That would depend on the transmit power, but in short, you wouldn't want to be outside the vehicle for a long time when the transmitter is on. A typical x-ray

That would depend on the transmit power, but in short, you wouldn't want to be outside the vehicle for a long time when the transmitter is on. A typical x-ray machine emits about twenty watts of x-ray power when in use with a typical shutter speed of 1/10 to 1/2 of a second. There's no data about how much power NASA is using in this experiment or how much a production model transmitter would use, but ground-to-ISS transmission over FM can be done with a 25-watt transmitter. Now, the x-ray transmitter wouldn't be focused the right way to send maximum radiation into an astronaut and it would have a reduced duty cycle because it's not just a simple x-ray flashlight, but giving it an hour-long bear hug while it's in use would be a very bad idea. Of course the most relevant point is that the vast majority of spaceships don't have humans on them.