The instrument complement included detectors to measure the directional and omnidirectional fluxes of protons and electrons. These instruments and the high quality of the resulting measurements made the AZUR mission particularly well suited for the study of the trapped radiation environment, despite the short duration of the mission. The energetic proton measurements, which were collected during the maximum of Solar Cycle 20, were the basis for the low altitude part of the NASA model AP-8 MAX (Sawyer and Vette, 1976).
The mission goals were the measurements of the following quantities:
The payload consisted of seven instruments. Descriptions of each instrument package can be found in Achtermann et al. (1970).
After about 24 h in orbit, a command system instability developed and persisted intermittently throughout the flight. The tape recorder failed on 08 Dec 1969. Prior to this failure, the German project office estimated that 85 - 90 % of the expected data had been obtained. All experiments were operating normally until the spacecraft telemetry system malfunctioned on 18 June 1970.
The experiment measures the directional proton flux in the energy range 1.5 - 100 MeV. The aperture opening is constructed with a number of Al and Ta collimators and is continued through a plastic scintillator surrounding the detectors and absorbers. The scintillator is connected to a photomultiplier by means of a plexiglass light conductor. The detectors respond to particle beams through the aperture opening. The energy dependent reach of the incident particle determines the number of detectors and absorbers they penetrate. Through the implementation of seven detectors and a treatment of the detector signal logic the total measurement range is divided into six energy ranges for protons and one channel for alpha particles. The anticoincidence rates are referred to as channel 8.
The lower limit of the detector range is determined by the thickness of the Ni foil placed before the scintillator, the thickness of the first detector and the electronic treshold of the second detector. The Ni foil with thickness 1 µ (8.9 10-4 g cm-2) serves to shield the scintillator and the detectors from incoming light. The upper energy limit of the instrument is given by the absorption thickness of the combined detector cage up to the aft inner wall of the scintillator. In addition to its role as upper energy limit for particles coming in through the aperture, the scintillator also tags particles that penetrate from outside the aperture through the combined shielding. An anticoincidence switch between scintillator and detector prohibits these particles to be measured. In order to limit the impuls rate of the scintillator and, correspondingly, the dead time of the instrument, the electronics is constructed around the scintillator and the photomultiplier to provide additional shielding.
The electronic tresholds of the semiconductor detectors are chosen sufficiently high so that electrons penetrating the aperture without scattering do not produce a signal. This arrangement does not rule out electrons undergoing multiple scattering and pile-up effects. Therefore, the instruments are equipped with a sweeping magnet which ensures that the influence of electrons on the ion count rates is negligible (Achtermann et al., 1970).
The plastic scintillator surrounds an Al cage that contains the seven detectors and the three absorbers. The detector connectors are fed through holes in the scintillator and the closest Ta shield to the amplifiers, which are arranged around the detector cage. The detectors EI-88/1 and EI-88/2 are identical except for a small difference in aperture angle, and thus geometric factor. The integration time for both instruments is fixed at 10 s. Due to the slow spin rate of the satellite, this rather long integration time does not compromise the quality of the directional measurements.
Unfortunately, the data gathered after 5 March 1970 have been lost.
Remarks:
Achtermann, E., B. Häusler, D. Hovestadt, and G. Paschmann, Die Experimente EI 88 und EI 93 zur Messung von energiereichen Elektronen, Protonen und Alphateilchen im Satelliten AZUR, Physikalische Eigenschaften und Testmessungen, BMBW-FB W 70-67, 1970.
Häusler, B., Untersuchungen des Verhaltens hochenergetischer Protonen und Elektronen in der inneren Magnetosphäre, MPI-PAE/Extraterr. 66, 1972.
Heynderickx, D., and M. Kruglanski, Flight Data Comparisons, TREND 3, Technical note 5, part 1: The AZUR data, ESTEC Contract No. 10725/94/NL/JG(SC), 1998.
Hovestadt, D., E. Achtermann, B. Ebel, B. Häusler, and G. Pachmann, New Observations of the proton population of the radiation belt between 1.5 and 104 MeV, Earth's Magnetospheric Processes, B. M. McCormac (ed.), D. Reidel Publishing Company, Dordrecht, Holland, 115 - 119, 1972.
Sawyer, D. M., and J. I. Vette, AP-8 Trapped Proton Environment for Solar Maximum and Solar Minimum, NSSDC/WDC-A-R&S 78-06, 1976.
Last update: Mon, 12 Mar 2018