The space 2 K cryogenic technology is one of the critical supporting technologies for deep-space explorations. With the development of space detectors, such as infrared and X-ray detectors, the demands for the space 2 K cryogenic technology have become much more urgent. Early space detection missions used superfluid helium cryostats (SHCs) to meet their requirements. However, cryostats have been gradually replaced by the 2 K mechanical cryocoolers due to the large volume, heavy weight, and short life of cryostats. Hybrid JouleThomson (J-T) cryocoolers are the best alternative to cryostats in the 2 K mechanical cryocoolers because of their relatively higher efficiency at 2 K. This paper provides an up-to-date review of space missions involving 2 K hybrid J-T cryocoolers and a summary on the key issues that need to be solved in the 2 K J-T cryocoolers.