Re: SID ...and orbital mechanics

Definitely. With one important assumption... The Utronic detection
equipment does not work when earth-based.

>Surely to have provided comprehensive coverage there would have to have
been
>at least one more SID in complementary earth orbit?
>Nick

First Example: Even if SID were to be in an orbit opposing the moon, (same
obit, opposite side of earth, Earth-Moon L3), for the most deep-space
coverage Moonbase would have to be on the far side of the moon (which it is
not) and there would still be a large wedge between the Earth and Moon that
would be invisible to both. It would be bad tactics anyway to be blind to
such a critical corridor and it is also very poor tactics to not be able to
have Moonbase and SID able to cover each other. There would also be
communications problems requiring 2 relay satellites probably in wide
figure 8's of the Earth-Moon L2 Lagrangian point (crummy location and
vulnerable to alien attack) or a small constellation of relay satellites in
close lunar orbit so that Moonbase could communicate with everything else.
Really, one SID and even a far-side Moonbase is impractical, you'd never
get Henderson to spring for the extra commo sats anyway. (BTW: Orbits of
L1,2&3 are a figure 8 shape.)

Information: An explanation of Lagrangian points is here:
[http://map.gsfc.nasa.gov/m_mm/ob_techorbit1.html] The example shown is
for Earth-Sun Lagrangian points but they exist for Earth-Moon too and work
the same way for many other heavy orbiting bodies. All of the Lagrangian
points I refer to are Earth-Moon because all of the Earth-Sun points are
simply too far away to be defendable. Interceptors couldn't cover anything
that far away from what we have seen.

Second Try: With Moonbase on the Earth-side of the moon, even with SID on
the opposite side of Earth (Earth-Moon L3) for maximum coverage, a blind
spot is behind the Moon and into deep space... a huge hole in detection.
More practical from a hardware point of view maybe but also more
vulnerable. All of SID's messages would also have to be relayed through
earth or a synchronized, earth-polar-orbiting satellite and Moonbase and
SID wouldn't be able to cover each other. So this is also unworkable.

Last Attempt with one SID: Seems to me that the very best coverage of all
with only one SID is to have SID in a very high polar orbit at an angle
normal to the position of The Moon, and Moonbase on the Earth-side (an
orbit that precesses at the same rate as the Moon's orbit around Earth).
That way, from Moonbase's point of view, SID is always in view and seeming
to circle the Earth. There is a constantly revolving blind cone behind the
moon but at least it moves. This arrangement provides the very best
coverage without having 2 SIDs as well as eliminating all of the
communications relay problems. The aliens could still slide up to the back
side of the Moon if they knew the orbit of SID and predicted where the
blind spot was going to be, then flew a corkscrew course to stay within the
moving blind spot. So this is the best with one SID but clearly
inadequate. Sorry Gen. H. you're gonna have to spring for another SID. :)

So:
With 2 SIDs it really is easy, you could easily park one each at Earth-Moon
L4 and L5 and they would have near-complete coverage of each other's blind
spots as well as being able to be seen by earth and Moonbase. Earth,
Moonbase and 2 SIDs in this configuration would all be able to communicate
with each other without the need for relays either. L4 and L5 are stable
points unlike L1,2&3 which require constant station-keeping, what is put at
L4 or L5 stays there. With this configuration, there would only be two
tiny blind spots near the surface of the far sides of the Earth and Moon
and no blind spots at all away from Earth or Moon. Bada-Bing. :)

Now, if the Utronic equipment WERE to function from Earth: Then three
Earth-based stations (to cover for Earth's rotation), Moonbase and a single
SID at Earth-Moon L4 or L5 could indeed provide complete coverage.
Earth-based; seeing everywhere but behind the Moon, Moon based; seeing
everywhere but behind itself and behind the Earth, and SID; seeing behind
both. Only behind the Moon would not be seen by more than one station. If
this were true perhaps our one and only SID is simply coordinating data
from itself and 4 other Utronic stations and making the announcements.
Still seems illogical however since Earth based coordination would be
safest from attack. Do we know for sure whether the Utronic gear works on
Earth or not?

S

Shawn, neat analysis, but you left out at least one possibility that
would cover all areas with just one SID and moonbase.....

Put SID at, say, L5, or the trailing lagrange pt, whichever one that
might be. Put moonbase on the leading edge of the moon, the western limb,
like has been suggested in the crater Riccioli.
Now SID can cover all 360 degrees of the 3 dimensional globe of space
around the earth with the exception of two narrow tunnels of space shadowed
(shado'ed - ha!) out by the earth and the moon. But moonbase, sitting on the
leading edge of the moon can cover the whole half sphere of space in front
of the moon as it circles the earth, in perfect sychronicity with ol' SID
sitting back there at L5, thus moonbase covers those two narrow tunnel blind
spots of SID, as they would project through moonbase's coverage area.
Now go to Henderson and collect your medal for saving him money guy!....
:-)
Dave H.