Mission Event Planning & Error-Recovery for CubeSat Applications
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NTNU Test Satellite (NUTS) is a student-built double CubeSat with a scheduled launch in 2015. The project is multidisciplinary where students from all specialities can apply both for thesis assignments and volunteer work. The satellite will be in a low earth orbit (LEO) where radiation creates a challenging environment for electronics and on-board systems. To counter the effects of space radiation, a thorough and detailed mission event plan, as well as battery estimation and methods for removing lasting faults have been evaluated and implemented.Two watchdog solutions have been suggested, a global watchdog with triple modular redundancy (TMR) on the backplane and a solution with a local watchdog on each master module. Both solutions have the capability to remove single event latchups (SEL) by temporarily removing power to the affected module. Based on results and analysis, the solution with two local watchdogs are the preferred solution due to the increased complexity of the TMR solution. Furthermore, the voter necessary in a TMR implementation is a single point of failure which if malfunctioning, will leave the satellite unresponsive. Guidelines for choosing a new watchdog system's parameters are given. This includes the watchdog's time-out period, power-on-reset (POR) delay and a threshold voltage for the voltage supervisory function.Mission event plans are proposed for initial power-up, in-orbit power monitoring, payload verification and satellite self-tests. A flowchart defining a software watchdog responsible for maintaining an operational satellite is also presented.An adjustable beacon rate enables power conservation by defining three different transmission rates; low, normal and full rate. For the full rate, the power consumption is estimated to 2200 mW, 233.33 % higher than in low rate and 100 % higher than normal rate. A battery management framework has been proposed in order to avoid a low battery condition.