Non-‘space-qualified’ cryocoolers having a cooling source temperature below 218 K (– 55 °C), as follows: (a) Closed cycle type with a specified Mean-Time-To-Failure (MTTF) or Mean-Time-Between-Failures (MTBF), exceeding 2 500 hours; (b) Joule-Thomson (JT) self-regulating minicoolers having bore (outside) diameters of less than 8 mm;