Author Topic: Realistic, near-term, rotating Space Station  (Read 945174 times)

Offline Roy_H

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Re: Realistic, near-term, rotating Space Station
« Reply #880 on: 07/05/2018 01:35 pm »
@Paul451 I do not propose any counter rotating mass either flywheel or counter rotating hab. You mis-understand the axis of rotation, it is north-south, but not tilted like the earth. No change in orientation realitive to sun over the year.

@Jim As I understand it, the Bigelow style has better radiation shielding and micrometorite protection than aluminum. Inflation is not the only reason to choose this style.
« Last Edit: 07/05/2018 02:25 pm by Roy_H »
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Offline Coastal Ron

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Re: Realistic, near-term, rotating Space Station
« Reply #881 on: 07/05/2018 02:51 pm »
@Jim As I understand it, the Bigelow style has better radiation shielding and micrometorite protection than aluminum. Inflation is not the only reason to choose this style.

If you are trying to avoid the secondary radiation issues with aluminum, then why not assume rigid composite sections instead of flexible ones? That way what you launch with is what you build with, and you don't have to add additional mass to hold up or secure the inflatable material. And 5m diameter sections are going to be pretty big for any needs.

Just a thought...
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Offline LMT

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Re: Realistic, near-term, rotating Space Station
« Reply #882 on: 07/05/2018 03:11 pm »
the Bigelow style has better radiation shielding and micrometorite protection than aluminum. Inflation is not the only reason to choose this style.

Kevlar-style material presently gives micrometeorite protection to BEAM and also to ISS aluminum modules.  So this form of protection would seem to be required, at least around crewed modules, irrespective of construction method.

As for radiation, is BEAM's non-metallic construction now proved to be a better radiation shield?  I haven't seen the experimental results; are they published?  Press release May 26 2017: "...GCR dose rates inside the BEAM are similar to other space station modules..."

--

Note:  A lower orbit would likely give a more significant improvement in both micrometeorite impact rate and also radiation dose rate.  For example, lowering a station from 400 to 250 km:

1.  cuts impacts ~ 90%



2.  cuts radiation dose ~ 50%



Refs

Benton, E. R., & Benton, E. V. (2001). Space radiation dosimetry in low-Earth orbit and beyond. Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 184(1-2), 255-294.

Englert, C. R., Bays, J. T., Marr, K. D., Brown, C. M., Nicholas, A. C., & Finne, T. T. (2014). Optical orbital debris spotter. Acta Astronautica, 104(1), 99-105.

Kessler, D. J. (1989). Orbital debris environment and data requirements.
« Last Edit: 07/05/2018 03:56 pm by LMT »

Offline LMT

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Re: Realistic, near-term, rotating Space Station
« Reply #883 on: 07/05/2018 10:57 pm »
Not viable.  Magnetic torqueing for attitude control is for small or passive spacecraft.  They are good for CMG unloading, see H ST.

No, you scale the magnetic moment as needed and replace CMG.  Works very best in VLEO, where field is strongest.

No, still not feasible. Can't scale it large enough and then there is the power question.   It isn't strong enough or quick reaction.  It is good for long term torques for unloading CMGs.  For example, magnetic torquing can't handle loads from a spacecraft docking.

Sure it is.  Scaling is linear irrespective of power: e.g. recalc torque w/HTS loop @1,000 A/mm2.  Plus docking loads are small at hub, cf '2001'.
« Last Edit: 07/05/2018 11:31 pm by LMT »

Offline LMT

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Re: Realistic, near-term, rotating Space Station
« Reply #884 on: 07/06/2018 12:20 am »
Suppose you do design a human scale, short radius, baton-style AG station..., and... at martian gravity the bone loss continues unabated...

A concerning possibility.  Assuming your radius is too short for tolerable spin-up to 1 g, you might:

1.  Periodically undock a pair of "gym airlocks" from the station "floor", and lower them "down" cables to a radius that grants 1 g for bone-building exercise.

Or

2.  Mount the gyms in a linear sled "hybrid" configuration, alongside the station's centerline.  The sleds would accelerate and decelerate to give 1 g, with a mid-point interior flip.  Fortunately the flips have proved tolerable in pilot studies.  See Seyedmadani et al. 2018.



Bonus:  if your station radius were barely human scale, as with your DeTA, you could leverage the wicked Coriolis effect to make a Yeh fountain.



Refs

Seyedmadani, K., Gruber, J. A., & Clark, T. K. (2018). The Linear Sled" Hybrid" Approach for Artificial Gravity as a Countermeasure for Crewed Deep Space Gateway Missions. LPI Contributions, 2063.
« Last Edit: 07/06/2018 12:45 am by LMT »

Offline Roy_H

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Re: Realistic, near-term, rotating Space Station
« Reply #885 on: 07/06/2018 02:17 am »
@LMT thank you for your information on radiation and micro meteorite impact versus altitude. Your data looks pretty official, and I can't remember where I read about the Bigelow style being superior to aluminum for radiation. So this data shows equal. On the NASA website I found the study shows that there is a lot of debris in the 600km to 1000km altitude, and yes it starts rising significantly at the ISS altitude of 400km, but not nearly as steeply as your micrometer it impact graph. However I suspect that the low altitude lack of debris is the result of atmosphereic drag, which is good for safety but means high maintenance for reboost.
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Offline LMT

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Re: Realistic, near-term, rotating Space Station
« Reply #886 on: 07/06/2018 03:34 am »
I can't remember where I read about the Bigelow style being superior to aluminum for radiation. So this data shows equal.

Or is it a bit more mass-efficient?  C (12) vs. Al (27).

I suspect that the low altitude lack of debris is the result of atmosphereic drag...

Yes, drag deorbits things quickly @250.

...which is good for safety but means high maintenance for reboost.

Reboost?  Not often.  Just raise a pirate flag upon the mainmast and raid the VLEO seas.

(i.e., deploy a multi-km axial ISEP boom to counter drag @250 electrodynamically.)





Offline mikelepage

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Re: Realistic, near-term, rotating Space Station
« Reply #887 on: 07/06/2018 08:33 am »
What he's saying is that you wouldn't need to actually expend propellant because each rotating segment effectively serves as reaction mass for the other.

Yes, electrical energy moving the mass is an advantage, but something from my youth tells me that counter-rotating wheels sharing the same axis will be unstable in the Z axis.

If by unstable you mean that there's no net spin stabilization, then yes, this is correct. From an idealized physics standpoint, the station would behave as if it were not rotating at all. The question becomes, is spin stabilization useful? Depends on where you want this station to exist, I'd imagine.

At the moment my thinking is that you do want some net angular momentum to stabilise the structure, and to torque against, and you do any axis reorientation when the flywheel and main habitat are not rotating relative to each other.  In this state, the angular velocity for the whole structure would be half the angular velocity for the main habitat during nominal operations.

Electric motors can go just as fast backwards as they can forwards, so you have the flywheel going full speed counter spin during nominal operations, and full speed forward spin to bring the main habitat to a halt.  Down the line at some point, the structure will get too big to bring the entire habitat to a halt, but once we get to that point you'll use this same principle to bring a docking module to a halt.

Quote
Quote
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I'm not too concerned about additional mass. If we already decided to make space station strong enough to rotate, the need for additional mass is already a long foregone conclusion.

The additional mass would not be related to the structural mass needed for holding a rotating structure together, but since you mentioned it you would have to beef up that same structure to be able to survive in case the bearing seizes up.

And besides, if you are already spinning both wheels to generate artificial gravity, why not have them spinning in the same direction? I see no advantage to adding the mass and complexity for splitting them up. Do you?

The main advantage to keeping L=0 is that the station can be reoriented at will without expending any fuel. See Mikelepage's post about possible benefits of having one side always facing the sun. If the station has an overall angular momentum, then you'll need to continually expend reaction mass to induce a net torque on your station (or choose your orbit around massive body very carefully).

Of course, thermal cycling is a relatively well understood phenomenon, and we may decide that we don't care which side of the station faces the sun in which case this benefit loses utility. A list of benefits/drawbacks to each scheme would be worthy of its own discussion.

But I agree that two counter rotating rings would be a significant engineering challenge that may well prove to not actually be worth the trouble regardless. If I went the zero angular momentum route, I think I'd rather have the entire main body of the station rotate in a single direction while using a central, enclosed flywheel (flyrod?) for counter-rotation. Still a mass penalty, but the rod could be magnetically suspended and you wouldn't have to worry about things like wearing out mechanical bearings or maintaining a vacuum seal across moving parts.

While it's probably possible to have two equal counter-rotating halves to the structure, I think at least in these early days it's important to eliminate or minimise anything that needs to go through a rotating joint.  To me the most obvious first configuration is to keep all your pressurised space in one main half/hab, and then have an additional non-pressurised flywheel. 

I agree thermal cycling is fairly well understood, but the problem remains that you have a net energy input from the sun.  If your main structure is constantly rotating in and out of sunlight, this means you can't use any part of it to get rid of waste heat, so you'll have to have systems to pump your excess heat-laden radiator fluid through a joint from your rotating section to some permanently-shaded radiators on some additional, non-rotating, structure. I'm not 100% on this, but I have yet to see why it isn't easier to point your rotation axis at the sun and mount your radiators on the permanently shaded side of your rotating structure.


Offline Jim

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Re: Realistic, near-term, rotating Space Station
« Reply #888 on: 07/06/2018 03:28 pm »
@Jim As I understand it, the Bigelow style has better radiation shielding and micrometorite protection than aluminum. Inflation is not the only reason to choose this style.


No, not true.  Both are easy to add to aluminum.

Offline Jim

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Re: Realistic, near-term, rotating Space Station
« Reply #889 on: 07/06/2018 03:29 pm »
[
Sure it is.  Scaling is linear irrespective of power: e.g. recalc torque w/HTS loop @1,000 A/mm2.  Plus docking loads are small at hub, cf '2001'.

wrong, you really don't know what you are talking about.  It is too weak.  That is why it is has never been employed in a large spacecraft.
« Last Edit: 07/06/2018 03:30 pm by Jim »

Offline 1

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Re: Realistic, near-term, rotating Space Station
« Reply #890 on: 07/06/2018 07:12 pm »
I'm not 100% on this, but I have yet to see why it isn't easier to point your rotation axis at the sun and mount your radiators on the permanently shaded side of your rotating structure.

It might be easier for many reasons. But this feature requires constant reorientation of your station. Thus spin stabilization is NOT desirable here. It actually hurts you; a lot. Here's what I think the problem is.

you do any axis reorientation when the flywheel and main habitat are not rotating relative to each other.

I think you (and a few other folks) are unaware of exactly how conservation of angular momentum manifests. If you try to change the orientation of a rotating object, it will push back against you and cause you to spin in the direction it was formerly going.

Check out the video below, where a fellow spins up a bicycle tire and then, while sitting on a stool, tries to turn it upside down.



Note that when pulls his feet up and turns the wheel upside down, the whole system of tire-and-guy-holding-it is still spinning the exact same direction it was before. He's imparted a momentum of -2L on the wheel (turning it over) but at the same time imparted a momentum of +2L on himself.

Your proposed orientation of always facing the sun effectively flips the station over every six months. This requires the same torque as what would be needed to completely spin down the station, and then spin it back up in the opposite direction. And then it needs to be done again, and again, and again. If your station has a net momentum greater than zero, then it will need to constantly expend fuel to reorient.

Note that refueling a space station is also relatively well understood; and since the station will almost certainly need resupply flights of some kind anyway, simply adding fuel to the manifest may well be easiest thing to do if you go with the always-face-the-sun route.

As a side note, I will say that I believe the solar panel / radiator issue is trivial to solve. Radiators can be placed inside the wheel, so to speak, and simply radiate up and down rather than inward or outward; and if you need more solar panels, just bolt them onto the hab ring. We're already beefing this thing up to withstand rotation; adding additional hardpoints is easy.

Offline LMT

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Re: Realistic, near-term, rotating Space Station
« Reply #891 on: 07/06/2018 11:45 pm »
Sure it is.  Scaling is linear irrespective of power: e.g. recalc torque w/HTS loop @1,000 A/mm2.  Plus docking loads are small at hub, cf '2001'.

wrong, you really don't know what you are talking about.  It is too weak.  That is why it is has never been employed in a large spacecraft.

It hasn't been done at that scale because no one's done satellite HTS at that scale.  But here we are, talking about big ol' AG space stations.  So we scale up.

And you shouldn't accuse, especially when you're the one who hasn't demonstrated familiarity.  Do you even know how to coax 1,000 A/mm2 out of HTS?  Even theoretically?   

::) 

Demonstrate familiarity and calculate some useful HTS torques for us. That would be a good post number forty-odd-thousand.
« Last Edit: 07/08/2018 04:12 pm by LMT »

Offline Bob Shaw

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Re: Realistic, near-term, rotating Space Station
« Reply #892 on: 07/07/2018 12:27 am »
I don't know if anyone has mentioned this before, but references to the 2001 Space Station are a bit more problematic than one might expect. Kubrick used optical printing effects to consyantly change the size of the Orion shuttle and the station during docking - there is no actual explicit space station diameter, and thus no real 'gravitational' pull.

Offline Paul451

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Re: Realistic, near-term, rotating Space Station
« Reply #893 on: 07/07/2018 02:18 am »
Sure it is.  Scaling is linear irrespective of power: e.g. recalc torque w/HTS loop @1,000 A/mm2.  Plus docking loads are small at hub, cf '2001'.
wrong, you really don't know what you are talking about.  It is too weak.  That is why it is has never been employed in a large spacecraft.
It hasn't been done at that scale because no one's done satellite HTS at that scale.  But here we are, talking about big ol' AG space stations.  So we scale up.
And you shouldn't accuse, especially when you're the one who hasn't demonstrated familiarity.  Do you even know how to coax 1,000 A/mm2 out of HTS?  Even theoretically?   
Demonstrate familiarity and calculate some useful HTS torques for us. That would be a good post number forty-odd-thousand.

Again, stop demanding other people prove your claims.

If you think a millinewton-metre system can be turned into a kilonewton-metre system, show your work.

Offline mikelepage

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Re: Realistic, near-term, rotating Space Station
« Reply #894 on: 07/07/2018 05:22 am »
Check out the video below, where a fellow spins up a bicycle tire and then, while sitting on a stool, tries to turn it upside down.
<snip>
Your proposed orientation of always facing the sun effectively flips the station over every six months. This requires the same torque as what would be needed to completely spin down the station, and then spin it back up in the opposite direction. And then it needs to be done again, and again, and again. If your station has a net momentum greater than zero, then it will need to constantly expend fuel to reorient.

I've watched a number of such videos but that one is short and sweet and I'll use it, thanks! I'm fairly comfortable with my understanding of angular momentum - but I hadn't considered that issue of maintaining a net angular momentum in this context.  There's nothing about the geometry of the prototypes we're building that requires net L, but it did seem to be a cute way of using a flywheel and I hadn't had reason to question it yet.  Thanks for the feedback.

Quote
Note that refueling a space station is also relatively well understood; and since the station will almost certainly need resupply flights of some kind anyway, simply adding fuel to the manifest may well be easiest thing to do if you go with the always-face-the-sun route.

Of course, but that constrains you badly as soon as you exit cis-lunar space.  Double checking your thinking, fuel use for reorientation would only be necessary in the case of net L station.  In a L=0, sun-facing, station, a gimballed gyro/flywheel should be sufficient for normal reorientation operations, with token fuel only needed for desaturation.

Quote
As a side note, I will say that I believe the solar panel / radiator issue is trivial to solve. Radiators can be placed inside the wheel, so to speak, and simply radiate up and down rather than inward or outward; and if you need more solar panels, just bolt them onto the hab ring. We're already beefing this thing up to withstand rotation; adding additional hardpoints is easy.

Nice.  Might be trivial to you, but I've not seen that solution proposed before.
« Last Edit: 07/07/2018 05:23 am by mikelepage »

Offline LMT

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Re: Realistic, near-term, rotating Space Station
« Reply #895 on: 07/08/2018 06:05 am »
Terrestation with 1g Elevator Gym

Suppose you do design a human scale, short radius, baton-style AG station..., and... at martian gravity the bone loss continues unabated...

A concerning possibility.  Assuming your radius is too short for tolerable spin-up to 1 g, you might:

1.  Periodically undock a pair of "gym airlocks" from the station "floor", and lower them "down" cables to a radius that grants 1 g for bone-building exercise.

Or

2.  Mount the gyms in a linear sled "hybrid" configuration, alongside the station's centerline.  The sleds would accelerate and decelerate to give 1 g, with a mid-point interior flip.  Fortunately the flips have proved tolerable in pilot studies.  See Seyedmadani et al. 2018.



Refs

Seyedmadani, K., Gruber, J. A., & Clark, T. K. (2018). The Linear Sled" Hybrid" Approach for Artificial Gravity as a Countermeasure for Crewed Deep Space Gateway Missions. LPI Contributions, 2063.

The possibility of bone loss and other medical problems under martian g suggests a need for a 1 g gym facility, e.g., on a LEO space station designed only for martian centripetal g.

One application example:  adapt the linear sled hybrid gym of Seyedmadani et al. 2018 to the notional Terrestation.   This would add a 1 g gym to a station designed only for martian g.

Running the numbers, hopefully correctly, we get this:



Terrestation parameters:

Radius:  782 m

Rotation period:  90 s

Centripetal acceleration at rim:  Mars g

Terrestation layout:

Booms connect the hub dock to crewed facilities at rim.

Elevators run along the booms.  Each elevator is an ITS cargo:  8 m in diameter, constructed as a mobile airlock with battery power.

Each elevator attaches to a motorized sled.  The sled rolls on the boom. 

Gym mod:

These typical and necessary facilities are modified to serve as 1 g gym.

The elevator mount is modified for rotation.  It now connects to the sled via rotary motor:  visually, a drink can impaled on a coat hook.

The sled is beefed up to provide a max acceleration of 8.4 m/s2, and max speed of 75 m/s.

Illustrated results:

The elevator gym is drawn as a "T" figure, with the t-cross indicating the crew-weighted gym floor.  The gym position is shown at 2-second intervals.  The gym rotates freely under varying force vectors to maintain constant floor-down acceleration, synchronizing visual and vestibular orientation and preventing motion sickness.  Force vectoring produces a maximum gym deflection from vertical of ~ 30 degrees near the hub.

As in Seyedmadani et al. 2018, a flip is required at the midpoint of each run.  The Terrestation's deflection angle reduces the required flip angle from 180 degrees to 120 degrees. 

As envisioned, sled acceleration ends as the gym passes the hub.  The rotary motor engages and rotates the gym 120 degrees.  Then the rotary motor disengages and the sled decelerates the gym.

A full gym cycle runs ~ 90 s, coincidentally equaling Terrestation rotation period.

Notes:

As this gym configuration would leverage existing station hardware, it has a good economic case.

Max speed of 75 m/s would produce significant wear on the sled and boom over time.  Perhaps wheeled mechanisms should be supplanted with superconducting magnets arranged in a frictionless electrodynamic suspension configuration.  Electrodynamic suspension, acceleration and braking on the boom could be accomplished by the station-adapted electrodynamic methods of Jevtovic 2017.


Refs:

Jevtovic, P. (2017). Electrodynamic Gravity Generator for Artificial Gravity Modules. In AIAA SPACE and Astronautics Forum and Exposition (p. 5140).

Seyedmadani, K., Gruber, J. A., & Clark, T. K. (2018). The Linear Sled" Hybrid" Approach for Artificial Gravity as a Countermeasure for Crewed Deep Space Gateway Missions. LPI Contributions, 2063.

« Last Edit: 07/08/2018 07:21 pm by LMT »

Offline Paul451

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Re: Realistic, near-term, rotating Space Station
« Reply #896 on: 07/08/2018 09:56 am »
Radius:  782 m
Rotation period:  90 s
Centripetal acceleration at rim:  Mars g

That's 2/3rds of an RPM. At 780m radius, less than 1.1 RPM produces a full 1g. (With the Mars-g level at 300m from centre.)

In which case, what on Earth do you need the hideously complex elevator-gym-piston-thing for? (Also the rotation of the elevator-pod-thing is given at 30RPM. If that is somehow tolerable when repeated every few seconds, then surely a constant 4 RPM at a more reasonable 60m is fine.)

Offline LMT

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Re: Realistic, near-term, rotating Space Station
« Reply #897 on: 07/08/2018 02:38 pm »
At 780m radius, less than 1.1 RPM produces a full 1g.

Working assumption was a station "designed only for martian g".  To get 1 g, you can:

1.  increase the structural mass considerably to handle 1 g across the entirety of the very large station,

or

2.  just rotate the elevators. 

(1.) is of course astronomically more expensive.

Also the rotation of the elevator-pod-thing is given at 30RPM.

:D 

No, the gym rotates, from passengers' perspective, only 120 degrees, once every 45 s.  Where'd you get 30 rpm?  Did you not understand the paper on the linear sled hybrid?
« Last Edit: 07/08/2018 05:38 pm by LMT »

Offline LMT

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Re: Realistic, near-term, rotating Space Station
« Reply #898 on: 07/08/2018 06:56 pm »
@LMT thank you for your information on radiation and micro meteorite impact versus altitude. Your data looks pretty official, and I can't remember where I read about the Bigelow style being superior to aluminum for radiation. So this data shows equal.



One way to eliminate most radiation concerns at a space station:

1.  OLTARIS simulation indicates that 20 g/cm2 C-C hull + 40 g/cm2 water cuts proton flux by more than 90%. 

2.  A single ITS 150-ton water payload could shield ~ 380 m2 under that 40 cm water depth. 

3.  And as we saw above, radiation dose rate in VLEO is ~ 50% of ISS rate. 

4.  Therefore a Bigelow-style vessel in VLEO, having surface area of 380 m2, could be fully water-shielded by one ITS water payload, to give a dose rate < 5% of the ISS dose rate.

It would be a dose rate in the ballpark of airliner dose rate.

--

Update: 

h/t mikelepage:  Globus & Strout 2015, Table 6, gives a further OLTARIS shielding result, showing the modeled effect of LEO orbit inclination on biological effect.  The result indicates that an equatorial low-Earth orbit (ELEO) should encounter radiation having significantly lower biological effect. 



This suggests that point (2.), above, may overstate the shielding requirement for "airliner-class" protection, where orbit inclination is much less than ISS inclination (52 deg) and orbit is also safely outside the common extent of the South Atlantic Anomaly (red).



An orbit with inclination < 5 deg might safely skirt the South Atlantic Anomaly and win the ELEO benefit of Globus & Strout. 

As it happens, the ISEP method can:

(1.)  maintain VLEO without propellant expenditure

while also

(2.)  unavoidably decreasing orbit inclination toward ELEO, due to the electrodynamic force vector.  Estes et al. 2000.

Result:

The resulting "EVLEO" altitude and inclination would allow a thinner water shield.  "Airliner-class" shielding thickness would be much less than 40 cm.  A single ITS water payload could therefore shield far more than 380 m2 of crewed surface area, offering airliner-class radiation levels potentially across thousands of square meters of crewed facility surface.

Refs:

Estes, R. D., Lorenzini, E. C., Sanmart-egrave, J., n, Pel-Uuml, J., ez, ... & Vas, I. E. (2000). Bare tethers for electrodynamic spacecraft propulsion. Journal of Spacecraft and Rockets, 37(2), 205-211.

Globus, A., & Strout, J. (2015). Orbital Space Settlement Radiation Shielding. preprint, issued July 2015 available on-line at space. alglobus. net.
« Last Edit: 07/14/2018 06:52 pm by LMT »

Offline ppnl

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Re: Realistic, near-term, rotating Space Station
« Reply #899 on: 07/08/2018 07:32 pm »
Radius:  782 m
Rotation period:  90 s
Centripetal acceleration at rim:  Mars g

That's 2/3rds of an RPM. At 780m radius, less than 1.1 RPM produces a full 1g. (With the Mars-g level at 300m from centre.)

In which case, what on Earth do you need the hideously complex elevator-gym-piston-thing for? (Also the rotation of the elevator-pod-thing is given at 30RPM. If that is somehow tolerable when repeated every few seconds, then surely a constant 4 RPM at a more reasonable 60m is fine.)

780m seems excessive. Anything at or below 2 rpm seems to have no negative effect at all. So at most a radius of 225 meters is needed. People seem to be able to adapt to ten times that so you could go much smaller.

For a first time rotating space station I would suggest keeping it as simple as possible. Just a habitat connected to a counterbalance by 225m cable. Maybe the counterbalance could be a large flywheel so that you could spin up and down without the need of reaction mass. And maybe solar panels mounted on the counter balance that can point in any direction so there is no need to change the axis of rotation.

 

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