![]() ![]() The second consideration is the size of the asteroid. When selecting an asteroid for a potential capture, the most important consideration is simply the proximity of an asteroid’s orbit to a useful keyhole through which the orbital engineers can design a capture mission in a reasonable timeframe. The people who dreamed up the Cassini and Messenger missions are both geniuses and artists, and I have every confidence that they can find suitable mission plans to capture any potentially hazardous asteroid into Earth orbit, although the missions may be very long and complex thanks to a shortage of appropriate close encounters and/or the need for significant changes to the asteroid’s orbital parameters. The Moon can (in principle) remove up to 2 km/s of velocity relative to the Earth, although less is easier.Ī point I’d like to emphasize: In my opinion, gravitational slingshots are as much art as engineering, especially when considering the variations involved in multiple slingshots around one or more bodies. If we can adjust the asteroid’s orbit such that it makes a subsequent close approach to the Moon with a relatively low velocity, the resulting slingshot can drop that asteroid into an Earth orbit. ![]() We aren’t limited to the Earth, in that close encounters to other planets might be used to alter an asteroid such that it passes close to the Earth at a later time where its orbit can be further tuned by the Earth’ gravitational field. More importantly, small changes in the position or timing of an existing close approach are enormously magnified. In principle, the Earth can impart a delta-V of up to 60km/s to an asteroid in orbit around the Sun, although in practice the limits are a small fraction of this. When a spaceship or asteroid passes close to a planet or large moon, its orbit is changed, sometimes dramatically. So, how do we capture an asteroid? Even a tiny one masses millions of tons, and we don’t yet have the technologies to manhandle them and put them wherever we want. Of course, a space habitat providing food, water, oxygen, fuel, construction supplies, gravity, radiation shielding, and skilled human workers situated above much of the Earth’s gravity well is an ideal platform from which to continue the exploration and exploitation of space.Īnd we should not forget that placing an asteroid into a stable Earth orbit prevents it from colliding with the Earth. The oxygen freed from iron compounds during smelting amounts to well over a million tons more than is needed for the habitats, valuable fuel mass for ion thrusters to move the habitats and solar power satellites into their chosen orbits and to spin them up. The asteroid Apophis (likely one of those LL chondrites) contains enough materials to construct about 150 five-gigawatt solar power satellites at 25,000 tons of steel and silicon each, plus Kalpana One style habitats for 100,000 people, all shielded by the slag remaining after iron is smelted out of asteroid ore. Even a relatively resource-poor low-iron, low-metal LL chondrite contains 20% iron, significant quantities of water and other volatiles in the form of minerals such as clays, and oxygen to burn. So why capture an asteroid? The main reason is to gain convenient access to its resources. Using the asteroid 99942 Apophis, I outline a possible capture mission, its requirements, and a timeline. The focus of this presentation is on a specific technical approach which enables us to capture an asteroid using essentially current technologies the missions, tools, and complications of that approach and then some asteroid selection criteria and a few specific asteroid capture opportunities. See also Retrieval of Asteroidal Materials in Space Resources and Space Settlements, NASA SP-438, 1977. Updates will be posted here as available. Alternative mission profiles are being explored that should work with an applied delta-V of around 1 m/s, although the mission duration and cost will increase. Re-analysis using better tools and more recent data indicates that 95 cm/s of delta-V is needed instead of 10 cm/s, and that in 2030 Apophis approaches the Moon with too great a velocity for orbital capture in a single pass. NOTE: The orbital slingshot model used for the Apophis capture example below had a significant flaw. International Space Development Conference, May 2011
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