Impact cratering experiments into highly porous bodies

Asteroids represent both an opportunity and a risk. Their pristine environment captures the early collision evolution of the solar system; while their inherent ground impact potential could result in the mass extinction of life. Amongst the many possibilities of asteroid deflection, kinematic impactors have been theoretically proven to be a promising technique. However, this is primarily based on modelling rocky, brittle bodies. Little experimental consideration has been made for highly porous bodies. Therefore to advance current mitigation scenarios a series of experiments have been conducted. Under an accelerated reference frame this aimed to assess the impact cratering response of highly porous asteroids. All events were examined relative to the increasing levels of porosity and the impact’s resultant morphological profile. This included crater shape and depth, and the ejecta profile. The latter was considered critical in assessing the overall contribution to the momentum enhancement exchange of any kinematic impact event

Evidence-based robust design of deflection actions for near Earth objects

This paper presents a novel approach to the robust design of deflection actions for Near Earth Objects (NEO). In particular, the case of deflection by means of Solar-pumped Laser ablation is studied here in detail. The basic idea behind Laser ablation is that of inducing a sublimation of the NEO surface, which produces a low thrust thereby slowly deviating the asteroid from its initial Earth threatening trajectory. This work investigates the integrated design of the Space-based Laser system and the deflection action generated by laser ablation under uncertainty. The integrated design is formulated as a multi-objective optimisation problem in which the deviation is maximised and the total system mass is minimised. Both the model for the estimation of the thrust produced by surface laser ablation and the spacecraft system model are assumed to be affected by epistemic uncertainties (partial or complete lack of knowledge). Evidence Theory is used to quantify these uncertainties and introduce them in the optimisation process. The propagation of the trajectory of the NEO under the laser-ablation action is performed with a novel approach based on an approximated analytical solution of Gauss’ Variational Equations. An example of design of the deflection of asteroid Apophis with a swarm of spacecraft is presented

Orbit determination and control for the European Student Moon Orbiter

Scheduled for launch in 2014-2015 the European Student Moon Orbiter (ESMO) will be the first lunar microsatellite designed entirely by the student population. ESMO is being developed through the extensive use of flight spared and commercial of the shelf units. As such ESMO is significantly constrained by the available mission delta-V. This provides a considerable challenge in designing a viable transfer and stable orbit around the Moon. Coupled with an all-day piggy-back launch opportunity, where ESMO has little or no control over the launch date, ESMO is considered to be an ambitious design. To overcome these inherent challenges, the use of a Weak Stability Boundary (WSB) transfer into a highly eccentric orbit is proposed. However to ensure accurate insertion around the Moon, ESMO must use a complex navigation strategy. This includes mitigation approaches and correction strategies. This paper will therefore present results from the ongoing orbit determination analysis and navigation scenarios to ensure capture around the Moon. While minimising the total delta-V, analysis includes planning for orbital control, scheduling and the introduction of Trajectory Correction Manoeuvres (TCMs). Analysis was performed for different transfer options, final lunar orbit selection and available ground stations

Investigation and modelling of large scale cratering events : Lessons learnt from experimental analysis

Initiated as part of the 2010 Spin Your Thesis campaign, a new ESA Education programme, a group from the University of Glasgow Space Advanced Research Team successfully conducted a series of impact cratering experiments under a highly accelerated reference frame. This aimed to: reproduce and define the physical conditions of large-scale cratering events onto highly porous asteroids; provide cratering response data for the validation and advancement of numerical models; and support the generation of a reliable scaling theory for cratering events. Impact cratering is a fundamental process that has shaped and continues to shape the formation and evolution of our solar system and other planetary systems. Although much is known on the impact dynamics of rocky, brittle bodies, such as asteroids, little is known on the physical response of highly porous bodies. Consequently the physical response of porous bodies can not be compared to conventional models. Therefore throughout the experiment campaign, variation into the target material’s porosity and projectile density was examined. All in-situ measurements were recorded relative to the crater’s morphological profile and ejecta distribution. This occurred under increasing levels of acceleration, thereby validating that the experiment occurred within the crater dominated gravity regime. This paper details the programmatics issues of the initiative, experiences and lessons learnt from the student perspective. From its initial proof-of-concept the Spin Your Thesis campaign provided a solid foundation from the development of an experimental idea, enabling high scientific return and personal development

Orbit determination and control for the European Student Moon Orbiter

This paper presents the preliminary navigation and orbit determination analyses for the European Student Moon Orbiter. The severe constraint on the total mission Delta nu and the all-day piggy-back launch requirement imposed by the limited available budget, led to the choice of using a low-energy transfer, more specifically a Weak Stability Boundary one, with a capture into an elliptic orbit around the Moon. A particular navigation strategy was devised to ensure capture and fulfil the requirement for the uncontrolled orbit stability at the Moon. This paper presents a simulation of the orbit determination process, based on an extended Kalman filter, and the navigation strategy applied to the baseline transfer of the 2011-2012 window. The navigation strategy optimally allocates multiple Trajectory Correction Manoeuvres to target a so-called capture corridor. The capture corridor is defined, at each point along the transfer, by back-propagating the set of perturbed states at the Moon that provides an acceptable lifetime of the lunar orbit. (C) 2012 Elsevier Ltd. All rights reserved

Asteroid belt multiple flyby options for M-Class Missions

Addressing many of the fundamental questions in modern planetary science, as well as in ESA’s cosmic vision, requires a comprehensive knowledge of our Solar System’s asteroid belt. This paper investigates potential opportunities for medium-class asteroid belt survey missions in the timeframe of 2029-2030. The study has been developed in support to CASTAway Asteroid Spectroscopic Survey mission proposal, which is to be submitted to the latest ESA’s medium size mission call. CASTAway envisages the launch of a small telescope with relatively straightforward (i.e. high TRL) remote sensing instrumentation to observe asteroids at a long-range (i.e. point source), but also at a short-range, resolving them at ~10 m resolution. This paper presents a challenging multi-objective optimization problem and discusses the feasibility of such a mission concept. A baseline trajectory is presented that meets both ESA’s medium size mission constraints and the science requirements. The trajectory loops through the asteroid belt during 7 years, visiting 10 objects of a wide range of characteristics, providing sufficient survey time to obtain compositional information for 10,000s of objects and the serendipitous discovery of also 10,000s of 10-m class asteroids. The methodology developed has enabled the exploration of the entire design space for a conservative Soyuz-launch performance, and has found a total of 200 different tour opportunities of the asteroid belt; all compliant with ESA’s 5th call for medium size missions

Laser ablation for the deflection, exploration and exploitation of near Earth asteroids

Laser ablation has been investigated as a possible technique for the contactless deflection of Near Earth Asteroids. It is achieved by irradiating the surface of an asteroid with a laser light source. The absorbed heat from the laser beam sublimates the surface, transforming the illuminated material directly from a solid to a gas. The ablated material then forms into a plume of ejecta. This acts against the asteroid, providing a controllable low thrust, which pushes the asteroid away from an Earth-threatening trajectory. The potential of laser ablation is dependent on understanding the physical and chemical properties of the ablation process. The ablation model is based on the energy balance of sublimation and was developed from three fundamental assumptions. Experimental verification was used to assess the viability of the ablation model and its performance in inducing a deflection action. It was achieved by ablating a magnesium-iron silicate rock, under vacuum, with a 90 W continuous wave laser. The laser operated at a wavelength of 808 nm and provided intensities that were below the threshold of plasma formation. The experiment measured the average mass flow rate, divergence geometry and temperature of the ejecta plume and the contaminating effects - absorptivity, height and density - of the deposited ejecta. Results were used to improve the ablation model. A critical discrepancy was in the variation between the previously predicted and experimentally measured mass flow rate of the ablated ejecta. Other improvements have also included the energy absorption within the Knudsen layer, the variation of sublimation temperature with local pressure, the temperature of the target material and the partial re-condensation of the ablated material. These improvements have enabled the performance of the ablation process and the specifications of the laser to be revised. Performance exceeded other forms of electric propulsion that provided an alternative contactless, low thrust deflection method. The experimental results also demonstrated the opportunistic potential of laser ablation. Using existing technologies, with a high technology readiness level, a small and low-cost mission design could demonstrate the technologies, approaches and synergies of a laser ablation mission. The performance of the spacecraft was evaluated by its ability to deflect a small and irregular 4 m diameter asteroid by at least 1 m/s. It was found to be an achievable and measurable objective. The laser ablation system could be successfully sized and integrated into a conventional solar-power spacecraft. Mission mass and complexity is saved by the direct ablation of the asteroid's surface. It also avoids any complex landing and surface operations. Analysis therefore supports the general diversity and durability of using space-based lasers and the applicability of the model's experimental verification

Europe's future exploration of Main Belt Comets

We discuss possible European missions to explore the recently identified population of "main belt comets", which are small bodies with some asteroid-like properties and some comet-like ones. Various options have been proposed to ESA in recent years, and we will present these, and discuss future possibilities