Dual-band Spacecraft Sensor Suite for Lunar and Small-Body Landing

NASA is planning missions to small planetary bodies in which low-risk high-accuracy soft-landing must be accomplished independent of ground control. Accurate estimates of range, descent rate, attitude, and translational drift rate are needed for precision landings (< 1 in CEP) in low gravity. Operational ranges for the landing phase are expected to vary from a kilometer down to one meter. Poorly characterized landing sites may require real-time obstacle avoidance. Although passive sensors are being considered, active sensors enable the spacecraft to exploit more optimal measurement techniques in which surface illumination is controlled by design rather than accommodated by default. This paper addresses the development and validation of a robust combination of sensors, which reduce risks while minimizing spacecraft mass and power. This paper describes the design, test, and evaluation of two sensors: a miniature pulsed Nd:YAG lidar and a Ka-band CW Doppler radar. These sensors are co-bore sighted on a two-axis gimbal, along with an inertial measurement unit and a data acquisition PC on a mobile test-bed. Test results will be presented and discussed for conditions that emulate appropriate landing operations. Fixed test structures with corner reflector targets are used to validate this approach and calibrate sensor sensitivity to different geometries and kinematics.