1,721,012 research outputs found
Integrating Density-Based Uncertainty Propagation with Object-Oriented Re-Entry Models
Full text linkA Density-Based Approach to the Propagation of Re-Entry Uncertainties
Full text linkThe proposed study aims at implementing a density-based approach for the propagation of uncertainties in the initial conditions and parameters for the analysis and prediction of spacecraft re-entries. Using the continuity equation together with the re-entry dynamics, the joint probability distribution function of the uncertainties is propagated and the final uncertainties in the re-entry corridor, impact location, and casualty area are quantified. The paper considers uncertainties in the initial conditions at re-entry and in the ballistic coefficient of the satellite for different types of re-entry scenarios, studying the effects that such uncertainties have on the impact location and entry corridor
Modeling Re-Entry Break-Up Uncertainties with Continuity Equation and Gaussian Mixture Models Interpolation
Full text linkThe effect of uncertainties in the re-entry and break-up of satellites is analyzed. Two contributions are considered: the effect of the initial uncertainties of the parent trajectory and the break-up event, characterized by high thermal and mechanical loads and tumbling motion. Specifically, this last phenomenon may cause the scattering of the components off the nominal trajectory of the parent spacecraft. The presented study describes the uncertainties and the break-up event through probability distributions, propagates them using a continuum approach, and reconstructs the uncertainties at future states using the Starling suite developed at Politecnico di Milano
Analysis of Possible Definitions of the Space Environment Capacity to Pursue Long-Term Sustainability of Space Activities
Full text linkThe ability of space activities to benefit Earth and its people is now threatened by the increasing density of objects in orbit. If no mitigation measures are taken, the population could reach a level in the future at which collisions would continue to increase the number of debris in orbit, even without new launches. Addressing the need for space sustainability means preventing negative trends from becoming norms and ensure that outer space can be used for many years to come. The expansion of space activities offers opportunities to expand access to the benefits of space applications on Earth, but it poses new challenges to maintaining a safe operational environment in space. Space may seem vast, but the orbits around Earth in which satellites reside are a limited natural resource. Like the Earth's non-renewable resources (i.e., minerals and fossil fuels), these unique orbital regions, that are now essential for humanity, exist in nature in a limited way because their regeneration involves the passage of many years. The topic of sustainability is not a new one, and many studies have been conducted on the Earth's resources over the years. From what has been done and is being done for this problem on Earth, we take the cue to analyse and address a possible application in the space field as well. Particularly, the concept of capacity of an ecosystem is investigated and related to the space debris environment. In this work a debris evolution model, based on MISSD (Model for Investigating control Strategies for Space Debris) developed by in Somma et al. (2017), is built. The model is a source-sink debris evolutionary model based on a set of first order differential equations, which describe the injection and removal rates of objects in several altitude bands. Explosions and collisions generate fragments via the standard NASA breakup model, while drag, the only natural sink mechanism, is computed through a piecewise exponential model of the atmospheric density. The post mission disposal is the other significant removing mechanism considered in the model. The evolutionary model is used to study the future trends of the space environment and different definitions of capacity are investigated to find a sustainable future scenario. Various possible thresholds were assumed and checked; values derived from studies of the limits of space environment as well as techniques used on earth regarding limitations of CO2 and other harmful agents in different domains
Attitude Control of the Disposal Phase of the eCube Mission for Atmospheric Data Acquisition
Full text linkThis paper aims at providing a new perspective on the attitude dynamics and control system of a new CubeSat mission concept for atmospheric data acquisition, in the region between 200 km and 100 km, for more accurate reentry predictions. It discusses the main challenges and the feasibility of analysing the main atmospheric parameters via onboard sensors of a 12-unit CubeSat, designed at Politecnico di Milano. The paper presents the attitude control system feasibility during the data-acquisition phase, when the disturbance given by the atmospheric density is highly affecting the CubeSat dynamics, before the atmospheric disposal. After the estimation of the maximum momentum storage and the maximum torque acting on the satellites, a control law is provided to control the attitude via reaction wheels, allowing the data acquisition from the onboard sensors. Moreover, an analysis of the desaturation strategy is presented, to satisfy the pointing accuracy for the measurements of the network of sensors. The analysis could provide a baseline for future similar mission in the same orbital region, to enhance the acquisition of atmospheric data
Ejecta Dynamics Around Asteroids in View of In-Orbit Particle Collection Missions
Full text linkThis work explores the possibility of performing in-orbit particle collection for sampling and exploration missions towards asteroids. Ejecta is generated via a small kinetic impactor and two possible collection strategies are investigated: collecting the particle at the L2 Lagrangian point or collecting them while the orbit the asteroid and before they re-impact. Combining the dynamics of the particles in the Circular Restricted Three-Body Problem with realistic models for the ejecta generation, we evaluate the feasibility of the mission concept and characterised possible target asteroids given their physical properties
Sensitivity Analysis of Asteroid Ejecta Models for Future In-Orbit Sample Collection Mission
Full text linkThis work presents a sensitivity analysis on ejecta models used to model impact events onto small bodies in the Solar System. The application in exam is focused on kinetic impacts on Near Earth Asteroids to study the possibility of collecting the generated fragments in orbit, thus avoiding landing or touchdown operations. The sensitivity analysis shown in this work is articulated in three phases. A first analysis that studies the effect of the impactor and target properties on the overall fate of the ejecta. A second analysis that focuses on quasi-stable orbits: here we estimate the number of particles expected to be trapped into quasi-stable orbits depending on the impact location and the characteristics of the impact event. A third and final phase that focuses on a numerical methodology to predict the flux of impacts on a spacecraft positioned around the asteroids. This allows the estimate of the number of collectable particles by the spacecraft ass a function of its position. For each one of these analyses, we study their sensitivity to different aspects of the ejecta model
- …
