NASA Logo, National Aeronautics and Space Administration
NASA Space Science Data Coordinated Archive Header

S-Band Transponder

NSSDCA ID: 1971-063D-03

Mission Name: Apollo 15 Subsatellite
Principal Investigator:Mr. William L. Sjogren


The purpose of this experiment 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. Because the fractional part of a cycle count was measured, the resolution was 0.01 Hz, or 0.6 mm s.

Alternate Names

  • Apollo15Subsatellite/S-BandTransponder
  • S164

Funding Agency

  • NASA-Office of Manned Space Flight (United States)


  • Planetary Science: Geology and Geophysics

Additional Information

Questions and comments about this experiment can be directed to: Dr. David R. Williams



NameRoleOriginal AffiliationE-mail
Mr. William L. SjogrenPrincipal InvestigatorNASA Jet Propulsion
[] NASA Logo -