NSSDCA ID: 1972-031D-03
Mission Name: Apollo 16 SubsatelliteThe purpose of this experiment (S-164) was to measure the lunar gravitational field based on dynamical motion of the spacecraft in free-fall orbit by precise earth-based radio tracking measurements. A stable frequency of 2115 MHz obtained from a cesium reference was transmitted to the subsatellite which transponded the received signal, after multiplying it by the constant 240/221 (to avoid self-lockup), back to Earth. At the Earth receiver, the initial transmitted frequency was multiplied by 240/221 and subtracted, and the resulting cycle-count differences were accumulated for data reduction. The motion of the spacecraft towards or away from the Earth caused a Doppler shift in the frequency, which could be used to estimate the velocity along the line of sight between the spacecraft and Earth. Because the fractional part of a cycle count was measured, the resolution was 0.01 Hz, or 0.6 mm s. For a 5-day period after May 9, 1972, subsatellite periapsis altitudes near 12 km provided new detailed gravity measurements of many near-side features such as Copernicus, Sinus Medii, and Mare Fecunditatis.
Questions and comments about this experiment can be directed to: Dr. David R. Williams
Name | Role | Original Affiliation | |
---|---|---|---|
Mr. William L. Sjogren | Principal Investigator | NASA Jet Propulsion Laboratory | wls@nomad.jpl.nasa.gov |