Orbiting Carbon Observatory-2: Spacecraft

OCO-2 is based on the previously launched Orbiting Carbon Observatory (OCO) satellite and carries a single science instrument consisting of three high-resolution grating spectrometers. The spacecraft bus is the LeoStar-2 multi-mission platform, built by Orbital Sciences Corporation (now Northrop Grumman) and previously used on missions including SORCE and GALEX. It provides all on-orbit support services for the OCO-2 instrument.

The bus is constructed primarily from aluminum honeycomb panels (lightweight and structurally strong) assembled into a hexagonal structure approximately 1 meter (3.3 feet) in diameter and 2 meters (6.6 feet) tall.

I&T (Integration and Test) personnel and the OCO-2 observatory (spacecraft bus and instrument) are shown in the image above. The solar array panels are in the stowed position, a configuration that allows the observatory to fit within the launch vehicle payload fairing.

Solar array wings, each approximately 3 meters (10 feet) long, extend from either side of the bus on movable motors. The total mass of the observatory (spacecraft bus and instrument combined) is approximately 450 kg (990 lbs).

An onboard radiation-hardened computer controls both the spacecraft and the instrument, executing stored command sequences or responding to real-time uplinks from ground controllers. The spacecraft communicates via S-band for command and housekeeping data, and transmits science data via X-band, which supports the higher data rates the instrument requires. Solar arrays provide power in sunlight; a rechargeable battery covers eclipse periods when the spacecraft passes through Earth's shadow. Attitude is determined using a star tracker, inertial measurement unit, and GPS receiver, while momentum wheels orient the telescope for each observation mode: looking straight down in Nadir Mode, tracking the solar glint point in Glint Mode, or dwelling on a fixed ground target in Target Mode.