Shooting down 'Bandit Satellites'

[Steve Schear]

At 08:21 AM 3/1/01 -0500, An Metet wrote:
>[Sorry about the name. "Pirate" satellites don't sound 'dangerous'
>enough to need shooting down.]
>
>
>Suppose can-sats WERE launched illegally, and then started broadcasting
><time synchronisation signals/OTP/other cypherpunk related> signals,
>along with a spoken commentary by Radio Free North America (so Joe
>Sixpack has an excuse when those nice detector van gentlemen knock on
>his door and ask why he's listening to 128.0 FM)

A more insidious plan would put up a fleet of retro-reflector satellites. 
Before Telstar two Echo aluminized plastic film balloon reflectors were 
launched.  Over 100ft in diameter they weighed about 50 lbs apiece and 
remained in orbit and operational for over a year, one using compressed gas 
and another using a sublimation-based generator to keep the structure inflated.

An upgraded reflector using a inflated array of smaller corner cubes would 
have much higher effective reflectivity due to a lower dispersion of the 
return signal then Echo.  An array of smaller cubes also increase the life 
span since they can be compartmentalized after inflation reducing the 
effects of micrometeorite punctures.  Depending upon orbital height such 
sats could be effectively used to communicate over metropolitan and larger 
distances.

Since its passive, there are no electronics to fail and no costs for ground 
control.  You can use most any UHF and higher frequency because its a 
broadband device.  This means many of the frequencies below 11 GHZ, which 
are not much affected by rain scatter and atmospheric absorption and now 
used for terrestrial microwave, can be reused with little or no 
interference because the beam path is largely orthogonal to the current 
users.  By having so much bandwidth available very broadband communication 
techniques like UWB may be entirely feasible.

Due to the narrow angle of the return beam's cone, only backyard sized 
dishes (maybe even the smaller "dish network" jobbies) married with 
inexpensive alt/azimuth mounts might be required at the receiving end. 
However, since the satellites are moving continuously communication would 
be problematic (and require better sky coverage then working geosynchronous 
sats) without a large number of birds and/or steerable beam receiving 
antennas.  Then again, with enough bandwidth spreading a low data rate (10s 
kbps) signal might be receivable from such a bird with a simple whip in the 
same way as GPS.

The transmitter end requires a considerably larger dish, to put the maximum 
amount of energy on the sat, but not beyond that used by advanced amateurs 
radio buffs doing moon bounce communications.  A maser transmitter with 
cavity modified to form a single, non-zero-order Bessel beam could reduce 
dispersion by an order of magnitude over the divergence angle of beams 
emerging from the dish using a Gaussian profile, but this is probably too 
exotic for non-commercial consideration.

steve