Bruce Johnson wrote:

 > Also subject of interest: what does orbital space around a civilized
 > planet with a few thousand years of routine spaceflight look like?

To start, tightly controlled out to at least 100 diameters. It's a
grossly enlarged version of the
air traffic control problem, with the added complications of zoning
(e.g. allocating construction space,
preventing orbital crowding, especially of the synchronous altitude, etc).

High population worlds will be like flying into Heathrow, O'Hare or Hong
Kong in terms of crowding.

Everything that can be tracked in that volume will be, with a
combination of surface and
orbiting sensors.

Note current tracking capability is ~5cm diameter at LEO and ~1m at
synchronous orbit
with the DoD Space Surveillance Network. ESA claims 1cm at altitudes up
to 1000km.

So we can improve on this with Traveller tech, at least down to
diffraction limits and using wide-baseline
interferometry across most of the electromagnetic spectrum.

Debris will be cleared regularly as hazard mitigation.
Foreign Object Debris is bad. Depending on law level, the entities
responsible for the debris will also be responsible for cleanup costs.

So using Earth as an example, 100 diameters is ~1.3 million km, and
marks the start of the 'mainworld outer control zone'.
Geosynchronous orbit is ~2.8 diameters (35900km) and marks the start of
the 'inner control zone'.

Beyond 100 diameters the situation is analogous to the oceans with
regard to air traffic control today. Transponders must be on, and will
try to announce their presence when the next planetary control zone is
reached.

 > How hard is it to spoof a real satellite, or just put one in orbit?

Hacking the ground station seems like a better spoofing strategy if you
don't have access to space.
Otherwise hack the satellite, especially if you can hide in a crowd of
spacecraft.

As you mention, gravitics make it easy for almost anyone to put stuff
into orbit, pull stuff out of orbit and make ballistic missiles.

Law level will determine who can put stuff into orbit/space, and their
responsibilities with regard to creating navigation hazards, cleanup, etc.

Rob O'Connor