Final Report Summary - ASTEROIDRETRIEVAL (Asteroid Retrieval Missions Enabled by Invariant Manifold Dynamics) Near Earth Objects (NEOs), i.e. asteroids and comets whose orbits come close to that of the Earth, are today extremely attractive targets for future space missions. This is, to a great extent, because of their scientific importance to understand the formation, evolution and composition of the Solar System. However, the impact threat that these objects pose to Earth and the potential of their resources to enable a sustainable access to space have become increasingly important factors. The asteroid retrieval mission concept has thus arisen as a synergistic approach to tackle these three facets of interest in one single mission. An asteroid retrieval mission envisages a spacecraft that rendezvous with an asteroid, lassos it and then hauls it back to Earth neighbourhood. Moving an entire object into an orbit in the vicinity of Earth entails an obvious engineering challenge, but would also allow a much more flexible mining phase in the Earth’s neighbourhood. Not to mention other advantages such as scientific return or possible future space tourism opportunities. Current interplanetary spacecraft however have masses on the order of 103kg, while an asteroid of 10 meters diameter will most likely have a mass of the order of 106kg. Hence, moving such an object or larger, with the same ease that scientific payload is transported today, would demand propulsion systems order of magnitudes more powerful and efficient; or alternatively, orbital transfers orders of magnitude less demanding than those to reach other planets in the Solar System.Asteroidretrieval project was consequently aimed at gaining further understanding of the current and near-term capability to modify the asteroid’s trajectory by judicious use of orbital mechanics. The project focused on exploiting the subtle underlying dynamics of multi-body systems, in order to benefit from simultaneous gravitational interactions between the Sun, Earth and Moon to find effective means to transport asteroid material to the Earth’s vicinity.The projects run from 1st June 2013 to 15th February 2015, and concluded after reaching the following research achievements:• A methodology was improved upon to detect Easily Retrievable Objects (EROs) and compute optimal opportunities for impulsive retrieval to Libration Point Orbits (LPOs) near the collinear equilibrium points in the Sun-Earth system.• A systematic method to compute low thrust trajectories for previously detected EROs was established. This also allowed the computation of the largest mass that could possibly be retrieved from a given asteroid’s orbit, given a specific propulsion system design. Hence, if this mass was larger than the actual mass of the asteroid, the asteroid retrieval mission for the particular object was said to be feasible.• The feasibility of actively controlling asteroids during retrieval, and once in their parking orbits, was studied. The work aimed at understanding the difficulties posed by epistemic uncertainties due to lack of knowledge of the asteroid physical characteristics. • A novel general perturbation method was developed based on a series expansion in the mass parameter µ of the Circular Restricted Three Body Problem. The method allowed a rapid assessment of all possible third-body effects onto a given trajectory, which in turn facilitated the computation of Earth multi-resonant capture transfers. • With regard to the visionary concept theme of the project, as described in the original project proposal, a multidisciplinary approach to the field of geo-engineering demonstrated the feasibility for optimal design of multiple sunshades flying in formation near the L1 point.At its completion on February 2015, Asteroidretrieval has applied the methods developed during the project to compute an updated list of 15 EROs, and their optimal low thrust retrieval trajectories. The following table summarizes these results: The table reproduces the name of the asteroids, their mean mass estimate, maximum retrievable mass (Mret) by means of high-power low-thrust propulsion and a mission feasibility flag. The latter is designated as Mmin depending if Mret is smaller or larger than the minimum possible asteroid mass, taking into account uncertainties on the asteroid’s mass estimates, as >Mmean if Mret is larger than mean mass and >Mmax if Mret is larger than the maximum possible asteroid mass. Note that asteroid mass estimates are highly uncertain, since most of the asteroids are only points of light in Earth’s telescopes, thus preliminary considerations on mission feasibility depend in great measure on the exact mass of these objects. Asteroid Mean Mass Isp=3000s [t] Electric Propulsion Mret [t] Mission Feasib. 1. 2006 RH120 105 2,100 >Mmax 2. 2007 UN12 318 973 >Mmax 3. 2011 UD21 420 925 >Mmean 4. 2012 TF79 1,919 739 5. 2010 VQ98 635 727 >Mmean 6. 2010 UE51 553 677 >Mmean 7. 2013 RZ53 9 595 >Mmax 8. 2008 UA202 121 576 >Mmax 9. 2011 BL45 3,335 562 10. 2008 EA9 1,268 556 11. 2009 BD 730 493 12. 2014 WX202 88 459 >Mmax13. 1991 VG 420 407 >Mmin14. 2000 SG344 80x10^3 340 15. 2011 MD 838 277 These retrieval trajectories benefit from the computation of the so-called stable hyperbolic invariant manifold structures associated with particular equilibrium configurations in multi-body systems. These mathematical structures represent all the trajectories that asymptotically, hence without the need of any manoeuvre, reach an equilibrium configuration, as shown in the figure.Asteroidretrieval carried out foundational research in space engineering science. As such, it provided the grounds to understand the feasibility of space missions aimed at transporting large masses near the Earth for subsequent utilization. The project showed that there are a number of objects that could be transported into special orbital configurations that do not actually orbit the Earth in a classical sense. The objects inserted into these types of orbits would become extremely accessible for all sort of scientific equipment launch from Earth, but also for technologies aimed at advancing and demonstrating the potential for resource extraction and utilization. Ultimately, these potentially disrupting technologies may allow humankind to access space on a scale never seen before, but already dreamt by rocketry pioneers such as K. Tsiolkovsky. final1-figure-1.jpg
