THE LASER RANGEFINDER ON THE NEAR-EARTH ASTEROID RENDEZVOUS SPACECRAFT

In 1999, the Near Earth Asteroid Rendezvous (NEAR) mission will place a spacecraft with five facility instruments, including the NEAR Laser Rangefinder (NLR), into a low-altitude (similar to 50 km) orbit about the asteroid 433 Eros. The NLR is a high-fidelity altimeter capable of 31.5-cm resolution and <2-m accuracy, and will be operated continuous ly while at Eros. The NLR design is quite robust and is the first spac eborne altimeter to have continuous inflight calibration capability. S lant range is measured using precise time-of-flight epochs originating with laser pulses from a solid-state 1.064 mu m transmitter to detect ion of surface backscatter by a photodiode-based receiver. Total mass of the NLR is 4.9 kg and average power consumption is less than or equ al to 15.1 W. This paper describes the design of the NLR instrument an d preliminary performance based on prelaunch calibrations and tests. A ll requirements imposed on the NLR by the NEAR altimetry mission were met. When combined with tracking data, NLR data will permit detailed g eophysical modeling. The resulting global grid will achieve an absolut e accuracy of similar to 10 m to the center of mass and will reveal as pects associated with asteroid evolution and genesis. Copyright (C) 19 97 Published by Elsevier Science Ltd.