Jean de Lafontaine

Linearized Dynamics of Formation Flying Spacecraft on a J2-Perturbed Elliptical Orbit

A linearized set of equations of relative motion about a J 2 -perturbed elliptical reference orbit is developed. This model uses analytical relations that are well suited for onboard applications. The inclusion of the J 2 perturbation in a simple analytical model can lead to formation flying guidance and control algorithms that make use of the natural J 2 -induced relative motion to perform maneuvers instead of constantly compensating for this perturbation. The model uses the linearized differential drift rate of mean orbit elements to predict the impact of the J 2 perturbation on relative osculating spacecraft motion. It analytically provides the relative motion in Hill coordinates at any given true anomaly using only the initial osculating relative orbit elements and the initial orbit elements of the reference trajectory. A linear time-varying state-space form of the model is also presented. Simulation results show that relative motion prediction remains accurate over several orbits.

Innovative Navigation Schemes for State and Parameter Estimation During Mars Entry

Accurate navigation systems are required in the scope of Mars precision landing missions. This paper reviews some assumptions of the literature concerning the availability of the vehicle states for guidance during its atmospheric entry on Mars. It is demonstrated that currently used measurements are not sufficient to get complete observability of the entry dynamics. Therefore, four innovative measurement scenarios based on radio ranging are proposed to resolve the observability issue. The analyses and simulations show that the addition of the range measurements from known references helps to estimate accurately the position states along with some critical model parameters, contrary to inertial measurement unit navigation alone. Finally, the addition of the range measurement from a secondary free-falling dummy vehicle with known aerodynamics also ensures the observability of aerodynamic parameters of the lander vehicle.

Autonomous atmospheric entry on mars: Performance improvement using a novel adaptive control algorithm

Upcoming landing missions to Mars will require on-board guidance and control systems in order to meet the scientific requirement of landing safely within hundreds of meters to the target of interest. More specifically, in the longitudinal plane, the first objective of the entry guidance and control system is to bring the vehicle to its specified velocity at the specified altitude (as required for safe parachute deployment), while the second objective is to reach the target position in the longitudinal plane. This paper proposes an improvement to the robustness of the constant flight path angle guidance law for achieving the first objective. The improvement consists of combining this guidance law with a novel adaptive control scheme, derived from the so-called Simple Adaptive Control (SAC) technique. Monte-Carlo simulation results are shown to demonstrate the accuracy and the robustness of the proposed guidance and adaptive control system.

Improvement to the analytical predictor-corrector guidance algorithm applied to mars aerocapture

Introduction O NE of the state-of-the-art technologies considered to reduce the cost of planetary exploration is aerocapture. This technique allows the reduction of fuel cost for planetary insertion by using atmospheric drag to decrease the total orbital energy of the vehicle. It consists in a reduction of velocity from a hyperbolic orbit or highly elliptical orbit to a low-altitude near-circular planetary orbit. It has previously been demonstrated that aerocapture would be beneficial for human exploration of Mars.1 The purpose of an aerocapture maneuver is to bring the vehicle from given atmospheric entry conditions to desired atmospheric exit conditions. The desired exit conditions are typically expressed as a given apoapsis radius of the unperturbed orbit once the vehicle is out of the atmosphere. This apoapsis radius is chosen to minimize the velocity impulse that is required to reach the final mission orbit. Up to now, several types of algorithms, such as the analytical predictor-corrector,2−6 the energy controller,4,7 the numerical predictor-corrector,4,8−10 and the terminal point controller6,11 have been developed, considering only the vehicle bank angle as control parameter. As shown in Fig. 1, the authors classify these algorithms in three main categories: the analytical algorithms, the numerical algorithms, and the predefined-trajectory algorithms. Firstly, the analytical predictor corrector (APC) and the energy controller are part of the first category. These algorithms make certain assumptions that lead to an analytical guidance solution to the exit conditions for the current vehicle state. Secondly, the numerical predictor corrector numerically integrates the remaining part of the trajectory to predict the atmospheric exit conditions from the current position and updates the commanded bank angle for the remaining part of the trajectory. It is therefore part of the second category. Finally, the terminal point controller, part of the third category, uses a predefined optimal trajectory. In this case, the vehicle tries to remain on the optimal trajectory at any moment in time.

Neighboring Optimum Feedback Control Law for Earth-Orbiting Formation-Flying Spacecraft

Thispaperdevelopsafeedbackcontrollawthatguaranteesneighboringfuel-optimalityofthereconfigurationofa formation of Earth-orbiting formation-flying spacecraft. It aims for the case in which a specific formation is to be achieved at a specific true anomaly. It guarantees neighboring fuel-optimality of such a reconfiguration maneuver, assuming that the formation evolves in the vicinity of an uncontrolled reference trajectory. It is in the semi-analytic form,as onlyone time-varyinggain matrixneedstobecomputed beforethe maneuver. Itallows afuel consumption/ formation accuracy tradeoff with the selection of only one scalar gain. Simulations compare the performance of this controller with the linear-quadratic regulator and the mean orbit elements controller in the context of a 1 km size formation reconfiguration. Simulations show that this neighboring optimum controller can perform the maneuver with better accuracy while spending as much or less propellant than the other controllers.

Feature Matching Navigation Techniques for Lidar-Based Planetary Exploration

When landing on planetary bodies it is desired to determine accurately the velocity and the position of the spacecraft relative to a selected target position on the surface of the body. This paper responds to that requirement by proposing Lidar-based advanced navigation techniques based on feature matching. Some of the techniques proposed are inspired from conventional 2D and 1D correlation techniques while others are taking advantage of technologies already validated in space and known as star constellation matching algorithms. After presenting the concepts of each algorithm, a realistic validation scenario based on a Mars landing reference mission is presented with comprehensive simulation results. At the end, analyses of the advantages and drawbacks are presented.

Robust Guidance and Control Algorithms using Constant Flight Path Angle for Precision Landing on Mars

This paper proposes four guidance laws aimed at reducing the most significant sources of landing dispersion during atmospheric entry at Mars. The autonomous guidance algorithms rely on simple analytic and semi-analytic solutions that prescribe segments of constantflightpath angles (FPAs) that match the trajectory constraints in terms of desired final altitude, velocity and downrange. Two one-segment solutions and two two-segment solutions are presented. A nonlinear dynamic inversion of the translational dynamics and a robust attitude controller, designed with the Robust Modal Control technique, complete the guidance and control system whose performance is demonstrated through numerical simulations of a Mars entry scenario.

TICFIRE: a far infrared payload to monitor the evolution of thin ice clouds

The TICFIRE mission concept developed with the support of the Canadian Space Agency aims: 1) to improve measurements of water-vapour concentration in the low limit, where cold regions are most sensitive and 2) to determine the contribution of Thin Ice Clouds (TIC) to the energy balance and the role of their microphysical properties on atmospheric cooling. TICFIRE is a process-oriented mission on a micro-satellite platform dedicated to observe key parameters of TIC forming in the cold regions of the Poles and globally, in the upper troposphere. It locates cloud top profiles at the limb and measures at nadir the corresponding upwelling radiance of the atmosphere directly in the thermal window and in the Far Infrared (FIR) spectrum over cold geographical regions, precisely where most of the atmospheric thermal cooling takes place. Due to technological limitations, the FIR spectrum (17 to 50 μm) is not regularly monitored by conventional sensors despite its major importance. This deficiency in key data also impacts operational weather forecasting. TICFIRE will provide on a global scale a needed contribution in calibrated radiance assimilation near the IR maximum emission to improve weather forecast. TICFIRE is therefore a science-driven mission with a strong operational component. The TICFIRE payload consists of two instruments; the main one being a Nadir-looking multiband radiometer based on uncooled microbolometer technology and covering a large spectral range from 7.9 μm to 50 μm. The secondary one is an imager that performs Limb measurements and provides cloud vertical structure information. This paper presents the key payload requirements, the conceptual design, and the estimated performance of the TICFIRE payload. Current technology developments in support to the mission are also presented.

Full-scale testing and platform stabilization of a scanning lidar system for planetary landing

In August 2007, the engineering model of the Rendezvous Lidar System (RLS) was tested at the Sensor Test Range Facility that has been developed at NASA Langley Research Center for the calibration and characterization of 3-D imaging sensors. The three-dimensional test pattern used in this characterization is suitable for an empirical verification of the resolving capability of a lidar for both mid-range terminal rendezvous and hazard avoidance landing. The results of the RLS lidar measurements are reported and compared with image frames generated by a lidar simulator with an Effective Instantaneous Field of View (EIFOV) consistent with the actual scanning time-of-flight lidar specifications. These full-scale tests demonstrated the resolving capability of the lidar under static testing conditions. In landing operations, even though the lidar has a very short exposure time on a per-pulse basis, the dynamic motion of a lander spacecraft with respect to the landing site will cause pulse-to-pulse imaging distortion. MDA, Optech, and NGC Aerospace have teamed together to resolve this issue using motion compensation (platform stabilization) and motion correction (platform residual correction) techniques. Platform stabilization permits images with homogenous density to be generated so that no safe landing sites will be missed; platform residual errors that are not prevented by this stabilization are then corrected in the measurement data prior to map generation. The results of recent developments in platform stabilization and motion correction are reported and discussed in the context of total imaging error budget.

Performance Assessment of the Drag-Based Formation Control for the JC2Sat Mission

ठThe paper describes an innovative method for the performance assessment of drag-based formation flying control techniques. The method aims at avoiding time-consuming longduration closed-loop simulation campaigns with high fidelity simulators. The methodology quickly provides statistical insight into the formation control performance, thus supporting quick design iterations and systems engineering trade-off analyses. The paper reviews the drag-based guidance and control algorithm proposed for the JC2Sat mission, presents the methodology developed to assess performance, discusses the application of this methodology in the context of the JC2Sat mission and shows typical analysis results.