Most likely it would be a very simple core without power throttling or control at all and will be used as a disposable booster and jettisoned once the accelerat

Most likely it would be a very simple core without power throttling or control at all and will be used as a disposable booster and jettisoned once the acceleration phase is complete. Another core can then be used for deceleration and disposed off as well before entering earth orbit where for the final orbital insertion a much smaller chemical rocket can be used. Alternatively you don’t get back to earth at all but rather back to the moon where you could jettison the core even on the surface during final approach without giving much thought to radiation. Then use moon to earth transit via chemical rockets.