Space station artificial gravity - how to spin up to speed?

[jbriggs444]

The illusion of gravity is limited. If you release an object from the periphery it will not follow a path that appears to be vertically 'downwards'

On the contrary. It will follow a path that appears to be vertically downwards -- at least until it attains a velocity significant enough for Coriolis to rear its head.

If you are standing in front of the counter on a space station trying to make an omelette and you drop an egg, it will land on the floor at your feet -- to a first approximation.

 

[sophiecentaur]

Show your work.

I can't draw diagrams on my iPhone, I'm afraid but my description of the diagram is reasonably accurate.
Must reconsider, I think.

 

[A.T.]

I can't draw diagrams on my iPhone

What radius and tangential velocity did you assume to get that 1m separation after 1s?

 

[jbriggs444]

30 meters/sec on a 100 meter radius is 0.3 radians after 1 second. Cos of 0.3 radians is 0.955. That's 4.5 meters separation. As expected for 0.9 gee by SUVAT.

Edit: $\frac{v^2}{r}$ is 9.0 meters/s² for that setup.

 

[sophiecentaur]

That figure I came up with was clearly rubbish (back of envelope let me down - sorry chaps) and the distance would be something like 4.5m. But that approach was totally unsuitable. What needs to be considered is how to deal with the effect of a step function of 0 to 1 g. This is the equivalent of what the suspension has to deal with if you suspend a car with its wheels not quite touching the ground and then let go. That is a trivial requirement and all cars will cope easily with that. It's essential for protecting the road surface as much as anything. The advantage for the docking mechanism is that it can afford to move much more than a car suspension. It can be a lot softer and would involve a much lighter weight mechanism. And, of course, from what's been written here, we are talking in terms of g/5, rather than g.

 

[David Pass]

If a space station has artificial gravity created by spinning, how can it best be spun up to speed? Little attitude rockets could do it, but they would use up fuel, and limit your ability to change the spin rate in future. What if you had an external wheel that you spin up very fast in the opposite direction? If you did this, would it cancel out the gyroscope effect because the total angular momentum of the whole would be zero, and make it easier to orient the station with respect to the Sun, spacecraft , etc.?

Could Feraday's Law of Induction be employed to generate sufficient energy to sustain gyroscopic motion? Would this effectively produce a perpetual motion device? I picture a system of tubes within the structure of the gyroscope. I'm thinking, though, that the structure would be to large to be practical.

 

[mfb]

Could Feraday's Law of Induction be employed to generate sufficient energy to sustain gyroscopic motion?

Using induced voltages would slow the rotation. That is the opposite of what we want.

You could use electric power (from solar cells) to induce a current in a tether, and use that to generate torque. JAXA tried that recently, although not for rotation.

Would this effectively produce a perpetual motion device?

There is no such thing.

 

[Sue Rich]

Has anyone considered doing penetrating ground radar? Is it possible the moon or Mars has fossil fuel like we do? If so couldn't that be used to run the artificial gravity mechanism?

 

[sophiecentaur]

Fossil fuels come from long dead life forms. There is no evidence (or reason to believe) that the Moon had life at any time.

 

[mfb]

And even if there would be hydrocarbons, there is no free oxygen to burn it.

Artificial gravity is interesting in space, but not so much on Moon/Mars.