Heat lift of the ⁴He-JT cooler as a function of precool temperature, stroke half amplitude ΔS (“DS” in the figure), and proportional, integral, differential (PID) control power. For ΔS = 3.45 mm, a precool temperature of 19.5 K gives the minimum required heat lift (Table 2) of 13.3 mW. The in-flight precool temperature of  ~17.0 K (vertical dotted line, and Table 10) allows the use of a low stroke amplitude, minimising stresses on the cooler, and provides a large margin in heat lift.