Microwave Instrument for the Rosetta Orbiter (MIRO) is the first microwave instrument sent into space to study a solar system body.

Microwave Limb Sounder (launched in 1994) during spacecraft integration. MLS measures thermal emission spectra for retrievals of atmospheric composition.

Prototype amplifier chain built at JPL for evaluation of the technologies involved.

Spectrometers for ground-based, suborbital, and space flight observations have been developed for Earth science applications, with emphasis on stratospheric composition and

photochemistry, for studies of composition in the vicinity of a comet nucleus, and for studies of distant galaxies and the composition of the inter-galactic medium. Examples of space flight

spectrometers are

• Microwave Limb Sounder (MLS), the first generation space flight instrument was launched in 1991 in the Upper Atmosphere Research Satellite (UARS) payload, and the second generation

  instrument was launched in 2004 on the Aura spacecraft. The MLS on Aura is a large, complex instrument containing six heterodyne receivers, the highest-frequency receiver operating at 2.5

  THz. Atmospheric emission spectra from these receivers provide vertical profiling of a large number of constituents in the Earth's middle atmosphere, constituents that play key roles in e.g., the

  ozone photochemistry.
• Microwave Instrument for the Rosetta Orbiter (MIRO), launched in 2004, in the payload of the ESA Rosetta spacecraft. MIRO will be used to measure surface temperatures of a comet nucleus

  as well as gas/vapor fluxes of water, CO, and other gases. The ratios of the oxygen isotopes will be measured also. The study of cometary materials can provide insight into the conditions in the

  early pre-solar and solar nebula.
• Herschel Space Observatory Heterodyne Instrument for Far-Infrared (HIFI), scheduled for launch in late 2008 or early 2009. HIFI is a very high resolution heterodyne spectrometer. It won't produce pictures of stars and galaxies, but rather extremely detailed spectra of their atoms and molecules. The HIFI data will be used to study evolution of galaxies in the early universe, star formation, chemistry in the Milk Way galaxy, and molecular chemistry in nearby comets and planets. "Heterodyne" refers to a technique that mixes the frequency of each incoming photon with one generated by the instrument, itself. The result is a lower-frequency signal (microwave instead of the original far-infrared or submillimeter) that is easier to amplify, copy, and resolve in extremely fine detail. HIFI will observe the complete range of frequencies from 480-1250 GHz, and 1410-1910 GHz, divided into six bands. It will be the first heterodyne device to cover the far-infrared and submillimeter spectrum so comprehensively, and the only instrument capable of making continuous-frequency high-resolution spectral surveys in the sub-millimeter region. HIFI is being designed and built by a consortium that includes NASA, and is led by Thijs de Graauw of Space Research Organization Netherlands (SRON), the Dutch space agency. NASA is contributing mixing elements for the two highest-frequency bands. Band 5 covers 1120-1250 GHz, and Band 6-High covers 1600-1910 GHz. NASA is also providing the frequency sources (local oscillators) for Band 5 and all of Band 6 (1410-1910 GHz), as well as components for the remaining frequency sources. They are being developed by the Jet Propulsion Laboratory in Pasadena, California.