The polarimetric and helioseismic imager instrument for the Solar Orbiter mission from the European Space Agency requires a high stability while capturing images, specially for the polarimetric ones. For this reason, an image stabilization system has been included in the instrument. It uses global motion estimation techniques to estimate the jitter in real time with subpixel resolution. Due to instrument requirements, the algorithm has to be implemented in a Xilinx Virtex-4QV field programmable gate array. The algorithm includes a 2-D paraboloid interpolation algorithm based on 2-D bisection. We describe the algorithm implementation and the tests that have been made to verify its performance. The jitter estimation has a mean error of 125 pixel of the correlation tracking camera. The paraboloid interpolation algorithm provides also better results in terms of resources and time required for the calculation (at least a 20% improvement in both cases) than those based on direct calculation.
The tip/tilt driver is part of the Polarimetric and Helioseismic Imager (PHI) instrument for the ESA Solar Orbiter (SO), which is scheduled to launch in 2017. PPHI captures polarimetric images from the Sun to better understand our nearest star, the Sun. The paper covers an analog amplifier design to drive capacitive solid state actuator such ass piezoelectric actuator. Due to their static and continuous operation, the actuator needs to be supplied by high-quality, low-frequency, high-voltage sinusoidal signals. The described circuit is an efficiency-improved Class-AB amplifier capable of recovering up to 60% of the charge stored in the actuator. The results obtained after the qualification model test demonstrate the feasibility of the circuit with the accomplishment of the requirements fixed by the scientific team.
The Polarimetric and Helioseismic Imager (PHI) instrument is part of the remote instruments for the ESA Solar Orbiter
(SO), which is scheduled to launch in 2017. PHI captures polarimetric images from the Sun to better understand our
nearest star, the Sun. A set of images is acquired with different polarizations, and afterwards is processed to extract the
Stokes parameters. As Stokes parameters require the subtraction of the image values, in order to get the desired quality it
is necessary to have good contrast in the image and very small displacements between them. As a result an Image
Stabilization System (ISS) is required. This paper is focused in the behavior and the main characteristics of this system.
This ISS is composed of a camera, a tip-tilt mirror and a control system. The camera is based on a STAR1000 sensor that
includes a 10 bits resolution high-speed Analog-to-Digital Converter (ADC). The control system includes a Correlation
Tracking (CT) algorithm that determines the necessary corrections. The tip-tilt mirror is moved based on this corrections
to minimize the effects of the spacecraft (S/C) drift and jitter with respect to the Sun. Due to its stringent requirements, a
system model has been developed in order to verify that the required parameters can be satisfied. The results show that
the ISS is feasible, although the margins are very small.
A very high precision Image Stabilization System has been designed for the Solar Orbiter mission. The different components that have been designed are the Correlation Tracking Camera (CTC), Tip-Tilt controller (TTC) and the system control in order to achieve the specified requirements. For the CTC, in order to achieve the required resolution of 12 bits and reduced power consumption, we used an external ADC. For the TTC, a special focus has been dedicated to a 55 V linear regulator in a QUASI-LDO configuration and a Tip-Tilt driver in a transconductance amplifier architecture. Results show that the full system reaches an attenuation of 1/10th of a pixel at 10Hz. The TTC provides a high voltage span, enough slew-rate and the needed stability levels.