Uranus and Neptune

On 15 May 2012 21:28, brooksn wrote:

> So wouldn't that mean that the closer you are to the Sun the more
> difficult it would be to make the rays parallel? So further out, I would
> think, you could straighten out the lines 'more'. But it also seems
> distance is relevent, (according what people have said) in other words the
> further out you 'shoot' your straight lines, the less able you are to keep
> them straight by then end of your 'shot'.
>

No, for solar thermal you want a BIG angle on something! You want as much
of the sky, as seen by the thing you're trying to heat to be full of Sun,
as possible (within reason). That's the problem. When you're a long way
away, the angle is very tiny. That means that the disk of the sun is very
small, so you get a lot less light and heat.

Interesting, so I'm wondering, if you're out to Venus (in a polar orbit of
> the Sun though, so you always face Mars from the same distance), then use
> concave mirrors to redirect and 'straigten' the suns rays to Mars.

That's what I'm saying, they don't straighten AT ALL.

Think about this in terms of mirrors. At any flatt-ish point on a mirror,
the angle of incidence is equal to the angle of reflection, so if two sides
of the sun hit the mirror at different angles, they will still be the same
angle after they've bounced off.

And you don't care if the lines diverge some by the time they reach Mars,
> since the whole planet is a target, if it would produce a useful effect.
> The advantage being that the mirrors could be comparably smaller then
> mirrors in Mars orbit.
>

No, the mirrors would have to be stupendous!!! At Mars orbit they only have
to be twice as big as at Earth (so if you had a window on Earth 1m^2 you
would need ~2m^2 of mirror at Mars). If they were at Venus pointing at mars
they would have to be the same apparent diameter as the Sun as seen from
Mars; which means that their actual size would be freaking enormous!

> I also wonder what the limits are, how close to the sun can you get and
> how far into the solar system can you 'shoot'? Or is Venus to Mars already
> too much?
>

The smallest mirrors you can make are the ones stuck right next to the
habitat, with the habitat at the focus. (Unless you use lasers).

> Brooks
>

--
-Ian Woollard