The design and architecture of the OCO-2 spacecraft bus will be based on the successful Solar Radiation and Climate Experiment (SORCE) and Galaxy Explorer (GALEX) missions. The spacecraft structure will be made of honeycomb panels that form a hexagonal shape. This structure will house the instrument and the spacecraft bus components. The total weight of the Observatory will be about 530kg (1170 lb). Panels with solar cells will be attached and stowed such that the whole structure fits inside the small fairing of the Taurus launch vehicle. A metal ring, which will be mounted to the bottom of the structure to connect the Observatory to the launch vehicle and separate the two after launch.

The on-board computer, which will be designed to fly in the harsh space environment, will controll the spacecraft bus components. This computer will host software, that will receive 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 will manage the pointing of the spacecraft. Ground commands will tell the computer where to point the instrument. The computer will use four wheels to move the spacecraft. A star tracker will verify that the spacecraft had reaches 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 will provide that information.

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

A-Train Configuration

Larger Image (JPG, 626 KB)

The OCO-2 spacecraft will fly in formation with several other spacecraft in what is called the Aqua train or A-Train. OCO-2 will use a hydrazine based propulsion system and four thrusters, which will be located below the spherical tank, to maintain the spacecraft's location within this formation.