A Miniaturized Single-Photon Counting Laser Altimeter for Solar System Exploration Missions

Kurzfassung

Laser altimetry is a key technology for Solar System exploration, providing absolute surface topography and key context for geological, geophysical, and compositional investigations as well as shape reconstruction, hazard detection, and landing support. To date, most planetary laser altimeters have been hosted on large spacecraft due to their substantial mass, power, and volume requirements. This contribution presents the development and validation of a miniaturized single-photon counting laser altimeter designed specifically for resource-constrained platforms such as CubeSats, small satellites, landers, and rovers. The instrument concept is based on single-photon time-of-flight measurements using a multi-pixel single-photon avalanche diode (SPAD) array. In contrast to classical analogue waveform altimeters, the single-photon approach enables precise ranging at significantly reduced laser pulse energy. A compact transceiver architecture, combining transmitter and receiver optics in a single opto-mechanical unit, together with a fully digital detection and processing chain, allows a substantial reduction in size, weight, and power while retaining scientific capability. A 3×3 SPAD array provides spatial sampling of the laser footprint, enabling surface structure and albedo measurements in addition to seamless range determination with sub-decimeter uncertainty. A flight demonstrator using commercial off-the-shelf components was developed and tested during an airborne campaign over heterogeneous terrain showing TRL 5. The campaign demonstrated the feasibility of photon-counting laser altimetry under realistic background-light conditions and provided important lessons learned regarding background suppression, detector dead time, and statistical range estimation. Reconstructed range profiles successfully discriminate between surface types such as vegetation, buildings, and open terrain. Further tests to quantify measurement uncertainty and first-photon bias have been conducted at the sizing section of Berlin’s land surveying office, a facility used for calibrating optoelectronic equipment at distances of up to 516 m. The instrument uses a laser wavelength of 532 nm and works at pulse repetition rates of typically a few hundred Hz. The concept is compatible with CubeSat-class platforms, with projected resources of approximately 4 kg mass and 30 W power. Owing to its modular design, the concept is readily adaptable to future orbital, landed, and mobile platforms across the Solar System, supporting next-generation exploration architectures and low-cost missions.