Opportunities for asteroid retrieval missions

Asteroids and comets are of strategic importance for science in an effort to uncover the formation, evolution and composition of the Solar System. Near-Earth Objects (NEOs) are of particular interest because of their accessibility from Earth, but also because of their speculated wealth of material resources. The exploitation of these resources has long been discussed as a means to lower the cost of future space endeavours. In this chapter, we analyze the possibility of retrieving entire objects from accessible heliocentric orbits and moving them into the Earth’s neighbourhood. The asteroid retrieval transfers are sought from the continuum of low energy transfers enabled by the dynamics of invariant manifolds; specifically, the retrieval transfers target planar, vertical Lyapunov and halo orbit families associated with the collinear equilibrium points of the Sun-Earth Circular Restricted Three Body problem. The judicious use of these dynamical features provides the best opportunity to find extremely low energy transfers for asteroidal material. With the objective to minimise transfer costs, a global search of impulsive transfers connecting the unperturbed asteroid’s orbit with the stable manifold phase of the transfer is performed. A catalogue of asteroid retrieval opportunities of currently known NEOs is presented here. Despite the highly incomplete census of very small asteroids, the catalogue can already be populated with 12 different objects retrievable with less than 500 m/s of Δv. All, but one, of these objects have an expected size in the range that can be met by current propulsion technologies. Moreover, the methodology proposed represents a robust search for future retrieval candidates that can be automatically applied to a growing survey of NEOs

Near-Earth asteroid resource accessibility and future capture mission opportunities

In-Situ Resource Utilization (ISRU) has always been suggested for ambitious space endeavours; and asteroids and comets in particular are generally agreed to be ideal sources, both in terms of its accessibility and wealth. The future utilisation of asteroid resources is here revisited by, firstly, providing an estimate of the total amount of accessible resources in the Earth’s neighbourhood and, secondly, by envisaging a series of missions in order to retrieve resources from the most accessible objects known today. An analytical multi-impulsive transfer model is proposed in order to define the region in Keplerian space from which resources are accessible, and mapped subsequently into a near-Earth asteroid model, to understand the availability of material. This estimate shows a substantial amount of resources can be accessible at relatively low energy-cost; on the order of 1014 kg of material could potentially be accessed at an energy cost lower than that required to access the resources in the Moon. Most of this material is currently undiscovered, but the current surveyed population of near-Earth asteroid provides a good starting point for a search for future capture opportunities. The possibility of capturing, i.e., placing the asteroid into an orbit in permanent close proximity to Earth, a small-size NEO or a segment from a larger object would be of great scientific and technological interest in the coming decades. A systematic search of capture candidates among catalogued NEOs is presented, which targets the L2 region as the destination for the captured material. A robust methodology for systematic pruning of candidates and optimisation of capture trajectories through the stable manifold of planar Lyapunov orbits around L2 has been implemented and tested. Five possible candidates for affordable asteroid retrieval missions have been identified among known NEOs, and the transfers to the L2 region calculated. These transfers enable the capture of bodies with 2-8 meters diameter with modest propellant requirements. Because of the optimal departure dates, two of them have been identified as attractive targets for capture missions in the 2020-2030 time frame

Effective approach navigation prior to small body deflection

The largest threat for asteroids impacts on Earth is currently posed by small bodies of diameter less than 40 m. Even though incapable of causing a global catastrophe, they can still potentially cause significant local and regional damage. One of the main challenges for deflecting asteroids in this size range is the precise orbit determination and approach navigation prior to implementing any deviation mechanism. This paper addresses this particular problem and presents an approach strategy that was proposed for the contactless deflection technology demonstrator SysNova challenge of ESA

Gravitational capture opportunites for asteroid retrieval missions

Asteroids and comets are of strategic importance for science in an effort to uncover the formation, evolution and composition of the Solar System. Near-Earth objects (NEOs) are of particular interest because of its accessibility from Earth, but also because of their speculated wealth of resources. The exploitation of these resources has long been discussed as a means to lower the cost of future space endeavours. In this paper, we analyze the possibility of retrieving entire objects from accessible heliocentric orbits and moving them into the Earth’s neighbourhood. The asteroid retrieval transfers are sought from the continuum of low energy transfers enabled by the dynamics of invariant manifolds; specifically, the retrieval transfers target planar, vertical Lyapunov and halo orbit families associated with the collinear equilibrium points of the Sun-Earth Circular Restricted Three Body problem. The judicious use of these dynamical features provides the best opportunity to find extremely low energy Earth transfers for asteroidal material. With the objective to minimise transfer costs, a global search of impulsive transfers connecting the unperturbed asteroid’s orbit with the stable manifold phase of the transfer is performed. A catalogue of asteroid retrieval opportunities of currently known NEOs is presented here. Despite the highly incomplete census of very small asteroids, the catalogue can already be populated with 12 different objects retrievable with less than 500 m/s of Δv. All, but one, of these objects have an expected size and transfer requirements that can be met by current propulsion technologies. Moreover, the methodology proposed represents a robust search for future retrieval candidates that can be automatically applied to a growing survey of NEOs

Deflecting small asteroids using laser ablation : Deep space navigation and asteroid orbit control for LightTouch2 Mission

This paper presents a low-cost, low mass, mission design to successfully intercept and deflect a small and faint, 4 m in diameter asteroid. Intended to be launched after 2025, the laser-ablating mission, LightTouch2 will be used to deflect the orbit of the asteroid by at least 1 m/s. This will be achieved with a total mission lifetime of less than three years. Analysis includes the initial approach of the spacecraft, the operations of the laser at an optimal spacecraft-to-asteroid distance of 50 m and the relative orbit of the spacecraft that flies in formation with the asteroid. Analysis includes line-of-sight measurements with radiometric tracking from ground station to improve the trajectory estimate and observability of the spacecraft, collision avoidance and mapping strategies. The spacecraft will also need optimal discrete control. This is achieved by impulse-bit manoeuvres used to account for the perturbations caused by the resultant thrust on the asteroid, plume impingement, laser recoil and solar radiation pressure. The spacecraft controls its trajectory within a 1 m box from the reference trajectory to enable the laser to optimally focussing the laser beam. The proposed approach uses an unscented Kalman filter to estimate the relative spacecraft-asteroid position, velocity and perturbative acceleration

Coupled orbit-attitude dynamics of a captured asteroid during swing-bys

The rotational state and structure of minor bodies undergo major disruptions during very close encounters with massive bodies. This paper proposes the use of tidal interaction during a swing-by to modify or manipulate the spin and possibly the structure of asteroids, primarily during capture. The possibility of de-spinning, spinning-up or controlled break-up of a captured asteroid is considered. Three simple planar models are used to study the orbit-attitude interactions: the coupled dynamics of an ideal mass-point dumbbell, a simplified decoupled rigid body rotation dynamics, and a circular orbit binary. The evolution of the rotational state and structure of the asteroids is studied for the hypothetical cases of a single lunar or Earth swing-by prior to capture. The final conditions are shown to be highly dependent on the initial rotational state, the distance to the swing-by body, and, most importantly, the relative attitude of the asteroid to the local vertical at pericentre

On the a and g families of orbits in the Hill problem with solar radiation pressure and their application to asteroids

The focus of this paper is on the exploration of the a and g-g’ families of planar symmetric periodic orbits around minor bodies under the effect of solar radiation pressure. An extended Hill problem with solar radiation pressure (SRP) allows the study of spacecraft trajectories in the vicinity of asteroids orbiting the Sun. The evolution of the a and g-g’ families is presented with SRP increasing from the classical Hill problem to levels characteristic of current and future planned missions to minor bodies, as well as one extreme case with very large SRP for a small asteroid. In addition, the implications of considering a spherical body are analysed, in terms of trajectories colliding with the asteroid and eclipses, which limits the feasibility of various family branches. Finally, the influence of SRP on the linear stability of feasible orbits is calculated

Alternating orbiter strategy for asteroid exploration

This paper proposes the use of highly non-Keplerian trajectories enabled by solar radiation pressure and devices with variable area or reflectivity to map and characterize small asteroids. Strategies alternative to hovering involving a combination of retrograde and prograde orbits, together with inversions of the orbit direction by either maneuvers or exploiting the natural dynamics, are presented and analysed. As opposed to terminator orbits, this alternating orbiter strategy allows direct overflies of the subsolar point and other equatorial regions. A simple cost comparison demonstrates a significant improvement with respect to traditional hovering strategies. Additional orbits of interest for hopper spacecraft are also discussed. Finally, various possible implementations of variable-area spacecraft that could provide the required solar radiation pressure control are suggested and discussed

Ejection and recovery system for CubeSat sized ejectables on sounding rockets

Many sounding rocket experiments have the requirement to be free flying due to their size or the required precision of their measurements which would be falsified by other experiments on-board the same sounding rocket. This paper outlines the ejection and recovery system that was flown on the sounding rocket REXUS13 in May 2013 as part of the StrathSat-R experiment. The ejection system consists of two free flying units (whose dimensions are that of a one unit cube satellite) ejected from the side of an experimental module. The cubes are ejected via compressed springs which are constrained during launch by a stainless steel cable that holds the hatches in place. A pyro cutter is then used to sever the steel cable at apogee in order to release the cubes in free space. During descent, a recovery system consisting of a parachute, a GPS receiver, a Globalstar transmitter and a radio beacon is activated and used to locate the two cubes after impact. The parachute is automatically released at ~5km enabling the GPS receiver to locate the falling cubes and transmit their positions over the Globalstar satellite system and the radio beacon to the ground station. This paper will present the mechanical design of the ejection system and the electronic design and component selection of the recovery system