QUESTION:
What's the high-gain antenna?

ANSWER from FAQ:
The umbrella-like high gain antenna is located at the top of the
spacecraft, and is 4.8 meters (16 feet) in diameter. It was designed
to transmit data back to earth at rates of up to 134,000 bits of
information per second (the equivalent of about one television
picture each minute). Compare this to a fast home modem, which
only manages to send 28,800 bps!

The antenna, which is made of gold-plated metal mesh, was
stowed behind a sun shield at launch, in order to avoid heat damage
from the sun while the spacecraft flew "inside" the earth's orbit.