I assume the task would be made easier by having computers scan the space around the spacecraft through a wide range of wavelengths, from thermal to xray includ

I assume the task would be made easier by having computers scan the space around the spacecraft through a wide range of wavelengths, from thermal to xray including visible. We generally find near-Earth asteroids the day of their encounter with Earth. This would be all that's needed for a spacecraft to respond to a potential threat.