QUESTION:
Out of two years it will not be possible for 18 days to sent data back to
Earth because the Sun is in the way. But as Galileo circles Jupiter there
must be more periods of communications loss because Jupiter itself is in the
way? Isn't that the whole point of Radio Science, that the 'carier' from
Galileo dies away and returns? So, how much time is lost in
"Earth-Jupiter-Galileo conjunction" and more generally: in how much time
does Galileo make a complete tour of Jupiter? and is that beeing influenced
by the Oribital (or something) Raise Manoeuver ?

ANSWER from Jeffrey Chung on February 17, 1996:

 First of all some definitions:

1) Conjunction is the arrangement:  Earth-Sun-Jupiter, that is, Jupiter (and
Galileo) as viewed from the Earth are on the other side of the Sun and within
an angle of less than about 10 degrees causing interference in the radio
transmissions. This situation occurs about once every 13 months and will occur
again in January 1997.

2) Occultation is the arrangement:  Earth-body-Galileo, that is, a body such as
Jupiter or a satellite is between the Earth and Galileo and blocks the radio
signal. Occultation by Jupiter is valuable for gaining information about the
structure of Jupiter's atmosphere since the signal is gradually attenuated by
the atmosphere before being completely blocked. Occulatation by a satellite
is valuable for obtaining information of the exact size of the satellite
(from the
duration of the occultation) as well as pinning down its location (from the
start
and stop times). It will also be useful in determining if any of the satellites
have very tenuous atmospheres of their own. This is of particular interest
with the
satellite Io. The first occultation by Jupiter occured about 10 hours after
the Jupiter Orbit Insertion maneuver on December 8, 1995 and lasted about 3 1/2
hours. Several more Jupiter occultations occur during the orbital phase of the
mission as well as a number of occultations by the Galilean satellites.

The orbital phase of the mission or "Tour" lasts from December 8, 1995 until
December 7, 1997 (about one month after the flyby of Europa on the eleventh
orbit of Jupiter).

The Perijove Raise Maneuver (PJR) will occur on March 14, 1996 near apojove
(the farthest distance from Jupiter). Its purpose is twofold. It will raise the
perijove (the closest distance to Jupiter) of the orbit so that Galileo will not
return to the high radiation environment near Jupiter. Secondly PJR targets the
Galileo spacecraft to its first satellite encounter of the tour with Ganymede on
June 27, 1996.