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Sun-Earth Day Presents: Ancient Observatories, Timeless Knowledge

Technology Through Time: Issue #30, trace

The best views of the sun are from space where Earth's atmosphere no longer distorts the seeing. Satellites can capture clear images of solar activity, which help scientists understand the complex forces at work.


TRACE was launched on a Pegasus launch vehicle from Vandenberg Air Force Base in April 1998. It is in a polar orbit around Earth, with a perigee of 600 kilometers.


TRACE is designed to take high-resolution images of the sun's surface in the vicinity of active regions such as sunspots and likely locations for flaring activity. To do this, the 30-centimeter TRACE telescope was specially designed to remove as much of the spacecraft's image motion as possible. To do this, the Attitude Control System (ACS) uses three magnetic-torquer coils, one digital Sun sensor, six coarse Sun sensors, four reaction wheels, a three-axis magnetometer, and three two-axis inertial gyros. The result is image jitter less than 0.1 arcseconds or nearly 1/20,000 the angular diameter of the sun. Power is provided by four solar cell panels that produce 222 watts of power. The instrument and telescope use 35 watts orbit average. The remaining power is used for spacecraft and telescope operational and decontamination heating.


The magnetic field geometry of the sun can be seen in images of solar plasma taken in different temperature ranges by studying specific atoms that are being excited. The solar atmosphere is constantly evolving because the magnetic fields that dominate the Corona are continuously being shoved around by the convective motions in the outer layers of the Sun just below the Photosphere. A major objective of the TRACE investigation is to explore the relationship between the surface magnetic fields and the changes in heating and structure throughout the Transition Region and Corona.

TRACE will let solar physicists study the connections between fine-scale magnetic fields on the sun and the associated plasma structures on the Sun. It will do this by observing the photosphere, the transition region, and the corona nearly simultaneously, with a spatial resolution of one second of arc. The goal is to explore the three-dimensional magnetic structures that emerge through the visible surface of the Sun - the Photosphere - and define both the geometry and dynamics of the upper solar atmosphere: the Transition Region and Corona.



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