Effects on space systems
Spacecraft malfunction for a variety of reasons. Some malfunctions are reported but many are not reported. A few failures can be directly attributed to space weather; many more failures are suspected to have a space weather component; and many failures are unrelated to space weather. One indicator that space weather is a significant driver of spacecraft failure is that 46 of the 70 failures reported in 2003 occurred during the October 2003 geomagnetic storm. The two most common adverse space weather effects on spacecraft are radiation damage and spacecraft charging. Radiation (high energy particles) passes through the skin of the spacecraft and into the electronic components. In most cases the radiation causes an erroneous signal or changes one bit in memory of a spacecraft’s electronics (single event upsets). In a few cases, the radiation destroys a section of the electronics (single-event latchup). Spacecraft charging is the accumulation of an electrostatic charge on a non-conducting material on the spacecraft’s surface by low energy particles. If enough charge is built-up, a discharge (spark) occurs. Damage to the spacecraft is done by causing an erroneous signal to be detected and acted on by the spacecraft computer as if the signal came from the ground controller or the electronics are damaged by a surge of electrical current. A recent study indicates that spacecraft charging is the predominant space weather effect on spacecraft in geosynchronous orbit.
Spacecraft anomalies are grouped into broad categories based upon the effect upon the spacecraft. A list of potential effects follows:
- Surface charging
- Deep dielectric or bulk charging
- Single Event Upset (SEU) a) Galactic cosmic rays and b) Solar proton events
- Spacecraft drag (
- Total dose effects
- Solar radio frequency interference and telemetry scintillation
- Spacecraft orientation
- Photonics noise
- Materials degradation
- Meteorite impact
Spacecraft orbit changes
The orbits of spacecraft in low Earth orbit (LEO) decay to lower and lower altitudes due to the resistance from the friction between the spacecraft’s surface (i.e. , drag) and the outer layer of the Earth’s atmosphere (a.k.a. the thermosphere and exosphere). Eventually, a spacecraft’s orbit will decay so much that it will fall out of orbit and crash to the Earth’s surface. Many spacecraft launched in the past couple of decades have the ability to fire a small rocket (1) to increase the altitude to compensate for the decay and extend the lifetime in space, (2) to re-enter the atmosphere and crash into the ocean, or (3) change the orbit to avoid collision with other spacecraft. In order to accomplish the goal of firing a small rocket, very precise information about the orbit is needed. A geomagnetic storm can cause an orbit change over a couple of days that otherwise would occur over a year or more. The geomagnetic storm adds heat to the thermosphere, causing the thermosphere to expand and rise, which increases the drag on spacecraft in low Earth orbits. The 2009 satellite collision between the Iridium 33 and Cosmos 2251 demonstrated the importance of having precise knowledge of all objects in orbit. Iridium 33 had the capability to maneuver out of the path of Cosmos 2251 and could have evaded the crash, if a credible collision prediction had been available,
Effect of radiation on humans in space
The exposure of a human body to ionizing radiation has the same harmful effects whether the source of the radiation is a medical X-ray machine, a nuclear power plant or radiation in space. The degree of the harmful effect depends on the length of exposure and the energy density of the radiation. The ever-present radiation belts extend down to the altitude of manned spacecraft such as the International Space Station (ISS) and the Space Shuttle but the amount of exposure is within the acceptable lifetime exposure limit under normal conditions. During a major space weather event which includes a burst of solar energetic particles, the flux can increase by one to several orders of magnitude. There are areas within ISS where the thickness of the spacecraft surface and equipment can provide extra shielding and may keep the total dose absorbed within lifetime safe limits. For the Shuttle, such an event would have required an immediate termination of the mission.
Effects on ground systems
Disruption of GPS and other spacecraft signals
The ionosphere bends radio waves in the same manner that water in a swimming pool bends visible light. When the medium through which the light or radio waves travel is disturbed, the light image or radio information is distorted and can become unrecognizable. The degree of distortion (scintillation) of a radio wave by the ionosphere depends on the frequency of the radio signal. Radio signals in the VHF band (30 to 300 MHz) can be distorted beyond recognition by a disturbed ionosphere. Radio signals in the UHF band (300 MHz to 3 GHz) will propagate through a disturbed ionosphere but a receiver may not be able to keep locked to the carrier frequency. The Global Positioning System uses signals at 1575.42 MHz (L1) and 1227.6 MHz (L2) which can be distorted by a disturbed ionosphere and a receiver computes an erroneous position or fails to compute any position. Because the GPS signals are used by wide range of applications, any space weather event which makes GPS signal unreliable, the impact on society can be significant. For example the Wide Area Augmentation System (WAAS) operated by the Federal Aviation Administration is used as a precision navigation tool for commercial aviation in North America. It is disabled by every major space weather event. In some cases WAAS is disabled for minutes and in a few cases it has been disabled for a few days. Major space weather events can push the disturbed polar ionosphere 10° to 30° of latitude toward the equator and can cause large ionospheric gradients (changes in density over distance of 100’s of km) at mid and low latitude. Both of these factors can distort GPS signals.
Disruption of long-distance radio signals
Radio wave in the HF band (3 to 30 MHz) (also known as the shortwave band) are bent so much by the ionosphere that they are reflected back in the same manner as a mirror reflects light. Since the ground also reflects HF wave, a signal can be transmitted around the curvature of the Earth to a distant station. During the 20th century, HF communications was the only method for a ship or aircraft far from land or a base station to communicate. With the advent of systems such as Iridium, there are now other methods of communications but HF is still considered to be critical because not all vessels carry the newer equipment and even if the newer equipment is on board, HF is considered a critical backup system. Space weather events can create irregularities in the ionosphere that scatter HF signals instead of reflecting them and make HF communications over long distance poor or impossible. At auroral and polar latitudes, small space weather events which occur frequently disrupt HF communications. At mid-latitudes, HF communications are disrupted by solar radio bursts, by X-rays from solar flares (which enhance and disturb the ionospheric D-layer) and by TEC enhancements and irregularities during major geomagnetic storms which are infrequent.
Ground Induced Current: electrical transmission, pipelines, etc
A well-known ground-level consequence of space weather is geomagnetically induced current, or ground induced current or GIC. GIC flows through the ground to depths of 20 km or more during geomagnetic storms. A well-known example of the adverse effect of a GIC event is the collapse of the Hydro-Québec power network on March 13, 1989. This was started by a failure of an overloaded transformer, which led to a general blackout, which lasted more than 9 hours and affected 6 million people. The geomagnetic storm causing this event was itself the result of a Coronal Mass Ejection, ejected from the Sun on March 9, 1989.A large geomagnetic storm can affect electric power grids at all latitudes, A storm as large as the 1859 event could disable the entire electric power grid in Eastern Canada and Eastern United States. GICs enter power grids, pipelinesand other conducting networks through grounding wires. Pipelines and other activities at high latitudes are affected by GIC driven by modest levels of auroral activity which occur almost daily. GICs associated with space weather can affect other systems such as geophysical mapping and hydrocarbon production.