Re: How many satellites are in geosynchronous orbit by now?

Stuf4 wrote:
> >From Lou Scheffer:
> <snip>
> > Radar is a terrible search tool, because the beams are so tiny.
>
> Whoa. Yes, the beams can be quite narrow, but I certainly wouldn't go
> so far as to call it a terrible search tool!
>
> "Phased-array radar can maintain tracks on multiple satellites
> simultaneously and scan large areas of space in a fraction of a second.
> These radars have no moving mechanical parts to limit the speed of the
> radar scan - the radar energy is steered electronically."
> http://www.stratcom.mil/fact_sheets/fact_spc.html

Be careful here - these radars can steer fast, but do so by giving up
sensitivity. The first problem is that if you slew quickly, you don't
get nearly as much energy on a given target. GEO ranges often requires
Hz type bandwidths,. so you are restricted to about 1 pointing per
second no matter how fast your antenna can steer. This is no problem
for LEO, where the signals are 10s of thousands of times stronger.

Second, you need to steer the receiver, too. So you make it of lots of
modules, and do the summing electronically. However, this has much
worse noise (an order of magnitude worse, or so) because you cannot
afford thousands of super duper high tech cryogenically cooled
receivers (because of cost, size, and reliability).

The net result is that phased arrays in general have much less range.
PAVE PAWS, for example, states it can detect a car size object (10
m^2?) at 2800 miles. This would be hopeless at GEO range.

The phased array at Eglin can reach GEO distances, but the Air Force
states it's only used to track GEO objects and characterize them. It's
not for detection and discovery - they use optical stuff for that. And
it's no help for the part of GEO not visible from Florida.

The military puts a lot of work into space surveillance. See

http://www.fas.org/spp/military/program/track/mccall.pdf
http://satjournal.tcom.ohiou.edu/pdf/issue6/anz-meador.pdf

Note that they use optical stuff almost exclusively for GEO, except to
characterize stuff they have already found. For this, they use lots of
mechanically pointed radars with big dishes, for the reasons above.
And if radar detection was easy, why would they be building world wide
networks of very large, fancy, and expensive optical telescopes for
this purpose??

Lou Scheffer

.

Quantcast