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This article presents an innovative mechatronic design of a high-accuracy pointing mechanism for orbital laser communication terminals.The system is based on a dual-stage architecture and is miniaturized to fit nanosatellite-class spacecraft, aiming to enable optical communication on small-size space platforms. The focus is on control design aspects and on the performance assessment of an experimental prototype under emulated external environmental disturbances.

This paper provides a general description of a new Collision Simulation Tool (CST) to model the consequences of orbital impacts involving large debris and satellites, with the aim to predict fragments distributions in case of sub-catastrophic and catastrophic impacts. The new tool is being developed in the framework of the ESA contract “Numerical simulations for spacecraft catastrophic disruption analysis”, carried out by the Center of Studies and Activities for Space CISAS “G. Colombo” of the University of Padova (prime contractor) and etamax space GmbH. The CST makes possible to model a large variety of collision scenarios involving complex systems, such as entire satellites with many design details included, and provides statistically accurate results with a computational effort orders of magnitude lower than hydrocodes. To this end, the simulation approach is based on a hybrid modelling strategy, in which every colliding object is described as a gross net of Macroscopic Elements (ME) representing spacecraft elementary building blocks. On one hand, individual fragmentation of Macroscopic Elements is addressed through the use of semi-empirical breakup models applied, at element level, only to those spacecraft parts which are involved in the collision. On the other hand, structural distortion, fracture, and separation of satellite broken parts are modelled with a discrete-element approach through the simulation of momentum transfer to Macroscopic Elements through the net, taking into account energy dissipation inside elements and across links. This paper provides a description of the CST simulation methodology and framework; preliminary results are also shown with respect to the tool validation process. Validation is done by comparing the tool predictions with empirical data from ground-based impact tests on simple targets (simple plates and Whipple Shields) as well as sub-scale spacecraft models. In the first case, the tool capability of predicting fragments distributions from plates and ballistic limit equations of shields is verified. In the second case, fragments distributions calculated by the software are compared with those derived from published experiments on a micro-satellite.

The ever-increasing number of earth-orbiting spacecraft and related space junk is resulting in a dramatic rise in the risk of space debris impacting and damaging satellites and thereby negatively affecting the regular execution of several services provided by space-borne infrastructures. In the past years, the satellite market experienced a paradigm shift with the rise of small satellites and constellations formed by hundreds of satellites. It is anticipated that by the end of this decade, more than a thousand satellites per year will be launched, representing a potential market of more than $300 billion. With continued miniaturization of devices and the evolution of new mission requirements that rely on advanced sensor technology, future spacecraft will have an increasing density of devices and sensors. Moreover, a great research effort is required to improve the efficiency and reduce the weight of spacecraft shields. One route to achieve these goals is developing smart shields able to estimate the level of damage following the impact. In this context, the paper investigates a proof of concept based on the design, manufacture and testing of a measurement system, based on Thin Film Heat Flux Gauges (TFHFG), to assess the damage posed by orbital debris to the satellite shields upon Hyper Velocity Impacts (HVI). The system aims to measure the local increase in shield temperature, which is correlated to the kinetic energy of the debris. Following design and manufacturing, the proposed sensors were calibrated and mounted on a ductile aluminum alloy target, representative of the spacecraft shields, and subjected to a campaign of HVI tests. The results highlight that the signal is composed by the mechanical and thermal contribution, with a dominant mechanical factor.

Small satellite platforms are becoming very appealing both for scientific and commercial applications, thanks to their low cost, short development times and availability of standard components and subsystems. The main disadvantage with such vehicles is the limitation of available resources to perform mission tasks. To overcome this drawback, mission concepts are under study that foresee cooperation between autonomous small satellites to accomplish complex tasks; among these, on-orbit servicing and on-orbit assembly of large structures are of particular interest and the global scientific community is putting a significant effort in the miniaturization of critical technologies that are required for such innovative mission scenarios. In this work, the development and the laboratory testing of an accurate relative navigation package for nanosatellites compliant to the CubeSat standard is presented. The system features a small camera and two sets of LED fiducial markers, and is conceived as a standard package that allows small spacecraft to perform mutual tracking during rendezvous and docking maneuvers. The hardware is based on off-the-shelf components assembled in a compact configuration that is compatible with the CubeSat standard. The image processing and pose estimation software was custom developed. The experimental evaluation of the system allowed to determine both the static and dynamic performances. The system is capable to determine the close range relative position and attitude faster than 10 S/s, with errors always below 10 mm and 2 deg.

Recent plans for large constellations in Low-Earth Orbit have opened the debate on both their vulnerability and their influence on the already hazardous space debris environment. In fact, given that large constellations normally employ satellites of small size, there might be situations in which cm-size debris could have enough energy to cause fragmentation of a significant part of these spacecraft upon impact, while smaller debris could affect the functionalities of critical subsystems, even compromising the success of disposal operations planned at end-of-life. In this context, this paper investigates: (1) collisions with large objects that could initiate the fragmentation of a significant part of the satellite, and (2) impacts with small debris that might perforate the spacecraft hull thus causing relevant performance/functionality degradation. These two points are merged in a simple statistical tool for risk assessment, which analyses the effects of the main parameters of the constellations on its vulnerability (i.e. operational life, number of satellites, spacecraft cross section, satellites reliability). In more details, the tool relates impact probability (for both small and large debris) to the ballistic response of spacecraft structures and protections, defining the critical configurations that might compromise the expected disposal operations. This method requires a limited knowledge of the spacecraft internal layout, as it is based on a statistical analysis of impact damage instead of a complete evaluation of the vulnerability of each subsystem. In parallel, non-debris related failures are also investigated and statistic models of spacecraft reliability characteristic are proposed. Among the results, it is shown that reducing the lifetime of individual satellites in a constellation might improve the success rate of post-mission disposal, thanks to the reduction of the spacecraft exposure to the space environment with the consequential degradation of its performance. On the other hand, reducing the lifetime would seriously affect the debris environment: the increase in traffic in the most crowded altitudes would be not counterbalanced by the higher post mission disposal success rate, causing an overall increase of the total number of uncontrolled resident objects.

TED (Tethered Electromagnetic Docking) is a system proposed by a group of researchers and students of the University of Padova for close rendezvous and docking between spacecraft. It consists in a small tethered probe ejected by the chaser, reaching the proximity of the target with a controlled deployment, and then magnetically guided by a receiving electromagnet mounted on it. Because of the generated magnetic field, alignment and mating are possible, then, as the tether is rewound, the chaser is able to dock with the target. To perform a preliminary verification of TED, three groups of students have been involved in the project and contributed to the evaluation of its critical technologies in reduced gravity: in the framework of ESA &ldquo, Drop your Thesis!&rdquo, 2014 and 2016 campaigns the experiments FELDs and STAR focused on the test of the tether deployment and control, while PACMAN, in the framework of ESA &ldquo, Fly Your Thesis! 2017&rdquo, parabolic flights campaign, tested proximity operations by means of electromagnetic interactions. In this paper, a description of TED concept and its development roadmap is presented, introducing the critical technologies tested by FELDs, STAR, and PACMAN experiments. The second part of the paper focuses on the educational outcomes of the three experiments, introducing statistics on (1) student participation, (2) scientific publication production, and (3) influence of the educational programs on the students&rsquo, career.

Honeycomb sandwich panels (HC/SP) are the most common used structures for space vehicle. Under the threat of meteoroid and space debris, the distribution of the fragments produced in a hypervelocity impact event on HC/SP is critical to the vulnerability assessment of space vehicle. CISAS developed an engineering model to describe fragments clouds propagating inside spacecraft in consequence of space debris impact on HC/SP. In this model, the effect of the honeycomb core was modeled by an empirical corrective factor, which was not related to the physical of the impact. To improve this model, a new model to describe the effect of the honeycomb core was developed. In the new model, the honeycomb core was equaled to multi-parallel thin plates, which can represent the discontinuity of honeycomb core without complex boundary. Based on the knowledge of hypervelocity impact on a simple thin plate and approximation supported by numerical simulation results, the model was deduced. The coefficient of the model was fitted by the numerical simulation results.

The main limitation of the currently adopted method for predicting spacecraft catastrophic fragmentation due to a collision with large debris is the total independence of the critical value of the energy-to-target mass ratio from both the satellite configuration and the impact point; in fact these two issues are not accounted for by the classical 40 J/g rule. To go beyond this limitation, the method proposed in this paper evaluates the distribution of impact energy into the system using the mechanical properties of the structural parts and the knowledge of the impact location. In this way, it becomes possible to predict how impact energy is partitioned among some selected macroscopic structural parts, each of them is finally evaluated versus its own minimum value of impact energy for which the part is fragmented (shattering threshold). Energy partition is performed by solving a system of equations written according to Statistical Energy Analysis (SEA). The paper describes in detail the proposed energy-partition method and presents its application to a geometrical representative model of a spacecraft subject to impact at different points. Results are finally compared to those obtained by the application of the classical 40 J/g rule. It is shown that the evaluation of spacecraft disintegration is highly influenced by the impact point and the structural properties of the components.

This paper presents a novel docking mechanism to provide small spacecraft with the ability to join and separate in space. At today small satellites mating technologies have never been verified in space nor scaled to CubeSat size; the few proposed ports implement simple probe-drogue interfaces, with the limitation to dock only with different-gender ports, or androgynous geometries, with complex and non-axis-symmetric latches. The mechanism presented in this work overcomes the aforementioned drawbacks, using a hybrid port that can act both as probe and drogue. This paper presents the mechanism design and analysis, focusing on the port kinematics and on the load transmission during its actuation and docking procedures. Experimental verification allows us to validate numerical simulations and determine the operative range of the port in terms of alignment ranges allowing the solid joint creation. Transmitted loads always under 3 N are shown during the docking transient, while the port displays to manage misalignments up to 5 ° and 15 mm.

The H2020 ReDSHIFT project aims at finding passive means to mitigate the proliferation of space debris. This goal is pursued by a twofold research activity based on theoretical astrodynamics, computer simulations and the analysis of legal aspects of space debris, coupled with an experimental activity on advanced additive manufacturing (3D printing) applied to the production of a novel small satellite. Several different aspects related to the design and production of a debris compliant spacecraft are treated, including shielding, area augmentation devices for deorbiting (solar and drag sails) and design for demise. A strong testing activity, mainly based on design for demise wind tunnel experiments and hypervelocity impacts is performed as well. The main results obtained so far in the project are outlined.

Over the last years, nanosatellites based on the CubeSat standard have been increasingly exploited by both academic institutions and commercial companies. The low cost and short development time of CubeSats make such miniature spacecraft interesting for a variety of applications. A particularly appealing future field of application for nanosatellites is On-Orbit Servicing of existing orbital assets. A number of mission concepts foresee the employment of miniature spacecraft to perform a variety of operations on orbital vehicles, ranging from inspection and monitoring to assembly and repairing. In this framework, the development of technologies that enable proximity navigation and/or docking between a nanosatellite chaser and a target object is of interest. In particular, miniaturized navigation sensors for the estimation of relative position and attitude of the involved vehicles are required. The work presented here focuses on the development of an IR-based relative navigation sensor compatible with CubeSat standard nanosatellites. The system estimates the relative pose and position of the target by taking images of the object, which is equipped with retro-reflecting fiducial markers illuminated by an array of IR LEDs on the chaser. The system architecture and operation are described, and preliminary laboratory test results are presented.

Electrodynamic tethers (EDT) represent one of the possible means to de-orbit defunct satellites from Low-Earth-Orbit at end-of-life. However, considering the large area exposed to the space environment and the consequent high number of debris impacts per unit time, a high tether survivability to orbital debris is of primary importance. This paper provides an estimation of the number of fatal impacts per unit time and per unit length on a tape tether, using for the first time an experimental ballistic limit equation that was derived for tapes and accounts for the effects of both the impact velocity and impact angle. It has recently been shown that, tape tethers, as opposite to round wires, are more resistant to space debris impacts. It is shown that considering a tape tether with cross section 45 mm × 50 μm , the number of critical events due to impact with non-trackable debris is always less than 0.01/yr/km, being maximum for orbit inclination of i = 90 ° .

Proximity relative navigation systems for autonomous small spacecraft and Micro Aerial Vehicles are under continuous investigation, aiming to obtain low-cost and low-resources miniaturized sensors. In this paper, after a review on the state of the art of relative navigation systems for cooperative and non-cooperative miniature space and aerial vehicles, two simple, low cost devices for proximity navigation are presented. The first one is conceived for operation between cooperative vehicles, and exploits a dual system comprising a small camera imaging an array of LEDs and a LED-photodiode couple for precise range estimation based on intensity measurements. The second sensor is designed to perform proximity ranging and attitude determination with respect to non-cooperative objects in space, air or ground. It is based on a miniature camera that detects the light spots on the target surface generated by three lasers mounted on the chaser vehicle. Theoretical models have been developed for both sensors, and were used to perform a preliminary assessment of performance through numerical simulations.

This paper presents the 2D close-range navigation sensor for cooperative spacecraft developed in the framework of the experiment ARCADE. The sensor exploits an infrared LED transmitter mounted on the target, and two photodiode receivers mounted on the chaser. Laboratory tests were performed to assess the sensor performance and range of application. The accuracies of estimates were, on average, 1.9 mm for distance and 1.0 deg for yaw angle, in ranges of [0.20, 0.42] m and [-40, 40] deg, respectively.

All spacecraft in Earth orbit are exposed to the risk of impact with micrometeoroids and orbital debris. When such particles have enough energy to penetrate the hull of the vehicle, clouds of fragments are ejected into spacecraft and they can eventually compromise the functionality of various components encountered in their flight path. Knowledge of the clouds׳ properties (e.g. fragments mass and velocity) is therefore a key factor to obtain accurate predictions of the response of interior equipment to space debris threat. However, generation and evolution of debris clouds from hypervelocity impact is a complex phenomenon governed by a large number of parameters, and existing models mostly refer to fragments originated by impact on simple aluminum plates only, while the models available for sandwich panels do not provide information on the fragments mass. In such context, this paper presents an engineering model describing debris clouds created by space debris impacts on honeycomb sandwich panels representative of satellites structural bodies. The model describes the cloud as a cone with one large central fragment and several finely fragmented particles which behave like a jet of dust, and it provides a set of empirical equations predicting the cone geometry, the velocity and mass of the central fragment, as well as the total mass ejected downrange. The proposed equations are derived from analogous formulas for debris clouds originated by impacts on simple aluminum plates, by applying proper corrections to account for different materials effects and different behavior of sandwich panels compared to plates of same material. The model is finally evaluated by comparing its predictions with few experimental data on triple wall structures (sandwich panel plus internal equipment cover plate), where debris clouds exiting the panels’ rear skin are used to assess the failure of the third wall. In this latter case, the proposed model is also compared with the SRL equations.

During the last 40 years, the mass of the artificial objects in orbit increased quite steadily at the rate of about 145 metric tons annually, leading to a total tally of approximately 7000 metric tons. Now, most of the cross-sectional area and mass (97% in LEO) is concentrated in about 4600 intact objects, i.e. abandoned spacecraft and rocket bodies, plus a further 1000 operational spacecraft. Simulations and parametric analyses have shown that the most efficient and effective way to prevent the outbreak of a long-term exponential growth of the catalogued debris population would be to remove enough cross-sectional area and mass from densely populated orbits. In practice, according to the most recent NASA results, the active yearly removal of approximately 0.1% of the abandoned intact objects would be sufficient to stabilize the catalogued debris in low Earth orbit, together with the worldwide adoption of mitigation measures. The candidate targets for removal would have typical masses between 500 and 1000 kg, in the case of spacecraft, and of more than 1000 kg, in the case of rocket upper stages. Current data suggest that optimal active debris removal missions should be carried out in a few critical altitude–inclination bands. This paper deals with the feasibility study of a mission in which the debris is removed by using a hybrid propulsion module as propulsion unit. Specifically, the engine is transferred from a servicing platform to the debris target by a robotic arm so to perform a controlled disposal. Hybrid rocket technology for de-orbiting applications is considered a valuable option due to high specific impulse, intrinsic safety, thrust throttle ability, low environmental impact and reduced operating costs. Typically, in hybrid rockets a gaseous or liquid oxidizer is injected into the combustion chamber along the axial direction to burn a solid fuel. However, the use of tangential injection on a solid grain Pancake Geometry allows for more compact design of the propulsion unit. Only explorative tests were performed in the past on this rocket configuration, which appears to be suitable as de-orbiting system of new satellites as well as for direct application on large debris in the framework of a mission for debris removal. The paper describes some critical aspects of the mission with particular concern to the target selection, the hybrid propulsion module, the operations as well as the systems needed to rendezvous and dock with the target, and the disposal strategy.

This paper presents a case study of Micrometeoroids and Orbital Debris risk assessment for a spacecraft flying in an orbit close to that of the Italian Cosmo-Skymed constellation. The aim of the analysis was to calculate the failure flux impinging on the satellite external shell, taking into account both geometry and materials of satellite surfaces. Furthermore the analysis included the evaluation of the contribution to debris population at the selected orbit of the fragments produced by a Chinese Anti-SATellite experiment, which caused the catastrophic break-up of the satellite Fengyun 1C in January 2007. A first computation was carried out using ESABASE2/Debris v.1.4.2. This software made it possible to perform geometrical analysis of a satellite subjected to a given debris environment, but the most up to date available models, ORDEM2000 and MASTER2001, gave significantly different results. An independent procedure for risk assessment analysis was implemented to further analyse such issue and to provide damage equation adequate to represent the behaviour of the selected structural aluminium honeycomb sandwich panels covered by Multi-Layer Insulation. Debris fluxes were calculated applying MASTER2005 and ORDEM2000 environment models, then results were compared to those of ESABASE2. Failure fluxes were calculated implementing special damage equations for honeycomb structures available from the open technical literature. The expected flux contribution of catalogued debris from the Chinese Anti-SATellite (ASAT) experiment was estimated independently using the code SDIRAT (Space Debris Impact Risk Analysis Tool) developed at the Institute of Information Science and Technologies (ISTI).

In order to analyze the propagation of shocks due to hypervelocity impact of micrometeoroids and space debris on spacecrafts, it was necessary to analyze the high-frequency shock-propagation-dynamic on complex structures representative of real spacecraft structure. Objective of this research is the GOCE satellite due to its highly accurate accelerometer very sensitive to the micro-vibration environment. After a detailed analysis of the most-probable shock-propagation-path within the satellite, several representative targets have been designed. Then an extensive test campaign has been conducted on these targets exploring a wide range of impact conditions. As a result, a database was established which correlates the impact conditions in the experimental range (0.6–2.3 mm projectiles at 2.5–5 km/s) with the shock spectra on selected locations on various types of structural models. The behaviour of structural joints was also analyzed under shock conditions that are not normally reproduced by pyroshock testing. The database represent a fundamental tool in order to validate the numerical analysis that will be used to assess the vibration environment, due to in-orbit micrometeoroids and space debris at the accelerometer location. This paper presents the test procedure applied and the general results achieved.

This paper presents an overview of the hypervelocity impact test campaign ongoing in the frame of the ESA contract “spacecraft disturbances from hypervelocity impact”. The project aims at analyzing the propagation of shocks due to hypervelocity impacts from the external shell of a spacecraft to its internal components. The object of the study is the GOCE satellite, which has been recognized to be very sensitive to small disturbances because of its payload that has been designed to measure even very low acceleration levels. In the first step presented hereafter, the test campaign has been focused on the qualification of the background environment inside the impact chamber and on the determination of the vibration levels induced by perforating and non-perforating hypervelocity projectiles on simple aluminum plates. The results currently obtained and a preliminary data analysis will be presented in the following.