The POLAR Spacecraft Experiment

The POLAR
Spacecraft
Experiment

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.

Additional information about the POLAR mission and the International Solar-Terrestrial Physics Science Initiative is on-line at Goddard Space Flight Center. For current mission status, see the Mission Operations Home Page for POLAR and WIND.

Artist's concept of the POLAR spacecraft.
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The University of Washington's research is based primarily upon data from the Ultraviolet Imager (UVI). (See below). Extensive documentation on UVI is also available at the Marshall Space Flight Center UVI home page.

Schematic of POLAR's instrumentation.
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The POLAR Ultraviolet Imager:

View the latest UVI image

Background: The aurorae are the result of collisions between the atmosphere and energetic particles which have their origin in the solar wind, and which reach the atmosphere after being accelerated and redistributed within the Earth's magnetosphere. The global-scale phenomenon represented by the aurorae therefore contains considerable information concerning the solar-terrestrial connection. For example, by correctly measuring specific auroral emissions, and using comprehensive models of the region, we can infer the total energy flux entering the atmosphere and the average energy of the particles causing these emissions. Furthermore, from these auroral emissions we can model the ionospheric conductances that contribute to the closing of magnetospheric currents through the ionosphere, and from these we can obtain the electric potentials and convective patterns that are an essential aspect of the interaction between the ionosphere, thermosphere, and mesosphere. Simultaneous images of the auroral oval and polar cap not only yield the temporal and spatial morphology from which we can infer activity indices, they also allow the comparison of parts of the oval with measurements made by other spacecraft of source regions in the magnetosphere.

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. (157 K)

Here is the UVI in its thermal blanket prior to spacecraft integration. (210 K)

Who's Doing It:

At the University of Washington
- George Parks
- Ken Clark
- Michael McCarthy
- Mitch Brittnacher
- Matt Fillingim
- Damien Chua
- Joanne Kang
Collaborators
- Glynn Germany (University of Alabama at Huntsville)
- Jim Spann (NASA Marshall Space Flight Center, Huntsville, Alabama)
- Bruce Tsurutani (Jet Propulsion Laboratory, Pasadena, California)

More UVI Information

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The POLAR Spacecraft Experiment / Updated 13 October 1999 / britt@geophys.washington.edu