The ALTIUS Mission
In the context of a looming dramatic drop of limb sounders, there is a crying need for new missions capable of probing the atmospheric composition with good vertical resolution. This is particularly important for the continuation of the long-term time series of ozone, aerosols, and greenhouse gases that help monitoring the impacts of political decisions to protect our environment. This is also crucial for the modeling community pushing for a better inclusion of the stratospheric composition both for improving short-term (weather) and long-term (climate) numerical predictions.
As an element of answer, ALTIUS (Atmospheric Limb Tracker for Investigation of the Upcoming Stratosphere) aims at building on the great success of previous limb-scatter and occultation instruments to provide globally distributed key atmospheric species concentration profiles. A number of target species will routinely be measured: O3, NO2, aerosols, H2O, CH4, PSC, PMC, OClO, BrO, NO3, and temperature. In particular, O3 profiles will be retrieved and delivered in near real time (NRT) in order to meet the requirements of operational services such as numerical weather prediction (ECMWF) and NRT atmospheric models (CAMS, C3S). Other occasional targets are, among others, mesospheric emissions, spectro-polarimetry of the limb, northern lights, tomographic analyses.
The ALTIUS spacecraft: main body, deployed solar panels, and instrument (in red). (Courtesy Qinetiq)
The mission concept aims at bringing the limb scattering and occultation techniques a step further. First, by the introduction of hyperspectral imaging, a method that enables higher pointing calibration accuracy than scanning approaches. Second, by exploiting the synergies between different geometries: solar, stellar, and planetary occultations data not only extend the coverage of the mission beyond that of the limb scattering technique, they enable inter-comparisons across different measurement modes of a same species.
Platform and baseline operations.
A P-200 class PROBA micro-satellite could host the payload. This platform has demonstrated excellent attitude control and agility with previous missions such as PROBA-1, PROBA-2, and PROBA-Vegetation. ALTIUS will heavily rely on these capabilities to operate its baseline measurement scenario: from a sun-synchronous orbit, the three channels will (1) observe the bright limb, (2) follow a sunset, (3)-(4)-(5) go through a number of stellar/lunar/planetary occultations, and (6) find daylight back with a sunrise. The orbital plane will have a 10:30 AM UTC time at the equator crossing node. The launch is expected for 2021, with a design lifetime of minimum 3 years.
Different observation modes of ALTIUS: (1) limb, (2) solar occultation (3) stellar occultation (4) lunar occultation (5) planetary occultation 6) solar occultation.
Status of the Mission
The ALTIUS mission concept has been studied since 2006 by the Royal Belgian Institute for Space Aeronomy (BIRA-IASB), together with OIP Sensor Systems and Qinetiq Space Belgium up to phase B. The payload successfully underwent the intermediate design review (IDR) in June 2015. In December 2015, ALTIUS successfully passed two reviews which concluded that (1) ALTIUS could meet the requirements of an operational ozone mission, and (2) the mission is capable of furthering atmospheric and climate research with its additional objectives. In December 2016, ALTIUS was submitted by Belgium to ESA's ministerial council as an element of the Earth Watch program.
(1) Fussen D, Dekemper E, Errera Q, Franssens G, Mateshvili N, Pieroux D, Vanhellemont F,. "The ALTIUS mission". Atmos Meas Tech Discuss 2016. http://dx.doi.org/10.5194/amt-2016-213 [download link]
(2) BISA ALTIUS team, "Mission Requirement Document", as submitted to ESA-EO (Jan 2017) [download link]
(3) ALTIUS as an element of the European Earth Watch Programme (Excerpt from the ALTIUS Mission Proposal) [download link]