In article , "William Sommerwerck" wrote:
I suppose they still use klystrons as deep-space power amplifiers
such as in Apollo missions.

The Apollo mission was not "deep space". Nevertheless, I installed several
Varian klystrons in NASA's STDN.

Well the moon was a bit farther away. I don't remember what things
were tracked by the maser. Maybe it was just a backup, but easily overloaded
on strong signals. All the 3 main 85 foot MSFN/STDN stations had masers.
After Apollo, ERTS or Landsat was the main preoccupation. Tracking the
Alsep packages on the moon was also done for a VLBI experiment.
After that the stations were also recording Helios orbiting the Sun, a
very week signal. You really had to play with it to get phase lock.

Here is a link to the NASA bible for the stations. Its a big file....
http://zekfrivolous.com/nasa/NASA-SP-87.pdf

greg