Figure 10.6: The background in the V-channel for orbit 75 (December 1989). The
peaks towards Perigee perigee are due to the radiation belts. The double peaks
around apogee are the transits of the two fields of view through the galactic plane.
Transits through the ecliptic plane (zodiacal light) can also be distinguished. Digitisation of the response occurs at low photon-count levels.