Development of a Controlled Dynamics Simulator for Reusable Launcher Descent and Precise Landing

This paper introduces a Reusable Launch Vehicle (RLV) descent dynamics simulator coupled with closed-loop guidance and control (G&C) integration. The studied vehicle's first-stage booster, evolving in the terrestrial atmosphere, is steered by a Thrust Vector Control (TVC) system and planar fins through gain-scheduled Proportional-Integral-Derivative controllers, correcting the trajectory deviations until precise landing from the reference profile computed in real time by a successive convex optimisation algorithm. Environmental and aerodynamic models that reproduce realistic atmospheric conditions are integrated into the simulator for enhanced assessment. Comparative performance results were achieved in terms of control configuration (TVC-only, fins-only, and both) for nominal conditions as well as with external disturbances such as wind gusts or multiple uncertainties through a Monte Carlo analysis to assess the G&C system. These studies demonstrated that the configuration combining TVC and steerable planar fins has sufficient control authority to provide stable flight and adequate uncertainties and disturbance rejection. The developed simulator provides a preliminary assessment of G&C techniques for the RLV descent and landing phase, along with examining the interactions that occur. In particular, it paves the way towards the development and assessment of more advanced and robust algorithms

Asteroids Coupled Dynamics Analysis by Means of Accurate Mass Distribution and Perturbations Modeling

One of the most important aspects when dealing with a Potentially Hazardous Object (PHO) is the accurate determination of its dynamical state. In particular, the determi-nation of orbital and rotational perturbations is important to propagate accurately the heliocentric orbital path of an asteroid or a comet, and to be more precise in the im-pact risk determination and related uncertainty containment. The paper discusses the analysis and study of the motion of an irregularly-shaped celestial body, with par-ticular attention to its complex three-dimensional rotational dynamics: the rotation state, nutation and precession motions are considered while modelling. All perturba-tions, relevant to the case of study, are included in the dynamical model, from the classical to the more complex, such as the Solar Radiation Pressure (SRP), the third body gravitational effect (presence of the Sun), the YORP effect and the internal dis-sipation of energy. In addition, particular attention has been paid to accurately model the shape of the asteroid: simple spherical models demonstrated to possess low ac-curacy when the asteroid or the comet is not spherically shaped. Irregular shapes represent, indeed, one of the most important aspects to compute the disturbances affecting the dynamics of these objects. The study has been performed by consider-ing different characteristic shapes for typical irregular bodies: from the quasi-spherical, to the dog-bone and the elongated shapes. The perturbations due to ex-ternal sources are modelled numerically. The sources of disturbances are then ranked and different criteria to propagate rotational motion have been derived de-pending on the shape of the observed asteroid. Even if the simulation results have been verified on selected asteroids dynamics, the presented methods and approach apply to the dynamical propagation of any kind of asteroid or comet

Uncooperative Objects Pose, Motion and Inertia Tensor Estimation via Stereovision

Autonomous close proximity operations are an arduous and attractive problem in space mission design. In particular, the estimation of pose, motion and inertia properties of an uncooperative object is a challenging task because of the lack of available a priori information. In addition, good computational performance is necessary for real applications. This paper develops a method to estimate the relative position, velocity, angular velocity, attitude and inertia properties of an uncooperative space object using only stereo-vision measurements. The classical Extended Kalman Filter (EKF) and an Iterated Extended Kalman Filter (IEKF) are used and compared for the estimation procedure. The relative simplicity and low computational cost of the proposed algorithm allow for an online implementation for real applications. The developed algorithm is validated by numerical simulations in MATLAB using different initial conditions and uncertainty levels. The goal of the simulations is to verify the accuracy and robustness of the proposed estimation algorithm. The obtained results show satisfactory convergence of the estimation errors for all the considered quantities. An analysis of the computational cost is addressed to confirm the possibility of an onboard application. The obtained results, in several simulations, outperform similar works present in literature. In addition, a video processing procedure is presented to reconstruct the geometrical properties of a body using cameras. This method has been experimentally validated at the ADAMUS (ADvanced Autonomous MUltiple Spacecraft) Lab at the University of Florida

Exploiting Lunar Navigation Constellation for GNC Enhancement in Landing Missions

To support the increasing number of planned lunar missions, a collaborative international initiative is underway to conceptualise and establish a lunar satellite constellation for communication and navigation. In this context, the goal of the current paper is to analyse what the obtainable performance is for a lunar lander that executes state estimation employing one-way ranging signals from such a Lunar Navigation Service (LNS). In particular, a small-sized optimised navigation constellation is considered as the main source of measurements, which, coupled with an accelerometer and an altimeter, is used to estimate the lander absolute trajectory during the main braking phase. The guidance is extracted on board by interpolation of a ground-optimised trajectory, followed by a reference-tracking regulator. Two alternative control tuning cases are presented, one targeting high performance, the other targeting low propellant mass. Nominal performance and associated sensitivity analyses assessed the feasibility of supporting such a critical phase with a reduced LNS constellation, reaching final control errors below 500 (Formula presented.), with the better performing one going down to 56 (Formula presented.). Among the two proposed alternatives, the one targeting low fuel expenditure has proven, however, to also be more robust against time and state uncertainty, providing much larger success rates

N-body gravitational and contact dynamics for asteroid aggregation

The development of dedicated numerical codes has recently pushed forward the study of N-body gravitational dynamics, leading to a better and wider understanding of processes involving the formation of natural bodies in the Solar System. A major branch includes the study of asteroid formation: evidence from recent studies and observations support the idea that small and medium size asteroids between 100 m and 100 km may be gravitational aggregates with no cohesive force other than gravity. This evidence implies that asteroid formation depends on gravitational interactions between different boulders and that asteroid aggregation processes can be naturally modeled with N-body numerical codes implementing gravitational interactions. This work presents a new implementation of an N-body numerical solver. The code is based on Chrono::Engine (2006). It handles the contact and collision of large numbers of complex-shaped objects, while simultaneously evaluating the effect of N to N gravitational interactions. A special case of study is considered, investigating the relative dynamics between the N bodies and highlighting favorable conditions for the formation of a stable gravitationally bound aggregate from a cloud of N boulders. The code is successfully validated for the case of study by comparing relevant results obtained for typical known dynamical scenarios. The outcome of the numerical simulations shows good agreement with theory and observation, and suggests the ability of the developed code to predict natural aggregation phenomena

Implicit Extended Kalman Filter for Optical Terrain Relative Navigation Using Delayed Measurements

The exploration of celestial bodies such as the Moon, Mars, or even smaller ones such as comets and asteroids, is the next frontier of space exploration. One of the most interesting and attractive purposes from the scientific point of view in this field, is the capability for a spacecraft to land on such bodies. Monocular cameras are widely adopted to perform this task due to their low cost and system complexity. Nevertheless, image-based algorithms for motion estimation range across different scales of complexities and computational loads. In this paper, a method to perform relative (or local) terrain navigation using frame-to-frame features correspondences and altimeter measurements is presented. The proposed image-based approach relies on the implementation of the implicit extended Kalman filter, which works using nonlinear dynamic models and corrections from measurements that are implicit functions of the state variables. In particular, here, the epipolar constraint, which is a geometric relationship between the feature point position vectors and the camera translation vector, is employed as the implicit measurement fused with altimeter updates. In realistic applications, the image processing routines require a certain amount of time to be executed. For this reason, the presented navigation system entails a fast cycle using altimeter measurements and a slow cycle with image-based updates. Moreover, the intrinsic delay of the feature matching execution is taken into account using a modified extrapolation method

TEASPOON: a once in a lifetime opportunity to Sedna

In the challenge of unveiling the enigmas that still surround the origin and early evolution of the Solar System, the study of trans-Neptunian objects plays a crucial role. For this purpose, Sedna is probably the most intriguing candidate for a space mission. A better understanding of its highly elliptical orbit could improve our knowledge of the evolution of the Solar System and could potentially lead to the discovery of an unknown planet. Moreover, the planetoid is expected to host a significant amount of tholins and probably a subsurface ocean of liquid water, making the analysis of its composition extremely interesting. In 2076, Sedna will reach its minimum distance of 76 AU from the Sun. This is a scientific opportunity that will not happen again in the next 11400 years. Exploiting this instance, TransnEptuniAn Sedna PrObe for Outer exploratioN (TEASPOON) is a mission proposal to send a probe to Sedna, featuring a payload suite to perform an optical characterization, study the particle environment and conduct a radio-science experiment. Moreover, the long travel will be an opportunity to explore the Kuiper Belt looking for observations or, hopefully, discover new objects. The harsh environment, characterized by objects with unknown trajectories, requires Collision Avoidance strategies, while long-term radiation exposition demands electronics shielding and the preference for rad-hard components. More generally, the 77 AU distance and 30 years duration of the mission makes the design even more demanding. Therefore, solving those challenges would inaugurate a new generation of space missions to the edges of the Solar System and beyond. This proposal has been developed in the framework of a Space Mission Analysis and Design course by a team of students at the master level in Space Engineering at Politecnico di Milano. A concurrent engineering approach has been followed, leading the study through its phase 0/A. This enabled them to practice in actual working conditions of a space agency’s mission study, and underlined the importance of this kind of experience at a Master’s level course

ORIGO: A mission concept to challenge planetesimal formation theories

Comets are generally considered among the most pristine objects in our Solar System. There have thus been significant efforts to understand these bodies. During the past decades, we have seen significant progress in our theoretical understanding of planetesimal/cometesimals (the precursors of comets) formation. Recent space missions—such as ESA’s Rosetta mission to comet 67P/Churyumov-Gerasimenko—have provided observations claimed by proponents of different comet formation theories to validate their scenarios. Yet, no single formation paradigm could be definitively proven. Given the importance of understanding how the first bodies in our Solar System formed, we propose a dedicated mission to address this issue. ORIGO will deliver a lander to the surface of a cometary nucleus where it will characterise the first five m of the subsurface. With remote sensing instruments and the deployment of payload into a borehole, we will be able to study the physico-chemical structure of ancient, unmodified material. The mission has been designed to fit into the ESA M-class mission budget