Formation flying, with ESA’s mission PROBA-3, is providing the chance of creating a giant solar coronagraph in Space. The scientific payload, the solar coronagraph ASPIICS, has been selected in January 2009 [1]. The advantages of formation flying are: 1) larger dimensions for the coronagraph, which leads to better spatial resolution and lower straylight level and 2) possibility of continuous observations of the inner corona. The PROBA-3/ASPIICS mission is composed of two spacecrafts (S/Cs) at 150 meters distance, the Occulter-S/C (O-S/C) which holds the external occulter, and the Coronagraph-S/C (C-S/C) which holds the main instrument, i.e. the telescope. In addition of the scientific capabilities of the instrument, it will continuously monitor the exact position and pointing of both S/Cs in 3D space, via two additional metrology units: the Shadow Position Sensor (SPS) and the Occulter Position Sensor (OPS). In this paper we are presenting the metrology of this formation flying mission combining the outputs of the above mentioned sensors, SPS and OPS. This study has been conducted in the framework of an ESA “STARTIGER” initiative, a novel approach aimed at demonstrating the feasibility of a new and promising technology concept (in our case formation flying applied to solar coronagraphy, cf. [2, 3]) on a short time scale (six months study).
Formation Flying is now considered to be the most promising and effective approach to deploy the forthcoming
generation of very large instruments in space. PROBA-3 is a technology mission devoted to the in-orbit demonstration of
formation flying techniques and technologies. PROBA-3 will implement a giant coronagraph (called ASPIICS) that will
both demonstrate and exploit the capabilities and performances of formation flying. ASPIICS is distributed on two
spacecrafts separated by 150m, one hosting the external occulting disk and the other the optical part of the coronagraph.
ASPIICS will incorporate metrology units which will allow determining both the absolute pointing and the relative
alignment of the formation. Photosensors located around the entrance pupil of the coronagraph will determine the
absolute positioning of the instrument by sensing the penumbra behind the occulting disk. Light sources located on the
rear-side of the occulting disk will allow verifying the alignment of the formation. We carried out a complete numerical
simulation of the metrology system and showed how corrections are derived from the measurements to be applied to
each spacecraft in case of misalignments. This simulation was validated by a scaled model of the coronagraph developed
at Laboratoire d'Astrophysique de Marseille. This study has been conducted in the framework of an ESA
"STARTIGER" Initiative, a novel approach aimed at demonstrating the feasibility of a new and promising technology on
a very short time scale (six months).
Sébastien Vives, Luc Damé, Philippe Lamy, A. Antonopoulos, W. Bon, G. Capobianco, G. Crescenzio, V. Da Deppo, M. Ellouzi, J. Garcia, C. Guillon, A. Mazzoli, T. Soilly, F. Stathopoulos, C. Tsiganos
Formation Flying opens the possibility to conceive and deploy giant solar coronagraphs in space permanently
reproducing the optimum conditions of a total eclipse of the Sun ("artificial" eclipse) thus giving access to the inner
corona with unprecedented spatial resolution and contrast (low stray light). The first opportunity to implement such a
coronagraph "ASPIICS" will be offered by the European Space Agency (ESA) PROBA-3 technology mission devoted to
the in-orbit demonstration of formation flying technologies. Two spacecrafts separated by about 150 m form a giant
externally-occulted coronagraph: the optical part hosted by one spacecraft remains entirely protected from direct sunlight
by remaining in the shadow of an external occulter hosted by the other spacecraft. We developed and tested a scale-model
'breadboard' (i.e., 30m) of the PROBA-3/ASPIICS Formation Flying coronagraph. The investigations focused on
two metrology systems capable of measuring both the absolute pointing of the coronagraph (by sensing the projected
shadow and penumbra produced by the external occulting disk) and the alignment of the formation (by re-imaging light
sources located on the rear-side of the occulting disk with the optical part of the coronagraph). In this contribution, we
will describe the demonstrator and report on our results on the crucial question of the alignment and pointing in space of
long instruments (> 100 m) with an accuracy of a few arcsec. This study has been conducted in the framework of an ESA
"STARTIGER" Initiative, a novel approach aimed at demonstrating the feasibility of a new and promising technology on
a very short time scale (six months).
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