The age where the United States could deploy large, maximally efficient satellites with a lot of capability, but little ability to maneuver are over. Orbital space is now highly contested, and to survive U.S. satellites must be able to maneuver.
ANTI-SATELLITE WARFARE
Both China and Russia have been developing the tactics and technologies to take out or cripple satellites. This technology includes radio-frequency jammers and illumination lasers that can jam and temporarily debilitate satellites. Other technologies include ground launched anti-satellite missiles and directed energy weapons.
Adding maneuverability provides additional defense and used properly can make it harder to maintain a target lock. Currently, most satellites use chemical rockets and carry a small amount of fuel allowing them to execute a limited number of maneuvers, including getting out of the way of an uncontrolled incoming object as well as making small adjustments in their orbit.
To get more maneuvering flexibility a more fuel efficient propulsion systems is needed. Two excellent propulsion candidates are candidate are:
1) Space Nuclear Thermal Propulsion (SNTP): This high-thrust system uses hydrogen as a propellant and can produce thrust comparable to a chemical rocket but is much more efficient, enabling the spacecraft to execute more and longer maneuvers. SNTP systems works by pumping a liquid propellant, most likely hydrogen, through a reactor core. Uranium atoms split apart inside the core and release heat through fission. This physical process heats up the propellant and converts it to a gas, which is expanded through a nozzle to produce thrust. It is at least twice a efficient as chemical rockets.
2) Space Nuclear Electric Propulsion (SNEP): This is more efficient than than SNTP, but does not provide as much immediate power. But over a long-period of time it can actually provide more range, albeit at much lower rates of acceleration. So it is not nearly as good at dodging fast incoming objects. It uses electricity to generate magnetically accelerated/directed ions which are very efficient by mass, but because the amount of ions produced is so small it have only a tiny amount of thrust.
Each of the systems has their place, but in terms of providing defensive maneuvering capabilities the SNTP is the better choice. If you have the time and want to go a great distance then SNEP is going to be the choice.
For more info see: https://www.airforcemag.com/article/powering-maneuvers-in-space/
Putting nuclear power in space does not sound like a great idea. What happens when the orbit degrades and they come back to earth?