The Use of Germanium Detectors in Space

Germanium detectors are the best solution to study γ-ray radiation with an excellent energy resolution. The high atomic number, together with low ionization and band gap energies, ensures a good detection efficiency and an accurate knowledge of the energy deposits. Whereas its use for scientific experiments conducted on Earth is mastered, the technological challenges are more numerous in the case of space missions. However, many astrophysical or planetary topics require high-precision measurements of γ-ray energies, which encourages technical developments in various domains, in particular Ge crystal manufacturing and operating mode as well as cooling techniques. The current status of some of the space-specific issues is described, together with several major instruments based on germanium detectors (GeD), implemented on astrophysics and planetary space missions or balloon-borne experiments in the past 50 years.