Asteroid retrieval missions enabled by invariant manifold dynamics

Abstract

Near Earth Asteroids are attractive targets for new space missions; firstly, because of their scientific importance, but also because of their impact threat and prospective resources. The asteroid retrieval mission concept has thus arisen as a synergistic approach to tackle these three facets of interest in one single mission. This paper reviews the methodology used by the authors (2013) in a previous search for objects that could be transported from accessible heliocentric orbits into the Earth's neighbourhood at affordable costs (or Easily Retrievable Objects, a.k.a. EROs). This methodology consisted of a heuristic pruning and an impulsive manoeuvre trajectory optimisation. Low thrust propulsion on the other hand clearly enables the transportation of much larger objects due to its much higher specific impulse. Hence, in this paper, low thrust retrieval transfers are sought using impulsive trajectories as first guesses to solve the optimal control problem. GPOPS-II is used to transcribe the continuous-time optimal control problem to a nonlinear programming problem (NLP). The latter is solved by IPOPT, an open source software package for largescale NLPs. Finally, a natural continuation procedure that increases the asteroid mass allows to find out the largest objects that could be retrieved from a given asteroid orbit. If this retrievable mass is larger than the actual mass of the asteroid, the asteroid retrieval mission for this particular object is said to be feasible. The paper concludes with an updated list of 17 EROs, as of April 2016, with their maximum retrievable masses by means of low thrust propulsion. This ranges from 2,000 tonnes for the easiest object to be retrieved to 300 tonnes for the least accessible of them.

Low-energy near Earth asteroid capture using Earth flybys and aerobraking

“…According to the work of and Sánchez and Yárnoz (2016), a candidate NEA can be captured directly from its orbit to the stable manifold of the target Sun-Earth L1/L2 periodic orbit. The candidate NEA is first assumed to leave its orbit with an initial manoeuvre and then will move onto the stable manifold of the Sun-Earth L1/L2 periodic orbit with a second manoeuvre.…”

“…where a, e and i are the semi-major axis (in AU), eccentricity and inclination of the NEA orbit. If an NEA's Jacobi constant is significantly different from that of the final periodic orbit, it may have too high a total cost for capture (Sánchez and Yárnoz, 2016). It should therefore be possible to achieve low energy capture with a Jacobi constant close to the Jacobi constant of the target periodic orbit.…”

“…The exploitation of these in-situ resources has long been proposed as a necessary part of long-term space development (Lewis and Hutson, 1993;Bottke, 2002;. Therefore, the idea of capturing NEAs, based on current technology, for scientific and potentially commercial purposes, has been studied in recent work (Hasnain et al, 2012;Lladó et al, 2014;Sánchez and Yárnoz, 2016). In these works, the Sun-Earth collinear libration points L1 and L2 repeatedly appear as ideal locations for captured NEAs Lladó et al, 2014;Sánchez and Yárnoz, 2016).…”

“…Meanwhile, a family of Easily Retrievable Objects (EROs) has been defined, corresponding to a subset of NEAs which are captured onto the Sun-Earth L1 or L2 periodic orbits with a total cost below 500 m/s . Accordingly, the list of EROs have been updated (Sánchez and Yárnoz, 2016) and low thrust has been considered to design retrieval trajectories (Mingotti et al, 2014;Tang and Jiang, 2016).…”

Capture of small near-Earth asteroids to Earth orbit using aerobraking

“…Most recent research work has investigated the possibility of capturing near-Earth asteroids in the vicinity of the Earth, including the Sun-Earth libration points L1 and L2 [9][10][11][12], the neighbourhood of the Moon [13][14][15] and bound orbits about the Earth itself [8,16,17]. As vantage points for space observatories, and candidate gateways for future deep space exploration, the Sun-Earth L1 and L2 points also serve as the ideal locations for captured asteroids due to their unique locations and dynamical characteristics [18].…”