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Nine years of Sun tracking on board the ISS

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On February 15, 2017, B.USOC switched off the external platform SOLAR on board the International Space Station after nine years of successful operations (so far, the longest running experiment of the Columbus module). The SOLAR operations accumulated 12 000 Sun trackings over 106 Sun Visibility Windows, requiring 35 120 hours on console and 30 150 hours of preparation. In order for SOLAR to observe full 27-day solar rotations, NASA performed –at B.USOC’s request– a change of the ISS attitude four times. SOLAR hosted three instruments (SOLSPEC, SOL-ACES, and SOVIM) dedicated to the study of spectral solar irradiance.
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The scientific objectives of the SOLAR instruments target the measurements of the solar spectral irradiance: SOLSPEC (SOLar SPECctral Irradiance measurements) covering the 180-3000 nm wavelength range at high resolution, SOL-ACES (SOLar Auto-Calibrating Extreme UV/UV Spectrophotometers) the extreme ultraviolet at moderate resolution and SOVIM (SOlar Variable & Irradiance Monitor) the near-ultraviolet, visible and thermal-infrared regions of the spectrum. The Belgian User Support and Operation Centre was the ESA Facility Responsible Centre for the SOLAR mission operations, i.e. operations preparation, in-flight operation and post-flight activities.

B.USOC got the ISS rotated

Due to the platform design and ISS orbit, the Sun could only be tracked during windows of about 2 weeks per month. To overcome this and get measurements during a full synodic solar rotation (27 days), B.USOC coordinated for almost 2 years to obtain a temporary change of the ISS attitude enabling extended visibility window. The feat was achieved four times!

Final deactivation

On 15 February 2017, SOLAR was parked and shut off. Lot of the involved actors gathered in Brussels to share memories and witness the final deactivation by ESA astronaut Thomas Pesquet.  In his space-to-ground message, Thomas Pesquet highlighted the great performance of SOLAR and its instruments, which initially supposed to last only 18 months.

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Patch designed for the Farewell SOLAR event and celebrating nine years of on-orbit operation
Credits: B.USOC
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Group picture of the participants to the Farewell SOLAR event on February 15, 2017
Credits: B.USOC