John D. Cook • 8/13/2026

How NASA’s Mariner 9 probe encoded images

This article explains how NASA's Mariner 9 probe encoded images of Mars in 1971 using a Hadamard code, specifically a (32, 6, 16) code. Each 6-bit pixel value was encoded as a 32-bit codeword, with all codewords differing in at least 16 positions. The encoding process involves constructing a 32×32 Hadamard matrix, stacking it with its negation to form a 64×32 matrix, and converting -1s to 0s. Decoding uses matrix multiplication and the FFT-like algorithm to correct up to 7 bit errors. The article provides a clear technical explanation of the mathematical foundations and practical implementation.

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#Signal Processing #Hadamard Matrices #Error Correcting Codes