Steen Eiler Jørgensen wrote:
Hop David wrote:


Sounds like a good idea to me. This is also the proposed location for
the James Webb space telescope:


One should be careful using a term like "L2". There is an important
distinction between which system "L2" refers to. The JWST is to be parked in
L2 in the Sun-Earth-system (in orbit around the Sun, 1.5 million km farther
out than the Earth, but with the same angular velocity around the Sun as the
Earth), while the LUFASIRS (homemade NASA acronym for Lunar Far Side Relay
Satellite :-) ) will be in orbit around L2 in the Earth-Moon-system (in
orbit around the Earth, somewhat farther out than the Moon, but with the
same angular velocity around the Earth as the Moon).

Of course it's obvious you meant the earth-moon L2 and not the earth-sun
L2. I didn't have my thinking cap on this morning.


A comms relay satellite at L2 in the Sun-Earth-system would only be able to
support comms from the far side of the Moon half of its 29,5 days synodic
period.

Another important distinction between the JWST and the LUFASIRS is that
while the JWST can probably be "parked" fairly close to the L2 (depending on
how many spacecraft are already out there),

IIRC correctly they also wanted a halo for the JWST that would keep a
minimum angular separation between earth and sun. I guess it's not good
to point your communication dish in a near sunward direction.

the LUFASIRS must orbit this
point at a considerable distance, as to prevent the Moon from blocking the
satellite's view of Earth.





--
Hop David
http://clowder.net/hop/index.html