Letter from Thomas Gold to Dr Gordon Pettengill, Director, Arecibo Ionospheric Observatory, Arecibo, Puerto Rico Asks if Gordon or Rolf would like to propose to NASA the inclusion of a receiver and transponder or recorder for the bistatic reception of the Arecibo transmission at the CSM in Lunar orbit. Also asks if they should take an interest in the reception of the direct and reflected signal from a radar altimeter on laster CSMs and gives characteristics. 18 March 1969