Logarithmic Compression of Digitally Telemetered Data

To express a number using true logarithmic compression, at least B = log2 [log R log(1 + Q/100 1 - Q/100/)] bits are required. (R = dynamic range, Q = ±error percent.) True logarithmic compression is rarely used in practice, but quasi-logarithmic methods such as normalized floating-point format are used frequently. A partially unnormalized floating-point format provides the best performance in the case of digital data. For this method B = log2 [100 log2 (4R Q/l00 Q 1 - Q/100)]-1. This paper contains analytical and graphical results that facilitate comparison of the various systems.     

The SDP-1 Stored-Program Computer

A stored-program computer could be used to advantage on small scientific spaeeraft because of its flexibility. This paper describes the design and programming of a stored-program computer specifically adapted to this particular application. In order to be suitable for use in a small scientific spacecraft, a computer must have the following characteristics: reliability, low power drain, light weight, small size, problem-solving power, and flexibility. To meet these requirements, a computer was designed that has 1024 words of program memory and 512 words of data memory. The words are 12 bits in length and both memories are randomly accessed. In order to protect the program, the program memory is of the nondestrutive read-out type. The data memory is the conventional read/write variety. The computer is organized such that the power drain is small and less hardware is required by restricting parallel gating of information, number of registers, and number and complexity of instructions. Considerable effort has been devoted to programming the computer. Analysis shows that it takes on the order of two milliseconds to perform one of the floating-point operations. These limitations should be acceptable; the computer is not expected to be required to perform extremely complex or lengthy computations.