The Attitude Control System Design for the Transition Region and Coronal Explorer Mission

This paper presents an overview of the Attitude Control System (ACS) design for the Transition Region And Coronal Explorer (TRACE) satellite mission. The TRACE spacecraft is the fourth in NASA's SMall EXplorer (SMEX) series of missions and is scheduled for launch in September 1997. The first part of this paper highlights the SMEX program directives and describes the science objectives and imposed requirements, while the remainder is devoted to the ACS design. The current ACS configuration is a three-axis stabilized, zero-momentum system which re-uses much of the third SMEX satellite design in an effort to decrease overall subsystem costs and increase system reliability. In addition to the primary sensors, TRACE will carry a Global Positioning System (GPS) sensor as part of NASA's technology development and demonstration. The GPS sensor will provide time, position, velocity and attitude information to the ACS and will become a prime sensor after initial verification and validation. The GPS information will not only be used to supplement the ACS attitude determination effort, but will also be utilized to predict ground station contacts onboard the spacecraft. The station contact information will then be sent to the ground and used for spacecraft operations and ground pass scheduling.