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The Space Technology 5 (ST5) mission is part of NASA's New Millennium Program developing new technology for space research. The ST5 program tests its cutting-edge technology in the milieu of space plasma physics with the acquisition of research grade data from new nano-satellite vehicles as a key element of its program. Below we briefly review the science objectives that will be furthered by the technological advances of the ST5 mission.

The first two decades of space exploration provided a detailed but qualitative picture of the structure and dynamics of the magneto-sphere. The magnetopause, bow shock and tail were mapped using single satellites of the Explorer and OGO series. The polar cusp was discovered at both high altitudes and low. The control of magnetospheric dynamics by the interplanetary magnetic field was revealed in the erosion of the magnetopause; episodic expansions and contractions of the plasma sheet and the control of the magnetospheric substorm .

ISEE mission poster.


ISEE launch.

The year 1977 brought the launch of the first co-orbiting satellites ISEE 1 and 2 and the ability to measure motions and derive scale lengths. The velocity and thickness of the bow shock were measured for the first time. The acceleration of plasma due to reconnection at the magnetopause was revealed proving the efficacy and reality of this long-proposed mechanism. The wave modes responsible for many upstream waves were identified and new previously unexpected phenomena were found such as the still controversial, slow-mode standing wave. Some phenomena could not be probed adequately even with two spacecraft. The flux transfer event is associated with a moving magnetic tube. Mirror mode waves in the sheath also have a very localized structure.

Following these highly successful missions, the next step was to resolve spatial gradients, since a pair of spacecraft can only resolve one component of a gradient, along the spacecraft separation vector. To address this problem European Space Agency with some assistance from NASA developed the four-spacecraft Cluster mission that has now been launched. However the separation of these spacecraft is too large to address the major issues raised by the ISEE 1 and 2 spacecraft. Thus, NASA's Magnetosphere Multiscale Mission (MMS) is planned to have much smaller separations, down to 10 km.

Both Cluster and MMS use an approximately tetrahedral configuration, which allows us to directly calculate the curl of the magnetic field, that is, the current density. This is an essential measurement in understanding the electrodynamics of different parts of the magnetosphere. Currents are the means by which stresses are communicated from one part of the magnetosphere to another, and also to the ionosphere, where the closure currents can induce significant perturbations on the ground. In the future, magnetospheric constellation (MagCon) may involve 50 to 100 spacecraft.

ST5 is a precursor mission to the multi-spacecraft missions such as MagCon. The ST5 mission involves three spacecraft flying in a close configuration (~ 100 km separation) in a 200x35,790 km elliptical orbit.



Summary of constellation missions within Earth's magnetosphere, showing the ISEE orbit, ST5 and a MagCon-like mission.

The spacecraft will each be instrumented with an energetic particle detector and a fluxgate magnetometer to measure particles and the magnetic field in the region of space where the ring current flows. This current, carried by energetic particles, couples to the ionosphere through field-aligned currents. Measuring the particles and the magnetic field together, and determining their gradients will provide significant new insights as to their interrelationship, as well as their variability during different levels of magnetospheric activity.




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For more information, contact Robert J. Strangeway, strangeway@igpp.ucla.edu.

Last updated June 11, 2001