[en] The shielding considerations for an unmanned space reactor system are somewhat different from those for a terrestrial reactor. An unmanned operation in space implies that only a shadow shield, rather than a 4π one, is required to protect payload hardware that typically can tolerate 10⁴ to 10⁶ times more radiation than can a human crew. On the other hand, the system mass, of which the radiation shield can be a significant fraction, is a severe constraint for space reactors and not normally a problem with terrestrial ones. The object of this paper is to briefly summarize advancements made on various aspects of low mass shield design for space reactors, including materials and their arrangements, geometric factors and their potential impact on system design optimization, and proposed new configuration concepts for further mass reduction