One of "key" instruments on board is micro-accelerometer ACC (MAC-04) measuring non gravitational perturbing accelerations (air drag, winds, Earth albedo).
It was made in Czech and just two days ago they were powered up, unlocked and tested - they survived launch and meneuvering in perfect condition on all three satelites - Yes! ... BIG relief for czech team and our local kosmo-gang
... sorry guys, I couldn't resist.
Many mission details including instrumentation in case someone's interested:
https://directory.eoportal.org/web/eoportal...issions/s/swarm