Abstract: Itis im portantto detect and diagnose allkinds ofabruptfaultcom ing fromtracking and telem etry system . Based on fault tolerance techniques, three new approachesare given in this paper. One is a fault tolerance sm oother w ithoutm odeling, the second isa fault tolerance estim ator based on m odelfitting and the third is a bounded filter underthe state space m odel. These new approaches can be used notonly after the eventbut alsoon line or on tim e. Sim ulation show s thatthese new approaches can detectisolated faultsw ith 100% accuracy and diagnose correlative faults very efficiently.