However, profitable mining entails balancing more than just the cost of travelling across a distance, and any asteroid mining operation must take into account the expense of the rendezvous—slowing the spacecraft down once it arrives—as well as the cost of shipping the ore back to a processing facility.
The cost (and weight) of the fuel needed to rendezvous is among the most critical parameters in the feasibility calculation. It is mainly determined by the parameter “delta-V,” a measure of the kinematic requirement of accomplishing a spacecraft maneuver, and is usually cited in units of kilometres per second. A rendezvous with an especially favourable NEO from a spacecraft in low-earth orbit involves a delta-V of about four kilometres per second.
But accessing asteroids in the Main Belt typically involves a delta-V of about seven kilometres per second, which leaves them energetically very difficult to reach from the earth.
Phobos, however, orbits about six thousand kilometres from Mars’s surface and offers a lower delta-V to the Main Belt asteroids.
According to Elvis, McDowell and Taylor, Mars itself offers some added orbital advantages because unlike the earth, with a nearly circular orbit, Mars’s orbital eccentricity and inclination also provide a lower delta-V path to the asteroids.
The authors, thus, suggest two-burn and three-burn scenarios (referring to the number of rocket ignitions needed) to accomplish a rendezvous, and they develop a computer code to calculate the energetics for known asteroid orbital classes. The results show potentially very significant reductions in the costs of exploration.
Whether or not a mission ultimately makes financial sense depends on many other factors, but, in the researchers’ view, the concept of launching and then returning to an operations center based in a Phobos-like orbit, or even on Phobos itself, is relatively convenient and advantageous.
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