Purpose of the flight and payload description
The payload was composed of a grille spectrometer associated with a telescope and a Sun pointer. With the objective of advance towards the determination of the natural variability of NO, the flight goal was to obtain simultaneous measurement of NO and NO2 using absorption spectrometry, with the Sun as a source, in two narrow spectral ranges: in the 5.2 µm band of NO and in the 6.2 µm band of NO.
The spectrometer used a Littrow mounting with an off-axis parabolic mirror whose focal length wass 60 cm. The grille was deposited on an 18 x 18 mm calcium fluoride window. The signal was chopped at 360 Hz by vibrating the collimating mirror at 180 Hz, which was the resonance frequency of the mechanical mounting included in the servo system stabilizing the vibration amplitude. The spectral calibrations were performed by means of H2O and CO2 absorption lines and by the simultaneous recording of the spectra and of position grating marks. To maintain the instrumental performance during flight the optical path inside the spectrometer is servo controlled to balance the mechanical deformations due to temperature and attitude alterations. Two auxiliary grilles located alongside of the main grille were used for this purpose. The first was illuminated by a filament lamp, with ray paths close to the path of the solar radiation to be measured. The light flux was received on a gold doped germanium photodiode after reflection on the second grille. The detector signals were preamplified and telemetered to the ground through three channels having different sensitivities.
A 4.2 m focal length modified Cassegrain telescope of 32 cm diameter was used to image the Sun on the grille. The Sun pointing system controls the attitude of the spectrometer telescope assembly. The gondola on which the payload was mounted was uncoupled from the balloon on the three axis. In a first mode the gondola was oriented along a fixed axis referred to the Earth. The couples were provided by inertia wheels desaturated by means of moving masses. The pointing accuracy of the system was better than 30 arc/sec.
Details of the balloon flight
- Détermination de l'abondance de constituants stratosphériques minoritaires par spectrométrie d'absorption infrarouge Ph.D. Thesis by Christian Muller, Universite Libre de Bruxelles, May 1976
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- The CO fundamental bands in the solar spectrum Astronomy and Astrophysics, vol. 39, no. 2, Mar. 1975, p. 445
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