Near-Earth asteroids have attracted attention for both scientific and commercial mission applications. Due to the fact that the Earth-Moon L1 and L2 points are candidates for gateway stations for lunar exploration, and an ideal location for space science, capturing asteroids and inserting them into periodic orbits around these points is of significant interest for the future. In this paper, we define a new type of lunar asteroid capture, termed direct capture. In this capture strategy, the candidate asteroid leaves its heliocentric orbit after an initial impulse, with its dynamics modelled using the Sun-Earth-Moon restricted four-body problem until its insertion, with a second impulse, onto the L2 stable manifold in the Earth-Moon circular restricted threebody problem. A Lambert arc in the Sun-asteroid two-body problem is used as an initial guess and a differential corrector used to generate the transfer trajectory from the asteroid's initial obit to the stable manifold associated with Earth-Moon L2 point. Results show that the direct asteroid capture strategy needs a shorter flight time compared to an indirect asteroid capture, which couples capture in the Sun-Earth circular restricted three-body problem and subsequent transfer to the Earth-Moon 2 circular restricted three-body problem. Finally, the direct and indirect asteroid capture strategies are also applied to consider capture of asteroids at the triangular libration points in the Earth-Moon system.

This paper investigates the concept of capturing near-Earth asteroids into bound orbits around the Earth by using aerobraking. To guarantee that the candidate asteroids cannot present an impact risk during aerobraking, an initial aerobraking hazard analysis is undertaken and accordingly only asteroids with a diameter less than 30 m are considered as candidates in this paper. Then, two asteroid capture strategies utilizing aerobraking are defined. These are termed single-impulse capture and bi-impulse capture, corresponding to two approaches to raising the perigee height of the captured asteroid's orbit after the aerobraking manoeuvre. A Lambert arc in the Sun-asteroid two-body problem is used as an initial estimate for the transfer trajectory to the Earth and then a global optimisation is undertaken, using the total transfer energy cost and the retrieved asteroid mass ratio (due to ablation) as objective functions. It is shown that the aerobraking can in principle enable candidate asteroids to be captured around the Earth with, in some cases, extremely low energy requirements.

Since the Sun-Earth libration points L1 and L2 are regarded as ideal locations for space science missions and candidate gateways for future crewed interplanetary missions, capturing near-Earth asteroids (NEAs) around the Sun-Earth L1/L2 points has generated significant interest. Therefore, this paper proposes the concept of coupling together a flyby of the Earth and then capturing small NEAs onto Sun-Earth L1/L2 periodic orbits. In this capture strategy, the Sun-Earth circular restricted three-body problem (CRTBP) is used to calculate target Lypaunov orbits and their invariant manifolds. A periapsis map is then employed to determine the required perigee of the Earth flyby. Moreover, depending on the perigee distance of the flyby, Earth flybys with and without aerobraking are investigated to design a transfer trajectory capturing a small NEA from its initial orbit to the stable manifolds associated with Sun-Earth L1/L2 periodic orbits. Finally, a global optimization is carried out, based on a detailed design procedure for NEA capture using an Earth flyby. Results show that the NEA capture strategies using an Earth flyby with and without aerobraking both have the potential to be of lower cost in terms of energy requirements than a direct NEA capture strategy without the Earth flyby. Moreover, NEA capture with an Earth flyby also has the potential for a shorter flight time compared to the NEA capture strategy without the Earth flyby.

This paper investigates the concept of capturing small near-Earth asteroids into bound periodic orbits at the Sun-Earth L1 and L2 points using momentum exchange. A small asteroid is first maneuvered to engineer a fly-by with a larger asteroid. Two strategies are then considered: when the small asteroid approaches the vicinity of the large asteroid, it will either impact the large asteroid or connect to it with a tether. In both strategies, momentum exchange can be used to effect the capture of one of the asteroids. Then, a two-impulse Lambert arc is utilized to design a post-encounter transfer trajectory to the stable manifolds of the Sun-Earth L1 or L2 points. A selection strategy for candidate asteroids is proposed by considering both the deflection windows for capturing asteroids and the size of the asteroids.

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