IMAGE Mission: Orbital Phases & Science Ops

IMAGE Science Objectives and Mission Phases

The IMAGE mission will address three broad science questions that lie at the heart of our efforts to understand the geospace environment and its response to the solar wind:

What are the dominant mechanisms for injecting plasma into the magnetosphere on the time scales of substorms and geomagnetic storms?
What is the directly driven response of the magnetosphere to changes in the solar wind?
How and where are magnetospheric plasmas energized, transported, and lost during geomagnetic storms and magnetospheric substorms?

To address these questions, IMAGE will employ energetic neutral atom (ENA) imaging, conventional photon imaging at ultraviolet wavelengths, and radio sounding to obtain global images of the principal plasma regions and boundaries of Earth's inner magnetosphere. Changes in the latitude and local time of orbit apogee will allow the spacecraft to view the inner magnetosphere from a variety of perspectives and to focus on particular regions, processes, and phenomena. Science operations will thus be conducted in different phases, corresponding to IMAGE's different orbital phases. The five main mission phases are:

duskside phase (low latitudes) - science focus: dusk magnetopause and plasmapause structure
dayside phase (low to middle latitudes) - science focus: plasma entry into the magnetosphere
dawnside phase (middle to high latitudes) - science focus: dawn-dusk comparison
polar high-latitude phase - science focus: substorms and geomagnetic storms
end of mission phase - return to low-latitude dusk side/afternoon sector

The IMAGE Orbit

IMAGE will fly in an elliptical polar orbit with an apogee altitude of 7.2 Earth radii (45,922 km/28,472 mi). The location of the apogee will change during the course of the two-year mission, both in latitude and, because of the Earth's revolution about the Sun, in local time. At the beginning of the mission, apogee will be at approximately 40 degrees north latitude and at dusk local time. As the Earth moves around the Sun, the plane of the orbit will shift relative to the Earth-Sun line (by 30 degrees of longitude each month). Thus, after three and half months, apogee will occur at noon local time; after seven months, it will be at dawn, and after eleven months, at midnight. During this same period, the latitude of apogee will steadily increase, so that after a year of operation IMAGE will be at apogee nearly directly over the north pole. Apogee will be at high latitudes (90 degrees ą20 degrees) for approximately one year. For most of that time, IMAGE will be at apogee on the nightside. After reaching 90 degrees latitude, the apogee will begin to decrease it will until, two years after the start of the mission, it is once again at 40 degrees north latitude.