Magnetic Fields and Technology Destruction in Space

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Geomagnetic storms are natural magnetic field changes caused by processes that start on the Sun. An onrush of high-energy charged solar particles and fields temporarily disrupts the magnetosphere region of man-made Earth satellites (Figure 2.19). In March 2000, NASA launched a special IMAGE (Imager for Magnetopause-to-Aurora Global Exploration) spacecraft to explore and monitor this region. Space weather forecasting has become a major program for modern nations. We defer our detailed look at these special solar-terrestrial disturbances until Chapter 4. For now, consider the fact that during major magnetic storms, man-made satellites suffer a number of damaging radiation exposure effects in the following ways.

Soda Bottle Magnetometer
FIGURE 2.19 ► Particles and fields from the Sun initiate geomagnetic storms on the Earth.

Our Earth's atmosphere is held in place by the same gravitational pull that holds our feet to the ground. Although the air thins rapidly with increasing altitude (most climbers of Mt. Everest use oxygen masks, for example), the high region of the Earth's ever-circling satellites contains enough atmospheric molecules to slightly slow the forward motion of a satellite and change its orbit. Engineers design onboard jets to regularly compensate for this normal air drag and reestablish the satellite's prescribed position. The heating of our distant atmosphere by magnetic storm currents during solar-terrestrial disturbances can modify the usual atmospheric density. The resulting changed drag on the satellites makes them suddenly deviate appreciably from their expected orbital positions. More than 9000 artificial objects in space are tracked to prevent collisions with working spacecraft and to warn nations of undesirable impacts with the Earth by fragments that will not disintegrate upon reentry through the lower atmosphere. Following magnetic storms, technicians at the tracking installations must scramble to correct the disrupted orbital predictions. On occasions following a great magnetic storm, over a 1000 working satellites and bits of space debris are temporarily lost.

Longitude

FIGURE 2.20 ► Location of UoSat-2 satellite memory upsets recorded between September 1988 and May 1992. Note the concentration near the South Atlantic-South America magnetic field anomaly region. Less numerous upsets in the polar regions are caused by bombarding cosmic-ray particles guided by the Earth's field. Figure supplied by Craig Underwood, Surrey Space Center, U.K.

Longitude

FIGURE 2.20 ► Location of UoSat-2 satellite memory upsets recorded between September 1988 and May 1992. Note the concentration near the South Atlantic-South America magnetic field anomaly region. Less numerous upsets in the polar regions are caused by bombarding cosmic-ray particles guided by the Earth's field. Figure supplied by Craig Underwood, Surrey Space Center, U.K.

Solar panels provide electrical energy for most working satellites. During geomagnetic storm periods, the increased number of particles in space, naturally organized in their travel by the Earth's main magnetic field, bombard the solar panels and erode the satellite's electrical production efficiency. A prematurely aged power-supply panel shortens a satellite's effective lifetime. More damage occurs near years of maxima in the 11-year solar activity cycles because of a corresponding increase in magnetic storms.

Energetic charged particles, captured by the Earth's magnetic field during magnetic storms, have caused failures that completely disable the electronics of expensive satellites. The bombarding particles can directly hit an onboard computer element (Figure 2.20), upsetting program memory control. A spark from an accumulated static charge buildup on critical materials can ruin the satellite's electrical system. A solar-terrestrial disturbance in May 1998 temporarily disabled the Galaxy 4 satellite, blanking out 80% of telephone-pager customers in the United States.

During major geomagnetic storms, when destructive very-high-energy particles are involved in the penetration of the magnetosphere, astronauts are required to withdraw to the innermost regions of their spacecraft. The Apollo astronauts were lucky to not have received a lethal dose of radiation in their Moon voyage. Passengers of high-flying supersonic jet airplanes (such as the Concord) could be exposed to this unhealthy storm-time radiation; such

FIGURE 2.21 ► A global representation of the total main magnetic field for the year 2000. Note the significant minimum at the border of South America near the south Atlantic Ocean. Field levels are in gammas and contour lines are separated by 1000 gammas. Figure prepared by John Quinn of the USGS.

planes are required to descend to sheltering lower altitudes during threatening conditions. Particle impacts (Figure 2.20) can be particularly important in the upper atmospheric location over the western South Atlantic-South America region where the Earth's low-field anomaly (Figure 2.21) concentrates trapped particles closer to the Earth. To avoid unhealthy exposure, manned satellites are typically routed to avoid this main field region. To lessen the damage to its systems, the Hubble Space Telescope instruments are switched off during passage through this anomaly.

Electric currents are induced to flow in the conducting metal parts of a satellite as it moves through the natural space fields. Using their knowledge of such things as the behavior of the Earth's main field, the orbit and speed of the satellite, and its electronic configuration, engineers are required to design measures that protect the satellite's operation from these induced currents and the resulting magnetic fields.

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