Not an astronomer, but it looks like the Herschel Space Observatory was in the THz gap [1]. Interestingly, the limit to its lifetime was how much liquid Helium

Not an astronomer, but it looks like the Herschel Space Observatory was in the THz gap [1]. Interestingly, the limit to its lifetime was how much liquid Helium they could keep onboard to cool their detector. [1] https://en.m.wikipedia.org/wiki/Herschel_Space_Observatory https://en.m.wikipedia.org/wiki/Herschel_Space_Observatory