Status of MICROSCOPE, a mission to test the Equivalence Principle in space

MICROSCOPE is a French Space Agency mission that aims to test the Weak Equivalence Principle in space down to an accuracy of $10^{-15}$. This is two orders of magnitude better than the current constraints, which will allow us to test General Relativity as well as theories beyond General Relativity which predict a possible Weak Equivalence Principle violation below $10^{-13}$. In this communication, we describe the MICROSCOPE mission, its measurement principle and instrument, and we give an update on its status. After a successful instrument's commissioning, MICROSCOPE is on track for on-schedule launch, expected in 2016.Comment: Proceedings of LISA Symposium X; accepted for publication in Journal of Physics: Conference Serie

Integrated Flush Air Data Sensing System Modeling for Planetary Entry Guidance with Direct Force Control

Flush air data sensing (FADS) systems have been previously used at both Earth and Mars to provide onboard estimates of angle of attack, sideslip angle, and dynamic pressure. However, these FADS data were often not used in an in-the-loop sense to inform the onboard guidance and control systems. A method to integrate FADS-derived density and wind estimates with a numerical predictor-corrector guidance algorithm is presented. The method is demonstrated in a high-fidelity simulation of a human-scale Mars entry vehicle that utilizes a hypersonic inflatable aerodynamic decelerator (HIAD) with direct force control. Effects on guidance commands and state uncertainties both with and without FADS system modeling are presented and discussed

Evaluation of a load cell model for dynamic calibration of the rotor systems research aircraft

The Rotor Systems Research Aircraft uses load cells to isolate the rotor/transmission system from the fuselage. An analytical model of the relationship between applied rotor loads and the resulting load cell measurements is derived by applying a force-and-moment balance to the isolated rotor/transmission system. The model is then used to estimate the applied loads from measured load cell data, as obtained from a ground-based shake test. Using nominal design values for the parameters, the estimation errors, for the case of lateral forcing, were shown to be on the order of the sensor measurement noise in all but the roll axis. An unmodeled external load appears to be the source of the error in this axis

Calculating the Location of the Center-of-Gravity Using an Accelerometer Array

In this work, a method for determining a vehicle’s center-of-gravity using traditional commercially available sensors is developed. The method relies on using an accelerometer array along with rate gyro measurements for determining the linear acceleration of the vehicle along all directions at the center-of-gravity location. Once the acceleration at the center-of-gravity is formulated the location can be estimated by resolving measurements of acceleration not located at the center-of-gravity to the center-of-gravity location. Known kinematic equations are used to transform the accelerations at the instrument locations to the center-of-gravity location. An online parameter estimator is used to localize the center-of-gravity using a real-time resolution process. The algorithm uses known physics-based kinematic relationships among the accelerometer sensor array arranged in a unique configuration avoiding singularities for estimating the acceleration at the center-of-gravity location of a rigid body. An extensive simulation study was completed to evaluate the performance of the center-of-gravity localizer real-time estimator and resulting algorithms. A full nonlinear model of a flight vehicle was used for the simulation study. Multiple case scenarios were evaluated such as a slow moving center-of-gravity location and abrupt change as well along with various flight maneuver types. Results of the simulation study proved the feasibility of using traditional type measurements for accurately localizing the center-of-gravity of a vehicle

How to estimate the differential acceleration in a two-species atom interferometer to test the equivalence principle

We propose a scheme for testing the weak equivalence principle (Universality of Free Fall) using an atom-interferometric measurement of the local differential acceleration between two atomic species with a large mass ratio as test masses. A apparatus in free fall can be used to track atomic free-fall trajectories over large distances. We show how the differential acceleration can be extracted from the interferometric signal using Bayesian statistical estimation, even in the case of a large mass and laser wavelength difference. We show that this statistical estimation method does not suffer from acceleration noise of the platform and does not require repeatable experimental conditions. We specialize our discussion to a dual potassium/rubidium interferometer and extend our protocol with other atomic mixtures. Finally, we discuss the performances of the UFF test developed for the free-fall (0-g) airplane in the ICE project (\verb"http://www.ice-space.fr"

On sensor fusion for airborne wind energy systems

A study on filtering aspects of airborne wind energy generators is presented. This class of renewable energy systems aims to convert the aerodynamic forces generated by tethered wings, flying in closed paths transverse to the wind flow, into electricity. The accurate reconstruction of the wing's position, velocity and heading is of fundamental importance for the automatic control of these kinds of systems. The difficulty of the estimation problem arises from the nonlinear dynamics, wide speed range, large accelerations and fast changes of direction that the wing experiences during operation. It is shown that the overall nonlinear system has a specific structure allowing its partitioning into sub-systems, hence leading to a series of simpler filtering problems. Different sensor setups are then considered, and the related sensor fusion algorithms are presented. The results of experimental tests carried out with a small-scale prototype and wings of different sizes are discussed. The designed filtering algorithms rely purely on kinematic laws, hence they are independent from features like wing area, aerodynamic efficiency, mass, etc. Therefore, the presented results are representative also of systems with larger size and different wing design, different number of tethers and/or rigid wings.Comment: This manuscript is a preprint of a paper accepted for publication on the IEEE Transactions on Control Systems Technology and is subject to IEEE Copyright. The copy of record is available at IEEEXplore library: http://ieeexplore.ieee.org

Center-of-gravity estimation of an aircraft solely using traditional aircraft measurement sensors

In this work, a novel algorithm for estimating aircraft center-of-gravity location based solely on traditional aircraft measurements is investigated. The algorithm uses known physics-based kinematic relationships between aircraft states for the estimation process and requires only traditional sensor measurements typically employed by aircraft. Three models are used in the algorithm development: one based on using attitude measurements, the second based on using air data measurements, and the third based on using navigation type measurements. Estimation of the aircraft\u27s aerodynamic parameters is not required in the new approach. However, sensor error such as accelerometer bias effects are estimated in the algorithm process. A high performance aircraft simulation model is used to test the feasibility of the approach. In all individual and combined model simulations center-of-gravity was estimated with a high degree of accuracy. In addition, flight test data is used to verify the effectiveness of the algorithm in localizing the center-of-gravity successfully

Application of parameter estimation to aircraft stability and control: The output-error approach

The practical application of parameter estimation methodology to the problem of estimating aircraft stability and control derivatives from flight test data is examined. The primary purpose of the document is to present a comprehensive and unified picture of the entire parameter estimation process and its integration into a flight test program. The document concentrates on the output-error method to provide a focus for detailed examination and to allow us to give specific examples of situations that have arisen. The document first derives the aircraft equations of motion in a form suitable for application to estimation of stability and control derivatives. It then discusses the issues that arise in adapting the equations to the limitations of analysis programs, using a specific program for an example. The roles and issues relating to mass distribution data, preflight predictions, maneuver design, flight scheduling, instrumentation sensors, data acquisition systems, and data processing are then addressed. Finally, the document discusses evaluation and the use of the analysis results