NSSDCA ID: 1989-033B-03
Mission Name: MagellanThe radio science occultation experiment made use of measurements of radio transmissions through the Venus atmosphere to Earth to determine characteristics of the atmosphere at different altitudes. The first of these experiments was done on 05-06 October 1991 (orbits 3212-3214). More experiments were done intermittently until 12 October 1994.
Radio occultation occurs when Earth, as viewed by the spacecraft, is occulted by the Venus atmosphere. In this experiment, the spacecraft modulation was switched off and continuous wave signals were transmitted by the spacecraft along the boresight of the high-gain antenna with linear polarization at 2.298 GHz (S-band, or 13 cm) and with circular polarization at 8.415 GHz (X-band, or 3.5 cm). Signals could be received coherently in both right- and left- circular polarizations at both wavelengths when a 70-m antenna was used at the Deep Space Network station. When a 34-m antenna was used, only a single polarization at each wavelength could be received; and, in some cases, only one wavelength was captured. To ensure that the frequency was stable, a reference signal of 2.116 GHz was uplinked to the spacecraft.
As the spacecraft moved behind the limb of the planet, the signal penetrated deeper into the atmosphere. Refraction resulted in an increase in the Doppler shift and refractive defocusing, absorption, and scattering cause a decrease in the signal power. A limb tracking maneuver was also required of the spacecraft during this period to keep the antenna focused on the uplink signal. Finally, changes in polarization of the signal occurred in the atmosphere. All these data can be related to the refracting and absorbing properties of the atmosphere as a function of raypath penetration depth and inverted to give the temperature and pressure structure and the density of absorbing species in the atmosphere.
Questions and comments about this experiment can be directed to: Dr. David R. Williams
Name | Role | Original Affiliation | |
---|---|---|---|
Dr. Jon M. Jenkins | General Contact | NASA Ames Research Center | jjenkins@mail.arc.nasa.gov |
Dr. Jon M. Jenkins | Lead Investigator | NASA Ames Research Center | jjenkins@mail.arc.nasa.gov |