Zephyr: A High Altitude Long Endurance Unmanned Air Vehicle ...

1.2.3 Cosmic RaysCosmic rays are energetic particles (90% of them are protons) that originate fromspace and enter our atmosphere. Due to their high energies (some have energies above1020eV), they can interact with interstellar matter and create secondary cosmic rays,or they can interact with molecules (mainly oxygen and nitrogen) in our atmosphereto create lighter particles. Both primary and secondary cosmic rays can alter the stateof elements in electronic circuits, causing transient problems like corrupted data inmemory or inaccurate behaviour of processors. As the intensity of cosmic radiationincreases with altitude, it causes problems for satellites and UAVs. The peak incosmic rays for both intensity and coincidences is at about 50,000ft (see graph 1).This is the altitude that Zephyr will be flying through when it is cycling so there is ahigh possibility that equipment could get corrupted. This could not only corrupt databut it could also create a critical fault. In the 100 hours of flying time that the Zephyraircrafts have had, not once have any of the onboard electronics been affected bycosmic rays.Graph 1. Graph to show variationof cosmic rays with altitude [2]13