Session
chnical Session VIII: Advanced Subsystem Developments
Abstract
The Wide-Field Infrared Explorer (WIRE), currently scheduled for launch in September 1998, is the fifth spacecraft in NASA's Small Explorer (SMEX) series. WIRE's mission is to perform a four month survey of galaxies with unusually high star formation rates ("starburst galaxies"). It is a momentum-biased three-axis stabilized stellar pointer which provides high-accuracy pointing and autonomous acquisition for eight to ten targets per orbit. Much of the design is based on previous SMEX missions, WIRE's short mission life and limited cryogen supply impose strict new Sun and Earth avoidance requirements which protect the instrument and preserve cryogen. This paper presents the design of WIRE's Attitude Control System flight software (ACS FSW), with a concentration on the parts of the design that are new or significantly modified for WIRE. These include its FDH and mode manager modules and its table-driven architecture. The ACS FSW performs all processing necessary for command and control of the spacecraft, and it performs autonomous failure detection and handling (FDH) to insure the safety of the instrument and spacecraft. All these software components are integrated with a control mode manager that dictates which software components are currently active. Lower modes are "safer" because they use a minimal complement of sensors and actuators; as higher control modes are achieved, more software functions are activated by the mode manager, and an increasing level of attitude control accuracy is provided. If a constraint violation is detected by FDH, a safing transition to a lower control mode is triggered. The WIRE ACS FSW satisfies all of its target acquisition, constraint checking, and pointing requirements, and it provides the ground with a simple means for reconfiguring system parameters via table load.
The Software Design for the Wide-Field Infrared Explorer Attitude Control System
The Wide-Field Infrared Explorer (WIRE), currently scheduled for launch in September 1998, is the fifth spacecraft in NASA's Small Explorer (SMEX) series. WIRE's mission is to perform a four month survey of galaxies with unusually high star formation rates ("starburst galaxies"). It is a momentum-biased three-axis stabilized stellar pointer which provides high-accuracy pointing and autonomous acquisition for eight to ten targets per orbit. Much of the design is based on previous SMEX missions, WIRE's short mission life and limited cryogen supply impose strict new Sun and Earth avoidance requirements which protect the instrument and preserve cryogen. This paper presents the design of WIRE's Attitude Control System flight software (ACS FSW), with a concentration on the parts of the design that are new or significantly modified for WIRE. These include its FDH and mode manager modules and its table-driven architecture. The ACS FSW performs all processing necessary for command and control of the spacecraft, and it performs autonomous failure detection and handling (FDH) to insure the safety of the instrument and spacecraft. All these software components are integrated with a control mode manager that dictates which software components are currently active. Lower modes are "safer" because they use a minimal complement of sensors and actuators; as higher control modes are achieved, more software functions are activated by the mode manager, and an increasing level of attitude control accuracy is provided. If a constraint violation is detected by FDH, a safing transition to a lower control mode is triggered. The WIRE ACS FSW satisfies all of its target acquisition, constraint checking, and pointing requirements, and it provides the ground with a simple means for reconfiguring system parameters via table load.
