shell could probably reach 20m diameter, perhaps as much as 30m. About 8m long.

By joining them end-to-end it is possible to create cylinders, rings, etc. Joints could be simple berthing or include a node.

One obvious design would be a ring, with 4 nodes, from those nodes a link is made to a central cylinder made of several more inflatables.

[drzerg]

you can pack any segmented torus inside a cylinder. just make enough small blocks that can be reassembled on orbit

[Lar]

I see the how. I don't see the why.

Large constructions will need to be built in space using asteroidal materials, as to do otherwise implies a LOT of launches. Better to work on developing the mining and refining and transport equipment, IMHO.

But that's not the OP's question. I think the answer is yes, it could be done.

[speedevil]

In-space construction is low TRL.
I'm trying to keep the design to ISS-level module-docking type construction, hence the 8 pie-wedge payloads design.

I do not disagree with this, but to a degree, it's because it's been designed as a complex fragile mass-reduced thing.

Do not make a complex multipurpose robot if a simple one will work.
Yes, the Canadarm is awesome.

However, for the price of the Canadarm, you can buy many, many industrial robots.

The TRL of a general purpose robot able to do up arbitrary fasteners rapidly over a large work envelope is not high.

The TRL of a special purpose  robot able to do up one size of fastener, all in one orientation and bolt pattern, flat against a surface, where it doesn't really matter if all of the fasteners are fixed properly due to massive redundancy is rather higher.
(to join adjacent segments)

The TRL of a simple drawer-slide like mechanism to extend and hold the segment to be bolted on is again quite high, especially if initially you don't care about speed, and are willing to use massive redundancy. (cylindrical is a lot simpler than toroidal, the end-caps would be done after some learning had been done)

Industrial robots are quite capable of most of the tasks - the problems are in the control. This is greatly mitigated if you accept that everything goes very slowly for the initial fixings.
Light modifications to the arms will need to be done for thermal control.

On asteroidal mining - well...
The technical readiness of that is considerably below that of any in-space construction. The bare shell of the ~30m*240m*25mm cylinder above could be purchased for $3m in aluminium cost.
It will cost considerably more to have the segments fabricated into appropriate near-identical shapes, but this is something your average shipyard can do.

I can write a contract, and get people working on it today, for a remarkably small amount of money if I don't tell them it's for space.

Once you have the pressurised volume that the ITS can dock with, start to bring up lightly tested industrial and other equipment and start trying stuff.

[TrevorMonty]

I'm fan Oneil Cylinder as it provides varying levels of gravity, from 0 in middle to max on   shell. Settlements may need 1g but space tourism would prefer low G eg 0.1-0.3. Why go to space to experience 1g may as well stay at home. Gravity needs to be high enough to make daily living enjoyable without hassles associated with 0g. For long term stay being able to sit down for dinner without it floating off plate is must, along with bathroom activities.
With 0g just meters away in centre of cylinder tourists can have best of both worlds.

Depressurization due haul breach by debris  is not as serious as you think, a large cylinder takes 10-100s minutes to depressure with inch hole. Long enough to reach safe areas in haul while plugging  hole. I would hope anything big enough that can make large life threating holes could be avoided. Haul is likely to be layered with all services between floor and outer haul.

BFR definitely bring launch costs down for contruction, $100-200/kg  is realistic when buying dozens of flights all carry low value items like metal sheets. In space assembly where pieces are welded together by robotic arms is biggest challenge but achievable. Ideally construction of pressure haul wouldn't need any humans in space. Fitting out pressurized haul would need humans but they would be working in shortsleeve envirnoment, with gravity.

[rakaydos]

It sounds like the thread consensus is that in-space construction is a significantly better option than ground assembly and docking.

How much progress is being made on assembler robots? I saw the post on the spiderbot, but is it actually funded? What else is out there?

[speedevil]

It sounds like the thread consensus is that in-space construction is a significantly better option than ground assembly and docking.

How much progress is being made on assembler robots? I saw the post on the spiderbot, but is it actually funded? What else is out there?

Nobody has yet tried to do this as a conventional engineering project, which happens to be in space.
You do not try to design space hardware.
You take industrial hardware and make minimal modifications to it, and try it to see if it works.

You do not even go as far as http://mashable.com/2017/11/02/nasa-updates-international-space-station-printer/ - for example, if launch cost drops enough. The ISS needed a new printer, it actually required as far as I can tell one spring and some sponges.
Instead, it got composite parts, completely reengineered cover, lightened, more fastnings, ...

This made 50 $129 printers (as a lifetime buy) cost likely well over $50K each, probably $1M each, counting the fact that maybe four of them are likely to be used.

Compared to, for example, buying 50 different printers, and just trying them on orbit. (in a ventable cupboard, for the first few tests).

With cheap launch, actually trying stuff on orbit may be significantly cheaper than doing a 'proper' design or even test of earth hardware past first blush screening.

[Lar]

With cheap launch, actually trying stuff on orbit may be significantly cheaper than doing a 'proper' design or even test of earth hardware past first blush screening.

I think this is something that people are really struggling to internalise. But it is hugely important.

[rakaydos]

With cheap launch, actually trying stuff on orbit may be significantly cheaper than doing a 'proper' design or even test of earth hardware past first blush screening.

I think this is something that people are really struggling to internalise. But it is hugely important.

"Failure IS an option."

[John Alan]

The first country or entity that builds an honest to goodness space dock in orbit and offers assy services on orbit will make a fortune.
Just saying... a pressurized in orbit workshop that humans and robots can weld and assemble stuff  from brought up piece parts and chunks... is where long term this needs to go... 

[envy887]

Another way would be to use inflatable structures. Central core + inflatable shell could probably reach 20m diameter, perhaps as much as 30m. About 8m long.

By joining them end-to-end it is possible to create cylinders, rings, etc. Joints could be simple berthing or include a node.

One obvious design would be a ring, with 4 nodes, from those nodes a link is made to a central cylinder made of several more inflatables.

Inflatables can be much, much larger than this. If you use 1 mm thick Kevlar sheets you can make a 100 meter diameter sphere, holding 524,000 cubic meters of air at STP (almost 600 times larger than ISS). Double the wall thickness for a safety factor of two and it still only masses ~90 tonnes, and folded down and vacuum packed needs less than 100 cubic meters of launch volume - easily launched on one BFS.

This approach could yield huge pressurized volumes that could be internally fitted out by crew or robots. With such huge volumes depressurization is an unlikely emergency, since even a huge 1 meter hole would take over an hour to depressurize that volume.

IMO, the approach of first inflating a pressure vessel, then constructing usable space inside it, is far easier than making everything modular and docking or doing EVA for construction. Obviously the inflatable needs a bus for a launch mount, visiting vehicle docking, an airlock to the interior, propulsion, comms, some power and thermal control, and to carry the initial inflation charge.

I'm fan Oneil Cylinder as it provides varying levels of gravity, from 0 in middle to max on   shell. Settlements may need 1g but space tourism would prefer low G eg 0.1-0.3. Why go to space to experience 1g may as well stay at home. Gravity needs to be high enough to make daily living enjoyable without hassles associated with 0g. For long term stay being able to sit down for dinner without it floating off plate is must, along with bathroom activities.
With 0g just meters away in centre of cylinder tourists can have best of both worlds.

Depressurization due haul breach by debris  is not as serious as you think, a large cylinder takes 10-100s minutes to depressure with inch hole. Long enough to reach safe areas in haul while plugging  hole. I would hope anything big enough that can make large life threating holes could be avoided. Haul is likely to be layered with all services between floor and outer haul.

BFR definitely bring launch costs down for contruction, $100-200/kg  is realistic when buying dozens of flights all carry low value items like metal sheets. In space assembly where pieces are welded together by robotic arms is biggest challenge but achievable. Ideally construction of pressure haul wouldn't need any humans in space. Fitting out pressurized haul would need humans but they would be working in shortsleeve envirnoment, with gravity.

This, but "construction" of the pressure hull is as simple as unpacking and inflating it. Kevlar has the advantage of being extremely cut and puncture resistant, and if built in 2 to 4 multiple inflatable wall layers (e.g. 1 mm of Kevlar / 10 cm of air / 1 mm Kevlar / repeat) works as a MMOD shield. A thin sheet of Mylar on the exterior could be reflective insulation. Thin-cell solar panels with wiring or flex circuits could be stitched to the outside and folded in with the shell before launch.

Some type of active thermal control like a variable albedo coating or a movable sunshade/reflector would be nice for controlling internal temperatures, although the thermal inertial of 600 tonnes of air helps a lot with smoothing out short term insolation variations.

[rakaydos]

IMO, the approach of first inflating a pressure vessel, then constructing usable space inside it, is far easier than making everything modular and docking or doing EVA for construction. Obviously the inflatable needs a bus for a launch mount, visiting vehicle docking, an airlock to the interior, propulsion, comms, some power and thermal control, and to carry the initial inflation charge.

Also stationkeeping and reactionwheel spindown thrusters. If the raptorRCS from the BFR becomes industry standard, so will the BFS "refueling port"docking standard,, which is another thing to include.