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Gef · 02-01-2006, 02:53 PM

Its also true that the greater its mass the more its weight, but its weight is the Sun's gravitational pull on it, and the Sun pulls it inward.

Nope. The sun exerts no net gravitational pull on a ringworld at all!

Suppose the sun is off-center inside the ring.

Some part of the ring is closeset to the sun, experiencing a greater gravitational force. Some part is farthest away, experiencin a weaker force, and all other points in the ring are somewhere in between.

If you draw a line through the sun so it intercepts the shortest possible arc on the ring (can you visualize that?), you'll see a short section close to the sun and a large section that's mostly farther away.

The problem is that the extra mass in the larger portion exactly compensates for the distance.

What this all means is that the ring is under no net gravitational force from the sun at all, and so it tends to drift, until the inhabitants in one arc get cooked!

Suppose you put a big lump in one spot. Now the lump moves the center of gravity away from the middle, and the center of gravity orbits, but the whole structure will revolve around its center of gravity.

You could set it up with a rotational period of 1 year, i.e., one day equals one year, but rotations precess, and eventually you'd get that cooking effect again.

You'd need massive attitude jets to make this whole thing work.

Now, I understand your middle ring rotates inside the outer ring, and the outer ring supports it. That's good, because even though there's no net gravitational force from the sun, there's centrifugal force. The support ring either physical touches the middle ring, or else it interacts with some kind of force like mag lev. Either way, there's friction (or there's some system to mitigate friction which itself requires maintenance).

Short version, this thing requires a huge maintenance commitment. You design it to be self-maintaining. If the self-maintenance system ever fails, everybody on a big, big world dies.

What engineer would approve such a design? Do you propose that in 1M AD, engineers have discovered a way to reduce the mean-time-between-failures (MTBF) of complex system to infinity?

Actually, it's not as challenging as all that: You just hve to get the MTBF up to the remaining durtion of the univere.

GEF

02-01-2006, 02:53 PM	#5
Gef Join Date: Sep 2004 Location: Yucca Valley, CA	Re: GURPS Ringworld 1,000,000 AD Its also true that the greater its mass the more its weight, but its weight is the Sun's gravitational pull on it, and the Sun pulls it inward. Nope. The sun exerts no net gravitational pull on a ringworld at all! Suppose the sun is off-center inside the ring. Some part of the ring is closeset to the sun, experiencing a greater gravitational force. Some part is farthest away, experiencin a weaker force, and all other points in the ring are somewhere in between. If you draw a line through the sun so it intercepts the shortest possible arc on the ring (can you visualize that?), you'll see a short section close to the sun and a large section that's mostly farther away. The problem is that the extra mass in the larger portion exactly compensates for the distance. What this all means is that the ring is under no net gravitational force from the sun at all, and so it tends to drift, until the inhabitants in one arc get cooked! Suppose you put a big lump in one spot. Now the lump moves the center of gravity away from the middle, and the center of gravity orbits, but the whole structure will revolve around its center of gravity. You could set it up with a rotational period of 1 year, i.e., one day equals one year, but rotations precess, and eventually you'd get that cooking effect again. You'd need massive attitude jets to make this whole thing work. Now, I understand your middle ring rotates inside the outer ring, and the outer ring supports it. That's good, because even though there's no net gravitational force from the sun, there's centrifugal force. The support ring either physical touches the middle ring, or else it interacts with some kind of force like mag lev. Either way, there's friction (or there's some system to mitigate friction which itself requires maintenance). Short version, this thing requires a huge maintenance commitment. You design it to be self-maintaining. If the self-maintenance system ever fails, everybody on a big, big world dies. What engineer would approve such a design? Do you propose that in 1M AD, engineers have discovered a way to reduce the mean-time-between-failures (MTBF) of complex system to infinity? Actually, it's not as challenging as all that: You just hve to get the MTBF up to the remaining durtion of the univere. GEF