[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]


At 10:51 AM 3/6/96 -0800, you wrote:
>I was saying that you couldn't use the sail to produce greater acceleration
>towards the star than you would get by just falling towards the star.
At the risk of repeating myself, yes you are right. Producing a vector
component counter to orbital motion results in a parabolic orbit.

However, by accelerating AWAY from the sun first towards a large planet such
as a gas giant and using the planet for a gravity assist manuever, you can
then free fall back towards the sun on a hyperbolic orbit (without sails).
By unfurling the sail behind an occulter at perihelion, you will get maximum
radial thrust (in the direction of your orbit). If you were also using some
form of auxillary power at the same time you can perform what is called a
powered perihelion manuever and further augment your velocity.

Because of the reduction in light pressure as distance increases, the
acceleration drops off rather rapidly. From a theoretical maximum of 400 G
at one solar radius it would be nearly imperceptible at Earth's orbit.

As far as a straight acceleration away from the Sun, yes a sail can do it.
It really depends on the "Lightness Number" of the sail material being used.
The Lightness Number is the ratio of the sails acceleration by sunlight
pressure to the star's gravitational acceleration. Sails currently examined
by NASA are more than light enough to accelerate directly away. (See Eric
Drexler, "High Performance Solar Sails and Relatred Reflecting Devices" AIAA
Paper 79-1418, May 1979.)

Lee Parker
+                                                                             +
+  Weave a circle 'round him thrice, and close your eyes with holy dread...   +
+                                                                             +