During storage off the telescope, a temperature somewhat higher than that of LN2 may be acceptable, although the difference should be as small as possible in order to minimize stress from thermal cycling and keep the time to reach LN2 temperature as short as practical.
Using only the PTR for cooling, the temperature will settle at about -170C
after a few days. The pressure will increase, but should stay below
mBar. The temperature seems adequate for storage, so no LN2
is required in this state. The development of temperature and pressure during
initial storage is shown in figure 2.
