Re: Space Geography

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On Fri, Sep 23, 2011 at 2:08 PM, Samuel Penn <sam@glendale.org.uk>
wrote:

> On Friday 23 September 2011 14:30:28 Indy wrote:
> > On Fri, Sep 23, 2011 at 9:23 AM, Samuel Penn <sam@glendale.org.uk>
> wrote:
> > > [...]
> [...]
> > (1) - one way around this is to set up a handful (3-4 minimum) of
area
> > detectors in polar orbit around the Sun.
>
> How about sticking them in the same orbit as the main world, at
> the 3 Lagrange points (L3, L4, L5)? That would give similar coverage
> I would have thought.
>

It would be difficult to have a direct comms link with the L3 sensor
since
the primary would be directly interposed. Either L4 or L5 would have to
relay, and if one (or both!) of them is down...

In a polar orbit, with 3 satellites, at least two of them will be out of
the
ecliptic plane at any one time, and able to look 'down' (or 'up') to see
the
entirety of the ecliptic plane (assuming one is concentrating toward the
plane for an invading force; elsewise the sensors should be basically
360).
Also, while above/below the ecliptic plane, the sensors could have
direct
comms to the main world.

If one of the polar sats is offline for some reason, you still get some
pretty good coverage of the system as the crossing-the-ecliptic plane
satellite will only be there for a short bit. And can see any blind
areas
the out-of-the-ecliptic plane satellite can't. If two of the polar sats
are
offline, the primary will be the blind spot in the whole detection
sweep,
but depending on the orbital parameters of the sensor satellites, any
given
direction could be blind for a fairly minimal time (an invading fleet
would
have to either be very lucky or VERY exacting in their arrival vector
and
timing to be in the blind spot).

Mk