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| | | | | | | Radiation effects
Radiation belt particles cause radiation damage to electronic components, solar cells and materials. A feature of the Low Earth Orbit (LEO) environment is the importance of single event upsets and biological effects arising from nuclear interactions between very energetic trapped protons and materials (sensitive parts of components, biological experiments, detectors).
Degradation
The best known radiation effects are radiation damage, that is, degradation of a material due to radiation impinging on it. This degradation can be induced by the ionisation that radiation causes in a material, defects created in the molecular structure of a material and similar displacement damage effects.
Single event upset
In space, energetic heavy ions passing through materials generate intense tracks of ionisation. If the ion passes through a sensitive part of a semiconductor chip, for example parts of a "bit", the free charge generated in the track is often sufficient to flip the logic state of the bit. This results in a single-event upset (SEU).
A SEU can also result from energetic protons or ions hitting the nucleus of an atom in a sensitive component location. The nuclear interaction can produce spallation, which is the splitting of the nucleus, the heavy debris from which carry away a sizeable portion of the initial particle's energy. The spallation products generate the ionisation which can flip the bit state.
Single Event Upset for Uosat-3 spacecraft
This problem is most commonly seen in the South Atlantic Anomaly (as can be seen in the figure above). This results in a strong localisation of the errors. The figure shows the spatial distribution of errors from the UoSAT-3 spacecraft in polar orbit. Note that a significant number of errors occur at high latitudes. These are due to cosmic-rays.
Radiation background
Radiation can interfere with detectors in the payloads of spacecraft, most notably on astronomy missions where they produce a `background' signal which may not be distinguishable from the photon signal being counted or which can overload the detector system. All astronomy missions from infra-red (e.g. ISO), through visible (e.g. HST, Hipparcos), UV (e.g. IUE) and X-ray (e.g. Exosat, XMM) to gamma-ray wavelengths (e.g. GRO, Cos-B, Integral) are affected.
This interference can come from the primary components of the radiation environment:
- Energetic trapped radiation, (mainly protons and electrons)
- solar particle events (mainly protons with some ions) and
- cosmic rays (protons and other ions).
The secondary radiation generated by the interactions of these primaries in matter can also generate interference. The most common secondary radiation in space is bremsstrahlung which is electromagnetic radiation, in the gamma-ray spectral region, produced when energetic electrons slow when passing through spacecraft material. Other secondary radiations (gamma-rays, electrons and ions) can arise from nuclear interactions with materials. In optical components, energetic particles cause scintillation (fluorescence) and Cerenkov radiation which are intense flashes of light caused by particles travelling close to the speed of light in optical media.
Last update: 5 April 2007 | |
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