Researchers are preparing for missions to capture asteroids and bring them closer to the earth, where they could one day be mined and even provide a source of fuel for interplanetary spacecraft.
Sending a spacecraft up to an asteroid, grabbing hold of it and bringing it back to the earth’s vicinity, may sound far-fetched, but demonstration missions to small asteroids could take place within a decade, according to Dr Joan Pau Sánchez Cuartielles, at the Polytechnic University of Catalonia in Spain.
His Marie Curie-funded ASTEROIDRETRIEVAL project is calculating the trajectories that will lead an asteroid in the direction of earth’s orbit. ‘By changing a tiny bit the velocity of the asteroid, you could put the asteroid on a trajectory that will be eventually naturally captured by the gravity of the earth,’ he said. If it’s no longer of use, the asteroid could then be nudged back away from earth.
Dr Sánchez Cuartielles is modelling the combined gravitational effects of the earth, sun and moon, and incorporating this into the design of the complex engineering systems needed to capture an asteroid in space.
The most straightforward and cheapest asteroids to fetch are those that require only a slight change in their velocity – for now only small rocks, which pose no risk to the ground below as they would burn up entirely on contact with earth’s atmosphere. The aim of testing the technology is to ensure that if missions are one day scaled up to larger rocks, they would not present any risk.
‘By changing a tiny bit the velocity of the asteroid, you could put the asteroid on a trajectory that will be eventually naturally captured by the gravity of the earth.’
Dr Joan Pau Sánchez Cuartielles, Polytechnic University of Catalonia, Spain
So far, the project has identified 15 suitable targets, from an initial survey of 12 000 known objects, that could be retrieved with current space propulsion technology. Dr Sánchez Cuartielles hopes that when the project ends in May 2015, his research will be combined with technology to make contact with the asteroid as part of a future mission.
The ASTEROIDRETRIEVAL project is a continuation of research he began with Dr Daniel García Yárnoz on the EU-funded VISIONSPACE project at the University of Strathclyde, UK, which finished in 2014. While investigating asteroid manipulation, the pair started to explore the concept of asteroid capture. When they came to publish results in 2012, it turned out the US-based Keck Institute for Space Studies was also publishing research in the same area.
Shortly after, NASA announced plans for its Asteroid Redirect Mission, a test mission to an asteroid by the mid 2020s. The mission is looking to bring back rocky samples for scientific analysis, help develop new techniques to ward off more threatening asteroids, and prepare for an eventual Mars mission.
A key difference is that NASA will focus on trajectories for orbit around the moon, whereas ASTEROIDRETRIEVAL is working on an earth-based orbit. However, the method developed by ASTEROIDRETRIEVAL could also be applied to lunar orbit by splitting the asteroid’s journey into two steps.
According to Dr Sánchez Cuartielles, test missions like this may also help in the development of technology for capturing bigger rocks, or for the in-situ extraction of resources – from metals for use in industry, to water for fuel. A vehicle could travel to an asteroid and either return to earth with its payload, or refuel and continue out into space.
Asteroids could be a source of platinum group metals, which are rare on earth, making them one of the most sought-after materials to transport back down. Two companies have already been set up in the US for asteroid mining and are helping to fund technology development. The challenge is to find ways of separating the precious metals or water from the rest that is largely waste material, explained Dr García Yárnoz.
Some asteroids may contain as much as 40 % substances that vaporise easily, such as water and methane, and other liquids and gases. The idea is that this water could potentially be extracted in-situ and then split into hydrogen and oxygen using solar energy. The hydrogen could then be turned into fuel for the docked spacecraft. Another idea would be to use water to make radiation shielding to protect astronauts from harmful cosmic rays.
One advantage of enabling a spacecraft to fill up on its route is that it could significantly reduce the costs of space discovery, even space tourism. ‘Asteroid and comet propellant could reduce the cost of exploration missions almost by half, since you could potentially launch your space vehicle without propellant and save a lot of weight and money at launch,’ Dr Sánchez Cuartielles said.
While technology to enable this is only at an early stage, Dr Sánchez Cuartielles is cautiously optimistic and believes it will be feasible in future, potentially within decades. ‘You could be optimistic and say less than a few decades, but obviously it depends a lot on the budgets and the technologies that should come along on the path towards these technologies,’ he said.
NASA is planning a demonstration mission to an asteroid by the mid-2020s. The aim of the Asteroid Redirect Mission is to travel up to an asteroid, grab hold of it, and bring it into lunar orbit. NASA is yet to select one of two approaches for grabbing onto the asteroid and plans to make a decision in early 2015. One is to use a bag-like inflatable system to wrap a small asteroid inside and transport with spacecraft propulsion; the second, more expensive approach, is to use a robotic lander to break a chunk off a larger rock, and bring back the sample.
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