The PROBA-3 double-spacecraft formation flying mission of the European Space Agency (ESA) has been presented in recent papers with details about the mission profile, the operation objectives, and the implemented technologies. PROBA-3 will fly the externally occulted coronagraph ASPIICS (Association of Spacecraft for Polarimetric and Imaging Investigation of the Corona of the Sun), with the telescope on one satellite and the occulter on the other one, at 144m. The scientific objective is to realize an artificial total solar eclipse to observe the lower Sun corona. The high accuracy metrology control is the core of the mission and several sub-systems will be verified and validated to realize the coronagraphic formation. Between these, the Shadow Position Sensors (SPS), composed of eight photo-multipliers mounted around the ASPIICS entrance pupil monitoring the solar penumbra symmetry, will return the 3D positioning of the formation with the highest accuracy. The SPS on-ground calibration was completed in 2021 and one of the main aspects of the test has been the implementation of an illumination scheme to simulate the same conditions the SPS will experience in flight. This was realized using a suite of LED sources properly assembled in a testbed used to reproduce the expected observation configurations. This testbed is supported by a dedicated software able to simulate the different illumination conditions and to drive the control of the LEDs in order to feed each SPS sensor with the proper light flux. In this paper, we review the SPS metrology system, the calibration testbed setup, and we discuss the interface control software, the simulation tool, and the data acquisition procedure adopted to calibrate the LED sources. Additional presentation content can be accessed on the supplemental content page.
The Coronal Magnetograph - CorMag - experiment aims at studying the magnetic field topology of the solar corona. The direction of the coronal magnetic field vector would be derived from narrow-wavelength bandpass observations of the linearly polarized FeXIV line-emission (530.3 nm), interpreted through the "saturated" Hanle effect. CorMag will be a medium-duration, high-altitude balloon payload of the European Union-funded HEMERA Program. CorMag is an internally-occulted coronagraph whose design was derived from the externally-occulted, formation-flying ASPIICS coronagraph of the PROBA-3 ESA solar mission. The configuration for this mission will be illustrated, together with the expected polarization sensitivity. This mission is a demonstrator for future space-based coronagraphs with the capability of visible-light and infrared polarization measurements for coronal magnetic field diagnostics.
The PROBA3 mission of the European Space Agency is the first formation flying (FF) mission that will be flown in high elliptic geocentric orbit aiming at verifying and validating different metrology control systems and algorithms in order to realize and maintain the formation of two independent spacecraft, in total autonomy. The final target accuracy for the relative and absolute alignment of the two satellites is of about 2mm over an inter satellite distance of 144.3m. During the FF, the two spacecraft will realize a giant coronagraph with the external occulter on one payload and the telescope on the other one. The Sun Corona observation will be the scientific tool for the FF validation. Between the different metrology systems that will be tested, the Shadow Position Sensor (SPS) is the most challenging one, aiming at returning the relative and absolute position of the formation with the finest accuracy: 0.5mm out of the guidance and navigation and control loop and 2mm within the loop. The mission program is now in the Phase D with the realization and the testing of the flight model. Due to the high expected performance, a fine calibration of the SPS subsystem is mandatory. In this paper, we discuss the radiometric and spectral calibration plan, the algorithm validation procedure, and the laboratory test-bed realized to reproduce the in-flight observation conditions of the SPS by using a set of calibrated LED and a mechanical set-up equivalent to the SPS system. Preliminary results are also reviewed.
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