Principles of gravitation

[Hazen]

I looked up a book at the reference library with the above title but only got as far as the third paragraph before the math went way over my head.

Basically the question is this: If you were to build an object such as the habitats that Iain Banks describes in his SF novels, (basically a massive wedding band shaped space station) would you get a doughnut shaped gravity well?

[Soapy Sam]

Look up Larry Niven's original Ringworld novel- a lot of folk did a bunch of engineering calculations about that back in the eighties.

[Diamond]

If you're talking about Gravitation by Misner, Wheeler and Thorne, then you'll have to know that it goes above most people's heads.

John Wheeler did write a non-math book called "A Journey into Gravity and Spacetime", which is a lot easier.

[PixyMisa]

Basically the question is this: If you were to build an object such as the habitats that Iain Banks describes in his SF novels, (basically a massive wedding band shaped space station) would you get a doughnut shaped gravity well?

Sort of. Gravity doesn't fade away to nothing, of course. So a local plot of gravitational gradients would be doughnut-shaped, but from a sufficient distance the habitat could be treated as a point mass just like a planet or whatever.

As I recall, Banks' habitats spin for gravity (like Niven's Ringworld, only much smaller), so their real gravity might be quite low.

[Alkatran]

Wasn't the main problem of a ring world the fact that it can't orbit? Send a planet flying and it tends to come back (assuming you didn't throw it at the sun), throw a ring and it tends to... hit the sun.

[PixyMisa]

Yep. It's not dynamically stable, it's just sort of sitting there. And any imbalance gets accelerated by gravity until pffft. Or rather, PFFFFT!!!!, since the thing is not exactly small.

Banks' "orbitals" are much smaller than the Ringworld, only a couple of thousand kilometres wide and a million or so kilometres in diameter, and they do orbit their suns.

[Hazen]

If you're talking about Gravitation by Misner, Wheeler and Thorne, then you'll have to know that it goes above most people's heads.

John Wheeler did write a non-math book called "A Journey into Gravity and Spacetime", which is a lot easier.

Thanks, I shall look out for that one.

[Hazen]

On another subject, has anyone seen the liftport group website, where they have a clock counting down to 'first lift' which they reckon to be April 2018.
Does this seem just a tad optimistic?