[Illustration: particle detectors used to count protons]
[Illustration: transistors used to measure radiation damage]
[Illustration: solar cells used to measure radiation damage and as
solar aspect indicators]
[Illustration: particle detector used to count electrons]
There are two other special devices: Six single solar cells are spaced
at regular intervals around the satellite; these “solar aspect”
indicators report the quantity of sunlight hitting them—and thus tell
the direction in which the satellite is pointing. Three highly polished
metal mirrors are also placed on Telstar; flashes of sunlight reflected
from them can be seen in a telescope. To give a precise indication of
the satellite’s position, the data obtained from both the solar aspect
cells and from the flashes off the mirrors are combined.