Enhanced decoding for the Galileo low-gain antenna mission

Due to a malfunctioning high-gain antenna, the Galileo spacecraft is transmitting all its data through a low-gain antenna, and the data rate will seldom exceed 100 bits per second during its two-year tour of Jupiter´s satellites. To offset some of the performance loss, the spacecraft´s computer will be extensively reprogrammed to include new data compression and coding algorithms. The baseline coding system for the low gain antenna mission uses a Reed-Solomon (RS) outercode of block length 255 concatenated with a (14, 1/4) convolutional inner code, and interleaves the RS symbols to depth eight. The convolutionally encoded symbols are decoded by a maximum likelihood (Viterbi) decoder, and each RS codeword is decoded algebraically. Two types of decoding enhancements were proposed as feasible due to the low data rate. The first type of redecoding is confined to the RS decoder and utilizes information from neighboring codewords within the same interleaved block to erase unreliable symbols in undecoded words. The second type involves redecoding by the Viterbi decoder, using information fed back from codewords successfully decoded by the RS decoder