Orbiting antennas

[cestes@argos5.DNET.NASA.GOV (Chris Estes)]

Paul Baclace asks about receiving data on a polar oribiting spacecraft.

That's what my company does for a living.  I'm not a radio specialist, and
not involved in the design of the on-board instrumentation, but the
gear is not to sophisticated.  We transmit in the 401 Mhz area, the 
antenna on the spacecraft is a simple, omnidirectional affair, that I
don't have any handy specs for. It's about a meter long and 8cm in diameter;
what's inside?  I don't know.

We typically hit the spacecraft with one watt (at an altitude of 870km), but
have one guy who is able to get it at 150 milliwatts (!).  I haven't been
following the thread, but if you're thinking about phone-type systems, 
remember that with polar orbiters, you're only going to have about a 15
minute window during which the spacecraft will be overhead.  Unless you're
doing store and forward messaging, the sender and receiver of the signal
have to be in the footprint at the same time.

I hope that's relevant (I should do a better job of keeping up!)

-Chris Estes-

cestes@argos5.dnet.nasa.gov