Ideas for capturing an asteroid and towing it with a spacecraft for parking it within lunar orbit was floated several years ago and received initial seed funding from the National Aeronautics and Space Administration (NASA) of the United States. Technical challenging and hugely expensive, the mission is conceived as a stepping stone for enabling humans to gain the necessary experience in developing the technologies for facilitating long duration space flight beyond the lunar orbit.
Briefly, the mission entails the capture, by a spacecraft, of an asteroid beyond the lunar orbit and towing it for orbital entry around the Moon. Not without risk given the challenge of chasing a fast moving asteroid and altering its orbital trajectory, the mission is designed with a focus on developing several key technologies for expanding human capabilities in space. Specifically, a large payload rocket system with sufficient thrust and lift capability is needed. A candidate launch vehicle for the space mission is Space Launch System (SLS), a large lift and payload rocket system designed to enable humans to go into deep space such as Mars.
After launch, reliable tracking and navigation is requisite for the spacecraft to gain the necessary speed to reach the target asteroid, enter orbit around it and capture it. One common method for accelerating a spacecraft is to sling shot it using the Earth’s gravitational field. While technically difficult, the navigation methodology needed to reach an asteroid has been validated before in NASA’s Dawn mission to Ceres and Vesta as well as European Space Agency’s (ESA) Rosetta mission to Comet 67P. What is not done before in space exploration is the capture of an asteroid with a high speed spacecraft. Several proposals and ideas have been put forward to this end, and the mission is still at the design and conceptualization stage before Donald Trump’s administration cancelled the asteroid redirect mission.
Although likely to be terminated, there is still value in discussing the asteroid redirect mission given its scale and potential scientific possibilities, both in delivering breakthrough technologies that could propel future human endeavors in space as well as allowing hitherto unknown mysteries of asteroid geology and, by extension, origins of the Solar System to be uncovered.
Past the capture phase, the towing of the asteroid to lunar orbit represents a key hurdle to mission success. Outrageous in conceptualization, the idea of towing an asteroid to lunar orbit for future repeated examination and landing by humans within the lunar orbit deserves closer scrutiny and debate. Specifically, the advantages are evident for having an asteroid available for geological examination and collection of large amount of samples for more detailed analysis on Earth in a sample return mission. Additionally, landing a human on an asteroid and providing him with the necessary equipment for surviving and manoeuvring in a low gravity environment will provide the required preparation, in technology, for future human spaceflight to Mars. While conceptually interesting and practically not insurmountable, the cost entailed in towing an asteroid into lunar orbit must be fully factored in and weighted against the scientific possibilities it engendered given its availability as a new satellite of the Moon for future repeat visit missions.
Focusing on the scientific possibilities, lack of samples is always a limitation in astrophysical and astrogeology research; thus, with an easily accessible asteroid in lunar orbit, humans may be able to finally open a sizeable window into early Solar System development and evolution through a lens of an appropriately chosen asteroid. The key to unlocking the mystery of Solar System history and development lies in selecting the appropriate asteroid for analysis. For example, a dark chondrite asteroid may harbour a thin layer of organic material useful for understanding how cosmic radiation influence the formation of small organic molecules over eons. Alternatively, metallic asteroids portend significant mining potential, but their density and weight precludes their movement into lunar orbit without the aid of spacecraft of large thrust. In addition, metallic asteroids offer a glimpse of the formation of the Solar System different from the most pertinent question asked by planetary scientists and astrophysicists of the contemporary era. Specifically, unlocking the secrets of the formation of rocky planets is the overriding question guiding our new understanding of how asteroids coalesce to form planets.
But, are there dangers of towing an asteroid to lunar orbit? Yes, given the relative small size of the asteroid and the significant gravitational tug between Earth and Moon, possibilities exist that orbital perturbation could disturb the parked asteroid sufficiently to dislodge it into an Earth bound trajectory. An asteroid of 1 km across could cause significant, and maybe, catastrophic impact on Earth. Hence, there are inherent dangers of a space mission initially conceived to provide humans with multiple benefits with regards to expanding human capabilities in space, and elucidating deeper truths about Solar System development and evolution as well as asteroid geology.
Overall, the Asteroid redirect mission of NASA has been cancelled with the realigned space mission priorities of the Trump’s administration. A scientific bounty at first glance with additional benefits in providing the impetus towards developing the necessary capabilities for human long duration space flights, the mission is nevertheless confounded by critical dangers associated with possible orbital perturbation leading to the dislodgement of the parked asteroid in lunar orbit towards Earth. While downplayed, the probability of a parked asteroid becoming Earth bound is something that mission planners must not discount in assessing the risk profile of the mission. The necessary question to ask remains: do we need to have an asteroid parked in lunar orbit for providing easy access to asteroid rock samples for analysis? The answer is no given that other sample return missions have been conceptualized and is at the active phase of achieving a sizeable sample return from near Earth asteroids in the asteroid belt between Mars and Jupiter. Specifically, Japanese spacecraft has succeeded in returning grain level samples from an asteroid. Hence, in contrast to towing an asteroid for orbital insertion into lunar orbit, developing a couple of smaller spacecrafts for latching on fast moving asteroids and grabbing a sample may be more viable, both from the perspective of gleaning an understanding of the geological history of a wider diversity of asteroids as well as safety of the Earth-Moon neighbourhood, where humans should not insert another astronomical object of size capable of destroying the human race on impact with Earth.
Category: space exploration,
Tags: asteroid redirect, geological history, chemical analysis, lunar orbit, long duration human space flight, chemical composition,
Acknowledgement: Ng Wenfa thank Seah Kwi Shan for co-authoring this blog post.