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Radio Science Subsystem (RSS)

NSSDCA ID: 2010-020D-06

Mission Name: Akatsuki


In addition to routine tracking for navigation and data return purposes, the Radio Science Subsystem (RSS) will be used to perform radio occultations to determine the vertical structure of the atmosphere of Venus. The scientific objectives are to derive vertical profiles of density, temperature, and sulfuric acid amount in the neutral atmosphere of Venus; derive vertical profiles of electron density in the ionosphere; and study the solar corona during superior conjunctions.

RSS comprises spacecraft elements that are distributed among several subsystems on the spacecraft and a ground element that includes tracking stations at the Usuda Deep Space Center (UDSC) of JAXA, the Indian Deep Space Network of the Indian Space Research Organization, and the Weilheim station of the German Aerospace Center. A 0.9 m radial line slot array antenna is used as the X-band (8.4 GHz) high gain antenna for downlink. Two medium gain horn antennas mounted on turntables and two low gain antennas are used for command uplink. The medium gain horn antennas are used for housekeeping data downlink when the high gain antenna is not facing Earth.

The one-way downlink at X-band (8410.932 MHz) is used for occultation experiments. During the experiments, one of two X-band transponders is locked to the Ultrastable Oscillator (USO) which generates reference and transmission (downlink) frequencies at 38 MHz and 8.4 GHz, respectively. The downlink signal is amplified by a 23.4 W traveling wave tube amplifier then radiated by the high gain antenna through the atmosphere of Venus and toward tracking stations on Earth. The tracking stations collect, amplify, down-convert, and record the radio signals (typically 4-bit or 8-bit digitized). The primary ground station used for occultation experiments is the 64-m antenna at UDSC.

Radio occultations of the Venusian atmosphere began in March 2016. Ten occultation experiments, including 10 ingress and 9 egress measurements, have been conducted by February 2017. Altitude distributions of the temperature, the sulfuric acid vapor mixing ratio, and the electron density were derived from these data.

Radio occultations of the solar corona were conducted during the solar conjunction periods in June - July 2011 and May - June 2016. The outward flow velocity was derived from the fluctuation of the signal intensity, and the plasma density fluctuation was determined from the fluctuation of the frequency. The 2011 observations revealed the radial profile of the flow velocity, the radial distribution of compressible waves, and the internal structure of a coronal mass ejection.

Alternate Names

  • Akatsuki/RadioScienceSubsystem(RSS)
  • RS
  • USO
  • urn:jaxa:darts:context:instrument:vco.rss

Funding Agency

  • Japan Aerospace Exploration Agency (Japan)


  • Planetary Science: Atmospheres

Additional Information

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



NameRoleOriginal AffiliationE-mail

Selected References

  • Imamura, T., et al., Radio occultation experiment of the Venus atmosphere and ionosphere with the Venus orbiter Akatsuki, Earth Planets Space, 63, 493-501, doi:10.5047/eps.2011.03.009, June 2011.
  • Imamura, T., et al., Initial performance of the radio occultation experiment in the Venus orbiter mission Akatsuki, Earth Planets Space, 69, 137, doi:10.1186/s40623-017-0722-3, Oct. 2017.
  • Imamura, T., et al., Outflow Structure of the Quiet Sun Corona Probed by Spacecraft Radio Scintillations in Strong Scattering, ApJ, 788, 117, doi:10.1088/0004-637X/788/2/117, May 2014.
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