Heterodyne Technology in Submillimetre Astronomy: Towards Implementation in Herschel

In this chapter, we introduce the heterodyne technique and its early history. The Herschel-HIFI instrument involved two important technical lineages that were just emerging at the time of the initial mission proposal to ESA in 1982: superconducting mixers and local oscillator (LO) devices. We review the 15 years of progress and development carried out to advance these technologies before the HIFI instrument project began in 1997. The status and performance of the HIFI instrument are reviewed, and HIFI’s huge improvements in sensitivity and broad frequency coverage, securing both the robustness and reliability, which are mandatory for a successful space mission, are discussed. Like the other two Herschel instruments, HIFI represents a powerful example of how enabling technology and programmatic opportunities can fruitfully interact in a space project.