Attitude determination and control for the new millennium EO-1 spacecraft

The Earth Orbiter 1 (EO-1) mission is the first in a series of smaller, faster, cheaper Earth observing spacecraft that will be developed through Goddard Space Flight Center (GSFC) under NASA´s New Millennium Program (NMP). In a broad sense, the mission objectives focus on the development and flight testing of new remote sensing spacecraft and operations technologies that could be applied to 21st century NASA missions. A major goal for EO-1 is flight validation of the Advanced Land Imager (ALI), a Landsat-type hyper-spectral Earth science instrument being built by the MIT Lincoln Laboratory. The pointing and stability requirements for this “push-broom” imaging instrument are the main drivers of attitude control performance. The EO-1 Attitude Control Subsystem (ACS) is three-axis stabilized with on-axis reaction wheels for control actuation and a hydrazine propulsion system for ΔV capability. Pointing requirements for the roll, pitch, and yaw axes are 0.02°, 0.02°, and 0.01° 2-sigma respectively, and the ACS supports cross-track pointing of ±6.5° about the roll axis. Sub-arcsecond jitter requirements will be met by adjusting the operating profiles of the on-board actuators. There are ACS operating modes for “B-dot” despin following launch vehicle separation, initial sun acquisition, nadir-pointed science data collection, constant slew rate lunar and solar inertial calibrations, and ΔV manoeuvres for orbit adjustments and close formation flight