Where We've Been
Launched out of Yasny, Russia in June of 2010, PICARD is a satellite dedicated to measuring the absolute total and spectral solar irradiance, the diameter, solar shape and the distance to the Sun's interior probing by the helioseismology method. The result of these measurements and images will allow scientists to further study and understand variations as a function of solar activity.
The PICARD payload is composed of the following instruments:
- SOVAP SOlar VAriability PICARD: composed of a differential absolute radiometer and a bolometric sensor to measure the total solar irradiance (previously called solar constant)
- PREMOS PREcision MOnitor Sensor: a set of 3 photometers to study the ozone formation and destruction, and to perform helioseismologic observations, and an absolute differential radiometer to measure the total solar irradiance.
- SODISM SOlar Diameter Imager and Surface Mapper: an imaging telescope accurately pointed and a CCD, which allows to measure the solar diameter and shape with an accuracy of a few milliarc second, and to perform helioseismologic observations to probe the solar interior.
Vincent Associates was proud to provide PICARD's SODISM telescope with the durable, 35mm aperture VS35 shutter. This VS type shutter has been modified and tested to survive shock, vibration and environmental extremes along with the ability to survive a minimum of 1,330,000 exposures. The main function of this custom shutter is to provide CCD exposures at specified wavelengths.
With the shutter, PICARD took its first successful photograph of the sun on July 22, 2010. On June 5-6 2012, PICARD observed the Venus Transit. The information gathered was instrumental in improving scientist's knowledge of the shape of the Sun, and provided an accurate measure of the Sun's diameter. For more information about the PICARD satellite, visit: http://smsc.cnes.fr/PICARD, or for more information on Vincent Associates' work on this project, visit: www.uniblitz.com/company-info/where-weve-been/shutter-aboard-picard-satellite/. Please also review this article, "The space instrument SODISM of the PICARD mission and the Vincent Associates shutter" written by Dr. Mustapha Meftah of CNES. You can also read the complete White Paper titled “Mechanisms for Space Applications”.
The space instrument SODISM of the PICARD mission and the Vincent Associates modified VS35 shutter
On June 15, 2010, a Dnepr-1 launcher from Dombarovskiy Cosmodrome, near Yasny (Russia), launched the PICARD satellite. The satellite was placed in a 735 km Sun Synchronous Orbit (06h00-18h00) with inclination of 98.28 degrees. A few days later, the SODISM (Solar Diameter Imager and Surface Mapper) instrument was powered on. The cover of the telescope (door at the entrance of the telescope) was closed. The first months in orbit have been dedicated to the outgassing of the instrument. The CCD detector was maintained at a temperature above 20°C to avoid any effect of contamination. Several operations were carried out to verify the good health of the instrument.
Mechanisms (shutter, filters wheels) were tested individually. Images of dark current were taken. At the end of the outgassing operation, the temperature of the CCD was changed gradually in order to characterize the effect of the CCD dark current as a function of temperature. SODISM instrument remained in test mode until July 20, 2010 when its cover was opened for a first light. The satellite stabilized the image of the Sun with an accuracy of 36 arcseconds using a solar tracking sensor. The PICARD SODISM pointing mechanism completed the centering of the image on the CCD with accuracy better than 0.2 arcseconds. The SODISM instrument took the first image of the Sun on July 22, 2010.
The image of the Sun at 393.37 nm shown in the figure below has been recorded with SODISM on August 31, 2012. It has been processed to correct the main optical and radiometric defaults of the raw image. This image enables the display of several features such as sunspots. This image confirms the increase of the solar activity. The sunspots appear at high solar latitude and move slowly towards the solar equator, their number increasing with the solar activity.
The electronic shutter in operation aboard PICARD/SODISM is an electro-programmable shutter with an aperture of 35 mm (VS type), modified for this particular space flight application. The shutter allows a great deal of flexibility for mounting the shutter in a limited area (uncased version). This is especially important when design space is critical. Vincent Associates shutters (Uniblitz) have been used in other space-borne applications in the past. VS35 type shutter was a part of the SOLSE (in 1997) and SOLSE-2 (in 2003) experiment packages aboard the Space Shuttle, and the 25mm shutters, flew to Halley’s comet aboard the Vega Probes (in 1986). Several changes were made on the nominal shutter (Figure 19). The main objective was to obtain a shutter more suited for space environment.
The objective of functional tests was to demonstrate full operability and performances of the mechanism in SODISM configuration, and their compatibility with the space environment. A set of functional tests were developed and used repeatedly to quickly check the health of the shutter at key points in the test campaign. The main characteristics of the shutter were also verified. A life test program on a dedicated shutter was implemented. The shutter is a critical mechanical and electrical element that has limited lifetimes. The shutter has been qualified to survive a minimum of 1,329,560 exposures. Commercial Off-The-Shelf (COTS) mechanisms usually will not work for space because they will not survive the launch loads and they will stop functioning under space conditions: space is a very hostile environment. With a dedicated program, it’s possible to adapt a mechanism for a use in space.
The PICARD/SODISM shutter is in orbit since June 2010 and is operational. 382,743 openings and closings are used per year. 828,738 openings and closings are made from June 2010 to October 2012. The mechanism is already operational and functional in space.
The evolution of total opening time and temperature of the shutter is shown below.
Here are some additional photos provided by Dr. Meftah:
Written by Dr. Mustapha Meftah, Ingénieur de Recherche en Thermique et Mécanique, CNRS - Service d'Aéronomie, and Mr. Stephen Pasquarella, Sr. Vice President Vincent Associates.