PoSAT-1 Cosmic-Ray Experiment Monitors Massive Solar Particle Event (Forwarded)

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Surrey Satellite Technology Limited
Surrey Space Centre
University of Surrey
Guildford, U.K.

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Audrey Nice
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4 November 2003

PoSAT-1 Cosmic-Ray Experiment Monitors Massive Solar Particle Event

The 10-year-old PoSAT-1 microsatellite, built by SSTL for Portugal in 1993 and 
still operational in orbit, has been monitoring the recent massive solar storm 
that has affected both satellites in orbit and ground-based power distribution 
systems.

The Cosmic-Ray Experiment (CRE) has been monitoring the changes in the low-Earth 
orbit (LEO) ionising radiation environment related to changes in solar activity 
in virtually continuous operation since launch on the PoSAT-1 microsatellite 
built at SSTL over a decade ago. Currently the Sun is in a very active state 
with many large Sun-spot groups, and in the last week a number of massive solar 
storms (known as coronal mass ejections -- CMEs) have erupted, ejecting large 
numbers of particles (protons and other ions) out into space. As these particles 
reach Earth they temporarily fill the outer magnetosphere, greatly affecting the 
ionising radiation environment of Earth-orbiting spacecraft. Such events are 
known as solar particle events (SPEs). The geostationary Earth-orbit (GEO) 
(36,000 km altitude) is greatly affected. However, these same particles follow 
the magnetic field lines down towards the Earth’s polar regions where they can 
affect LEO satellites (typically 700-1500 km).

The PoSAT-1 CRE proton data for the last few days are shown below. The regular 
thin spikes are due to the passage of the spacecraft through the protons in the 
inner Van Allen belt. Note that the vertical scale is logarithmic, with particle 
fluxes exceeding 100,000 protons in the 3cm x 3 cm detector per integration 
period (150 s).

This solar particle event also appears to have had a significant heavy-ion 
content, as detected by Channel 7 of the PoSAT-1 CRE instrument. These ions are 
a particular threat to spacecraft electronics and may cause single-event 
latch-up (SEL) as well as single-event upsets (SEU).

All of SSTL’s spacecraft showed significantly enhanced SEU activity during these 
events. However, these SEUs have been successfully handled by the on-board 
error-detection and correction circuits resulting in no operational interruptions.

[NOTE: Images supporting this release are available at
http://www.sstl.co.uk/images/library/PoSAT_CRE.jpg (19KB)
and
http://www.sstl.co.uk/images/library/PoSAT_CRE2.jpg (14KB)]