The region over the poles of the Earth is one of the most important regions of space that is studied by the ISTP Project. The Polar spacecraft was launched on February 24, 1996, to obtain data from both high- and low-altitude perspectives of this active region of geospace. High above the poles the particles of the solar wind and the energy of the wind can find their way into the magnetosphere. At lesser altitudes energy is transferred from electric fields and electromagnetic waves to electrons that then plunge into the atmosphere to create the aurora. At mid-altitudes nearer the equator the satellite passes through the Earth's trapped radiation, the Van Allen belts. Out of the polar ionosphere flows plasma to populate the magnetosphere. Through this region particles and energy flow from the geomagnetic tail to the atmosphere. Thus the instruments on the Polar satellites see a lot of
action in the various plasma parameters that they measure.
Data for scientific studies are obtained not only from instruments on Polar but also from the fleet of other ISTP satellites and collaborating missions, supported by a large array of ground-based instruments. The Polar science team expects to measure and learn how the solar wind plasma energy enters into the magnetosphere through the polar cusp on the dayside of the magnetosphere. The scientists will determine the mechanisms that cause the ionospheric plasma outflow. They will discern the importance and characteristics of various processes that accelerate the aurora-producing particles. They will investigate the many ways in which energy and momentum are exchanged between the collisionless plasmas and with the electromagnetic fields accessible to the Polar spacecraft. From the images they will determine the rate of energy input into the atmosphere from auroral particles and their effects on the atmosphere.
Three of the twelve scientific instruments aboard the Polar satellite are used to image the aurora in various wavelengths when the satellite is near apogee, high over the northern polar region. The other nine instruments make measurements in-situ, at the location of the satellite, around the entire orbit. They measure the fluxes of charged particles, electrons and protons, as well as heavier ions, from thermal energies into MeV energies. They measure magnetic and electric fields, plus electromagnetic waves. They must make these measurements in great detail in order for scientists to be able to learn new things about the environment in the region over the poles of the Earth.
The Polar satellite is in a highly elliptical orbit, with apogee at 9 earth radii and perigee at 1.8 earth radii geocentric. The inclination is 86° and the period about 18 hours. Initially apogee was over the northern polar region, but apogee has been moving towards the equator at about 16° per year. The nominal mission duration was two years, but a three year extended mission has been approved.