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

S-Band Transponder (CSM/LM)

NSSDCA ID: 1971-063A-11

Mission Name: Apollo 15 Command and Service Module (CSM)
Principal Investigator:Mr. William L. Sjogren

Description

The purpose of this experiment, carried on the Apollo 15 mission, was to measure the lunar gravitational field, which in turn provided information on the lunar mass distribution and its correlation with surface features. The lunar gravitational field was measured by observing the dynamical motion of the spacecraft in orbit. The observational data were the precise radio tracking measurements used initially for real-time navigation. However, these line-of-sight velocity measurements could only be obtained while the spacecraft was in view of the Earth (thus, no farside data were available). The data were derived as follows -- a 2106.4-MHz radio signal was transmitted from the Earth to the spacecraft, where it was multiplied by a factor of 240/221 and retransmitted at the new frequency to Earth. At the earth, the initial transmitted frequency, multiplied by 240/221, was subtracted from the spacecraft signal. 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. The resulting differences in cycle count, along with the time at which they were measured, were recorded. Because the fractional part of a cycle count was measured, the resolution was 0.01 Hz or 0.6 mm/sec.

Alternate Names

  • Apollo15CSM/S-BandTransponder_CSM/LM_
  • S164

Funding Agency

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

Discipline

  • Planetary Science: Geology and Geophysics

Additional Information

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

 

Personnel

NameRoleOriginal AffiliationE-mail
Mr. Patrick E. LaffertyGeneral ContactNASA Johnson Space Center
Dr. Ben GottliebOther InvestigatorSouthwest Center for Advanced Studies
Mr. Jack LorellOther InvestigatorNASA Jet Propulsion Laboratory
Dr. Paul M. MullerOther InvestigatorNASA Jet Propulsion Laboratory
Mr. William L. SjogrenPrincipal InvestigatorNASA Jet Propulsion Laboratorywls@nomad.jpl.nasa.gov
[USA.gov] NASA Logo - nasa.gov