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Van Kane

Bringing an Asteroid Home

Posted by Van Kane

2013/04/03 01:08 CDT

Topics: Future Mission Concepts

Aviation Week and Space Technology reports that the President’s next budget request for NASA will include funds to begin developing a mission to bring an asteroid to the Earth-moon system. The initial goal will be to provide a destination for a manned mission to an asteroid, but if the idea works, it could kick start asteroid mining.

Conceptual design for an asteroid capture and retrieval spacecraft

Rick Sternbach/Keck Institute for Space Studies

Conceptual design for an asteroid capture and retrieval spacecraft

The insight behind the mission is that it’s technically easier and cheaper to bring a small asteroid to where it can easily be reached by a manned mission than it is to send astronauts to an asteroid. This may seem counter-intuitive. The feasibility study that proposed the idea defined a small asteroid as around 7 meters in diameter with a mass of 250,000 to 1,000,000 kg. The robotic spacecraft will have to travel to the asteroid, match its spin, net it, de-spin it, and then drag it back to the Earth-moon system. However, robotic spacecraft and asteroids don’t require complex life support systems and near fail safe engineering systems. If the robotic mission fails, it’s a shame. If a human mission fails with the loss of the astronauts, it’s a catastrophe.

This concept was originally proposed last year in a study carried out by the Keck Institute for Space Studies at the California Institute for Technology (which is also home to the Jet Propulsion Laboratory). The study participants included scientists and engineers from a wide range of institutions. You can read the report here.

The mission would be enabled by three key developments. First, we need the technology to be able to find a number of very small asteroids so that one can be selected with the optimum trajectory, size, and spin. (An asteroid spinning too fast would exceed a spacecraft’s capacity to de-spin it.) The desired C-type of asteroids would be dark and spotting them is considered by at least one of the authors of the feasibility study as the toughest part of the concept. The size of the target asteroid was selected as the smallest that was believed to be detectable in large enough numbers to find a good candidate.

Second, high powered solar electric engines would be needed to be able to transport the asteroid back to the Earth-moon system. The spacecraft will need to simultaneously operate four 10-kW engines to enable the mission. For comparison, the total power system for the Dawn spacecraft, which also uses ion propulsion, is 10-kW. Bringing the asteroid to the vicinity of the moon puts it near the top of the Earth-moon system’s gravity well and greatly diminishes the propulsion requirements for the mission compared to bringing the asteroid to lower Earth orbit. A near lunar destination also minimizes the risk of impact with the Earth (it’s impolite, to say the least, to drop a small asteroid in someone’s back yard, although a C-type asteroid would likely disintegrate before reaching the Earth’s surface).

The final key development will be the launch system and spacecraft needed to deliver astronauts to the asteroid. NASA already is working on these – the Space Launch System and Orion spacecraft. What it has lacked has been a credible use for the system. Flights to near Earth asteroids require months or years to a destination that lacks drama, lunar missions require landers that aren’t funded, and Mars is a distant dream. What the proposers of this scheme – and now NASA, apparently – believe is that a relatively short flight to an asteroid brought to our backyard would be a winning combination.

Once an asteroid is returned, what would the astronauts do? The proposers suggest that early missions would be focused on scientific examination, testing operations near and on a tiny body, and validation of methods that eventually could lead to mining and processing the asteroid’s material. C-type asteroids are rich in volatiles and conveniently have the consistency of dried mud, simplifying mining. A 7 m carbonaceous asteroid is estimated to contain 100 tons of water, a similar amount of carbon-rich compounds, and 90 tons of metals (mostly iron). A key problem with enabling human exploration beyond the moon is the cost of delivering fuel and water beyond low Earth orbit. One or more small asteroids could become fueling stations for missions two or three decades from now.

The cost to deliver the asteroid to the vicinity of the moon was estimated at $2.65 billion, or somewhat more than the cost of the Curiosity Mars rover mission. The human spaceflight system is being paid for separately. The proposers do not give a cost estimate for developing and operating the mining equipment. For the coming year, NASA reportedly will ask to $100M to refine the technical requirements of the asteroid capture spacecraft and operations. A launch to an asteroid presumably would not occur until the end of this decade or early in the next.

Editorial thoughts: As a scientific mission, I don’t know how the science community would rank an asteroid retrieval. For the same price as the $2.65B cost estimate, NASA could fly a Europa mission, conduct sample returns from several types of asteroids, cover much of the cost of a Mars sample return, or fly an orbiter and probe to Uranus. (In reading the proposer’s report, it appears that the technical analysis of the mission is in the early stages. I would not be surprised to see the final cost of the mission be substantially more than the current estimate.)

However, if humanity is to move into deep space, then this mission, I believe, could be a brilliant interim step. It would provide a target for sustained operation at the cusp of deep space, much as the early Gemini missions tested the technology and operations that led to the success of the Apollo mission. The asteroids brought back could also provide the raw materials needed to enable missions deeper into the solar system. (Bringing back other types of asteroids could also provide more valuable metals that might be mined for return to Earth.)

At the moment, political leaders have not been willing to fund bold initiatives for human spaceflight. Perhaps the greatest value of this mission would be that it would enable forward momentum so that future politicians can make the bold choice.

 

Or read more blog entries about: Future Mission Concepts

Comments:

Andrew Planet: 04/03/2013 05:49 CDT

If it makes more economic sense to be selective on what asteroid is brought back then certainly send probes first to sample what individual asteroids are made out of. If the raw materials extractable from asteroids pays for the expeditions to them as much as possible to whatever extent, that reduces the costs of an exploration that is bound to take place some time anyway. I wonder if sample extraction or localised compositional analysis of several asteroids could be effected in the one trip? Could we build and send a sort of asteroid rover that makes use of the relatively low energy requirements needed to escape the gravitational attraction of small asteroids by jumping to another in a calculated directional fashion? I wonder if a lot of the energy required to jump from a small low gravity asteroid could be mechanically obtained by solar panels powering some type of spring loaded ratchet wheel lock mechanism? By releasing the lock in the general direction desired alterations in course could be fined tuned using minimal rocket fuel as it targeted another asteroid to land on.

Ethan Walker: 04/04/2013 12:51 CDT

Andrew, what you describe is essentially the Minerva lander http://en.wikipedia.org/wiki/Hayabusa#MINERVA_mini-lander . While this sort of mission could provide useful experience for asteroid mining, it also moves away from one of the original functions of a manned asteroid mission, which was actually to provide experience for sending manned missions well beyond lunar orbit.

Grant Dexter: 04/04/2013 01:06 CDT

Asteroid mining will prove unprofitable.

Paul McCarthy: 04/04/2013 02:47 CDT

Unfortunately, a wasteful idea. But not nearly as wasteful as the Space Launch System and Orion. Any experience of mining, or even excavation, shows that it's extremely complex, messy, variable and unobliging. Reliably (as opposed to theoretically) extracting and processing viable quantities of proto-fuels etc will be completely economically impractical (viz the huge effort to drill 5cm X 2cm on Mars!). Ditto in spades for even the most precious metals. This will be true until it could be reliably and self-maintainingly done on an industrial scale some significant fraction of that of a mine and processing plant on earth; say 1/100th? The stepping stones to that are vast! It is devastatingly tragic that the US, by far the most visionary and ambitious player, is sidetracked from, and costed out of, the monumental yet eminently practical and affordable discoveries now just beyond our fingertips (are those coloured organics lying all over the surface of Europa, just waiting for a lander to analyse? what's in the plumes of Enceladus? etc,etc) by the pipe-dreams, showmanship and astronomical costs of human deep-space flight. The latter is all clearly just a waste of time. Opportunity and Curiosity have established once-and-for-all the way to do it. I know about the "inspiration", the "dream", etc, etc. But sadly it's all just showmanship, hokum and waste of money. The US is basically bankrupt (look at the deficit and debt forecasts). So the truth is: a big chunk of every dollar spent lifting a Jock into orbit is money not spent on answering the greatest questions ever asked - in our own lifetimes. I see it as part of an American tradition: a divide between the Baar-shootin' frontiersmen (Davy Crockett, Daniel Boone) and your inspirational, incomparable, scientist/philosopher/free-thinkers (Benjamin Franklin, Thomas Jefferson etc)

Andrew Planet: 04/04/2013 05:44 CDT

Thanks Ethan. I was thinking about something considerably larger than Minerva. If the Minerva Lander had had fuel from which to automatically realign its trajectory as it travelled to the asteroid it would not have missed its target. Also, my intent for a multi asteroid sampling mission would be for the vehicle to hop from asteroid to asteroid not to hop around an asteroid itself. I'd use a vehicle with arthropod like pincer legs so as to grasp the terrain and to avoid the inadequacies of locomotion in a low gravity situation. I'd then use the mechanically spring loaded legs, say if there were few of them, to accurately gauge its position relative to each other from which to jump of to another asteroid. @ Paul. I too could not escape what must be the difficulties involved in mining an asteroid in very low gravity situations. You'd have to be pretty well dug into an asteroid to do any material extraction and have to figure out how to traverse an asteroid from the inside the same way an earthworm does underground, processing the material sourced as it travelled. For the time being, using my great lack of knowledge based on purely imaginary notions, I could only figure out a round about way from which to mine asteroids after capturing them. I'd send them plummeting to some predetermined area of the moon well outside any future inhabited zone. Even though gravity is lower on the Moon than on Earth its still easier to manipulate objects relative to the gravitational pull of the larger object you are standing on. Crashing asteroids into the moon might even break them apart into smaller pieces therefore less work having to be used to technologically do that. I don't know how much material could be lost by rebound if indeed an asteroid were slammed into the Moon. Maybe that could be minimised by crashing it at a certain angle into a slope?

Paul McCarthy: 04/06/2013 12:15 CDT

What's needed is for someone to say to Mr Obama face-to-face (and then his successors): "Mr President, someday, once you leave this job and you're wondering what it's all about, you're really, really, REALLY gonna wonder, like so many others: is there any other life out there? And you're really, really, REALLY gonna wish you'd authorised, when you had it in your power, what's basically a minute amount of money, in the budget context, to find out in your lifetime, by checking Europa, Enceladus and the other most likely places in our solar system!" If it's not started very soon, t'aint gonna happen in his lifetime.

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