A European Laser Altimeter for Planetary Exploration (LAPE)

Kurzfassung

In the past year, our team has developed a concept for a high-performance planetary laser altimeter fo fly on the BepiColombo Mercury Planetary Orbiter. Hence, the instrument must be capable to operate in harsh thermal environments and must stay within BepiColombo's strict mass and cost limits. Our design is mainly characterized by a low-power laser and a small receiver optics to keep mass, thermal influx, and overall complexity of the system down. To offset low signal levels, the laser will operate at a high shot rate in the kHz range. In addition, a highly sensitive APD (Avalance Photo Detector) is used, operating in a single-photon detection (Geiger) mode. A powerful onbaord processor will stack photon detections and extract the returning laser signal among solar and instrument noise by histogram analysis techniques. In addition to range, surface albedo, slope, and roughness can be estimated from the data. Strong filters are applied in front of the optics and in front of the detector, respectively, to protect against thermal flux and to reject those solar noise photons not having the characteristic wavelength fo the Nd:YAG laser. The performance of the altimenter was simulated numerically. The models indicate that the instrument is able to operate fram ranges ov 400 to 1000 km (as required for BepiColombo if global coverage is to be accomplished), with detection probabilities above 90% on rough surfaces during nighttime. Operation over the daytime hemiphere is possible ist sunlight background is within moderate limits (Mercury near aphelion, solar elevation < 45°). Our altimeter is versatile to operate on any planetary mission beyond BepiColombo. This study was sponsored by ESA/ESTEC (AO/1-4283/02/NL/HB).