QUESTION:
Why was the antenna only capable of transmitting data at 8 bps in the first
place?  Is it harder to transfer data through radio waves?  Also, why was an
umbrella shaped antenna needed for transfer at 134,400 bps?

ANSWER from Dave Bates on January 16, 1996:

Some of the things that affect the rate that data can be sent through
space are: the distance between the antennas (closer is better), the
diammeter of the antennas (bigger is better), and the amount of power
pumped through the antennas (more is better). 

We could have designed a hard dish instead of an umbrella-like structure
for the spacecraft's main antenna, but since we launched from the space
shuttle, the size of the shuttle bay limited the diammeter of a hard dish. 

The secondary antenna that we're using now doesn't always transmit data at 8
bits per second.  It just so happens that with all the factors involved, such
the distance of the spacecraft from earth, the amount of power available on
board, etc., 8 bits per second is a good choice for the data rate.