SOLAR/SOLSPEC, a spectroradiometer measuring solar spectral irradiance is an instruments of the SOLAR payload mounted on the zenith external platform of the European Columbus module of the International Space Station. Solar flux is received by the SOLAR instruments thanks to the Coarse Pointing Device (CPD). A complementary Sun position tracking module, the Position Sensitive Device (PSD), is integrated in SOLAR/SOLSPEC. The PSD module has been a useful tool to monitor for misalignments between the CPD and the SOLAR payload. It is used in SOLAR/SOLSPEC’s operations to follow the quality of the Sun tracking. The PSD module is also valuable to monitor for SOLAR/SOLSPEC’s three spectrometers (ultraviolet, visible, infrared) angular response in orbit. We first give a detailed description of the PSD’s functionalities. We then present the results of the PSD data analysis. We will show that the PSD module has, despite working in a severe space environment, preserved its full potential from 2008 up to 2017 thanks to its design and appropriate selection of components. We conclude that its robustness makes of the PSD module a simple, yet reliable, instrument useful for future long term space-based missions.
PICARD is a mission devoted to solar variability observations through imagery and radiometric measurements. The main goal is to provide data for scientific investigation first in the area of solar physics, and second in the assessment of the influence of the solar variability on the Earth climate variability. PICARD contains a double program with in-space and on-ground measurements. The PICARD spacecraft was launched on June 15, 2010, commissioned in-flight in October of the same year and was retired in April 2014. The PICARD ground-based observatory is operational since May 2011. We shall give a short overview of the PICARD instrumentation. New estimates of the absolute values of the total solar irradiance, of the solar spectral irradiance at typical wavelengths, and of the solar oblateness will be given. We will also report about helioseismic studies. Finally, we will present our current results about solar radius variations after six years of solar observation.
The scientific objectives of a space mission result into instrumental developments and specific satellite operations
to observe astronomical objects of interest. The payload in its space environment is however subject to important
thermal variations that affect observations. This is well observed when images of the Sun are recorded with the
constraint of keeping the solar rotational axis in a constant direction relatively to the camera reference frame.
Consequences are clearly observed on image positions that follow the thermal variations induced by the satellite
orbit. This is, in particular, the case for the space mission PICARD. This phenomenon is similar to defocus
and motions of images recorded with ground-based telescopes. We first present some simulations showing these
effects. We then compare our results with real data obtained from the space mission PICARD.
The Earth’s atmosphere introduces a spatial frequency filtering in the object images recorded with ground-based instruments. A solution is to observe with telescopes onboard satellites to avoid atmospheric effects and to obtain diffraction limited images. However, similar atmosphere problems encountered with ground-based instruments may subsist in space when we observe the Sun since thermal gradients at the front of the instrument affect the observations. We present in this paper some simulations showing how solar images recorded in a telescope focal plane are directly impacted by thermal gradients in its pupil plane. We then compare the results with real solar images recorded with the PICARD mission in space.
The accurate determination of the solar photospheric radius has been an important problem in astronomy for many centuries. From the measurements made by the PICARD spacecraft during the transit of Venus in 2012, we obtained a solar radius of 696,156±145 kilometres. This value is consistent with recent measurements carried out atmosphere. This observation leads us to propose a change of the canonical value obtained by Arthur Auwers in 1891. An accurate value for total solar irradiance (TSI) is crucial for the Sun-Earth connection, and represents another solar astrophysical fundamental parameter. Based on measurements collected from different space instruments over the past 35 years, the absolute value of the TSI, representative of a quiet Sun, has gradually decreased from 1,371W.m<sup>−2</sup> in 1978 to around 1,362W.m<sup>−2</sup> in 2013, mainly due to the radiometers calibration differences. Based on the PICARD data and in agreement with Total Irradiance Monitor measurements, we predicted the TSI input at the top of the Earth’s atmosphere at a distance of one astronomical unit (149,597,870 kilometres) from the Sun to be 1,362±2.4W.m<sup>−2</sup>, which may be proposed as a reference value. To conclude, from the measurements made by the PICARD spacecraft, we obtained a solar photospheric equator-to-pole radius difference value of 5.9±0.5 kilometres. This value is consistent with measurements made by different space instruments, and can be given as a reference value.
SUAVE (Solar Ultraviolet Advanced Variability Experiment) is a far ultraviolet (FUV) imaging solar telescope of novel design for ultimate thermal stability and long lasting performances. SUAVE is a 90 mm Ritchey- Chrétien telescope with SiC (Silicon Carbide) mirrors and no entrance window for long and uncompromised observations in the UV (no coatings of mirrors, flux limited to less than a solar constant on filters to avoid degradation), associated with an ultimate thermal control (heat evacuation, focus control, stabilization). Design of the telescope and early thermal modeling leading to a representative breadboard (a R and T program supported by CNES) will be presented. SUAVE is the main instrument of the SUITS (Solar Ultraviolet Influence on Troposphere/Stratosphere) microsatellite mission, a small-size mission proposed to CNES and ESA.
Since the launch of the first artificial satellite in 1957, more than 6,000 satellites have been sent into space. Despite technological advances, the space domain remains little accessible. However, with the miniaturization of electronic components, it has recently become possible to develop small satellites with which scientific goals can be addressed. Micro-satellites have demonstrated that these goals are achievable. However, completion times remain long. Today, we hope through the use of nano-satellites to reduce size, costs, time of development and accordingly to increase accessibility to space for scientific objectives. Nano-satellites have become important tools for space development and utilization, which may lead to new ways of space exploration. This paper is intended to present a future space mission enabled by the development of nano-satellites and the underlying technologies they employ. Our future mission expands observations of the Sun (total solar irradiance and solar spectral irradiance measurements) and of the Earth (outgoing long-wave radiation, short-wave radiation measurements and stratospheric ozone measurements). Constellations of nano-satellites providing simultaneous collection of data over a wide area of geo-space may be built later and present a great interest for Sun-Earth relationships.
PICARD is a spacecraft dedicated to the simultaneous measurement of the absolute total and spectral solar
irradiance, the diameter, the solar shape, and to probing the Sun’s interior by the helioseismology method. The
mission has two scientific objectives, which are the study of the origin of the solar variability, and the study
of the relations between the Sun and the Earth’s climate. The spacecraft was successfully launched, on June
15, 2010 on a DNEPR-1 launcher. PICARD spacecraft uses the MYRIADE family platform, developed by
CNES to use as much as possible common equipment units. This platform was designed for a total mass of
about 130 kg at launch. This paper focuses on the design and testing of the TCS (Thermal Control System)
and in-orbit performance of the payload, which mainly consists in two absolute radiometers measuring the total
solar irradiance, a photometer measuring the spectral solar irradiance, a bolometer, and an imaging telescope to
determine the solar diameter and asphericity. Thermal control of the payload is fundamental. The telescope of
the PICARD mission is the most critical instrument. To provide a stable measurement of the solar diameter over
three years duration of mission, telescope mechanical stability has to be excellent intrinsically, and thermally
controlled. Current and future space telescope missions require ever-more dimensionally stable structures. The
main scientific performance related difficulty was to ensure the thermal stability of the instruments. Space is a
harsh environment for optics with many physical interactions leading to potentially severe degradation of optical
performance. Thermal control surfaces, and payload optics are exposed to space environmental effects including
contamination, atomic oxygen, ultraviolet radiation, and vacuum temperature cycling. Environmental effects on
the performance of the payload will be discussed. Telescopes are placed on spacecraft to avoid the effects of the
Earth atmosphere on astronomical observations (turbulence, extinction, ...). Atmospheric effects, however, may
subsist when spacecraft are launched into low orbits, with mean altitudes of the order of 735 km.
PICARD is a space mission launched in June 2010 to study mainly the geometry of the Sun. The PICARD mission has a ground program consisting mostly in four instruments based at the Calern Observatory (Observatoire de la Cˆote d’Azur). They allow recording simultaneous solar images and various atmospheric data from ground. The ground instruments consist in the qualification model of the PICARD space instrument (SODISM II: Solar Diameter Imager and Surface Mapper), standard sun-photometers, a pyranometer for estimating a global sky quality index, and MISOLFA a generalized daytime seeing monitor. Indeed, astrometric observations of the Sun using ground-based telescopes need an accurate modeling of optical effects induced by atmospheric turbulence. MISOLFA is founded on the observation of Angle-of-Arrival (AA) fluctuations and allows us to analyze atmospheric turbulence optical effects on measurements performed by SODISM II. It gives estimations of the coherence parameters characterizing wave-fronts degraded by the atmospheric turbulence (Fried parameter <i>r</i><sub>0</sub>, size of the isoplanatic patch, the spatial coherence outer scale <i>L</i><sub>0</sub> and atmospheric correlation times). We present in this paper simulations showing how the Fried parameter infered from MISOLFA records can be used to interpret radius measurements extracted from SODISM II images. We show an example of daily and monthly evolution of <i>r</i><sub>0</sub> and present its statistics over 2 years at Calern Observatory with a global mean value of 3.5<i>cm</i>.
For the last thirty years, ground time series of the solar radius have shown different variations according to
different instruments. The origin of these variations may be found in the observer, the instrument, the atmosphere
and the Sun. These time series show inconsistencies and conflicting results, which likely originate from
instrumental effects and/or atmospheric effects. A survey of the solar radius was initiated in 1975 by F. Laclare,
at the Calern site of the Observatoire de la Cˆote d’Azur (OCA). PICARD is an investigation dedicated to the
simultaneous measurements of the absolute total and spectral solar irradiance, the solar radius and solar shape,
and to the Sun’s interior probing by the helioseismology method. The PICARD mission aims to the study of the
origin of the solar variability and to the study of the relations between the Sun and the Earth’s climate by using
modeling. These studies will be based on measurements carried out from orbit and from the ground. PICARD
SOL is the ground segment of the PICARD mission to allow a comparison of the solar radius measured in space
and on ground. PICARD SOL will enable to understand the influence of the atmosphere on the measured solar
radius. The PICARD Sol instrumentation consists of: SODISM II, a replica of SODISM (SOlar Diameter
Imager and Surface Mapper), a high resolution imaging telescope, and MISOLFA (Moniteur d’Images SOLaires
Franco-Alg´erien), a seeing monitor. Additional instrumentation consists in a Sun photometer, which measures
atmospheric aerosol properties, a pyranometer to measure the solar irradiance, a visible camera, and a weather
station. PICARD SOL is operating since March 2011. First results from the PICARD SOL mission are briefly
reported in this paper.
Telescopes are placed on spacecrafts to avoid the effects of the Earth atmosphere on astronomical observations
(turbulence, extinction ...). Atmospheric effects however may subsist when satellites are launched in low orbits,
typically mean altitudes of the order of 700 km. We will present first in this paper how we are able to estimate
the mean Earth radiation flux when we consider temperature housekeeping data recorded with a specific space
solar mission having this orbit property. We will show after how some solar parameters extracted from images
recorded with the on-board telescope are correlated with the Earth atmospheric radiation flux. We will also
present how we find the limits of the South Atlantic Anomaly from affected images.
All space instruments contain mechanisms or moving mechanical assemblies that must move (sliding, rolling,
rotating, or spinning) and their successful operation is usually mission-critical. Generally, mechanisms are not
redundant and therefore represent potential single point failure modes. Several space missions have suffered
anomalies or failures due to problems in applying space mechanisms technology. Mechanisms require a specific
qualification through a dedicated test campaign. This paper covers the design, development, testing, production,
and in-flight experience of the PICARD/SODISM mechanisms. PICARD is a space mission dedicated to the
study of the Sun. The PICARD Satellite was successfully launched, on June 15, 2010 on a DNEPR launcher
from Dombarovskiy Cosmodrome, near Yasny (Russia). SODISM (SOlar Diameter Imager and Surface Mapper)
is a 11 cm Ritchey-Chretien imaging telescope, taking solar images at five wavelengths. SODISM uses several
mechanisms (a system to unlock the door at the entrance of the instrument, a system to open/closed the door
using a stepper motor, two filters wheels using a stepper motor, and a mechanical shutter). For the fine pointing,
SODISM uses three piezoelectric devices acting on the primary mirror of the telescope. The success of the
mission depends on the robustness of the mechanisms used and their life.
PICARD is a space mission developed mainly to study the geometry of the Sun. The satellite was launched in
June 2010. The PICARD mission has a ground program which is based at the Calern Observatory (Observatoire
de la C^ote d'Azur). It will allow recording simultaneous solar images from ground. Astrometric observations
of the Sun using ground-based telescopes need however an accurate modelling of optical e®ects induced by
atmospheric turbulence. Previous works have revealed a dependence of the Sun radius measurements with the
observation conditions (Fried's parameter, atmospheric correlation time(s) ...). The ground instruments consist
mainly in SODISM II, replica of the PICARD space instrument and MISOLFA, a generalized daytime seeing
monitor. They are complemented by standard sun-photometers and a pyranometer for estimating a global sky
quality index. MISOLFA is founded on the observation of Angle-of-Arrival (AA) °uctuations and allows us to
analyze atmospheric turbulence optical e®ects on measurements performed by SODISM II. It gives estimations of
the coherence parameters characterizing wave-fronts degraded by the atmospheric turbulence (Fried's parameter,
size of the isoplanatic patch, the spatial coherence outer scale and atmospheric correlation times). This paper
presents an overview of the ground based instruments of PICARD and some results obtained from observations
performed at Calern observatory in 2011.
PICARD is a satellite dedicated to the simultaneous measurement of the solar diameter, the solar shape, the
solar irradiance and the solar interior. These measurements obtained throughout the mission will allow study
of their variations as a function of solar activity. The objectives of the PICARD mission are to improve our
knowledge of the functioning of our star through new observations and the influence of the solar activity on
the climate of the Earth. PICARD was launched on June 15, 2010 on a Dnepr-1 launcher. SODISM (SOlar
Diameter Imager and Surface Mapper), an instrument of the PICARD payload, is a high resolution imaging
telescope. It was built on an innovative technological concept. SODISM allows us to measure the solar diameter
and shape with an accuracy of a few milliarcseconds, and to perform helioseismologic observations to probe the
solar interior. SODISM provides continuous observations of the Sun since mid-July 2010. A brief comparison of
measurements of solar diameter since the seventeenth century and solar diameter variability are described. In
this article, we present the instrumental concept and design and we give an overview of the thermal stability of
the telescope. First results from the SODISM experiment are briefly reported (housekeeping and image).
The PICARD satellite is dedicated to the monitoring of solar activity. It carries several imaging and radiometric
instruments. One of them, SODISM, is a high-resolution radio-imaging telescope measuring the Sun diameter and total
flux in near UV and visible wavelengths. Along with mirrors, SODISM includes highly reflective filters and
attenuators, which generate ghost images. These disturb the Sun edge area, the total flux measurement and also the fine
aiming channel. This is compounded with tilt tolerances, which shift and modify the ghosts images.
Stray light was studied through ASAP simulation, with broad sources and high order splits. Each path was studied
separately, checking its effect on instrument performance and the possible effect of tilts. Some design improvements
allowed to reduce the most critical paths, while others, although relatively intense, stood clear from the critical areas.
However ground tests and flight results show some residual ghosts, which could not be fully suppressed due to
mechanical tolerances. They shall be taken into account by image processing.
Carbon/Carbon has many attributes that make it an attractive material for satellite applications. It is low in
density, is dimensionally stable under a wide variety of conditions, has very low thermal expansion, is relatively
low in cost, and is a mature technology. Moreover, the material is flexible enough to enable the designer to select
such variables as fiber type, fabric architecture, fiber volume, and high temperature processing and thus custom
tailor the physical and mechanical properties to his specific requirements. A wide range of properties are available
- densities from 1.5 to 1.9 g/cm<sup>3</sup>, room temperature Coefficients of Thermal Expansion (CTE) from -0.3x10<sup>-6</sup>to -1.3x10<sup>-6</sup>/K, room temperature thermal conductivities from 7 to 210 W/m.K, and modulus from 60 to 190
GPa. A new type of structure developed by CNRS on the space instrument SODISM uses Carbon/Carbon.
PICARD is a French space scientific mission. Its objectives are the study of the origin of the solar variability
and the study of the relations between the Sun and the Earth's climate. The launch is scheduled for 2010 on
a Sun Synchronous Orbit at 725 km altitude. The mission lifetime is two years, however that can be extended
to three years. The payload consists of two absolute radiometers measuring the TSI (Total Solar Irradiance)
and an imaging telescope to determine the solar diameter, the limb shape and asphericity. SOVAP (SOlar
VAriability PICARD) is an absolute radiometer provided by the RMIB (Royal Meteorological Institute of Belgium)
to measure the TSI. It also carries a bolometer used for increasing the TSI sampling and ageing control.
PREMOS (PREcision MOnitoring Sensor) radiometer is provided by the PMOD/WRC (Physikalisch Meteorologisches
Observatorium of Davos / World Radiation Center) to measure the TSI and the Spectral Solar Irradiance.
SODISM (SOlar Diameter Imager and Surface Mapper), is an 11-cm Ritchey-Chr´etien imaging telescope developed
at CNRS (Centre National de la Recherche Scientifique) by LATMOS (Laboratoire, ATmosphere, Milieux,
Observations Spatiales) ex Service d'A´eronomie, associated with a 2Kx2K CCD (Charge-Coupled Device), taking
solar images at five wavelengths. It carries a four-prism system to ensure a metrological control of the optics
magnification. SODISM allows us to measure the solar diameter and shape with an accuracy of a few milliarcseconds,
and to perform helioseismologic observations to probe the solar interior. In this article, we describe the
space instrument SODISM and its thermo-elastic properties. We also present the PICARD payload data center
and the ground instrument SODISM II which will observe together with the space instrument.
PICARD is a space mission developed to observe the Sun at high angular resolution. One of the main space
objectives of PICARD is to measure the solar diameter with few milli arc-seconds accuracy. A replica of the space
instrument will be installed at Calern Observatory in order to test our ability to make such measurement from
ground with enough accuracy. High angular resolution observations with ground-based instrument are however
limited by atmospheric turbulence. The seeing monitor MISOLFA is developed to give all observation conditions
at the same moments when solar images will be recorded with the twin PICARD instruments. They will be
used to link ground and space measurements. An overview of the PICARD mission and the solar ground-based
experiments will be ¯rst given. Optical properties of MISOLFA will be after presented. The basic principles to
measure atmospheric parameters and the methods used to obtain them from solar images will be given. Finally,
some recent results obtained at Calern Observatory will be presented and discussed.
High angular resolution observations of the sun are limited by atmospheric turbulence. The MISOLFA seeing monitor (still under construction) is developed to obtain spatial and temporal statistical properties of optical turbulence by analyzing local motions observed on solar edge images. The solar flying shadows used for angle-of-arrival spatio-temporal analysis are observed in the pupil plane image by mean of a rectangular thin slit positioned on the solar edge image. A numerical simulation of the light propagation in both the atmospheric turbulence medium and the MISOLFA optical system is carried out studying the relation of the measured intensity variations in the pupil plane to angle-of-arrival fluctuations in the non-isoplanatic case. First results are presented and discussed.
The one-dimensional point spread function for long-exposure frames of the whole system atmosphere - instrument is calculated from solar limb observations using data recorded at OCA Observatory (France). It is then compared to the theoretical one deduced from the Von Karman model and various wave-front structure functions. Good agreement is found allowing to deduce the spatial coherence outer scale L<SUB>0</SUB> and the Fried parameter r<SUB>0</SUB>.