@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.
the Bigelow style has better radiation shielding and micrometorite protection than aluminum. Inflation is not the only reason to choose this style.
Quote from: LMT on 07/04/2018 07:05 pmQuote from: Jim on 07/04/2018 05:45 pmNot 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.
Quote from: Jim on 07/04/2018 05:45 pmNot 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.
Not viable. Magnetic torqueing for attitude control is for small or passive spacecraft. They are good for CMG unloading, see H ST.
Suppose you do design a human scale, short radius, baton-style AG station..., and... at martian gravity the bone loss continues unabated...
I can't remember where I read about the Bigelow style being superior to aluminum for radiation. So this data shows equal.
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.
Quote from: Coastal Ron on 07/04/2018 08:47 pmQuote from: 1 on 07/04/2018 07:57 pmWhat 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.
Quote from: 1 on 07/04/2018 07:57 pmWhat 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.
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.
QuoteQuoteI'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.
QuoteI'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?
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.
[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'.
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.
you do any axis reorientation when the flywheel and main habitat are not rotating relative to each other.
Quote from: LMT on 07/05/2018 10:57 pmSure 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.
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'.
Quote from: Jim on 07/06/2018 03:29 pmQuote from: LMT on 07/05/2018 10:57 pmSure 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.
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.
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.
Quote from: mikelepage on 01/17/2016 06:51 amSuppose 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.Or2. 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.RefsSeyedmadani, 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.
Radius: 782 mRotation period: 90 sCentripetal acceleration at rim: Mars g
At 780m radius, less than 1.1 RPM produces a full 1g.
Also the rotation of the elevator-pod-thing is given at 30RPM.
@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.
Quote from: LMT on 07/08/2018 06:05 amRadius: 782 mRotation period: 90 sCentripetal acceleration at rim: Mars gThat'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.)