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Lyman-Alpha Photometer

NSSDCA ID: 1973-049A-01

Mission Name: Mars 5
Principal Investigators:Prof. Jacques E. Blamont
Principal Investigators:Dr. V. G. Kurt


The Lyman-Alpha Photometer was a French-Soviet experiment intended to measure interplanetary Lyman-alpha emissions during trans-Mars coast and to measure scattered solar radiation in the Lyman-alpha line (1216 A) to detect atomic hydrogen in the Martian atmosphere from orbit. The instrument detectors comprised three Geiger photon counters filled with nitrogen oxide. Two cuvettes, one containing molecular hydrogen and one containing molecular deuterium, were aligned so that radiation from a 5 degree field of view could pass through the hydrogen cuvette and then the deuterium cuvette. This marked the first use of hydrogen absorption cells in spacecraft. The cuvettes had lithium flouride windows sensitive to the spectral region 1050 - 1340 A. Behind the deuterium cuvette was a one of the Geiger counters embedded in a scintillation counter. Each cuvette contained an incandescent filament. When the filament was on, the hydrogen or deuterium would dissociate into atomic elements, and would resonantly scatter radiation passing through in the centers of the lines centered at 1215.7 A and 1215.4 A, respectively. The other two Geiger photon counters were embedded in scintillation counters and mounted to a window on the side of the cuvettes, enabling measurement of scattered radiation. An anti-coincidence circuit connected the Geiger counters to the scintillation counters. This, with additional lead shielding, lowered the background counting rate to about 1 pulse/sec. There were four cuvette switching regimes: both cuvette filaments on, both filaments off, hydrogen filament on, deuterium filament on. These regimes would be cycled through, each lasting 12-13 seconds. Every four cycles the cosmic ray background counting rate for all three detectors was measured.

The instrument was mounted on the spacecraft hull on the side not illuminated by the Sun. The optical axis was in the orbital plane of the station around Mars and at orbital pericenter made an angle of 30 degrees with the line to the center of Mars. Measurements were made from 23 February to 1 March 1974. The instrument performed normally and returned good data.

Alternate Names

  • Mars5/Lyman-AlphaPhotometer

Funding Agencies

  • Centre National de la Recherche Scientifique (France)
  • Institut Kosmicheskich Issledovaniy(Inst. of Cosmophysical Research) (U.S.S.R)


  • Planetary Science: Atmospheres

Additional Information

Questions and comments about this experiment can be directed to: Coordinated Request and User Support Office



NameRoleOriginal AffiliationE-mail
Prof. Jacques E. BlamontOther Principal InvestigatorCNRS, Service d'Aeronomie
Dr. V. G. KurtPrincipal InvestigatorRussian Academy of Sciences
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