Low altitude nuclear detonations generate EMPs on the ground; high altitude ones may generate enough of an EMP to take out higher altitude satellites. Also, rad

Low altitude nuclear detonations generate EMPs on the ground; high altitude ones may generate enough of an EMP to take out higher altitude satellites. Also, radiation will be trapped by magnetic fields like the Van Allen belts, making those larger and more dangerous. There may also be fallout concerns, but I don't think those would be significant