The SMEI instrument is currently ﬂying on the US Department of Defence Space Test Program ‘Coriolis’ mission. The primary instrument on Coriolis is WindSat, which uses polarimetric microwave radiometry to measure the ocean surface wind vector from space. Coriolis was inserted into an 840-km circular, Sun-synchronous polar orbit along the Earth’s terminator.
SMEI consists of three identical sensors mounted at different viewing angles to the Sun on the Coriolis spacecraft, such that each camera covers a different 60◦ × 3◦ area of the sky in the zenith-facing hemisphere. Furthermore, the cameras were mounted so that any unwanted reflected brightness entering each bafﬂe from the spacecraft and payload appendages did not exceed the design limits.
Camera 3 views the region of space closest to the Sun, and Cameras 1 and 2 cover the regions of the sky from elongations approximately 120◦ to 180◦ and 60◦ to 120◦, respectively.