Physics, Instrumentation and Sensing
Ultra-Sensitive Accelerometry and Space Projects
Fundamental Physics
The missions here concern mainly testing the Equivalency Principle, detecting gravitational waves directly, precisely observing post-Newtonian effects (Lense Thirring effect, Shapiro, etc.), or, more generally, providing a better understanding of the most fundamental laws of physics.
MICROSCOPE Mission
Proposed jointly by Onera and the OCA, the MICROSCOPE project was confirmed in 2003 in the CNES scientific programs for a microsatellite mission. The objective is to test the Equivalency Principle with a precision of 10-15 while searching for a new fundamental interaction. This experiment requires the use of differential electrostatic accelerometers with a resolution of 10-12 ms-2/Hz1/2 in the very stable environment of a drag-compensated microsatellite. Onera’s activity concerns the supply of the satellite payload and the organization of the scientific mission center needed to process the measurements. Phase B final review for the satellite was successfully conducted early 2007
and phase C has now commenced. The detailed design, the associated mechanical and thermal analyses, and the manufacture and integration of the instrument’s development models
are underway. These models will be tested and qualified
in 2007-2008
– one
with light silicon proof masses with the electrostatic levitation,
in the laboratory using high-tension electronic outputs, and the other with high-density masses, in freefall at the Bremen drop tower.
The construction of the flight models will continue in 200 9 for delivery and integration in the satellite at the end of that year.
Both the differential accelerometers of MICROSCOPE instrument
for the test in orbit of the Equivalency Principle.
Thermal analysis: mapping of the sensor subject to a radiation
(temperature gradient : 1°C between the top and the bottom)
See also the site of the mission : microscope.onera.fr
PIONEER
The Pioneer 10 and 11 spacecraft were launched in the early 1970's and followed hyperbolic trajectories to opposite ends of the solar system. The Nasa analysis of the Doppler data received from the two spacecraft showed that they were subject to an unexplained acceleration which seems to have a constant value of (8.74 ± 1.33) x 10-10 m.s-2 and to be directed toward the sun.
Several French laboratories in the Groupe Anomalie Pioneer (GAP) have signed an agreement for research cooperation on this subject: ONERA, Laboratoire Kastler-Brossel, Observatoire de la Côte d'Azur, Institut d'Optique Théorique et Appliquée.
The work at ONERA began by assisting the Observatoire de la Côte d'Azur to develop interplanetary orbit determination software in order to analyse the available Doppler data. This enabled us (in collaboration with the Laboratoire Kastler Brossel) to confirm independently from the JPL the existence of an anomaly. The work in progress is focused on the study of the nature of the anomaly: constancy, direction, agreement with the expectations of theoretical models.
In parallel, GAP is proposing a mission to verify this anomaly, and more generally the gravity at large distance, in the context of the Cosmic Vision program. This mission will include an ONERA accelerometer. The current electrostatic accelerometers are accurate enough with respect to the value of the anomaly but their bias is too large; one of our objectives is to imagine a system to calibrate the accelerometer bias in-flight.
