Realistic, near-term, rotating Space Station

[lamontagne]

As the station turns at its 'gravity' inducing speed or 1 rpm ,the inner reaction wheel must be forced to rotate with it.  This induces strain in one direction, then in the other.  The stain is very slightly unbalanced over time, and induces a very small fraction of a rotation, about 1 degree per day, a tiny fraction of a degree per rotation of the station.  the vector of this strain turns slowly, eventually going back to its original direction after a year for a final work of 0.
I hope.

[LMT]

Alternatively, i still don't understand rotating bodies.

You could model the station's multi-body connections and simulate motion in FreeDyn.

Maybe try a team challenge, since others are commenting.

[lamontagne]

Calculation of the reaction wheel for John's station.

The energy in the reaction wheel is 1/2Iw^2, or in this case about 1750 kWh, or about 25 teslas.  The cars, not the unit:-)

[JohnFornaro]

Calculation of the reaction wheel for John's station.

The energy in the reaction wheel is 1/2Iw^2, or in this case about 1750 kWh, or about 25 teslas.  The cars, not the unit:-)

Hah!  Mucho Thankso.  I've been reading up on gyroscopic precession.  Turns out the bicycle wheel contraption they use in thos videos are inappropriate inspace.

[JohnFornaro]

Alternatively, i still don't understand rotating bodies. ;)

Tell me about it.

[1]

Unfortunately cancelling the slow rotation doesn't work. After 6 months the station axis is rotated around 180°, and conservation means you need to dump all that angular momentum somewhere.

It's actually worse than this. After rotating 180 degrees, your ring appears from the viewpoint of a distant observer to be rotating the exact opposite direction. This functionally means you need the equivalent energy (and, if no counterweight, equivalent RCS reaction mass) of completely spinning the ring down, and then spinning it back up the opposite direction. This would need to be done twice per year. Technically, this is also 'just' an engineering problem, but boy is it a sucky one.

I like the idea of an outer, counterrotating shielding ring because it doesn't really need most of the ancillary life support to keep the meatbags alive. That means you could feasibly 'attach' it with magnetic bearings; probably wouldn't have to worry about pressure seals across co-moving objects, etc. Both radiation shielding and spin-angular-momentum cancelling are potentially very high-mass operations. Combining the two as much as feasible is probably a good idea.

[lamontagne]

Unfortunately cancelling the slow rotation doesn't work. After 6 months the station axis is rotated around 180°, and conservation means you need to dump all that angular momentum somewhere.

It's actually worse than this. After rotating 180 degrees, your ring appears from the viewpoint of a distant observer to be rotating the exact opposite direction. This functionally means you need the equivalent energy (and, if no counterweight, equivalent RCS reaction mass) of completely spinning the ring down, and then spinning it back up the opposite direction. This would need to be done twice per year. Technically, this is also 'just' an engineering problem, but boy is it a sucky one.

I like the idea of an outer, counterrotating shielding ring because it doesn't really need most of the ancillary life support to keep the meatbags alive. That means you could feasibly 'attach' it with magnetic bearings; probably wouldn't have to worry about pressure seals across co-moving objects, etc. Both radiation shielding and spin-angular-momentum cancelling are potentially very high-mass operations. Combining the two as much as feasible is probably a good idea.

Sigh, guess it was too good to be true.  Well at least the other counter rotating ring idea works.

[Twark_Main]

Unfortunately cancelling the slow rotation doesn't work. After 6 months the station axis is rotated around 180°, and conservation means you need to dump all that angular momentum somewhere.

It's actually worse than this. After rotating 180 degrees, your ring appears from the viewpoint of a distant observer to be rotating the exact opposite direction. This functionally means you need the equivalent energy (and, if no counterweight, equivalent RCS reaction mass) of completely spinning the ring down, and then spinning it back up the opposite direction.

Correct. By "all that angular momentum" I just meant "a lot of angular momentum." I knew it was twice the total station angular momentum (less any manipulable gyroscopic devices like reaction wheels or CMGs, and/or flywheels or other station components that act like reaction wheels or CMGs) but I couldn't figure out how to phrase it without the paragraph becoming too verbose, so I went with (apparently insufficient) vagueness. Sorry if the wording was unclear, or implied false precision.

about 1750 kWh, or about 25 teslas.  The cars, not the unit:-)

Thanks, I would've been very confused without the clarification! Surely the car would be capitalized.

For the unit, lowercase is indeed correct. Same goes for watts, newtons, etc.

[1]

Sorry if the wording was unclear, or implied false precision.

On the contrary; the point of your post was crystal clear to me. My replay was intended to reinforce that point as it's generally a hell of a lot more difficult to build intuition regarding the behavior of rotating objects vs non-rotating. I am very much a poor-but-dedicated student of the Feynman technique.

[JohnFornaro]

After rotating 180 degrees, your ring appears from the viewpoint of a distant observer to be rotating the exact opposite direction.

How can the distant observer affect the direction of rotation of the station?  It seems to me more like an optical illusion as seen by the distant observer.

[lamontagne]

Unfortunately cancelling the slow rotation doesn't work. After 6 months the station axis is rotated around 180°, and conservation means you need to dump all that angular momentum somewhere.

It's actually worse than this. After rotating 180 degrees, your ring appears from the viewpoint of a distant observer to be rotating the exact opposite direction. This functionally means you need the equivalent energy (and, if no counterweight, equivalent RCS reaction mass) of completely spinning the ring down, and then spinning it back up the opposite direction.

Correct. By "all that angular momentum" I just meant "a lot of angular momentum." I knew it was twice the total station angular momentum (less any manipulable gyroscopic devices like reaction wheels or CMGs, and/or flywheels or other station components that act like reaction wheels or CMGs) but I couldn't figure out how to phrase it without the paragraph becoming too verbose, so I went with (apparently insufficient) vagueness. Sorry if the wording was unclear, or implied false precision.

about 1750 kWh, or about 25 teslas.  The cars, not the unit:-)

Thanks, I would've been very confused without the clarification! Surely the car would be capitalized.

For the unit, lowercase is indeed correct. Same goes for watts, newtons, etc.

To be honest I got it doubly wrong here, as I thought the unit was written like its symbol   

[lamontagne]

After rotating 180 degrees, your ring appears from the viewpoint of a distant observer to be rotating the exact opposite direction.

How can the distant observer affect the direction of rotation of the station?  It seems to me more like an optical illusion as seen by the distant observer.

He doesn't, but he sees more clearly what is happening and the overall frame of reference.

What happens is that the cancellation of angular momentum happens, but only on the vertical axis.  The very large angular momentum on the other axis remains.  So the stations doesn't stay pointing at the sun, it stays pointing at wherever it was pointing toward when it spun up.
If there was no counter rotating mass on te vertical axis, I guess the station would have a very slight wobble on a period of a year due to the angular momentum at 90 degrees from the main angular momentum. 

[lamontagne]

Cancelling the main angular momentum with very rapidly spinning smaller masses isn't working out.
I expect because there is a relationship between the maximum rpm and the strength of the materials.  So the mass seems to remain the same, but spinning much faster with a shorter radius.
The end result being, might as well counter spin the outer radiation shield, since then it at least has a function.  However that still leaves the inner radiation shield , and at the radius of the station that means the radiuses of the two masses will likely be similar, so the relative speed fairly high.
Explaining why the idea has not been pursued by wiser heads, I expect.

[JohnFornaro]

Calculation of the reaction wheel for John's station.

Lamontagne:

Thanks...  Checking your work, while trying to understand the calcs.

I = Mr^2  Fine...
L = wl?  Or wI?  What's w?  Rotation in rad/sec?

I get readily confused when I don't know the terms.  Speaking of confused, in your SketchUp above, you orbit the sun and rotate the station differently from what I illustrated.

Station rotation speed 1.4 rpm.  Expressed in rad/sec"

1.0 rpm = 6.2832 rad/minute [2pi]
0.4 rpm = 2.5133 rad/minute
_______________________
Add:      8.7965 rad/minute

Divide by 60 sec/minute = 0.1466 rad/sec

You wrote 0.140 rad/sec.  Did you just round off everything beyond the 0.14?  I'm not sure if it should matter much.

I know that modeling a hoop is easier than modeling a torus, but shouldn't the model be of a torus?  Admittedly, let the spokes and inner hub be ignored for the moment. [Moment, get it?]

As to the value of 1 rotation per year.  That's 6.2832 rad/yr.

Divide by 365 days/year
Divide by 24  hrs/day
Divide by 60  min/hr
Divide by 60  sec/min

I get 1.99 x 10^-7  Which agrees with you.

As to the Compensating rotating disk.  I didn't check your math there, but I get the gist.  The idea being  that it exactly counters the outer hub's angular momentum?

Only thing is, how do you park a starship in the central hub?

Questions, questions, questions.

[LMT]

From Terrestation to Deimostation

Deimos might be carbonaceous and hydrated.  This raises the possibility of an ISRU logistics hub, with propellant to start an "Omaha Trail" high-efficiency transport system.  A Mars-Deimos Lagrange point 1 (L1) "Deimos Dock" is the notional depot (orange line in image).  It's also conceivably an AG "Deimostation" site.  The thread's previous thoughts on efficient Terrestation construction might improve efficiency here also. 

Rationale:

A Deimostation could serve several functions:

- passive cryogenic and non-cryogenic ISRU propellant depot
- passive ISRU water depot
- AG station for crews manning Deimos ISRU plants, geosynchronous Arestations, and other facilities in Mars orbit

Construction and maintenance of high-value facilities in Mars orbit would plausibly require long-duration AG housing.  An AG station could repurpose Terrestation elements.  To this end, a modified Terrestation could be constructed and loaded efficiently in EVLEO.  Afterward, it burns for Deimos L1. 

Applying a previous post, a 500-m Kalpana-style pressurized segment could offer an initial hab.  It would face Mars at L1, presumably with panorama windows.

Notional points:

In EVLEO:

1.  If ASCENT is manufactured in EVLEO, 96% of propellant mass is trawled thermosphere O2 and N2.  Only 4% is H2: i.e., residual reformed Starship GCH4 or Earth-launch LH2 cargo.
2.  Some ASCENT is pumped into storage opposite the hab for counterbalance during burns.
3.  Over 90% of wet station mass is ASCENT, ~ 500,000 tons.  ASCENT production scale is paramount.

In transit:

4.  The station delivers up to 6.5 km/s delta-v to take up position at Deimos L1.

At L1:

5.  Trawling tethers now anchor Deimostation to Deimos, 14 km below.  Tethers and gravitational balancing maintain stability.  Tethers also support power lines to Deimos plants, and water lines and propellant lines to Deimostation.  They also enable easy bulk regolith transport between moon and station. 
6.  The hemispherical shell shields docked ships and crews against Deimos ejecta from meteoroid impacts.
7.  The ISEP boom gives no thrust at Deimos, but its field gives partial cosmic ray protection -- more per amp than the toroidal shield of the Starport 1 concept.
8.  Deimos regolith replaces residual ASCENT, offering coarse hab counterbalance.  The remaining tens of kilotons of ASCENT now offer convenient bimodal propulsion to service vehicles in Deimos g, or in orbit.
9.  Deimos ISRU water gives dynamic hab counterbalancing.  It also gives radiation shielding between panes of Mars-facing windows.
10.  Sifted, cleaned Deimos regolith gives radiation shielding as hab "soil" packed against the flooring hull.
11.  Deimos itself partially blocks radiation on the station's moon-facing side.
12.  Terrestation passive storage and other depot systems for methane, oxygen, ASCENT, and water are now applied toward allied fleet support at the Deimostation.  E.g., the crewed fleet now has options for fast, shielded Earth-return.  Notably, Deimos propellant production would be ~ 4x Mars rate per unit PV.
 

[LarryCanuck]

Hi all. Has there been any discussion of double-walled station modules with HDPE tanks in the annular space of the module for water (potable, grey. black, etc.)? LDPE, HDPE, liquid Hydrogen, methane, and water are all high-hydrogen materials, therefore are excellent cosmic radiation shielding. Some would require only a couple of inches of thickness to be effective. These materials (water, etc.) will be required anyway. Some thoughts? Best regards!

[Coastal Ron]

Hi all. Has there been any discussion of double-walled station modules with HDPE tanks in the annular space of the module for water (potable, grey. black, etc.)? LDPE, HDPE, liquid Hydrogen, methane, and water are all high-hydrogen materials, therefore are excellent cosmic radiation shielding. Some would require only a couple of inches of thickness to be effective. These materials (water, etc.) will be required anyway. Some thoughts? Best regards!

Nothing has been ruled out, it is just that some people favor certain materials for a variety of reasons. For my designs I plan on using High-density polyethylene (HDPE) extensively, but others seem to favor metals.

As to using non-structural material to add radiation protection, yes, there are proposed designs that rely on that approach. Some use regolith, which is pretty much just dead weight, whereas water at least has some utility value - though probably not a lot as a percentage of total mass.

The bottom line is that nothing should be ruled out at this point, since none of the designs we all have proposed have gone through enough of a review to validate them - or invalidate them. so don't worry about what others are doing, pursue whatever approach seems to make sense for you... 

[lamontagne]

Calculation of the reaction wheel for John's station.

Lamontagne:

Thanks...  Checking your work, while trying to understand the calcs.

I = Mr^2  Fine...
L = wl?  Or wI?  What's w?  Rotation in rad/sec?  Angular momentum(L)=w(rad/s)*Moment on inertia

I get readily confused when I don't know the terms.  Speaking of confused, in your SketchUp above, you orbit the sun and rotate the station differently from what I illustrated.

Station rotation speed 1.4 rpm.  Expressed in rad/sec"

1.0 rpm = 6.2832 rad/minute [2pi]
0.4 rpm = 2.5133 rad/minute
_______________________
Add:      8.7965 rad/minute

Divide by 60 sec/minute = 0.1466 rad/sec

You wrote 0.140 rad/sec.  Did you just round off everything beyond the 0.14?  I'm not sure if it should matter much. I just used a slightly different diameter.

I know that modeling a hoop is easier than modeling a torus, but shouldn't the model be of a torus?  Admittedly, let the spokes and inner hub be ignored for the moment. [Moment, get it?] Haven't found the equation for a torus, a hoop is good enough
As to the value of 1 rotation per year.  That's 6.2832 rad/yr.

Divide by 365 days/year
Divide by 24  hrs/day
Divide by 60  min/hr
Divide by 60  sec/min

I get 1.99 x 10^-7  Which agrees with you.

As to the Compensating rotating disk.  I didn't check your math there, but I get the gist.  The idea being  that it exactly counters the outer hub's angular momentum? Yes, but apparently only the one along the vertical axis.  It does nothing for than angular momentum of the main rotation axis.

Only thing is, how do you park a starship in the central hub?  Just make a big hub and park it outside, or use a non rotating hub.  Once you have one rotating part, might as well go for another.....

Questions, questions, questions.

[LMT]

...nothing should be ruled out at this point, since none of the designs we all have proposed have gone through enough of a review to validate them...

Oh, the rubble pile station of Miklavčič et al. can be ruled out.  It demands great effort to construct a multi-km radiation shield, in an essentially useless distant orbit, while giving no pressurized hab.  Assumptions are outdated, e.g., overlooking lightweight magnetic shielding methods such as the field-reversed superconducting coils of Moffett et al. 2022.

Abstract

Space radiation consists of solar particle events and galactic cosmic rays which are ever present threats to human exploration outside the protective magnetosphere of Earth. Space radiation mitigation is a necessity to protect the long term health of astronauts as NASA is building a cislunar space station with plans for human exploration of Mars. One possible solution to radiation shielding is a magnetic field configuration which is low mass, reduces the probability of secondary particle radiation scattering, and produces a magnetic null in the habitat region. This paper demonstrates the first experimental test of a functional field reversed configuration geometry that can deflect charged particles while minimizing the amount of structural material and producing low secondary radiation scattering both of which are inherent to its construction while also producing a magnetic null in the habitable zone...

Refs.

Moffett, M.B., Chesny, D.L., Cole, J.M. and Rusovici, R., 2022. Electron particle deflection using a field reversed configuration magnetosphere geometry as an analog for radiation shielding in deep space. Advances in Space Research, 69(9), pp.3540-3552.
 

[Coastal Ron]

...lightweight magnetic shielding methods such as the field-reversed superconducting coils of Moffett et al. 2022.

Abstract

Space radiation consists of solar particle events and galactic cosmic rays which are ever present threats to human exploration outside the protective magnetosphere of Earth. Space radiation mitigation is a necessity to protect the long term health of astronauts as NASA is building a cislunar space station with plans for human exploration of Mars. One possible solution to radiation shielding is a magnetic field configuration which is low mass, reduces the probability of secondary particle radiation scattering, and produces a magnetic null in the habitat region. This paper demonstrates the first experimental test of a functional field reversed configuration geometry that can deflect charged particles while minimizing the amount of structural material and producing low secondary radiation scattering both of which are inherent to its construction while also producing a magnetic null in the habitable zone...

Refs.

Moffett, M.B., Chesny, D.L., Cole, J.M. and Rusovici, R., 2022. Electron particle deflection using a field reversed configuration magnetosphere geometry as an analog for radiation shielding in deep space. Advances in Space Research, 69(9), pp.3540-3552.

This was something I was hoping was an option, since with my Mars-gravity rotating space station I was going to be having a cable structure "hung" off the body of the station for a couple of reasons, and I was hoping that there would be a way to charge the cables so that they provided some sort of magnetic shielding from GCR.

However the solution this paper provides would be more complicated that what I was thinking/hoping, so not sure I could incorporate it. But it is nice to know that people are thinking of this, since there is plenty of energy from the sun we can tap to power such magnetic fields.

What I was really hoping for was a design that could just be a wide band of cabling that was attached to the outer portion of the rotating station (like a fat tire), and by electrically charging it there would be some interaction with space radiation so that it would deflect some of the radiation. But it makes sense that there needs to be rotor AND stator in order to generate a magnetic field.