Artist's concept of the POLAR spacecraft. (83 K)
POLAR is the second mission of NASA's Global Geospace Science (GGS) initiative to study the dynamics of the magnetosphere. With 11 instruments on board, POLAR is designed to measure energy input to the Earth's polar regions. It provides global images of the aurora, as well as particle measurements of solar wind entering the magnetosphere and ionospheric plasma flowing out.
The University of Washington's research is based primarily upon data from the Ultraviolet Imager (UVI). (See below).
Schematic of POLAR's instrumentation. (29 K)
Additional information about the POLAR mission and the International Solar-Terrestrial Physics Science Initiative is on-line at Goddard Space Flight Center.
Instrument Description: The instrument operates in the far ultraviolet (FUV) and is capable of imaging the auroral oval in sunlight and in darkness. The instrument has an 8° circular field of view and is located on a despun platform which permits simultaneous imaging of the entire oval at apogee, for moderately disturbed times. The three-mirror, unobscured-aperture optical system (f/2.9) provides excellent imaging over this full field of view, with an angular resolution of 0.6 milliradians/pixel. The FUV filters have been designed to allow accurate spectral separation of the features of interest, allowing quantitative interpretation of the images to provide the parameters mentioned above. The system has been designed to provide ten orders of magnitude blocking against longer wavelength (primarily visible) scattered sunlight, thus allowing the first imaging of key, spectrally resolved, FUV diagnostic features in the fully sunlit midday aurora. The intensified-CCD detector has a nominal frame rate of one frame every 37 seconds, and the fast optical system has a noise equivalent signal of ~10 R. The dynamic range is >1000 and can be positioned within an overall gain range of 10^4, allowing measurement of both the very weak polar cap emissions and very bright aurorae. The optical surfaces have been designed to be sufficiently smooth to permit this dynamic range to be utilized without the scattering of light from bright features into weaker features. In summary, recent advances in optical, filter, and detector technologies have been exploited to produce an auroral imager to meet the ISTP objectives.
This image shows the UVI during assembly.
Here is the UVI in its thermal blanket prior to spacecraft integration.