In article , (Greg) writes:
wrote in message
The only extra gain you can have beyond the numbers I provided is by
getting the sail tilted around the closest approach point, to get a
force component along the trajectory. This only yields an advantage
along a short fraction of the trajectory in the case described. The
overall result doesn't chage appreciably. You're welcome to try and
calculate.


my point is that your *proof* was flawed. Your derived bound is not
indeed a bound.

It is close enough to a bound to not make any significant difference.

Example: Tether pair of solar sails with accurate independant tilt
control (also rapid), there speeds of rotation can simply continue to
incress untill the teather breaks...

You can play all the games you want, it doesn't matter. The scenario
I described is one in which you already played *all the possible
games*, within the system, using if needed multiple orbits to get
yourself to the optimal *final pass*. And the optimal final pass is
one where the excentricity of your orbit is as close to 1 as possible
(i.e. sum of kinetic and gravitational energy close to 0) and your
final perihelion is as close as survivable. And at this point you
unfold your sail and go out. Remeber, that's the finite pass.

So, what more you can do at this point? Well, the scenario I
calculated for is one where you let the sail point straight away from
the Sun. The optimal scenario (energy transfer wise) is one where the
sail points halfway between the "straight away" direction and the
"tangent to the orbit" direction. The difference between the two is
negligible except in the immediate vicinity of the Sun. And, the
contribution of this difference can be estimated as well. In the
limit where the force on the sail is just barely larger than gravity,
you can, by maintaining optimal orientation, improve on the final
energy by a tad less than 30% and on the finite velocity by about 15%.
But, as I said, that's for a poor sail. The better the sail (in the
sense of area/mass ratio) the smaller the improvement since the better
the sail the faster do the tangential and straight away directions
approach each other. For a realisticall good sail you won't gain more
than few extra percent above the previous estimate. And there are no
more gains available.

Using the reverse angular momentum manover speeds of up to 50 AU per
year are possable with moddest tech addvance in solar sails.

50 AU per year is about the number I got (and no, we're talking
serious, not modest advance). 210 km/s is 44 AU per year. And at
this rate it'll take you a very long time to get anywhere.

Sure you
need to wait a long time to get to the nearest star. But it *is*
doable. This kind of space exploration will need missions lasting many
10's of years and even lasting gererations.

Can you calculate? No, it is not "10s of years" or "generations".
We're talking below 0.001c. At this rate it'll take upwards of 4000
years to get to the nearest stars. That's comparable to the time
since the construction of the pyramids till today. Even the
assumption that the civilization which launched the probe will still
be around when the probe gets somewhere is quite optimistic (based on
prior data).

Mati Meron | "When you argue with a fool,
| chances are he is doing just the same"