The Aladin Laser - From Development Challenges to Early In-Orbit Operations

The Aladin instrument is the sole payload on board the European Space Agency’s Aeolus satellite. The purpose of the mission is to measure wind velocities through the Earth’s atmosphere using the Doppler effect in order to provide inputs to numerical weather prediction models and to better understand atmospheric dynamics. To this end, the instrument has two high intensity, Q-switched lasers that emit 20ns pulses at a wavelength of 355nm, with a pulse repetition frequency of 50Hz. The development of these lasers proved to be somewhat longer and more challenging than was first anticipated, with several technology hurdles to be overcome before they could be integrated and tested on the Aladin instrument. This paper will present these, along with the solutions that were eventually implemented for the flight built instrument along with the on-ground verifications which were undertaken to demonstrate fitness for launch. The Aeolus satellite was launched into a sun-synchronous, 320km orbit, from the Guiana Space Center, Kourou, French Guiana, on 22nd August 2018 on an Arianespace Vega rocket. The Aladin instrument, including the FM-A laser transmitter, was switched on 10 days later on 2nd September. The switch-on was successfully performed utilising several discrete energy steps, with intermittent assessments of the laser beam using the imaging mode of the Aladin spectrometers, in order to reduce the risk of laser damage. Full energy operation commenced on 4th September. This, along with an assessment of the early operations of the Aladin laser transmitter during the 3 month in-orbit commissioning phase and the subsequent early in-orbit operations will be described.