Nuclear Thermal Rocket relies on high internal temperature to provide thrust. Phase-change of the medium consumes significant heat and excessive use of thrusters can lead to overcooling and subsequent shutdown of the main drive. While Rosatom-Antonov specifies 2500K as minimum operating temperature, pilots widely report ship being able to operate with reactor at as low as 1500K.
As main reactor powers both engines, thrusters and electrical turbine, ships flying with cold reactor are plagued with impaired electrical performance. While even a cold turbine should be sufficient for most on-board systems, external draw from mass driver can rapidly deplete the ultracapacitor and lead to electrical shutdown.