Summary

The suite of instruments on Herschel is a particularly interesting example of the current technological state-of-the-art in the THz region. While taken as a whole, Herschel admirably addresses the scientific issues at hand, there is clearly still a gap between the extension of microwave-like technology up from long wavelength and optical-like technology down from short wavelength.

It is probably fair to say that the single technological advance which would most impact similar systems in the future would be the development of widely tunable Submillimeter/Terahertz sources with enough power to use as local oscillators for arrays of mixer elements throughout this spectral region. This would make possible the development of widely tunable heterodyne receivers (in contrast to receivers in carefully selected spectral regions) whose mixer arrays would have the spatial multiplex advantage of the 'optical' systems in PACS and SPIRE. This "ideal" system of the future would then be able to use both spatial and frequency multiplex principles to fully utilize the precious and expensive photons collected by the telescope.