Key weather relay satellite survives encounter with ZombieSat
On April 3, 2010, the sun's surface erupted in a magnetic disturbance known as a Coronal Mass Ejection (CME). A chuck of the sun's atmosphere ripped away and hurtled through space towards the Earth, arriving two days later. As Coronal Mass Ejections go, this was a garden-variety one, the kind we see dozens of times per year. However, when the high energy electrons and protons associated with the CME reached Earth's magnetosphere on April 5, an unusually strong solar storm developed, the strongest in three years. While we have no direct proof that this space weather storm was responsible, an Intelsat telecommunications satellite called Galaxy 15, used to relay television programs, suddenly lost contact with ground controllers and began drifting through space. According to scientists at NOAA's Space Weather Prediction Center whom I met with on a site visit this summer, solar storms have probably knocked out at least a dozen satellites in the fifty years humans have been launching them. Usually, these dead satellites pose no threat to other satellites. But the Galaxy 15 satellite has joined the ranks of the undead and become "ZombieSat". Although no television signals are being bounced off of the satellite, its transponders remain active and are spewing out a high volume of noise in the microwave C-band. As ZombieSat drifted uncontrolled through space this year, interference from the satellite threatened to shut down transmissions from a number of communications satellites in its path. In May, SES World Skies was forced to maneuver their AMC-11 satellite out of the way of ZombieSat to avoid its interference. And yesterday, on December 15, ZombieSat made a close pass by the SES-1 communications satellite. This satellite downlinks the NOAAPORT weather data feed, which supplies nearly all of the weather data used by wunderground, the National Weather Service, and many other users. For a ten hour period yesterday, interference from ZombieSat significantly interfered with the NOAAPORT data feed, causing many data transmission errors.
Figure 1. This is a close-up view of the active region observed by Proba-2's SWAP (Sun Watcher using APS detectors and imaging processing) instrument on 3 April 2010. Magnetic loops are visibly glowing--filled with cooling plasma (though cooling is a relative phrase, its temperature still exceeds a million degrees)--as the Sun's magnetic field knits itself together again in the flare's immediate aftermath. The area around the magnetic loops is darkened due to the Sun's surface reacting to the force of the flare. Image credit: European Space Agency.
Fortunately, little or no weather data was permanently lost during ZombieSat's encounter with SES-1. Much of the credit for this goes to NOAA technicians who devised an alternate satellite data transimission scheme to reduce the amount of interference from ZombieSat. Over the past week, the NOAAPORT data has been routed as usual from the National Weather Service in Washington D.C. to the Primary Master Ground Station located in Hauppauge, NY, via terrestrial communication lines. The Hauppauge ground station has been broadcasting the NOAAPORT feed to a "borrowed" satellite, which bounces the signal to the SES Americom Master Ground Station in Hawaii, which is outside the interference "footprint" of ZombieSat. NOAAPORT then is then uplinked to the SES-1 satellite, and then beamed down to Earth to Weather Underground, the NWS, and the other NOAAPORT subscribers. This way, NOAAPORT has been avoiding seeing interference from ZombieSat during the uplink to the SES-1 satellite. However, the signal is still subject to interference during the downlink process, and ZombieSat may still be able to cause trouble for NOAAPORT over the next few days. By Sunday, ZombieSat will be far enough from SES-1 that NOAA can return NOAAPORT back to its original configuration. Kudos go to NOAA for safely managing to keep NOAAPORT functioning during ZombieSat's passage--had they not acted to re-route the NOAAPORT signal, the U.S. could have seen a significant and potentially dangerous loss of weather data. (However, this did not go off without a hitch--technicians experimenting with adjusting power levels for the NOAAPORT feed during testing of the re-routing scheme accidentally knocked NOAAPORT out for several hours a week ago Sunday.)
Figure 2. Data flow diagram of how weather data gets from the National Weather Service (NWS) and NOAA's Satellite and Information Service (NESDIS) through the NOAA Network Control Facility (NCF) onto the NOAAPORT feed that is relayed off of the SES-1 satellite to NOAAPORT receive ground stations. Image credit: NOAA.
How solar storms damage spacecraft
The region of space where most Earth-orbiting satellites lie, 100 - 23,000 miles above the surface, experiences "space weather"--constant bombardment from high energy particles emitted by the sun. Periodically, the sun erupts in a massive magnetic disturbances known as Coronal Mass Ejections (CMEs), when a portion of the sun's atmosphere rips away and hurtles into space. The sun also sends out high-energy particles during solar flares, and when holes open in the sun's outer atmosphere (a coronal "hole"). When these solar particles reach Earth's upper atmosphere, they trigger geomagnetic storms that create the beautiful aurora displays often visible at high latitudes. However, these geomagnetic storms can damage a wide range of electronic systems, including power grids, communications systems, and spacecraft. When high-energy protons and ions hit spacecraft, the ionization tracks left in micro-miniaturized electronics can damage computer memory chips or disrupt circuits. Very energetic electrons can also penetrate deep into satellites bury themselves in insulating materials, such as coaxial cables or electronic boards. A powerful internal electronic discharge like a miniature lightning bolt can occur if the charge grows great enough. Numerous satellite failures have been attributed to this phenomena. Lower energy electrons that cannot penetrate the spacecraft's shielding can also cause problems--if enough electrons accumulate on the surface of the satellite, this "surface charging" can cause a powerful, disruptive discharge. Ionization tracks and discharges due to surface charging can result in the satellite experiencing "phantom commands" that instruct it to perform operations that can cut it off from contact with ground controllers. Such an occurrence is suspected in the sudden loss of communication with the Galaxy 15 spacecraft on April 5.
Damage to spacecraft due to space weather events does not necessarily happen during the peak of the 11-year solar cycle. The most recent sunspot cycle peaked in April 2000, and sunspot numbers steadily decreased through October 2003. In that month, three of the largest sunspot groups in ten years formed on the sun and began launching a series of CMEs and solar flares towards Earth, forcing NOAA's Space Weather Prediction Center to issue over 250 solar storm watches, warnings, and alerts over a 3-week period. NASA reported that 24% of their spacecraft either turned off instruments or took other protective acts during the solar storms. Japan's $640 million ADEOS-2 satellite, designed to collect weather and climate change data, failed during the height of the solar storms, and never recovered. Several other satellites permanently lost sensors, including the X-ray sensor on GOES-8 and the AMSU-A1 instrument on NOAA-17. The CHIPS satellite began tumbling through space when its main computer failed (the satellite was recovered after 27 hours), and Japan's DRTS geostationary communications satellite want into safe mode due to a proton barrage from a solar flare. The satellite was recovered ten days later.
Figure 3. The largest solar flare ever recorded was observed on April 2, 2001. It was rated X-22 on a scale that only goes from one to twenty. The flare was more powerful than the flare that accompanied the worst geomagnetic storm in history, the 1859 Carrington event. Fortunately, the 2001 flare was not aimed at the Earth. Image credit: NASA.
Space weather catastrophes
While damage to satellites is a serious concern from geomagnetic storms, my main concern is the possibility of a 1-in-100 year event taking out 30% of the U.S. power grid for a period of years, resulting in a multi-trillion dollar disaster. The possibilities are explored in my 2009 post, A future Space Weather catastrophe: a disturbing possibility.
Top ten weather events of 2010
I'll be on our Internet radio show, The Daily Downpour today at 4pm EST, 1pm PST, to talk about the top ten weather events of 2010. I'll also be discussion the same subject on NPR's Living on Earth radio show on Friday.