SPC05 - The Voyager Spacecraft - The First Intergalactic Spacecraft

In 1977, NASA sent Voyager 1 and Voyager 2 on a groundbreaking mission to explore the farthest parts of our solar system. These two spacecraft were packed with advanced scientific tools to study Jupiter, Saturn, Uranus, Neptune, and their fascinating moons and rings. They were powered by long-lasting radioisotope generators and aimed to uncover mysteries that had intrigued humans for centuries.

These spacecraft included two rare RCA 4061 CMOS static RAM memory chips, some of the first of their kind. The RCA-CD4061A chip was a single integrated circuit containing 256 bits of memory, organized as 256 individually addressed bits. It needed eight address input lines to access its storage locations and could store 64 bytes of data.

Back in 1972, RCA was leading in the development of CMOS logic and memory chips. RCA's experimental TA6335 256-bit CMOS static RAM chips were chosen for the Flight Data System (FDS) computers of Voyager 1 and 2. Before the RCA 4061, NASA's spaceflight computers used non-volatile magnetic memory. Using the 4061 CMOS memory on Voyager was risky because it was volatile, meaning it could lose data if power was lost. To prevent this, a dedicated power line from the radioisotope generators was used. By the time Voyager 1's FDS was built, the production version of the TA6335, called the CD4061A, was ready. The FDS used an 18-bit word length memory with a 4K word capacity, which is 72 kilobytes or 288 4061 chips. The original TA6335 number was kept on all 4061 chip dies, making no visible difference between the experimental and production chips.

Since their launch in 1977, only a few CD4061A chips have failed, the latest on Voyager 1 in November 2023. The affected code was moved to other memory locations to avoid the faulty bits, allowing the mission to continue. Voyager 1 still sends data back to Earth, taking about 22 hours to arrive.