Satellite Outage Caused by Sun
Events on the Sun have a surprisingly wide range of important effects on Earth and in space. One very interesting and important effect is on the operation of satellites. The space environment, through which satellites travel, is a harsh place filled with charged particles and radiation from the Sun. At times, the flow of charged particles can increase dramatically and affect satellite operations.
The flow of charged particles can produce a build-up of electric charge on the surface of a satellite (called spacecraft charging) and this can trigger electric circuits controlling the craft. In many cases, these "phantom" commands have no significance but occasionally they can initiate something important such as causing the craft to point away from the Earth direction. Spacecraft have been lost due to this effect - e.g. the loss of one of the Canadian Anik satellites in 1994.
Flows of electrons arising from coronal holes on the Sun (ASWFC Solar Geophysical Summary, November 1994) have been found to affect satellites and for this reason ASWFC provides forecasts of times when a large flow of electrons is expected.
On October 7, 1995 there was an outage of the Intelsat 511 which is in a geostationary orbit above longitude 180 degrees East. This satellite is used for communications between Australia and the USA. The following report from Intelsat describes the event.
"The exact cause of loss of Earth lock has now been determined as an ESD (Electrostatic Discharge) event. The ESD event fired manual thruster causing a large attitude disturbance. Due to the magnitude of the disturbance it was necessary to perform the satellite into a safe Sun acquisition mode. The anomaly occurred shortly after 6pm satellite local time. Recovery from Sun acquisition at this satellite local time requires the longest outage due to the configuration of the sensors on the satellite and the Earth Sun geometry.
As you are aware Earth acquisition was regained at 1624 UT and the satellite is in a satisfactory state of health at this time."
The outage caused some inconvenience but thankfully no lasting damage. However, it does serve to illustrate the importance of solar-related events on our technology.
The graph below shows the flow of electrons recorded during the anomaly. The peak electron flux, occuring between 6 and 9 October, corresponds to the time when the anomoly took place.
Material prepared by Richard Thompson
