Benjamin Lenoir

Electrostatic accelerometer with bias rejection for Gravitation and Solar System physics

Radio tracking of interplanetary probes is an important tool for navigation purposes as well as for testing the laws of physics or exploring planetary environments. The addition of an accelerometer on board a spacecraft provides orbit determination specialists and physicists with an additional observable of great interest: it measures the value of the non-gravitational acceleration acting on the spacecraft, i.e. the departure of the probe from geodesic motion. This technology is now routinely used for geodesy missions in Earth orbits with electrostatic accelerometers. This article proposes a technological evolution which consists in adding a subsystem to remove the bias of an electrostatic accelerometer. It aims at enhancing the scientific return of interplanetary missions in the Solar System, from the point of view of fundamental physics as well as Solar System physics. The main part of the instrument is an electrostatic accelerometer called MicroSTAR, which inherits mature technologies based on ONERA’s experience in the field of accelerometry. This accelerometer is mounted on a rotating stage, called Bias Rejection System, which modulates the non-gravitational acceleration and thus permits to remove the bias of the instrument from the signal of interest. This article presents the motivations of this study, describes the instrument, called GAP, and the measurement principle, and discusses the performance of the instrument as well as integration constraints. Within a mass of 3.1 kg and an average consumption of 3 W, it is possible to reach a precision of 1 pm/s 2 for the acceleration measured with an integration time of five hours. Combining this observable

Accommodation Study for an Anemometer on a Martian Lander

Abstract Measuring the wind velocity and its turbulent fluctuations near the surface of Mars is an important component of the future exploration of Mars, not only to minimize risk in landing, but also to understand some of the most important fundamental processes that dominate Mars’ behavior today. Previous missions have included instrumentation to measure 2D mean winds, but a more sophisticated instrument has been designed that allows for fast, precise 3D measurements of the wind and its turbulent properties. These richer observations raise the question of how best to place such an instrument on a future Martian lander to minimize the flow distortions imposed by the lander, and how to correct for the perturbations that cannot be avoided. To carry out this research, computational fluid dynamic simulations in three dimensions were performed using Fluent, a commercially available software. The first step was to model the conditions at the surface of Mars and, more particularly, the quantities describing the...

Experimental demonstration of bias rejection from electrostatic accelerometer measurements

Abstract In order to test gravitation in the Solar System, it is necessary to improve the orbit restitution of interplanetary spacecrafts. The addition of an accelerometer on board is a major step toward this goal because this instrument measures the non-gravitational acceleration of the spacecraft. It must be able to perform measurements at low frequencies with no bias to provide an additional observable of interest. Since electrostatic accelerometers suffer a bias, a technological upgrade has been proposed by Onera. It consists in adding to an electrostatic accelerometer a rotating platform which allows modulating the signal of interest and retrieving it without bias after post-processing. Using this principle, a measurement method and a post-processing method have been developed. The objective of this article is to validate these methods experimentally. To do so, a horizontally controlled pendulum was used to apply a known signal to an accelerometer mounted on a rotating platform. The processing of the experimental data demonstrates the ability to make acceleration measurements with no bias. In addition, the experimental precision on the unbiased acceleration obtained after post-processing corresponds to the precision predicted theoretically.