--- In spacesettlers@yahoogroups.com, Al Globus wrote:
> On Mar 30, 2013, at 11:36 AM, hitssquad wrote:
> > One advantage of a passive, geo-fixed-prientation system like this is that it largely avoids the tidal-force problem that plagues typical SPS proposals.
> Could you explain the 'tidal-force problem'?

A sun-oriented SPS will nominally be rotating with respect to the earth, completing one revolution every 24 hours. As this rotation occurs, half of the SPS is periodically brought closer to the earth, while the other half of the SPS is pushed farther away. The earth gravitationally tugs on the closer half more than it tugs on the farther half (possibly causing metal-fatigue and/or requiring a stronger SPS frame in the first place), and causing it to rotate out of alignment with the sun.

For example, viewing Earthspace from above the North Pole, we would see any sun-oriented SPS at local midnight being tugged into clockwise rotation as it orbited to the local 6AM position. Then, as it orbited to the local noon position, we would observe it being tugged in a counter-clockwise rotation. Every 24-hours, we would observe the SPS flap counter-clockwise twice and clockwise twice: left-right-left-right / flap-flap-flap-flap.

The two problems this potentially causes are:

1. fatigue of the SPS frame; and

2. difficulty in keeping an SPS oriented on the sun, especially if it's a solar-concentrating kind of SPS.

Interesting, I wonder if you using more flexible joints along the structure, essentially springs, would allow for enough 'give' for the platform not to be strained. Or possibly instead of connecting each section at a point, you have overlapping bars between the sections that have gears/ball bearings between them. As the tidal forces pull, the sections pull apart by sliding along the bearings, possibly even extracting energy, then you reverse gears to pull them back together. With so many smaller sections I would think it would allow for tidal forces to be mitigated.

Not sure on the clockwise counter clock wise issue. If the whole structure isn't spinning you maybe could allow the structure to 'slide' sectionally along the z/sun axis in sections as well. So from the North Pole view the structure appears to be going from a flat line to a stair case, then on the other portion of the orbit the stair case would go the other way.

Just some thoughts.

Brooks

--- In spacesettlers@yahoogroups.com, "hitssquad" wrote: