IN-ORBIT PERFORMANCE OF THE ARCTIC WEATHER SATELLITE

V. Kangas¹, D. Gherard¹, M. Lange¹, S. Thompson¹, F. Alvarez Lopez¹, A. Brown¹, D. Schobert¹, B. Samaniego¹, A. Graziani¹, G. Mason¹

¹European Space Agency

European Space Agency (ESA) has completed the development of a new Microwave Sounder Mission named Arctic Weather Satellite (AWS). The AWS is designed to be a prototype (PFM) for a future constellation of AWS satellites (named EPS-Sterna). The prime of the AWS mission is OHB Sweden with AAC Omnisys as Payload Prime and ThalesAlenia Space as Ground Segment Prime.

The development of AWS followed a “New Space” approach, achieving fast and cost effective development allowing affordable deployment of a constellation of AWS satellites. AWS development contract was kicked-off in February 2021 and was completed in just 36 months. Launch took place in summer 2024. First images from the Payload were taken 10 days after launch, confirming well performing Payload. After in-orbit commissioning and orbit raising, data distribution to end users started end of 2024.

The AWS provides two different data services for end users. The Stored Mission Data (SMD) is downlinked once every orbit through a ground station in Svalbard and distributed through EUMETSAT’s EUMETCast system. In additional, Direct Data Broadcast (DDB) service will be provided through L-band link providing real time measured science data from the mission. This data available to any end user having L-band Ground station.

The Payload of AWS is a 19 channel cross-track-scanning microwave radiometer covering frequency range from 50 GHz to 325 GHz. The four channels at 325GHz are for water vapour sounding and for clouds measurements. This is the first time these channels are used operationally. Antenna projected aperture is 16 cm, providing footprint sizes of 33km@54 GHz, 20km@89GHz and 10km@183/325 GHz and is rotating at around 45 RPM with a swath width of approx. 2000km. The spacecraft flies at 595 km altitude at 22:38 LTAN, which was defined by the rideshare launch.

At the time of the abstract writing, the AWS performance has been assessed by numerous European meteorological organisations (Danish Meteorological Office, the German Weather Service, the European Centre for Medium-Range Weather Forecasts (ECMWF), the Finnish Meteorological Institute, Météo-France, the Norwegian Meteorological Institute, the UK Met Office, and the Swedish Meteorological and Hydrological Institute). The ECMWF was the first centre to use the new AWS observations operationally. ECMWF started the operational assimilation in summer 2025 and results are leading to an improvement in weather forecasts.

In-orbit performance and lessons learned are being collected continuously from AWS. Further updates on level1 data processing are still planned during autumn 2025. By the time of the conference, AWS has flown for almost 2 years, and comprehensive assessment of the in-orbit performance is available.

The constellation of AWS satellites, named EPS-Sterna is designed to complement the existing microwave sounders from EUMETSAT and NOAA and not to replace them. Therefore, LTANs have been selected to complement the existing microwave sounders and will fly at 03:30, 07:30 and 11:30 LTDN. The EPS-Sterna will be developed in cooperation with EUMETSAT.

This paper will summarise the AWS in-orbit performance, including geolocation, noise, accuracy/biases, etc. The impact on weather forecast will be described and the lessons learned from in-orbit performance and planned improvements for the constellation (EPS-Sterna) will be identified.