Sharper than Hubble: Large Binocular Telescope achieves major breakthrough

In article ,
"Mike Dworetsky" writes:
Yes, but it reduces the amount of mass budget available for telescope and
detector equipment if the antenna has to be larger. Also, you can save a
small amount of delta-V by not having to go into orbit around the sun.

Other way around, I think: less delta-V to solar orbit. (The vehicle
has to "slow down" at L2.) I expect that more than compensates for a
bigger HGA or transmitter.

Yes, in solar orbit the available communication rate decreases with
time. The question is whether it's still adequate at the end of the
observatory's lifetime (which I think for JWST is set by hydrazine
supply). Communication rate depends on transmitter power and antenna
gain, so you have to size those for end of mission. That's bigger
than needed for L2, but as noted above, you need lower delta-V.
Spitzer just passed the 1 AU distance mark, and it's still operating.

Even in solar orbit, you need something for dumping momentum. That
can be hydrazine, in which case you need a whole lot less than for
station keeping at L2, or it can be cold gas, which avoids any risk
of contamination.

I don't see why round-trip communication time is an issue. These
observatories aren't operated in real time. The program for a week
or so gets uploaded, and the data acquired are stored onboard and
downlinked when convenient.

I wonder if there is a technical spec somewhere that explains why L2 vs
solar orbit.

There must have been a tradeoff study, but I haven't seen it. I did
see the one for Spitzer, which concluded solar orbit was better. (As
I recall, LEO and HEO were also considered, but neither was even a
viable second choice.) JWST has a higher data rate than Spitzer
(because of larger detector arrays), but it isn't obvious to me that
outweighs the contamination issue.

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