At over 50 miles above the earth’s surface, a nuclear explosion in the thermosphere would rain radiation down over a wide region and the blast would be blindingly bright, wide, diffused, and heard for hundreds of miles. Hard to say what damage would be sustained on the ground due to terrain.
Since there is no atmosphere in space, there would be no mushroom cloud nor a blast wave. Instead there would be an intense outpouring of not only heat and light but high intensity radiation in the form of gamma rays and x-rays.