🚀 go-pugleaf

henry@zoo.toronto.edu (Henry Spencer) writes:

>The stability produced by that spin is actively undesirable if you have
>a maneuverability requirement.  A sail designed to be deployed in Earth
>orbit, in particular, has to do 90-degree turns twice per orbit (to get
>full advantage of sunlight in the "downwind" half of the orbit and
>minimize losses during the "upwind" half).  JPL got away with it because
>their design was launched to escape by conventional propulsion.

Heliogyros would actually be quite good at this.  You wouldn't have to
turn the plane of rotation; you could just "feather" the blades 
when moving towards the sun.
  
  Unfortunately for the heliogyro, this isn't the best way to escape.
Except when you are moving directly into the sun, the sail can always
be tilted to produce some positive change in energy.  (Sometimes it's tilted at 
an extreme angle).  The sail angle changes continually, so as to always
maximize the component of thrust along the velocity vector, and thus maximize
the change in kinetic energy.  I have made some computer models of this, and
this does seem to be the best method.

  The heliogyro isn't so unmanueverable as to be impossible for planetary
orbits.  I figured the maximum rate of precession to be about 55 degrees/hour
This rules out very low orbits, but they were impossible anyway due to drag.

   Dave Patterson, Guest on this account