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Gravitational Potential as a Function of Time


Mission Name: GP-A
Principal Investigator:Dr. Robert F.C. Vessot


This experiment was intended to study the relation between time passage and gravitational potential. According to the Einstein general theory, time (frequency of an oscillator) passes slower in a strong gravitational field, than in a weaker field (frequency shift toward the red, or slower frequency, end of the visible spectrum). Frequency comparisons of equivalent hydrogen maser oscillators on the spacecraft and on the earth should provide observational support of this effect. Relativistic frequency shifts were expected to occur as a result of both vehicle velocity and change in gravitational potential. Two separate systems were used to measure these shifts. One system measured the elapsed phase changes in the transmission path, the other measured the phase of the spacecraft oscillator as received via the transmission path and compared to the earth-based oscillator. Phase changes in the transmission path due to atmospheric effects, ionospheric effects, and range variation were automatically and coherently corrected.

Alternate Names

  • GP-A/GravitationalPotentialasaFunctionofTime

Facts in Brief

Mass: 43 kg
Power (avg): 22 W

Funding Agency

  • NASA-Office of Space Science (United States)


    Additional Information

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



    NameRoleOriginal AffiliationE-mail
    Dr. Martin W. LevineOther InvestigatorSmithsonian Astrophysical Observatory
    Dr. Robert F.C. VessotPrincipal InvestigatorSmithsonian Astrophysical
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