The ALTIUS Mission (Atmospheric Limb Tracker for Investigation of the Upcoming Stratosphere) aims at the development of a limb sounder to monitor the distribution and evolution of stratospheric ozone at high vertical resolution in support of operational services and long-term trend monitoring. The ALTIUS Instrument novel concept consists of three hyperspectral channels using active tunable spectral filters to perform observations with a spectral resolution ranging between 1nm and 10nm. The spectral filters are using Acousto-Optic Tunable Filters (AOTFs) in the Visible (440-675nm) and NIR (600-1020nm) range, and a cascade of Fabry-Pérot Interferometers (FPI) in the UV (250-355nm) range. The ALTIUS Mission is currently in Phase C, with a Critical Design Review (CDR) planned in mid-2023 with Redwire Space N.V. as Mission Prime and OIP Sensor Systems N.V. as Instrument Prime. The paper presents the key technical challenges faced in the development of the ALTIUS Instrument up to its current CDR maturity level. Beyond a full system overview, detailed insight is provided of its optical concept, the choice and development challenges of its optical tunable spectral filters, the associated control electronics, the ALTIUS Instrument assembling (and alignment), its integration and testing strategy, the on-ground calibration plan and, finally, a summary of the achievable L0/L1 performances. A brief description of the ALTIUS Instrument in-flight calibration strategies will be presented too, along with a flavor of the stringent cleanliness and contamination control measures envisaged to ensure stable optical performances. Finally, the paper presents lessons learned from the subsystem qualifications activities and Instrument STM environmental test campaign, as well as an overview of the foreseen project milestones towards launch.
The ALTIUS Mission (Atmospheric Limb Tracker for Investigation of the Upcoming Stratosphere) aims at the development of a limb sounder based on a small satellite concept to monitor the distribution and evolution of stratospheric ozone at high vertical resolution in support of operational services and long-term trend monitoring. The ALTIUS instrument consists of three spectral imagers flying at an altitude of approximately 700 km Sun-Synchronous Orbit. The three hyperspectral channels are based on Acousto-Optic Tuneable Filters (AOTFs) in the Visible (440-675nm) and NIR (600-1020nm) range, and a cascade of Fabry-Pérot Interferometers (FPI) in the UV (250-355nm). The use of tuneable active spectral filters will allow the ALTIUS Instrument to perform observations with a spectral resolution ranging between 1nm and 10nm in an extremely versatile operational concept. This paper presents the key technical challenges to be controlled on the design and technologies of the ALTIUS 2D imager for limb sounding. A particular insight will be given on its optical concept including the choice of tuneable spectral filters in each channel and the key development of optical elements such as mirrors, filters and coatings, ensuring the straylight performances of the instrument. The paper also provides a deep dive into the structural and thermal design of the instrument ensuring the pointing accuracy, and the way to achieve L1 radiometric performances from L0 instrument performances through calibration needs and data processing strategies. Along the lines, the stringent cleanliness and contamination control and related envisaged strategy to ensure sustained optical performances will be also described
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