Quote:
Originally Posted by HarryT
Could I ask a question about "Threshold", Ryk? In that, you have "plasma sail" spaceships, and talk about "tacking" against the solar wind and light pressure. This immediately raised a big question mark in my mind. Sailing ships can only tack because of the process of vector addition of the force exerted by the wind against the sail AND the force the sea exerts against the keel of the ship. No keel - no tacking. A spaceship does not have any equivalent of a keel, so I'm a little curious as to how this tacking process would work. I can't see how the propulsion could be anything other than directly outwards from the Sun!
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The key is that the NET vector force exerted on a dusty plasma sail (or a regular lightsail, for that matter) is a combination of the force from the impinging radiation and the reflected radiation. If you can in effect angle the sail such that the net vector opposes your current orbital vector to a reasonable degree, you can actually reduce your orbital speed, coming "in", or increase it, going "out", and of course do other maneuvers by combining the vectors in various sequences. Poking around, I found a nice little diagram and explanation set
over here.
The dusty plasma sail used in
Threshold is better at this than a naive interpretation might indicate, too, because the "dust" is, to a large extent, smart dust and each mote can individually orient according to instructions and thus reflect the light more precisely... and can change its configuration to be reflective or absorptive. In the presence of a significant magnetic field (such as Jupiter's magnetosphere) the plasma/magnetosail component also allows maneuvering using the vectors imposed by the intersection of your magnetic field with the external one.
Hope this helps. While I do gloss over details and choose specific events for dramatics, I do try to make sure I don't VIOLATE the laws of physics in the Boundary series, just abuse them a little. (my other stuff, that's another matter entirely)