Optical Data Links For Deep Space Communication And Navigation

The data transmission and position determination of deep space probes is today performed with microwave systems. Large antennas have to be used at ground (up to 300 m in diameter) and on board (several meters in diameter). Low data rates of the order of 100 Kbps must be transmitted. The position of the deep space probe can be determined from Doppler measurements of the microwave carrier from observations made over some days. The application of advanced optical data links allows both a reduction of antenna diameters and position determination error by orders of magnitude. For a typical mission to planet Jupiter three different optical technologies are considered, using CO2, Nd:YAG and semiconductor diode lasers. The first two systems allow the realization of coherent optical transponders which are required for a two way Doppler measurement with the optical carrier. For the semiconductor laser system direct detection with pulse position modulation is assumed. Consequently position determination of the spacecraft can not be made as precise as with microwave or CO2 and Nd:YAG systems. The assumed laser diode pumped Nd:YAG laser with a modulated output power of 10 W and a tunable diode laser pumped-Nd:YAG laser local oscillator are not available at the present time. But the clear advantage of this technology for deep space missions must be taken into account for further technological developments.