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SPEDE Scientific Objectives

SMART-1 with SPEDE sensor booms

SPEDE monitors in real-time

  • The disturbances (electron flux and spacecraft potential variations) produced by the thruster operation
  • The variability of the electron flux / plasma density and dust flux around Earth and the Moon.
  • The variability of the electron flux in the solar wind during the Earth-Moon transfer phase


The SPEDE instrument is optimized to monitor the spacecraft's plasma environment using as little mass and power resources as possible. It consists of two short sensor booms, Boom +X and Boom -X (see the image above), mounted at opposite sides of the spacecraft, and a small electronics box inside the spacecraft's warm compartment with power converter and instrument control electronics.

Both SPEDE sensors can be used to monitor the potential difference between one sensor (current-biased) and the spacecraft, or (voltage-biased) to measure the electron flux.
The design should allow the instrument operation also during phases of little power availability like during Earth- or Moon-eclipse.

The electronics is similar to that of the Permittivity Probe, developed for the Rosetta Lander, but much simplified using new technologies. The electronics will be built by Finnish industry, while the sensor structure and power converter is contributions of the Co-I groups at ESTEC and at Uppsala group of the Swedish institute for Space Physics.

More information:
Walter Schmidt , tel. +358 9 1929 4658