Instrument design and test results of a small all-range LiDAR for altimetric mapping and navigation

We have built a prototype instrument of the Small All-range LIdar (SALI) for altimetric mapping of planetary bodies and real-time measurements of spacecraft altitude during touchdown or landing. SALI uses a return-to-zero pseudo-noise (RZPN) code laser modulation, which enables the use of optical fiber laser amplifiers for long-distance range measurement. The receiver uses a 2×8 pixel HgCdTe avalanche photodiode (APD) array in linear single-photon detection mode to give the highest receiver sensitivity at the infrared laser wavelength. The receiver measures the laser pulse time-of-flight and target reflectance by correlating the received signal with a patented three-state RZPN kernel. A field programable gate array processes the signal in real time at up to 120-Hz measurement rate for eight independent receiver channels. The laser output power, the APD gain, and the receiver integration time are all programable in orbit. The instrument can range continuously to planetary surfaces from >100-km orbit altitude to <1 m during descent and sample collection or landing. SALI uses electro-optic components from the terrestrial optic communications industry and can be built at a fraction of the cost of conventional planetary LiDARs. SALI is also modular and can use different fiber lasers and detectors at different wavelengths and modified receiver optics to best fit the specific mission requirements. The prototype instrument is 31×30×11 cm in size, <60 W in electrical power, and 9.2 kg in mass. A vibration and a partial thermal-vacuum test have been conducted. The measured ranging performance is close to the predictions given in our earlier publications. We described the detailed instrument design and the test results.