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Venus Radio Science (VeRa)

NSSDCA ID: 2005-045A-05

Mission Name: Venus Express
Principal Investigator:Dr. Bernd Hausler

Description

The Venus Radio Science experiment (VeRa) uses the Venus Express communications system to perform radio sounding experiments of: the neutral Venus atmosphere (occultation experiment), the ionosphere of Venus (occultation experiment), and the solar corona during the inferior and superior conjunctions of Venus. It will also use a bistatic radar experiment to study the surface of Venus. The scientific objectives are to derive vertical density, pressure and temperature profiles as a function of height, with a height resolution better than 100 metres of the neutral Venus atmosphere; derive vertical ionospheric electron density profiles and to derive a description of the global behaviour of the ionosphere through its diurnal and seasonal variations and its dependence on solar wind conditions; study the solar corona; and determine the dielectric and scattering properties of the surface of Venus in specific target areas.

The VeRa experiment will make use of the radio transponder and antenna carried by the spacecraft for communication with Earth. Frequency, amplitude, phase, propogation time, and polarisation information will be extracted from the received radio signal by the ground station. The radio signals are affected by the medium through which the signals propagate (atmospheres, ionospheres, interplanetary medium, solar corona), by the gravitational influence of the planet on the spacecraft and finally by the performance of the various systems involved both on the spacecraft and on ground. A simultaneous and coherent dual-frequency downlink at X-band and S-band via the High Gain Antenna is required to separate the effects of the classical Doppler shift due to the motion of the spacecraft relative to the Earth and the effects caused by the propagation of the signals through the various dispersive media in the signal path.

Uplinks are provided either at X-band, for routine operations, or at S-band for coronal sounding. In the coherent two-way mode the received frequency is used to derive the downlink frequencies by using the constant transponder ratios 880/221 and 240/221 for X-band and S-band downlink, respectively. The spacecraft transmits a dual-frequency downlink at X-band and S-band simultaneously and phase coherently via the HGA. Typically, the X-band and S-band frequencies are related by a factor of 11/3. If an uplink exists, the downlinks are also coherent with the uplink in their respective transponding ratios. The ground stations will employ a hydrogen maser frequency standard to achieve a frequency stability in the order of 10-15 over long integration time (> 100 seconds). This stability is required for precise two-way tracking in order to achieve velocity accuracy better than 0.1 mm/s at one second integration time.

The sounding of the neutral and ionised atmosphere is performed in the periods just before the spacecraft enters occultation by the planet. The High Gain Antenna is pointed toward the Earth. The radio link is a two-way dual-frequency downlink with unmodulated carriers. The radio link passes through a swath of the ionosphere and atmosphere.

Solar corona sounding will be performed when Venus is within 10 degree elongation on either side of the solar disk. The operational radio link for the sounding of the solar corona is the two-way dual-frequency radio with an S-band uplink. The experiment can be performed whenever the spacecraft is being tracked for data return.

A bistatic radar configuration is distinguished from a monostatic configuration by the spatial separation of the transmitter (the spacecraft) and the receiver (ground station). The HGA is inertially pointed toward the surface of Venus and an X-band signal without modulation is transmitted. Several passes above specific targets will be made. The reflected and/or scattered signal is received by the ground station. The experiment is partly based on the Rosetta radio science experiment.

Alternate Names

  • VeRa
  • VenusExpress/VeRa

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
Dr. Bernd HauslerPrincipal Investigatorberndhausler@unibw-muenchen.de
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