@article{31760,
      author       = "Petitfourt, J. and International astronautical Federation.
                      XXVIII Congress. September 25 - October 1, 1977. Praha,
                      Czechoslovakia. IAF - 77 - 213",
      title        = "Systéme d´observation de la Terre á double rythme  ",
      year         = "1977",
      note         = "1 sv.",
}