Radiation Induced Effects in Commercial Memories onboard Alsat-1

In this part, a review of radiation induced error on memory devices of an Algerian satellite, which named as Alsat-1, has been made. Alsat-1 was launched in November 2002 into a 686 km sun-synchronous orbit. This microsatellite had designed Earth imaging cameras which had capability to provide 32-meter resolution imaging in 3 spectral bands (green, red, and near infrared) with an extremely wide imaging swath of 600 km on the ground with a revisit of the same area at least every 4 days with just a single satellite.

Since Alsat-1 is placed in a LEO of 686 km, elevated levels of radiation caused by the lack of atmosphere increase the probability of SEUs. A SEU is a non-destructive error which usually affects logic cells in such a way that it can cause a bit in a memory device to change logic states. This phenomenon is caused by a false charge created by the transit of a single ionizing particle through a memory chip.

In this paper, the observations includes the whole Alsat-1 life-time (i.e. from November 29 2002 to August 14 2010). The Ramdisk memories are based on eight Samsung SYS 84,000 parts of 4 Mbytes each in size. The yearly average of the number of SEU/day is shown for the period from 29/11/2002 to 14/08/2010 in given figure, showing the increase of the upset rates with the increasing of time. During this period of observation, 265,649 errors were logged in the memory devices with a mean error rate of 4.04 × 10-7 error/bit/day. In 2002 and 2010, the average SEU rate is 41 SEU/day and 117 SEU/day, respectively.

We can see that the most significant events being those of 2009 which caused an average of 120 upsets per day in the Alsat-1 memory devices, whereas a maximum number of severe errors has been registered in December 2002.

References:

https://waset.org/publications/8200/a-review-of-in-orbit-observations-of-radiation-induced-effects-in-commercial-memories-onboard-alsat-1