"Unmanned vehicles, whether they fly, drive or float, usually have a simple rule when it comes to software: it only gets changed while the vehicle is back in the garage. That might be a hangar with a maintenance crew, or an automated docking station with nobody around at all. On paper, this makes over-the-air updates easy. In practice, it turns them into a logistics problem.
The time between two missions might be short, or devices are required to be on warm standby. An update that overruns or fails means a vehicle that isn't ready to go. You can't take the whole fleet off duty at once in a global maintenance window, and more often than not the vehicles aren't supposed to talk to an update server at all. Neither during the mission nor in the garage, because its network is isola ...