Spacecraft

The design and architecture of the OCO spacecraft bus was based on the successful Solar Radiation and Climate Experiment (SORCE) and Galaxy Explorer (GALEX) missions. The spacecraft structure was made of honeycomb panels that form a hexagonal shape. This structure housed the instrument and the spacecraft bus components. The total weight of the Observatory was about 530kg (1170 lb). Panels with solar cells were attached and stowed such that the whole structure fits inside the small fairing of the Taurus launch vehicle. A metal ring, mounted to the bottom of the structure, attached the Observatory to the launch vehicle and separates the two after launch.

The on-board computer, which was designed to fly in the harsh space environment, controlled the spacecraft bus components. This computer hosted software, which received commands from an Earth station through an S-band antenna and returned telemetry and science data back to Earth using a high data rate X-band transmitter.

The spacecraft computer managed the pointing of the spacecraft. Ground commands told the computer where to point the instrument. The computer used four wheels to move the spacecraft. A star tracker verified that the spacecraft had reached the correct orientation. In addition to pointing the instrument, the spacecraft must know where on Earth footprint the instrument was located. An on-board Global Positioning System (GPS) receiver provided that information.

Spacecraft software ensured that the solar arrays faced the sun so that adequate power was always available to charge the battery and run all the components and the instrument. The power required to run the entire observatory was equivalent to the power needed for nine common household light bulbs.

The OCO spacecraft would have flown in formation with several other spacecraft in what is called the Aqua train or A-Train. OCO used a hydrazine based propulsion system and four thrusters, located below the spherical tank, to maintain the spacecraft's location within this formation.