South Atlantic Anomaly affecting Fermi/GLAST

The South Atlantic Anomaly, a congenital dip of the life-protecting geomagnetic field affecting low-earth orbiting space craft, including the International Space Station.

A new study shows mission time for GLAST, the "Gamma Ray Large Area Space Telescope" renamed after Enrico Fermi in August is been strongly affected by its regular passes in orbit through the South Atlantic Anomaly (SAA).

Fermi delivered a spectacular and unprecedented in its detail First Light of the Gamma Ray sky in August, and is designed to detect tale-tale streams of highly energetic particles that precede a Gamma Ray Burst.

GRB's are Titanic explosions from the Dark Ages of cosmic history that flash intensely and then rapidly fade from view, nearly as old as the Universe. Fermi is designed to interrupt its mission to turn and rapidly study these still-mysterious phenomena in response to the sudden flash of highly energetic Gamma Rays known to herald an arrival of a visible counterpart since early in the Space Age.

Fermi's general mission is to study the Gamma Ray sky, most, but not all, of which appears to originate from within the edge-on disk of our own galaxy.

GRB's have been detected in every area of the sky, however, without any optical counterpart until spaceborne telescopes began to gradually increase their manuverability and sensitivity in recent years. Opinions differ whether GRB's result when super-massive proto-stars in the early universe collapsed or if they result from binary neutron stars or blackholes falling onto one another.

The energy released is of great interest because, given their great distances, it is estimated each GRB release nearly as much energy as is known to exist in the entire present visible universe, all in a very brief moment, relatively speaking.

Fermi's mission is being perturbed by another long-observed phenomena, the anomalous dip on Earth's Magnetic Field lines over the South Atlantic.

This dip in Earth's magnetic field consistently brings highly charged particles trapped within the Van Allen Belts closer to Earth enough to affect spacecraft in low Earth orbit, including the International Space Station.
Twice each day, the ISS, in it's orbit inclined relative to the equator by 51 degrees, the station passes through this unusually low "hot zone."

The particles trapped along these field lines are also triggering GRB sensors on the watch for Gamma Ray Bursters, giving mission planners headaches and robbing scientists of valuable viewing time.

C. R. A. Augusto, C. E. Navia, and K. H. Tsui of the Instituto de Física in Brazil detail the phenomena in a paper published in Physics Review, Oct. 7.