Laser Applikation for Space Instrumentation

Kurzfassung

A laser rangefinder provides a potent sensor for surface investigations of planetary objects. The instrument delivers accurate height profiles along-track for geo-morphological interpretation of surface features. Laser spot ground tracks allow exploration of impact basins, tectonic structures as well as potential cryo-volcanic features. ContData collection and analysis grants construction of digital terrain models (DTMs).Repeatedly gathered elevation data enables the study of time varying phenomena like tidal deformation, which in turn facilitates the investigation of dynamical processes in the planetary interior. A classical laser altimeter measures the time of flight between the outgoing laser pulse Tx and the backscattering return pulse Tx. The performance and signal to noise ratio is defined by the laser link budget equation. The talk reports about design, development, functional and performance tests of a laser altimeter instrument on-board the European Space Agency (ESA) mission JUICE. A diode-laser pumped Nd:YAG laser emits pulses at 1064 nm wavelength with nominally 17 mJ energy (9×1016 photons) and 5 ns duration at a repetition rate of 10 to 30 Hz. Q-switch pulse with repetition rate of up to 30 Hz within the analogue APD signal. The figure shows the transceiver unit of the laser instrument. The high integrated staggered laser and receiver electronics is mounted behind the M1 mirror (blue). APD is located in focus of the M2 mirror (green) and diode laser compartment is mounted on the bottom side of the unit. Spectral noise investigations and analysis provide operation on the theoretical limits. We point out the technical challenges of a laser application under space environmental condition and limited resources. The talk describes the functional subunits of the instrument split into Tx and Rx opto- electronics. The laser application completes a receiver channel using a single Si avalanche photodiode (APD) operating at a noise floor of about 300fA/√ in a 3dB bandwidth of 100MHz. During laser operation tests show that the instrument detects no crosstalk of any 200 A pumping pulse, duration 50 μs neither the 3 kV 10 ns active.