Development of a multi-payload 2U CubeSat: the Alba project

Alba CubeSat UniPD is a student team of University of Padova with the aim to participate to the ESA Fly Your Satellite! (FYS!) programme and to launch for the first time at University of Padova a CubeSat made by students. The proposed mission has three independent objectives: (1) to collect in-situ measurements of the sub-mm space debris environment in LEO, (2) to study the micro-vibration environment on the satellite throughout different mission phases, (3) to do precise orbit determination through laser ranging and evaluate procedures for fast satellite Pointing, Acquisition and Tracking (PAT) from ground. The proposed technological experiments aim to obtain data that will enrich the current knowledge of the space environment and will provide precious information useful for the further development of some research projects currently performed at University of Padova. In order to reach the objectives, in these years the activities of the teams aimed to develop a 2U CubeSat equipped with three payloads. The first payload is an impact sensor that will be placed on one of the outer faces of the satellite and will be able to count the number of debris impacting the spacecraft thus being able to measure the energy/momentum transferred to the satellite. The second one is a Commercial Off The Shelf (COTS) sensor that measures the micro-vibrations experienced by payloads in a CubeSat in different mission phases. The third one consists in a number of COTS Corner Cube Retroreflectors that will be placed onboard the satellite. Thanks to this, Satellite Laser Ranging (SLR) will be done to collect data on the satellite range and range rate using a facility currently under development at University. This paper presents the mission objectives and motivations. In addition, the mission phases and the preliminary design of the CubeSat reached during the activities of the project are shown. Particular attention is given to the payloads which are the most challenging aspect of this project

Simulation of robotic space operations with minimum base reaction manipulator

Autonomous robotic capture has been identified as a key technology for On-Orbit Servicing (OOS) and Active Debris Removal (ADR) missions. However, manoeuvring spacecraft-mounted manipulators is a challenging task since it generates disturbance torques on the satellite. To mitigate this problem several minimum reaction control strategies have been developed to reach the desired End-Effector (EE) pose while minimizing the dynamic disturbances transferred to the spacecraft by the robotic arm. This paper presents the development of a Simulation Tool in the MATLAB/Simulink environment capable of simulating the dynamics of a satellite equipped with a 7-DoF robotic arm during the target capture phase. The manipulator, as well as the spacecraft, is implemented by using Simscape Multibody and joint actuators are modelled as Brushless DC motors controlled by PID controllers. The spacecraft attitude is Nadir-Pointing, it is controlled by means of quaternion feedback and Linear-Quadratic-Regulator (LQR) and it is actuated by three Reaction Wheels (RW). Orbital perturbations such as non-spherical gravity potential (EGM2008 model) and atmospheric drag are considered. In addition, the minimum reaction control strategy called Kinetic Energy Minimization (MKE) is employed during the robotic arm manoeuvres. The goal of this study is to compare the performances obtained with the MKE method with those achieved by using the classic Inverse Kinematics (IK) in the free-flying case. The numerical results confirmed that MKE method is to be preferred since it minimizes the control torque that the Attitude Control Subsystem (ACS) must provide and reduces the EE orientation and position errors

Overview of spacecraft fragmentation testing

Spacecraft fragmentation due to collisions with space debris is a major concern for space agencies and commercial entities, since the production of collisional fragments is one of the major sources of space debris. It is in fact believed that, in certain circumstances, the increase of fragmentation events could trigger collisional cascade that makes the future debris environmental not sustainable. Experimental studies have shown that the fragmentation process is highly complex and influenced by various factors, such as the material properties, the velocity and angle of the debris impact and the point of collision (e.g. central, glancing, on spacecraft appendages). In recent years, numerous impact tests have been performed, varying one or more of these parameters to better understand the physics behind these phenomena. In this context some tests have been also performed at the hypervelocity impact facility of the university of Padova. This paper provides an overview of the main experiments performed, the most critical issues observed and proposes some future directions for further research. Moreover, it summarizes the current state of research in spacecraft fragmentation, including the methods and techniques used to simulate debris impacts, the characterization of fragment properties and the analysis of the resulting debris cloud

Combined control and navigation approach to the robotic capture of space vehicles

The potentialities of In-Orbit Servicing (IOS) to extend the operational life of satellites and the need to implement Active Debris Removal (ADR) to effectively tackle the space debris problem are well known among the space community. Research on technical solutions to enable this class of missions is thriving, also pushed by the development of new generation sensors and control systems. Among private companies, space agencies and universities, the European Space Agency (ESA) has been developing technologies in this field for decades. Several solutions have been proposed over the years to safely capture orbital objects, the majority relying on robotic systems. A promising option is the employment of an autonomous spacecraft (chaser) equipped with a highly dexterous robotic arm able to perform the berthing with a resident space object. This operation poses complex technical challenges both during the approach phase and after contact. In this respect, the design of an effective, reliable, and robust Guidance, Navigation and Control (GNC) system, for which several algorithmic architectures and hardware configurations are possible, plays a key role to ensure safe mission execution. This work presents the outcomes of a research activity performed by a consortium of universities under contract with ESA with the goal to develop the navigation and control subsystems of a GNC system for controlling a chaser equipped with a redundant manipulator. Both the final approach until capture and the target stabilization phase after capture are considered in the study. The proposed solution aims at the implementation of a combined control strategy. Robust control methods are adopted to design control laws for the uncertain, nonlinear dynamics of the chaser and of the complete chaser–target stack after capture. Visual–based solutions, i.e., relying on active/passive electro– optical sensors, are selected for relative navigation. A complete sensor suite for relative and absolute navigation is part of the GNC system, including transducers for robot joint measurements. To properly validate the proposed solutions, a complete numerical simulator has been developed. This software tool allows to thoroughly assess the system performance, accounting for all the relevant external disturbances and error sources. A realistic synthetic image generator is also used for relative navigation performance assessment. This paper presents the design solutions and the results of preliminary numerical testing, considering three mission scenarios to prove the flexibility of the solution and its applicability to a wide range of operational cases