The price per KW of SPS

>
> Charles, I am apologizing in advance if you are offended but the
> following is not directed at you.
>

Thank you for softening the blow :-)

I am glad my posting has provoked some more objective discussions.

> The paragraph above just tends to make my blood boil. It is full of
> the self serving NASA style propaganda. Papa NASA knows best so don't
> worry your little blond head. In case you really try to understand

NASA Glenn Research Center (frmerly NASA Lewis) has a lot of very
talented people working in this area, such as Dr. Geoffrey Landis. They
have a great space power web site with some excellent resources.

Having side that, there are definite problems with the thin film design
described, some of which you hit on.

The biggie is that the PV cells & the antenna need to be independently
steerable, because the direction of the sun verusus the direction of the
rectenna will not be fixed, and well continuously change.

>
> "Large effective transmitting antenna diameters" is more near field
> nonsense. Nobody knows how to make a very large near field antenna.

The theory is well understood.
How to actually build one that works is very difficult.

> Phased array antenna (a requirement for having a near field antenna)
> require precision alignment and a rock steady support structure. Just

These are key requirements which must be worked on.

> putting a bunch of emitters on a thin film does not make a phased
> array! The concept of the dynamics involved with spinning the thin
> film, the push from the microwaves leaving, the push from sunlight,
> the off axis mirror forces, the heat dissipation stuff. None of it
> decoupled so that any minor problem in one force could send the whole
> thing spinning out of control. A billion dollars of crumpled foil.

It is not that bad.
The disturbance forces you mention are all controllable.
It will require a sophisticated active control system.
Certainly this area needs more research.
Sophisticated computer models will be needed to optimize the control
laws.
But yes, it is not a simple passive design, which might have been
implied.

My preferred approach for large structures is inflatable concentric
toruses of different diamterers,
aligned with long inflatable tubes.
Spinning centrifugally would add some stiffness. but would complicate
the control system.
We need some realistic simulations and flight testing to decide between
the options.