QUESTION:
How can you hear Galileo if the radio signal is so weak?
What tricks do you do?

ANSWER from Bryon Yetter on December 21, 1995:
Being able to "hear" as you call it, Galileo's very weak signal depends on the
amount of data that the spacecraft can send to the ground in one second and the
amount of RF power available. This is called a "Bit Rate" as referenced to data
"bits". All Spacecraft modulate telemetry data on an Radio Frequency carrier
signal. As the bit rate requirements go up, the carrier power needs to also
increase. Modulation of data steals power from the carrier, higher the bit
rate, higher the carrier power consumption.

The Galileo mission plan was to use a umbrella like antenna (12 foot diameter)
to add receive and transmit signal strength. When Galileo's High Gain Antenna
failed to fully open and provide the added (required) gain to support Galileo's
highest bit rate of 134.4 Kilo bits per second, the Project was forced to use
the Low Gain (a Pole like) antenna to support the Mission. The Project has so
far reprogrammed Galileo's computers to support very low bit rates of 8, 10, and
16 bits per second. (Trick number #1)

Once Galileo is in orbit around Jupiter and we begin exploration of the
Satellites, the Galileo Project will once again reprogram the Spacecraft
to add special data encapsulation capabilities, special encoding of the
data (Reed Solomon), as well as allowing for variable bit rates from 8 b/s to
160 b/s. The data encapsulation is much like the commonly used PK ZIP technique
that we use now on our home PC's to make files smaller for storage. The data is
packed (non required bits are removed at the Spacecraft) and once the data is
received on the ground the data is unpacked. The Reed Solomon encoding will aid
error correction of the data once it is received on the ground. (Trick #2)

During the late 1996 time frame the DSN will Array very large antennas to
combine the received power from Galileo. As many as 5 antennas will be used to
allow Galileo to transmit up to 160 b/s. These antennas range in size from 70
meters across to 34 meters. The 70 meter antennas are round, and shaped like a
large bowl. From edge to edge the 70 meter antennas are a long as a football
field. (Trick #3)

Also, a new DSN support system will be utilized to process the second spacecraft
reprogramming. The Deep Space Network's Galileo Telemetry system (DGT) is
currently be installed and tested to support all the tricks referenced in
Trick #2. (Trick #4)