Posted on 05/16/2005 5:56:33 PM PDT by KevinDavis
CNN) -- A solar sail that scientists believe could power missions into deep space has passed its first major test.
(Excerpt) Read more at edition.cnn.com ...
This is definately for the trading tub that can only go before the "wind".
I am reminded of a SciFi novel I read once where they used "magnetic winds" to travel between stars and planets. They were currents in space and the ships used the magnetic fields of the planets to land and take-off, thus limiting them to landing fields between the poles and the 45 degree latitudes.
No, that analogy is more like sailing a raft in a straight river with an upstream wind. Raise the sail, you go one direction. Lower the sail, you drift with the water in the other direction. You still only have two directions to travel in.
You can change which radial you are riding on by using gravity of passing planets to change your direction, but once you are outside their influence you will either be heading directly away from or directly towards the Sun.
You can do the same maneuvers that current spacecraft use, where you do several loops around the sun to gain momentum. I don't dispute any of that. I just disputed that you can tack upwind with a solar sail like you can in a sailboat.
Nor can you carve banked turns in a Viper fighter ala Battlestar Galactica circa 1978.
I don't doubt that you are a competent sailor. It is true that there is not a one to one analogy between water sailing and solar sailing. But you need to brush up on orbital mechanics. Some parts are counter intuitive. It is simply untrue that a solar sailing craft is limited to only going directly away from or directly toward the Sun. A solar sailing craft can go anywhere in the solar system that it has sufficient time to travel to. Certainly, with current technology, that would be anywhere from Mars inward, and probably a lot more.
I don't doubt that you are a competent sailor. It is true that there is not a one to one analogy between water sailing and solar sailing. But you need to brush up on orbital mechanics. Some parts are counter intuitive. It is simply untrue that a solar sailing craft is limited to only going directly away from or directly toward the Sun. A solar sailing craft can go anywhere in the solar system that it has sufficient time to travel to. Certainly, with current technology, that would be anywhere from Mars inward, and probably a lot more.
Did you read this part of my posting?:
You can change which radial you are riding on by using gravity of passing planets to change your direction, but once you are outside their influence you will either be heading directly away from or directly towards the Sun.You can do the same maneuvers that current spacecraft use, where you do several loops around the sun to gain momentum. I don't dispute any of that.
Did you read this part of my posting?
I just disputed that you can tack upwind with a solar sail like you can in a sailboat.
To refresh your memory, this was the original question that I was responding to:
wonder if you can sail upwind like a sailboat ;)
To which you replied:
Short answer: Yes.
Which is blatantly untrue. You cannot "sail" upwind like a sailboat. There are other ways to get upwind, but you cannot sail upwind like a sailboat.
Perhaps we are disputing over semantics here. A sailboat can sail upwind. It uses the energy of the wind to move against the wind. A solar sail spaceship can sail upwind. That is, it uses the energy of the "wind" (sunlight coming from the sun) to move against the "wind" toward the sun. To me, that is clearly "sailing" upwind. This is not precisely the same as a sailboat tacking against the wind, but then, all of what we are talking about is an analogy.
The analogy that you used of a sailing vessel on a river is not correct, because while a craft on the river will move downstream without wind, a solar sailing craft will not fall toward the Sun without wind, because it does not depend on the "wind" to keep it in place. It must use the energy of the "wind" to move to an orbit either closer or further away from the Sun.
You can change which radial you are riding on by using gravity of passing planets to change your direction, but once you are outside their influence you will either be heading directly away from or directly towards the Sun.
This statement seems to be stating that aside from gravitational assists from "passing planets" a solar sail spaceship can only move directly toward or away from the Sun. In fact, perhaps the least likely motion of a solar sail spaceship is on a radial directly toward or away from the Sun. This is what led me to suggest that you needed to brush up on orbital mechanics.
One of the common errors of people who have not studied solar sails is to think that the craft can only go toward or away from the Sun. This is not the case, except in the general sense that all orbits, other than a perfectly circular one, go toward or away from the Sun. While you may not belong to the class of "people who have not studied solar sails", I only wished to correct that notion for the people who have not, and not to offend your sensibilities.
It is the lurkers who benefit most from these discussions, after all.
"Months or years after the rocket runs out of fuel, the sail is still pulling.]"
No way to reach another star with it, right?
Thanks, spinestein. You fishing old articles? That was from back in May!
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