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Stellar UV Radiation Experiment

NSSDCA ID: 1972-014A-01

Mission Name: TD 1A
Principal Investigators:Prof. Andre G. Monfils
Principal Investigators:Prof. R. Wilson


This experiment consisted of a 1.4-m telescope with an attached spectrometer box. An off-axis paraboloid mirror (f/3.5, diam 275 mm) reflected starlight onto a system of two slits situated in the prime focal plane. One of the two slits fed the stellar light into a single photometric channel with a filter limiting the passband to 400 A centered at 2750 A. The other slit was much wider (11.9 x 17 arc-min), and led into the three-channel grating spectrometer. Once per orbit, the telescope, aligned along the Z-axis, scanned a great circle of the sky. Because of this motion across the sky, the primary image of a certain star entering the telescope's field of view moved across the photometer and spectrophotometer slots. While the star image traversed the wide spectrophotometer slot, its corresponding spectrum moved in the focal plane of the spectrograph across the three exit slits, behind which there were three pulse-counting photomultipliers. By employing the scanning motion of the satellite, a spectrum scanning action was achieved without the need for moving parts. The three exit slits of the spectrophotometer were fixed at the following wavelengths -- 1350 to 1760 A, 1760 to 2160 A, and 2150 to 2550 A. The wavelength region from 1350 to 2550 A was fully covered by the three channels in 3.3 s, yielding a total of about 60 data points. In each channel the spectrum was scanned at 19.4-A intervals, the effective passband during each integration interval having a full-width, half-maximum of 35 to 40 A. Just before the telescope was integrated into the satellite, the instrument was extensively calibrated in order to achieve an absolute photometric accuracy between 10 and 20 percent, a relative photometric accuracy within 10 percent and a wavelength calibration accurate to a few Angstroms. This experiment was designed to detect 20,000 stars, of which 6,000 should have given useful UV spectra. It was able to measure stars of magnitude 10.5. Two major objectives were the study of interstellar extinction and the preparation of a UV star catalog.

Alternate Names

  • Multicolor Celestial Scan. 1000-3000A, IR S-1, S2, S-68
  • S1, S2, and S68
  • TD1A/StellarUVRadiationExperiment


  • Astronomy: Ultraviolet

Additional Information

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



NameRoleOriginal AffiliationE-mail
Dr. Claude JamarOther InvestigatorUniversite
Mr. P. J. BarkerOther InvestigatorScience Research Council
Prof. R. WilsonPrincipal InvestigatorUniversity College, London
Prof. Andre G. MonfilsPrincipal InvestigatorUniversite Liege
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