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Lyman Alpha Telescope

NSSDCA ID: 1961-032A-01

Mission Name: Ranger 2
Principal Investigator:Mr. Robert W. Kreplin


The experiment was designed to scan the Earth in the Lyman-Alpha region (1050 A to 1350 A) and to study the hydrogen constituent of the exosphere. The Lyman-Alpha telescope was an ultraviolet scanning telescope that could obtain a series of low-resolution pictures of the Earth and its exosphere in ultraviolet light near the Lyman-Alpha wavelength (1216 angstroms). It was also capable of providing information on the geographical extent of any auroral activity.

The telescope was mounted on the Ranger spacecraft in a gimbal system permitting motion of the telescope axis in two perpendicular planes. The telescope consisted of a 25.4 cm (10 in.) diameter parabolic mirror mounted inside a cylindrical radiation shield. Held above the mirror at its focus by a tripod was a cylindrical ionization chamber. The mirror was a magnesium shell backed by an epoxy matrix. The mirror was coated with aluminum and then MgF2 to enhance reflectivity at 1216 angstroms. The mirror had a reflectivity of 0.6 to 0.8 at 1216 angstroms and was F/0.6. The field stop was 0.295 cm (0.116 in.) in diameter. The optical gain was about 100 and the field of view was 1.1 degree full-cone angle.

The ionization chamber was 2.54 cm (1 in.) in diameter and 3.8 cm (1.5 in.) long. It was filled with 15-mm pressure NO gas and a filler gas, carbon dioxide, at 35 mm. It had a 1 cm (0.4 in.) diameter LiF window at one end, cemented with AgCl. The upper wavelength sensitivity cutoff was about 1350 angstroms, due to the ionization theshold of NO. The lower wavelength cutoff was about 1050 angstroms due to the LiF window absorption. The ionization chamber voltage could be adjusted to give the desired gas gain. Total mass of the experiment was 6.35 kg (14 lb.) and total power requirement was 1.15 W.

The telescope was made to operate by moving into a position with its axis of symmetry pointing 20 degrees away from the center of the Earth in the roll-yaw plane and the pitch-yaw plane of the spacecraft. It then scanned by sweeping out a raster, using two motors to scan along the elevation back and forth once, then stepping two degrees in the azimuth and repeating the elevation scan. During the upward motion of the elevation scan the gas gain was 13, during the downward motion 650. The resulting data would be two series (one for each gas gain) of 20-strip pictures of brightness vs. elevation, 1.1 degrees wide, 40 degrees long, separated by 2 degrees. After one scan the telescope remained in its final [position taking background data at 650 gas gain. As the telescope mechanically scanned the regions, the detector produced an electrical signal proportional to the amount of the Lyman-Alpha radiation incident upon it, giving a crude picture somewhat similar to a TV image.

The experiment returned several in-flight calibrations and background measurements of Lyman-Alpha, the limited amount of data being due to the failure of the spacecraft to reach its deep space trajectory and the short duration of the mission.

Alternate Names

  • Ranger2/LymanAlphaTelescope


  • Solar Physics: Visible

Additional Information

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



NameRoleOriginal AffiliationE-mail
Mr. Robert W. KreplinPrincipal InvestigatorUS Naval Research
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