Radio Communications

The radio communication system of Voyager 1 was designed to be used up to and beyond the limits of the Solar System. Voyager 1's main transmitter radiates around 22 watts, which is comparable to a typical ham radio or a refrigerator light bulb. Voyagers are powered by Radioisotope Thermoelectric Generators (RTGs) that convert heat from decaying plutonium-238 into electricity.

The communication system includes a 3*.7 meters (12 ft) diameter parabolic dish high-gain antenna* to send and receive radio waves via the three Deep Space Network stations on the Earth. Voyager 1 normally transmits data to Earth over Deep Space Network Channel 18, using a frequency of either 2296.481481 MHz or 8420.432097 MHz, while signals from Earth to Voyager are broadcast at 2114.676697 MHz. As of 2017, signals from Voyager 1 take over 20 hours to reach Earth. The frequencies are in a restricted satellite band, 8400 to 8450 MHz.

The computers aboard the Voyager probes each have 69.63 kilobytes of memory, total. That’s about enough to store one average internet jpeg file. The probes’ scientific data is encoded on old-fashioned digital 8-track tape machines rather than whatever solid state drive your high-end laptop is currently using. Once it’s been transmitted to Earth, the spacecraft have to write over old data in order to have enough room for new observations.

The Voyager machines are capable of executing about 81,000 instructions per second. The smart phone that is likely sitting in your pocket is probably about 7,500 times faster than that. They transmit their data back to Earth at 160 bits per second. A slow dial-up connection can deliver at least 20,000 bits per second.

The Voyager probes are always sending out a signal. Voyager 1 has a 22.4-Watt transmitter – something equivalent to a refrigerator light bulb – but by the time its beacon reaches us, the power has been reduced to roughly 0.1 billion-billionth of a Watt. NASA has to use its largest antenna, a 70-meter dish, or combine two 34-meter antennas, just to hear Voyager.

The science team communicates with Voyager 1 and 2 every day and typically needs at least four hours just to run through all their health and safety checks. On a good day, researchers might spend double that time sending commands and receiving data. The spacecrafts’ original control and analysis software was written in Fortran 5 (later ported to Fortran 77). Some of the software is still in Fortran, though other pieces have now been ported to the somewhat more modern C.

The Voyager uses a Vidicon camera. Instead of a digital CCD sensor, it has an analog tube sensor. It's sort of the reverse of an old CRT TV set.

Pictures take a long time to capture (like 15s to minutes) and then the sensor area has to be "cleared" after each shot by flooding it with light. It only captured about 800x800 "pixels" - .64 megapixels.