[amsat-bb] Re: Boost To higher Orbits?

[Tony Langdon]

At 11:17 PM 11/30/2009, Bob McGwier wrote:

>p=hk  where p is momentum,  k is Planck's constant, and k is an integer.
>
>So when a photon is captured or reflects/scatters, it transfers
>momentum. This equation is used to determine how much momentum is being
>transferred.
>
>Without tacking (sailing velocity change perpendicular to the wind) this
>means that only net OUTWARD force (wind or photon pressure) from the sun
>may be applied.  To achieve a higher orbit, one must speed up the
>spacecraft at a point with a net acceleration TANGENT to the orbital
>velocity at that point and the raising of the orbit will occur "on the
>other side of the orbit".

You can change the direction of the acceleration vector somewhat by 
angling the solar sail.  Remember that momentum is a vector quantity, 
and if the photon is deflected at an angle (rather than directly back 
to the Sun), you can apply the acceleration in a different 
direction.  You can't tack in the way a yacht tacks, because there is 
no keel, but you can direct the acceleration vector to increase or 
decrease relative speed at different points of the orbit.  That way, 
it may be possible to raise both sides of the orbit, by providing the 
maximum force not at right angles to the Sun's position, but somewhat 
before or after that point (by using an angled sail).

>I hope you see that you need a very complex control system to rotate the
>spacecraft to modify its sail angle with respect to the sun.  That piece
>of engineering HAS NOT BEEN ACCOMPLISHED SUCCESSFULLY BY PROFESSIONALS.

This is true.  It has been attempted, but no success... 
yet.  However, many great advances in technology have been developed 
by amateurs in the past.

>If you want to see this be successful, in oh,  your life time,  you need
>a huge sail.  The initial orbit needs to be high enough that atmospheric
>drag on this huge sail does not degrade the orbit faster than you can
>raise it.

I don't have the knowledge to do the calculations of drag, etc, so no comment.

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