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Radio Plasma Imager (RPI)

NSSDCA ID: 2000-017A-01

Mission Name: IMAGE
Principal Investigator:Prof. Bodo W. Reinisch


The main science objective of the Radio Plasma Imager (RPI) was to characterize plasma in the Earth's magnetosphere utilizing imaging in the radio frequency range.

The RPI on the IMAGE spacecraft was a pioneering instrument designed as a low frequency (3 kHz to 3 MHz) long-range magnetospheric radio sounder, relaxation sounder, and a passive plasma wave instrument. RPI was a highly flexible instrument capable of being programmed to perform these types of measurements at times when IMAGE was located in key regions of the magnetosphere. For the remote sensing RPI transmitted coded electromagnetic waves and used digital pulse compression and spectral integration to isolate the resulting echoes.

The RPI instrument consisted of an electronics unit, four 250-m wire antennas with antenna tuners, and a z-axis antenna with two 10-m lattice booms. RPI used the x axis antennas for all transmissions while echo reception was accomplished on all three. The x-axis dipole antenna was 500 m tip-to-tip at the beginning of the mission but was shortened to 370 m when it apparently collided with a micrometeoroid or orbital debris on 03 October 2000. The Y antenna suffered similar damage to its -Y segment 11 on August 2002 and complete loss of its +Y segment on 30 September 2004.

RPI was capable of detecting direct echoes from the plasmasphere from distances of 3 Earth radii or greater. RPI observed a large number of guided echoes in the plasmapause, plasmaspheric notches, in the plasma trough, and over the polar cap. These observations indicated that electromagnetic waves propagate along the magnetic field lines, often from one hemisphere to the other, possibly supported by field-aligned density structures. Inversion of RPI echo traces, guided or direct, provided a means of measuring evolving electron density distributions under a variety of geomagnetic conditions including plasmasphere depletion and refilling during a magnetic storm. RPI passive measurements also showed that AKR source locations move with season and local time and, when compared to Polar spacecraft observations, the overall intensity of AKR is less during solar maximum than solar minimum.

Alternate Names

  • RPI

Facts in Brief

Mass: 48 kg
Power (avg): 30.8 W

Funding Agency

  • NASA-Office of Space Science (United States)


  • Space Physics: Ionospheric Studies
  • Space Physics: Magnetospheric Studies

Additional Information

Questions and comments about this experiment can be directed to: Dr. Shing F. Fung



NameRoleOriginal AffiliationE-mail
Dr. Robert F. BensonCo-InvestigatorNASA Goddard Space Flight
Dr. Donald L. CarpenterCo-InvestigatorStanford
Dr. Patricia H. ReiffCo-InvestigatorRice
Dr. Jean-Louis Henry BougeretCo-InvestigatorObservatoire de Paris,
Dr. William W. L. TaylorCo-InvestigatorRaytheon ITSS
Dr. James L. GreenCo-InvestigatorNASA Goddard Space Flight
Dr. Dennis L. GallagherCo-InvestigatorNASA Marshall Space Flight
Dr. Shing F. FungCo-InvestigatorNASA Goddard Space Flight
Prof. Bodo W. ReinischPrincipal InvestigatorUniversity of Massachusetts at
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