Solar parachutes: without a keel, you'not sailing

hitssquad schrieb:
>
>> If they would design the SBPS like a solar sail spacecraft first, which has to change the pointing direction often, they could use Roller Reefing as a fuel-less way to change the pointing direction to slow the orbital speed down and gravity pulls the craft inwards while when the pointing direction is changed again to speed the orbital speed up, it heads outwards again.
>>
> I don't understand your description.
>

So I try it once again but do beg you, just to take a closer look onto
the link I already provided.
http://wiki.solarsails.info/index.php?title=Tacking_Solar_Sails
> The wind from the sun blows in one direction. How does a solar sailboat stay positioned in one geostationary spot? You mentioned tacking, in a previous message. Do you understand that to tack, or even to sail at all except downwind, a boat needs a keel?
A sailboat in water needs a keel or sufficient hull form, yes. But what
you really need is a second force (like the water pressure on your boats
rudder, keel and hull or like gravity on a solar sail spacecraft)
to adjust the driving force against it.
To adjust the one driving force (the wind for the sailboat, the solar
power pressure for the solar sail spacecraft) the second force has to
pull or to push into a different direction.
This second force for a solar sail spacecraft is gravity which only pulls.
For a planet centered orbit it is mainly the gravity of the planet, for
a sun centered orbit it is the gravity of our Sun.

Given the correct speed a bullet fired along Earth ground would circle
around Earth endlessly, if it wouldn't get slowed down through
atmospheric pressure.
It would be gravity which pulls the bullet into a circle. The ISS has
just the correct speed to circle Earth but atmospheric particles which
get into the orbit slow it down, so that it
would crash down to Earth if it doesn't get a regular lift.

So what a solar sail does, it can turn itself (either by moving masses
or/and by changing the solar sail area) and change it's attitude and the
angle to the power pressure.
In changing the boom position and with it the position of the sail to
the wind You do something similar on a sailboat. The second force that
helps you to steer is the pressure onto keel and
rudder.

Through turning the solar sail you change the vector direction of the
power pressure in relation to the direction of gravity.

> Have you ever sailed?
>
Yes, I do even own a sailing license.

> http://en.wikipedia.org/wiki/Centreboard
>
> "A centerboard is used to provide lift to counter the lateral force from the sails. This is required for sailboats to move in directions other than downwind, since the force of the sail is never closer than 45 degrees to the apparent wind."
>
> Perhaps a better name for solar sail would be solar parachute.
>
I was inclined to write,
"so, then please show me a parachute, which is able to move against the
direction of the wind."

But on a second thought I found out that you are correct. There is a way
for a parachute to move against
the wind. The man who holds the parachute, pulls it inward. That is what
gravity does also for a solar sail
spacecraft.
But there is a difference also, the means to steer the solar sailcraft
are better and the direction of the driving
force is much better predictable as it would be for a parachute.
>
>> You will need a constant flight crew which is operating the collector spacecraft and the transmission sender daughter unit spacecraft by remote control, but save the replacement reaction mass.
>>
> Why wouldn't a GPS-guided computer be used to control the craft?
If you have successfully flown a spacecraft like that, you are free to
develop
a perfect GPS assisted steering and attitude control software.
In fact you will have such a software at the starting point already.
But I don't think you should waive a control team.

> Would the transmission antenna have to have a solar sail, too?
>
There would be two ways for the antenna. The first would be to fix it onto
the larger collector unit, at best to the center and make it move able.
But I think this would complicate attitude control for the collector
unit since you
are moving constantly mass and have to counter that.
Also you would need two antennas, one for the near side to Sun and one
for the
far side of the orbit.

Best wishes

Frank