Autonomous lunar and planetary landers require a sensor for real time hazard detection during the terminal descent phase when landing in rough, hazardous terrain. The sensor must establish surface feature data from which on-board data processors can identify safe touchdown spots and provide guidance commands for the descent engines. The sensor should increase the probability of safe touchdown(no landing failure) from the less than 90% estimated for the Mars Viking mission to the current NASA planning requirement of ..98% for the Mars Rover Sample Return mission. The sensor must also satisfy mass, volume and power constraints imposed by the limited lander resources. We analyzed the sensor performance required, assuming the desired surface feature data is a range versus angle map of the accessible landing zone. Existing active and passive sensor technologies were evaluated for the estimated requirements of spatial resolution(lm at 2 km), working slant range(2 km), range precision(0.25m) and frame rates ?_ 1Hz. Pixel mapping rate was identified as the critical sensor parameter because of limited descent time and lander power. We have developed a concept of an active scanned laser radar and scan algorithm for a hazard sensor that meets the requirements using available technology. The sensor concept and supporting system analysis and trades will be presented.