Beamed power TO orbit? Forum: SSI-List
Thread: Beamed power TO orbit?
# 15081 byIan Woollard on June 19, 2001, 5:59 p.m.
Member since 2022-08-22
> There is a minimum size for the ground rectenna and the spacecraft
> antenna respectively. Because of the long distance, 30,000 some
> kilometres, and the Rayleigh criterion. The rectenna will have to be
> several kilometres in diameter, and the spacecraft antenna about a km or
> two. This is to keep sidelobe losses to an acceptable level.
According to this page, the efficiency t goes:
t = (At * Ar) ^ 0.5 / (lambda * distance)
where lambda is wavelength (0.12 m for microwaves),
Ar is area of receiver, At area of transmitter
> Also, for a satellite in a non-GEO orbit, at least three ground
> rectennas will be required.
Possibly. And they have to be big, perhaps a kilometer across. Still,
the power density is very low. It may be possible to build them from
aluminium foil for ~3 dollars per square meter; maybe a little less
or more.
On the spacecraft side the bigger the better, but a few square meters
might be usable at LEO at 300 km, although far from ideal. But that
bit is reusable and can grow bigger over time, is lighter than solar
panels per square meter and the power available is well above solar
intensity.
> For small power levels, up to a couple of Megawatts, it will be much
> cheaper to use an onboard solar panel (PV or thermal). For power
> levels in the tens of megawatts and above, beaming power from Earth
> might become attractive.
Yes, at GEO distance. However if the power is applied at LEO to raise
apogee (perhaps via an electromagnetic tether or an ion drive), then a
good few kilowatts can be delivered I think, several times what
DS1 had available.
When the spacecraft reaches GEO a small rocket can circularise the
orbit, and the tether and the receiver can continue back down to the
earth for reuse.
civilization?"