South Atlantic Anomaly Presents Dangerous Radiation
Contributions by Gabriel Spera – The Aerospace Corporation – FFRDC
Laboratory simulation of the Earth’s magnetic field.
Image source: wikipedia.org
A satellite in a typical low Earth orbit remains safely below the proton belt—except at the South Atlantic Anomaly. Spacecraft passing through this region are bombarded by protons with energies exceeding 10 million electron volts at a typical flux of 3000 particles per square centimeter per second. These particles can be a hazard for space systems and astronauts.
Under European Union Directive 96/29/Euratom: Article 42, which became effective May 13, 2000, airlines belonging to EU Member States are required to assess and limit their aircrews’ exposure to cosmic radiation. Compliance with the legislation would be satisfied by the use of a computer program to estimate route doses, which can then be used to plan rosters, taking the individual’s likely exposure into account.
As a result of customer concerns and request for support, SEC will implement a new warning and alert for >100 MeV protons exceeding 100 particle flux units (pfu) . The current NOAA Scales warning for high-energy protons is based on 10 MeV, which is not as useful for determining radiation hazards for humans.
Airline Radiation Concerns
United Airlines reported high frequency (HF) communications losses and solar radiation storms which caused planes to be diverted to less dangerous routes. Rerouting and general delays are costly to the airlines. One example of that was a storm that caused a flight to be diverted from a polar route, requiring additional fuel at Tokyo and extending the flight by 5 hrs 30 min.
During another period, 25 flights were flown on less than optimal polar routes due to HF communications problems. Northwest Airlines diverted a Detroit – Beijing flight to a non-polar route due to both HF communications problems (radio blackout) and a solar radiation storm, forcing an unscheduled stop at Fairbanks for fuel. This route change resulted in an approximately 3 hour delay and $100,000 cost to NWA, plus the inconvenience and loss attendants upon disrupting the travel of passengers.
The Director of Flight Operations of Continental Airlines reported that they diverted their daily flight for the second day in succession based on the S3 level of solar radiation storm. The direct impact was 2 hours of extra flight time and additional associated costs.
NASA launched the Terra Earth Observing System spacecraft in 1999 as part of a broad mission to study global climate change. Just one day after launch, the satellite’s high-gain antenna spontaneously went into “safe” mode, interrupting communications with the Tracking and Data Relay System satellites. A series of diagnostic tests indicated that an anomalously high current had passed through the motor drive assembly.
Similarly, the Hubble Space Telescope experienced bit errors in communications between subsystems when traveling through the Anomaly. Error detection and correction schemes prevented data loss, but the problem was still annoying to ground controllers. As a result, several high-voltage instruments are powered down before the Hubble enters the South Atlantic Anomaly.
Numerous other missions have been affected as well. ROSAT, the Roentgen Satellite, was an X-ray observatory that flew for much of the 1990s. The unit’s position-sensitive proportional counters had to be turned off during passage through the South Atlantic Anomaly to prevent severe damage. ROSAT’s high-resolution imager could be left on, but could collect no useful data while in the region. The Topex satellite, which flies at an altitude of about 1000 kilometers, is still prone to random upsets in its altimeter as it passes through the Anomaly, preventing proper data collection.
Perhaps the most serious case was NASA’s Modis satellite, which was rendered inoperative in 2001 as it passed through the South Atlantic Anomaly. The failure seemed to be caused by an overvoltage shutdown, probably started when a high-energy ion struck a vulnerable metal-oxide semiconductor field-effect transistor (MOSFET), causing it to fail. It took 16 days to get the satellite back on line.
Random glitches affect humans as well. Since the days of Apollo 11, astronauts in space have reported seeing random flashes of light—with their eyes closed. These flashes are believed to be caused by energetic particles striking sensitive areas of the retina. In a recent experiment, astronauts aboard the Mir wore detector helmets to help researchers correlate the number of reported flashes with the measured particle flux. If the flashes increased when Mir entered the South Atlantic Anomaly, then protons would be revealed as the likely cause; if not, then heavy ions (which appear in equal amounts inside and outside the proton belt) would be indicated. The frequency of the flashes increased in the Anomaly, but only slightly, suggesting that protons alone are not responsible, but neither are heavy ions.
So it seems that the South Atlantic Anomaly may well have a few more surprises in store.
Coming… Part III – Evidence the Magnetic Pole Shift Has Begun
Article from: ECTV Newsletter