We present the results of two sets of experiments that investigate laser-based metal-to-rock attachment techniques. Asteroids and comets have low surface gravity which pose a challenge to landers with moving parts. Such parts can generate torques and forces which may tip the lander over or launch it into deep space. Thus, if a lander on a small body is to have moving parts, the spacecraft must be equipped with an anchoring mechanism. To this end, we sought to use a laser to melt and bind a piece of metal mimicking a part of a spacecraft to a rock mimicking the surface of a typical asteroid. In the first set of experiments, extra material was not fed in during the processing. The second set were performed using a standard wire feeder used in laser welding, which added metal to the experiment during processing. During the first experiments, we discovered that a traditional weld, where two melt pools mix and solidify to form a strong bond, was not possible—the melt pools would not mix, and when they did, the resulting weld was extremely brittle. The second set of experiments resulted in a physico-mechanical bond, where a hole was drilled with a laser, and a wire was melted and fed into the hole. These latter experiments were successful in forming bonds as strong as 115 N. Such an attachment mechanism can also be used to maneuver small boulders on asteroid surfaces, to redirect small, monolithic asteroids, or in space-debris removal.

Asteroids are worth studying for three reasons: planetary protection, industrial applications, and scientific knowledge. It is critical we develop technologies capable of diverting objects on collision courses with our planet. We can use the same technology to move or process asteroids and comets for materials to build structures or refuel in Low-Earth Orbit. Asteroids are also windows into the past; they were formed in the early Solar System, and could potentially have been the source of water and/or life on Earth. There are unique challenges to manipulating an asteroid or asteroid materials, which means that much of what we know about material processing needs to be revamped to fit the situation. One of the motivating drives of this research was that a laser would be an excellent tool to perform many tasks at an asteroid.

One process of interest is laser drilling. The surface composition of asteroids is altered by aeons of space weathering; by studying the subsurface composition we can ascertain just how much it is altered and possibly by which processes. It is possible that hydrated minerals or ices exist below the surface as well, which are of great economic interest in asteroid mining. One of the greatest challenges to get under the surface of an asteroid is the low gravity: any forces or torques generated by a sampling mechanism may tip the spacecraft or launch it into deep space. A laser does not generate any significant forces, and can even be used without having to land; lasers do use a lot of electric power so the laser parameters need to be optimized to minimize the size and power requirements of the spacecraft. We found that nearly 1-cm deep holes can be made with as little as 18~J of energy using a 300-W laser.

Laser ablation has been studied as a mechanism to redirect asteroids, but it is not particularly energy efficient at material removal. If the idea is to create a momentum exchange by removing surface material beyond an object's gravitational pull, then there could perhaps be more energy efficient mechanisms. One mechanism we investigated was spallation, where the shock wave of a laser pulse breaks off a relatively large chunk of material without having to melt and vaporize it. We found that spallation may be many times more energy efficient than ablation.

Laser welding of metals has been of industrial interest for decades, though the welding of two different materials is still a challenge. We sought to develop a laser-based wire-attachment mechanism that can be used to anchor spacecraft to the surface of a small body or to maneuver boulders or small asteroids. When attempting to follow a traditional welding process, it was found that the two melt pools would not mix, and if it did, it was very weak. Instead, we used the laser to drill a hole and melt a wire while inserting it into the hole. This produced a solid anchor with a hold strength of up to 120~N.

Asteroid mining and redirection are two trends that both can utilize lasers, one to drill and cut, the other to ablate and move. Yet little is known about what happens when a laser is used to process the types of materials we typically expect to find on most asteroids. To shed light on laser processing of asteroid material, we used a 300-W, pulsed Ytterbium fiber laser on samples of olivine, pyroxene, and serpentine, and studied the process with a high-speed camera and illumination laser at 10 000 frames per second. We also measure the sizes of the resulting holes using X-ray micro-tomography to find the pulse parameters which remove the largest amount of material using the least amount of energy. We find that at these power densities, all three minerals will melt and chaotically throw off spatter. Short, low-power pulses can efficiently produce thin, deep holes, and long, high-power pulses are more energy efficient at removing the most amount of material.

The ability to deflect dangerous small bodies in the Solar System or redirect profitable ones is a necessary and worthwhile challenge. One well-studied method to accomplish this is laser ablation, where solid surface material sublimates, and the escaping gas creates a momentum exchange. Alternatively, laser-induced spallation and sputtering could be a more efficient means of deflection, yet little research has studied these processes in detail. We used a 15-kW Ytterbium fiber laser on samples of olivine, pyroxene, and serpentine (minerals commonly found on asteroids) to induce spallation. We observed the process with a high-speed camera and illumination laser, and used X-ray micro-tomography to measure the size of the holes produced by the laser to determine material removal efficiency. We found that pyroxene will spallate at power densities between 1.5 and 6.0 kW cm⁻², serpentine will also spallate at 13.7 kW cm⁻², but olivine does not spallate at 1.5 kW cm⁻² and higher power densities melt the sample. Laser-induced spallation of pyroxene and serpentine can be two- to three-times more energy efficient (volume removed per unit of absorbed energy) than laser-induced spattering, and over 40x more efficient than laser ablation.

This paper presents a comprehensive review of the science and technology of accessing near-Earth asteroids (NEAs), or making them accessible, for obtaining both information and resources. The survey is divided into four major groups of NEA study, namely a) discovery (population estimation and detection), b) Exploration (identification and characterization), c) deflection and redirection, and d) mining (prospecting, excavation, processing, refining, storage.). Recent research and development advancements from both industry and academia are discussed in each group, and certain specific future directions are highlighted. Some concluding remarks are made at the end, including the need for creating new educational programs to train competent engineers and researchers for the taskforce in the new field of asteroid engineering in near future

This paper introduces a mission concept for the remote characterization of a temporarily-captured asteroid, or “minimoon”, based on the utilization of the CubeSat form-factor. Minimoons are a subpopulation of the estimated two million Near-Earth Objects (NEOs) under 2 meters in diameter, which pass within the Moon’s orbit every year. These temporarily-captured objects do not remain in the Earth-Moon system for long, typically less than one year, and are thus a challenge for developing conventional spacecraft missions. A potential solution to this problem is to utilize the typical rapid-development timelines that CubeSat missions possess. This paper will analyze the requirements and limitations in developing a mission for a CubeSat to rendezvous or fly by a minimoon. This includes exploring the capabilities and applicability of the CubeSat technologies for such a mission, analyzing the erratic nature of minimoon orbits, lying out how such a mission project would be managed, and finally presenting a case study of such missions on the only known minimoon so far, Asteroid 2006 RH120.