ÆSIR is a student rocketry association founded at KTH Royal Institute of Technology in Stockholm in 2016. Its students design, build, and test sounding rockets through in-house airframe, hybrid propulsion, recovery, avionics, and flight-control work. The team's official project pages document the Signý rocket's 2023 European Rocketry Challenge launch and recovery, while Freyja is its next 3000 m hybrid-SRAD competition rocket.