The atmospheric probe is Galileo's third component. This probe will also have many pieces of equipment for the experiments it must conduct under Jupiter's cloud cover. Galileo's probe carries experiments to measure temperature and pressure along the descent path, locate major cloud decks, and analyze the chemistry of atmospheric gases. In addition, the probe will attempt to detect and study lightning on Jupiter both by looking for optical flashes and by listening for the radio "static" they generate. The detector will also measure high-energy electrons close to Jupiter just before entry into the atmosphere.

In order to protect Galileo's electronics and science instruments in interplanetary space, the spacecraft requires some sort of insulation, because in the environment of space, it's too cold for the instruments to operate (just as your camera shutter might freeze if you took it to the north pole). There must also be a way to keep micrometeorites from smashing into the spacecraft electronics. The black and gold blankets that surround Galileo's exterior are carefully designed to keep Galileo's insides at a "comfortable" temperature and well-protected. The black blankets, which are made up of 20 different layers, are very efficient insulation. Although the blankets are less than a centimetre thick, they are three times as good an insulator as the bulky fiberglass insulation in a standard house attic. The black colour is due to carbon in the outer layer, which keeps electrostatic charge from building up in one spot and then shorting out the spacecraft electronics.

Any black material sitting in the sun picks up lots of heat, just like a black t-shirt on a hot day. Black material in sunlight also emits a great deal of infrared light. The "gold" blankets used on Galileo, however, don't absorb a great deal of solar heat, though they do radiate well in the infrared. This material (called second-surface aluminized kapton) therefore is also used in insulation, to keep cool certain parts of the spacecraft that are exposed to direct sunlight.

The results of Galileo's travels will be transmitted to Earth over the low-gain antenna at much slower speeds than originally expected because of an in-flight failure of the high-gain antenna. The umbrella-like high-gain antenna is located at the top of the spacecraft, and is 4.8 metres in diameter. It was designed to transmit data back to Earth at rates of up to 134,000 bits of information per second (bps). That is the equivalent of about one television picture each minute. Compare this to an average home modem which transmits 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. Unfortunately, the antenna failed to open, and because Galileo is a space exploration satellite, it is not in Earth orbit, so a team of astronauts cannot chase after it to fix it.

Instead, scientists developed a way to transmit the key scientific data and to accomplish the project's Jupiter science objectives using on board data processing and compression, and other enhancements to the communications link performance. Among those enhancements are new encoding systems and advanced technology in the equipment receiving the data on Earth.

Galileo itself communicates with Earth, and the scientists who are responsible for controlling it, through NASA's Deep Space Network of communications, using tracking stations in California, Spain and Australia.