Proba-3 ESA mission lifted-off
On December 5th Proba-3 ESA mission lifted off on a PSLV-XL rocket from the ISRO (Indian Space Research Organisation) Satish Dhawan Space Centre in Sriharikota, India. This In-Orbit demonstration mission, injected in a highly elliptical (600-60530 km altitude, inclined at 59°) orbit, will provide unprecedented insights into the Sun's corona, the faint outer atmosphere usually concealed by the Sun disk's intense light.
It consists of 2 spacecraft: the Coronagraph spacecraft and the Occulter spacecraft, launched together in a stacked configuration.
The two satellites will fly together, maintaining a fixed configuration, 150m apart and aligned with the Sun, forming a rigid structure in space, to prove innovative formation flying and rendezvous technologies. The fly-formation system will orbit around the Earth with a 20 hours period and will lose and re-keep (near the apogee, for about 6 hours) repeatedly the nominal configuration.
During the science phase (with the Sun, the Occulter and the Coronagraph aligned) the Occulter's 1.4 m disk will block out the brilliant solar disk to create an artificial eclipse permitting the Coronagraph to observe the Sun's outer atmosphere. This will allow up to 6 hours of continuous observation of the Sun’s corona; for comparison natural eclipses last only a few minutes.
The Occulter and the Coronagraph satellites flying in formation. Credit: ESA – P. Carril
INAF contributed to the realization of ASPIICS (Association of Spacecraft for Polarimetric and Imaging Investigation of the Corona of the Sun), the main instrument: a visible light coronagraph.
But also to the SPS (Shadow Position Sensors), the ultimate metrology system allowing the final positioning of the two spacecraft with a sub-millimeter accuracy.
In fact, in order to obtain the desired performance, several systems are used in sequence, from laser ranging to relative GPS etc. and SPS is the last to intervene and the most accurate (in particular regarding lateral displacements).
The Coronagraph satellite. SPS is on the top, covered by the lid protecting the ASPIICS' optics from full Sun intrusion. Credit: ESA - P. Sebirot
The prototype of SPS with the two sets of four SiPM and their electronics. Credit: Dr. Steve Buckley
SPS surrounds the telescope's aperture with two sets of SiPM sensors detecting the penumbra and digitizing the signal with the levels of accuracy and the dynamic range necessary to assess the correct centering of the telescope with respect to the umbra (and satellites' interdistance, too) feeding to positioning algorithms the SPS digitized data.
The design was co-engineered between INAF and the Irish company SensL (now On-Semi).
INAF Astrophysical Observatory of Arcetri was involved in the co-engineering of SPS in conjunction with the Irish company SensL (now On-Semi). For the full next month the two satellites will fly connected and, after the separation, another month will be dedicated to test the anti-collision maneuvers.
After that, the "commissioning phase" will proceed switching on SPS and, at that point, Vladimiro Noce (INAF Arcetri) will be involved as an expert of the instrument to analyze and interpret the levels of luminosity measured.
At the beginning the first readout will concern the full Sun light measured through special filters placed on the closed lid. These "Neutral Density Filters" were studied purposely to obtain a signal that would not exceed the SPS dynamic range ("saturate").
Proba-3 will try to reach the "nominal" (centered and at 144 m distance) position using the SPS algorithms provided by INAF (OAA and Turin Observatory) in an automated way. Anyway, a comparison between the expected and the measured luminosity (in-flight calibration) will be necessary to improve the SPS algorithm effectiveness.
Multimedia
Video:
https://www.isro.gov.in/PSLV_C59_PROBA-3_Livestreaming.html
https://www.isro.gov.in/PSLV_C59_PROBA-3_onboardvideo.html
https://www.isro.gov.in/PSLV_C59_PROBA-3_Curtain_Raiser.html
Immagini:
https://www.isro.gov.in/PSLV_C59_PROBA3_Gallery.html
