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Program: Themis

Time History of Events and Macroscale Interactions during Substorms

US scientific program selected by the NASA Midex program and led by UC Berkeley. Will have 5 identical satellites in a constellation.

Will investigate the causes of the global reconfigurations of the Earth's magnetosphere that are evidenced in auroral activity. Will carry electric, magnetic and particle detectors. Every four days the satellites will line up along the Earth's magnetic tail, allowing them to track disturbances. Measurements will be coordinated with observatories across the Artic Circle.

Cost: $173 million

The mission consists of several phases. In the first phase, they will all orbit as a tight cluster in the same orbital plane with apogee at 15.4 Earth radii (RE). In the second phase, also called the Dawn Phase, the apogee of THEMIS 1 will be at 30 RE, of THEMIS 2 at 20 RE, of THEMIS 3 and 4 at 12 RE, and of THEMIS 5 at 10 RE. The orbits will continue to be in the dawn-dusk plane, approximately. Because of the Earth's rotation around the Sun, during the third phase (also known as the Tail Phase) the orbits will be in the noon-midnight plane, with all apogees on the night side at the same altitudes as during the second phase. The fourth phase is called the Dusk Phase, with all apogees on the dusk side, and at the same altitudes as in the third phase. In the fifth and final phase, the apogees will shift to the sunward side. In all phases the perigee will remain at around 450 km, and inclination at about 16°.

With the combination of space measurements from the Themis satellite constellation and ground base systems scientists were able to determine the process by which the northern lights suddenly brighten and break into spectacular formations moving towards the poles.

External resources


Technical data


EFI (Electric Field Instrument) carries three dipoles, one in the axial direction and two orthogonal ones in the spin plane.
FGM (Flux Gate Magnetometer) is capable of measuring the magnitude of the magnetic field and its fluctuations (<64 Hz) at an accuracy of 0.01 nT.
SCM (Search Coil Magnetometer) measures the waves in the frequency range 0.1 to 4 kHz in three directions.
ESA (Electro-Static Analyzers) is a pair of particle detectors, one for the electrons and the other for the ions. They measure the energetic particle fluxes from each direction in the range 3 eV to 30 keV, enabling the derivation of density, temperature and bulk-flow velocities.
SST (Solid State Telescopes) measures the more energetic particles in the energy range 25 keV to 6 MeV, specifying the energy and direction of each particle.

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