Greetings and a Question

[srjskam]

In a quick glance at the blog, I didn't see any mention of Larry Niven's Ringworld. Did I overlook it?

[...]One problem in particular is that a hoop (or torroidal) world doesn't have a stable orbit with reference to a central sun: there's no net radial restoring force.[...]

No, no mention of pretty much anything similar. I do know about Niven's ring, but thought it was different enough concept not to merit mentioning, relying on spin gravity and materials of great tensile strength. (Well, actually I recall erasing a sentence along the lines of "an unholy union of a torus planet and Niven's ring", but probably trying just to tone down wise-assery.)

The thing about orbital transverse instability is news to me. I've only thought of this as analogous to a long string of separate planets. Does it make any difference that the structure is not rigid but flexible/fluid-like, or is it just a question of the parts of the hoop attracting each other?

1) Re day and night - Is it really necessary to spin the hoop to get day and night?
[...]
2) Re issues with orbiting a star and stability - If you can build something like this in the first place, is it really necessary to put it in orbit around a star?

"No" and "no", but then it would be a traditional hoopworld or whatever and I wouldn't have had a reason to make a blog post . Same goes with the unnecessary and problematic helix arrangement. Rule of cool.

A minimum amount of active technology needed to make it work would be preferable to me personally, but at least you'd need some sort of active stabilization.