Asteroid capture

Traditional chemical propulsion is great for a thick atmosphere environment, but electric propulsion has a superior efficiency over chemical propulsion. One of the main electric propulsions used, Ion thruster has an efficiency of 90 percent while chemical propulsion's efficiency is around 35 percent.[6] In space, there is no friction between the environment and the spacecraft. Bringing a heavy asteroid requires an extremely efficient engine such as electric propulsion.

Based on NASA's Asteroid Redirect Mission, a satellite would grab a boulder and return to predetermined orbit. Robotic arms are used for various purposes including grabbing a boulder. Canadarm 2 is an example of an advanced robotic arm used in space. Canadarm 2 not only helps docking cargo spacecraft to the International Space Station but also performs station maintenance.[7] Advancement in robotic arms helps artificial asteroid capture to perform precise collection of samples on the asteroid's surface.

Lunar flyby can also be used to capture an asteroid.[8] The orbits of the asteroid have different Jacobi constants before and after lunar flybys. When the Jacobi constant of the asteroid orbits after the lunar flyby reaches a certain value, the asteroid will be captured. The capture regions of different pre-flyby initial Jacobi constants can be represented numerically, and these capture regions can be used to determine whether the asteroid can be captured or not through lunar flybys, which will finally be validated through the ephemerides model.[8]

Artificial Asteroid Capture Missions can potentially allow scientists to make significant progress in many areas relative to planetary defense against near-earth objects:[9]

1. Anchoring. Artificial Asteroid Capture Missions will enable the development of more reliable anchoring capability, which helps spacecraft attach to asteroids better, thus providing more options for the deflection of near-earth objects(NEO).
2. Structural Characterization. Asteroid Capture Missions will help engineers to improve structural characterization capability. One of the most mature NEO deflection technologies is through Kinetic Impact, but its effectiveness is highly unpredictable due to the lack of knowledge on the condition and structure of the NEO. If we can better characterize NEO's surface material and structure, we will be able to use Kinetic Impact to redirect a NEO with greater certainty.
3. Dust Environment. Scientists will gain knowledge on the dust environment of NEOs, and better understand forces that can trigger dust levitation and settling behaviors. This knowledge will help with the design of some NEO redirection approaches, such as Gravity Tractor and Conventional Rocket Engine.

One of the main reasons to capture an asteroid is to gain access to resources on it. A relatively resource-poor LL chondrite asteroid contains 20% iron, as well as a significant quantity of volatiles in the form of water, minerals and oxygen. Although it is possible to bring these resources back to Earth, due to its high cost and the abundance of resources on Earth, the primary goal of asteroid Retrieval in the near future will be for processing and utilization in space immediately after collection.[10] The advantage of obtaining resources from asteroids compared to sending those resources from earth is its relative low cost. Using conventional chemical propulsion, it is estimated by NASA that delivering one kilogram of mass to a high lunar orbit costs $100K. That would mean a $20B cost to deliver 500 tons of material to a high lunar orbit. An Asteroid Capture Mission that delivers the same amount of material to a high lunar orbit, would ideally only cost $2.6B.[9]

Artificial Asteroid Capture Missions can help scientists develop technologies that can be potentially useful for further exploration to other destinations in space:[11]

1. Trajectory and Navigation. From the experience of maneuvering a large mass such as an asteroid, scientists can gain knowledge on how to navigate in the gravity fields of different celestial bodies. Artificial Asteroid Capture Missions can also help perfect capability to deliver large amounts of resources required for further space exploration.
2. Sample Collection and Containment Techniques. Artificial Asteroid Capture Missions will require us to acquire samples from Asteroids. This can help with the development of techniques for sample collection and containment, which will be useful for all types of space exploration missions.
3. Docking Capability. Further explorations into the space will require much more robust docking capabilities to accommodate the utilization of vehicles, habitats and cargo modules. Asteroid Capture Missions will help engineers improve these capabilities.

If scientists can find an efficient way to utilize resources such as water, oxygen and metal collected from captured asteroids, these asteroids also have the potential to become bases for human habitation. The abundant mass of an asteroid can be valuable to a habitat due to its radiation shielding properties. Metals and other materials excavated from the asteroid can be immediately used  for construction of the habitat. If the asteroid is large enough, it could even provide some amount of gravity, which would be preferable for human habitation.[10]

An international panel can oversee all asteroid retrievals and studies on collected materials and provide balanced, fair distribution of retrieved materials. Nations without an expensive space national program can still conduct research.[9]

The goal of NASA Redirect Mission is to send a robotic spacecraft to a large near-earth asteroid and then collect a multi-ton boulder from its surface.[12] The astronauts would take samples of the boulder and bring them back to Earth for further scientific study, and finally they will redirect it into orbit around the moon so that it would not hit the Earth.[13] In addition, the interaction with the asteroids would provide much helpful data regarding the internal structure of the asteroid and therefore solve long-lasting questions about asteroids’ material. This mission integrates robotic and crewed spacecraft operations and, if successful, would demonstrate key capabilities necessary for NASA's journey to Mars.[13] However, White House Space Policy Directive 1 canceled the mission on Dec. 11, 2017 to accommodate increasing development costs.[13] Yet, many major progress in development for this mission, such as solar electric propulsion, detection and characterization of small near-earth asteroids, and the capability to capture large non-cooperative objects in deep space, will continue to be used in the future because they are indispensable to human deep space explorations.[13]

The goal of OSIRIS-REx(Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer) is operated by NASA to obtain a sample of a near-Earth asteroid named Bennu and learn about formation and evolution of the Solar System.[14] Osiris-REx was launched on 8 September 2016 and reached the proximities of Bennu on 3 December 2018.[15] On 20 October 2020, it reached Bennu and successfully collected a sample.[16] Prior to the collection process, the spacecraft descended slowly to minimize thruster firings prior to contact in order to avoid asteroid surface contamination. During the collection process, a burst of nitrogen was released to blow regolith particles smaller than 2 cm into the sampler head. The process took only 5 seconds to avoid potential collision with the asteroid.