Lunar Sample Return via Tether

Ian Stirling wrote:
Not at all. If you make the sail be slightly bowl shaped instead of flat,
then you should be able to make both "newtonian" and "cassegrain" sails
which will allow you to both thrust normaly, at odd angles to the sail
and even directly towards sun by moving of and changsing the angle of the
"secondary sail".

Sure, its not free.

But the overall thrust on the sail system can never be towards the
sun.
And the seperation between them can never be larger than some hundred times
the diameter of the primary sail, sharply limiting the use.

Why is that limiting? This is not, after all a telescope, so you don't really
care about optical quality and mass-center problems should be handle-able
(or probably even handled better) by placement of the payload.

Well, if the solar sail has a cenrtal pole that connects primary and secondary
sails, the mass-center could also be movable (by moving the payload), so as to
wary where the sail goes. but may well not be worth it.

Oh, a question - why would a "cassegrain" sail not have its thrust towards Sun?


| ... |
| /|\ |
| / | \ |
|/ | \|
..... | ......

(allowing that ... are curved surfaces, etc).

--
Sander

+++ Out of cheese error +++

In order to avoid spinning too fast when you are winching a sample
in on one tether, you let the other tether out on the other side
at the same time. This stores up the angular momentum and gets
the other tether ready to pickup a sample.

Sample #92 in my simulator now does this (one tether winching in
while another winching out).

In order to get rid of waves in the tether I gave the winches
a new option. You can specify that a winch should only pull
in when the tension is less than some percentage of the recent
average tension seen at the winch (you specify the time
period). Also when letting out you can specify that the
minimum tension for letting out is a percentage of the recent
average. This algorithm works well at minimizing waves even
though the speed and tension are changing as we come in or out.

Also, much of the power for winching in can come from the
winch/generator on the tether that is going out. They
won't be going the same speed most of the time, since
the tension is higher for whichever is longer at the time.
You can specify a winch/generator power limit too.

Simulator is at:
http://spacetethers.com/spacetethers.html

-- Vince

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~
Vincent Cate Space Tether Enthusiast
http://spacetethers.com/
Anguilla, East Caribbean http://offshore.ai/vince
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~

You have to take life as it happens, but you should try to make it
happen the way you want to take it. - German Proverb

(Vincent Cate) wrote:
In order to avoid spinning too fast when you are winching a sample
in on one tether, you let the other tether out on the other side
at the same time. This stores up the angular momentum and gets
the other tether ready to pickup a sample.

Sample #92 in my simulator now does this (winching one tether in
while another is winching out).

In order to get rid of waves in the tether I gave the winch
a new option. You can specify that a winch should only pull
in when the tension is less than some percentage of the recent
average tension seen at the winch (you specify the time
period). Also when letting out you can specify that the
minimum tension for letting out is a percentage of the recent
average. Values near 100% (so limit is recent average) work
well at minimizing waves even though the speed and tension
are changing as we come in or out.

Also, much of the power for winching in can come from the
winch/generator on the tether that is going out. They
won't be going the same speed most of the time since
the tension is higher for whichever is longer at the time.
You can specify a winch/generator power limit too.

Simulator is at:
http://spacetethers.com/spacetethers.html

- Vince

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~
Vincent Cate Space Tether Enthusiast
http://spacetethers.com/
Anguilla, East Caribbean http://offshore.ai/vince
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~

You have to take life as it happens, but you should try to make it
happen the way you want to take it. - German Proverb