SPC07 - The Galileo Spacecraft - The Great Jovian Journey


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NASA's Galileo mission was a major and groundbreaking journey to explore Jupiter and its moons up close. Launched aboard the Space Shuttle Atlantis, STS-34, in 1989, Galileo took a complex route, using gravity assists from Venus and Earth to gain enough speed to reach the outer solar system after a 6-year journey. In 1995, it became the first spacecraft to orbit Jupiter. Over nearly 8 years, Galileo made many discoveries about Jupiter's atmosphere, powerful magnetic field, and its four major moons - Io, Europa, Ganymede, and Callisto.

The Galileo spacecraft relied on several onboard computer systems to manage its operations and scientific observations during its mission at Jupiter. It had 19 microprocessors with about 320K of semiconductor random access memory (RAM) and 41K of read-only memory (ROM). The main computer system, called the Command and Data Subsystem (CDS), had six RCA 1802 COSMAC microprocessors running at 1.6 MHz. This central processor, along with 512 kilobytes each of RAM and ROM for program storage, controlled critical functions like the spacecraft's orientation, spin rates, data collection, and communications. Galileo's CDS also included other important components, such as a Fault Protection Computer to monitor system health, a Data Memory Unit with two 16-megabit Bubble Memory Data Cartridges to store science and engineering data, and dedicated computer systems for the Attitude and Articulation Control Subsystem (AACS) and the Atmospheric Entry Probe.

While the AACS had fewer overall tasks compared to the CDS, it had stricter performance requirements. The system needed to execute its operations very quickly and with high precision. The 1802 microprocessor used for the CDS was not fast enough for the real-time needs of the AACS.

Galileo's AACS had to handle the spacecraft's complex attitude control (orientation in space) needs, like dual-spin stabilization and pointing the science scan platform. Galileo had a rotating section spun at about 3 RPM, while a "despun" section counter-rotated to keep cameras and other sensors stable. NASA engineers chose Itek's 16-bit Advanced Technology Airborne Computer (ATAC), which used four AMD 2901 processors, as the core computing platform. This platform was used in Navy aircraft, though its specific uses are classified. NASA customized the ATAC by adding special instructions to optimize memory usage, and the AACS had dual ATACs for redundancy.

The artwork contains ceramic versions of the RCA 1802 and AMD 2901.