OTOH there are many satellites up there whose missions are unknown (to us). Who is to say that some party wouldn't try it, maybe during a geomagnetic storm? Or, maybe some crazy like NK because, hey, got china watching my Six!1!! Of course the orbits, and therefore the owners are known.
This does not need to be 'high tech' in the way some understand rocket science or reentry vehicles to be. Just some crude device which survives start and waiting 'up there', then being ignited later, without the complications of reentry heat and burn.
Last time I did the math though, you'd only get a few tens of kilometers of effect radius with an 20ft shipping container sized device so realistically, EMPs are only deployable using nuclear weapons detonated in the atmosphere.
