"Telecommunication satellites in geostationary orbit experience high levels of electrical charging as they are exposed to a variety of charged particles like electrons and protons," explains Mr. King Lam, ESA spacecraft engineer. "The charging, occurring especially when large areas of dielectric material are exposed to space, can result in an Electrostatic Discharge (ESD) between satellite surface elements.”
An ESD is a single, fast, high current transfer of charge to break down the high electrostatic field built up between two objects. When an ESD occurs on a satellite's solar panel that has not been designed with adequate protection, the solar cells can be seriously damaged and the satellite suffers significant power loss.
Several cases of severe power loss on operational telecommunications satellites occurred in the 1990s, triggering extensive research by ESA, other agencies and industry worldwide to better understand this phenomenon.
"The physics involved in the damaging processes on solar arrays has been investigated and explained in two previous ESA studies. This has led to a set of design rules and the definition of a test set-up for solar array designs that should minimise the risk of power loss caused by solar panel ESDs," says Mr. Lam.
Lam is ESA's representative on an ARTES activity being conducted in cooperation with The French Aeronautics and Space Research Center (ONERA) and the expertise of EADS Astrium and Thales Alenia Space. This activity is testing the flash-over current which forms an essential part of the primary ESD.
“An important point is the correct representation in the test set-up of the flash-over. The magnitude and duration of the current flowing during a flash-over depends on the total dielectric surface of the panel neutralised during the ESD,” explains Mr. Lam.
“Currently, the flash-over is represented in the test set-up by a capacitor but it is well-known that this does not sufficiently simulate the actual flash-over current. In order to be more representative, the maximum solar array surface that can be neutralised by a flash-over and the electrical characteristics of the flash-over current itself need to be established.”
Flash-over experiments on a large, flight-representative panel in a large thermal vacuum chamber were conducted to determine the maximum energy that can be released and the electrical characteristics of the associated flash-over current waveform. The experiments took place in September on an 8m2 solar array built by EADS Astrium in the large TV facility at IABG in Ottobrunn, Germany.
During a consecutive 10-day period, working around the clock, all planned experiments were carried out. A large amount of data was acquired and this data is still being analysed today. This data will be used to develop a test set-up that can generate a flight representative flash-over current for qualification tests on small solar array coupons.
The final results and conclusions are expected to become available in the first quarter of next year. For more information, see the contact link in the column to the right.
