As our society grows to depend more and more on advanced technology systems, we become increasingly more vulnerable to malfunctions in those systems. Some failures are not just inconveniences, but can have major economic impacts and potentially result in the loss of lives. Technology has reduced our risk to many kinds of natural disasters, but has actually increased the risk of some systems to space weather. For example, long-line power networks connecting widely separated geographic areas have increased the probability of power grids absorbing damaging electric currents induced by geomagnetic storms; the miniaturization of electronic components on satellites makes them potentially more susceptible to damage by energetic particles; aircraft designed to fly at 60,000 feet have increased human risk to radiation exposure during severe space weather.
Engineers use space environment information to specify the extent and types of protective measures that are to be designed into a system and to develop operating plans that minimize space weather effects. However, engineering solutions to some problems may be very costly or impossible to implement. After the fact, engineers use space environment information to determine the source of failures and develop corrective actions. Significant economic and societal benefits can be realized if designers of emerging technology can: (1) anticipate the properties of the space environment to which the hardware will be subjected; (2) depend on accurate and timely predictions of space weather; and (3) take advantage of post-event analysis to determine the source of system anomalies and failures and build a database for future planning.
Space weather affects satellite missions in a variety of ways, depending on the orbit and satellite function. Our society depends on satellites for weather information, communications, navigation, exploration, search and rescue, research, and national defense. The impact of satellite system failures is more far- reaching than ever before, and the trend will almost certainly continue at an increasing rate.
Energetic particles that originate from the sun, from interplanetary space, and from the Earth's magnetosphere continually impact the surfaces of spacecraft. Highly energetic particles penetrate electronic components, causing bit-flips in a chain of electronic signals that can result in spurious commands within the spacecraft or erroneous data from an instrument. These spurious commands have caused major satellite system failures that might have been avoided if ground controllers had had advance notice of impending particle hazards. Less energetic particles contribute to a variety of spacecraft surface charging problems, especially during periods of high geomagnetic activity. In addition, energetic electrons responsible for deep dielectric charging can degrade the useful lifetime of internal components.
Highly variable solar ultraviolet radiation continuously modifies
terrestrial atmospheric density and temperature, affecting spacecraft orbits and
lifetimes. Major geomagnetic storms result in heating and expansion of the
atmosphere, causing significant perturbations in low-altitude satellite
trajectories. At times, these effects may be severe enough to cause premature
re-entry of orbiting objects. It is important that satellite controllers be
warned of these changes and that accurate
models are in place to realistically account for the resulting atmospheric
effects. The Space Shuttle is also vulnerable to changes in atmospheric drag;
re-entry calculations for the orbiter are highly sensitive to atmospheric
density, and errors can threaten the safety of the vehicle and its crew.
Distribution of satellites at geosynchronous orbit. These satellites are subject to charging, bit-flips, and other adverse effects of the space environment.
Modern power grids are extremely complex and widespread. The long power lines that traverse the nation are susceptible to electric currents induced by the dramatic changes in high-altitude ionospheric currents that occur during geomagnetic storms. "Surges" in power lines from induced currents can cause massive network failures and permanent damage to multi- million dollar equipment in power generation plants. The resulting social chaos, economic impacts, and threat to safety during widespread power outages could far outweigh the cost of improving the electricity availability problem.
An electric power transformer destroyed by induced currents during a large magnetic storm. In April 1994, five transformers in the Chicago area failed in association with elevated geomagnetic activity.
The electric power distribution system has developed an increased susceptibility to geomagnetically induced currents because of widespread grid interconnections, complex electronic controls and technologies, and large inter-area power transfers. The phenomenon occurs globally and simultaneously, and industry operations allow for little redundancy or operating margin to absorb the effects. Mitigation of such effects is fairly straightforward provided advance notice is given of an impending storm; specific strategies presently exist within the power industry. An economic issue almost equally important to the industry is to minimize costly false alarms.
The accuracy of maritime navigation systems using very low frequency signals, such as LORAN and OMEGA, depends on knowing accurately the altitude of the bottom of the ionosphere. Rapid vertical changes in this boundary during solar flares and geomagnetic storms can introduce errors of several kilometers in location determinations.
The Global Positioning System (GPS) operates by transmitting radio waves from satellites to receivers on the ground, aircraft, or other satellites. These signals are used to calculate location very accurately. However, significant errors in positioning can result when the signals are refracted and slowed by ionospheric conditions. Future high-resolution applications of GPS technology will require better space weather support to compensate for these induced errors. Accurate specification and prediction of the properties of the ionosphere will aid in the design and operation of these emerging systems.
Communications at all frequencies are affected by space weather. High frequency (HF) radio wave communication is more routinely affected because this frequency depends on reflection from the ionosphere to carry signals great distances. Ionospheric irregularities contribute to signal fading; highly disturbed conditions, usually near the aurora and across the polar cap, can absorb the signal completely and make HF propagation impossible. Accurate forecasts of these effects can give operators more time to find an alternative means of communication. Telecommunication companies increasingly depend on higher frequency radio waves that penetrate the ionosphere and are relayed via satellite to other locations. Signal properties can be changed by ionospheric conditions so that they can no longer be accurately received at the Earth's surface. This may cause degradation of signals, but more importantly can prohibit critical communications, such as those used in search and rescue efforts, military operations, and other computer-linked networks.
Besides being a threat to satellite systems, energetic particles present a hazard to astronauts on space missions. On Earth we are protected from these particles by the atmosphere, which absorbs all but the most energetic cosmic ray particles. During space missions, astronauts performing extra-vehicular activities are relatively unprotected. The fluxes of energetic particles can increase hundreds of times, following an intense solar flare or during a large geomagnetic storm, to dangerous levels. Timely warnings are essential to give astronauts sufficient time to return to their spacecraft prior to the arrival of such energetic particles. High altitude aircraft crews and passengers on polar routes (e.g., SST, U-2) are also susceptible to radiation hazards during similar events.