REAL TIME SCHEDULER AN APPLICATION TO LAUNCH VEHICLES

Abstract

The need forfault tolerance within hard real-time critical systems is becoming well accepted in space. applications. In this direction efforts have been carried out by developing real-time software for an (AOCS) Attitude and Orbit Control Subsystem of the . Spacecraft. The on orbit mode which is an important please of the polar satellite launch vehicle consists of several real time tasks. In the on orbit mode the variations of Illcremental angles of the momentum/reaction wheels with respect to the pitch, roll and yaw axes have been calculated. The Attitude and Orbit Control Subsystem (AOCS) provides the spacecraft attitude determination and control ca- pability after the spacecraft is separated from its launch vehicle. 'I'I e times taken by the various real time tasks in the on orbit mode have been computed. These real time tasks are run on Vx works (Real Time operating system). The total time taken for the execution of the main program which in turn calls the ,real time tasks is calculated. To implement fault tolerance in Real time systems the checkpoint and Rollback techniq ie of the Recovery Block mechanism has beef used. setjlxlp () and longjnip () calls' have been used for this purpose. A Real Time Scheduler was simulated on the 113M t'C. The tinter interrupt (OXIC h) was used. The CPU executes more than one task in a time slicing fashion. Each task c