If we ever get an asteroid mining industry off the ground, one of the most important decisions to make in the structure of any asteroid mining mission would be how to put the resources back where all our infrastructure is, somewhere the earth. That decision will typically center on one of two propulsion methodologies: chemical rockets, like the ones we already use to get us into space in the first place, or solar sails, which, while slower and can’t put us in orbit, they don’t. require any type of fuel. So which propulsion methodology is best for these future missions? A study by researchers at the University of Glasgow analyzed these two scenarios and gave a clear answer: solar sails.
When answering these types of theoretical questions, it is essential to impose limits on the answers. For example, there are billions of asteroids in the solar system, so it is more realistic to look only at those known as near-Earth asteroids (NEAs). But even so, there are over 30,000 known NEAs. It would have been impossible for lead author Merel Vergaaij, then a Ph.D. University student, and their colleagues to calculate optimized trajectories for each of them.
So they divided the area around the Earth into generalized orbital parameters: distance from the semi-major axis, eccentricity and inclination. With these three parameters, it is easier to know what a general transfer orbit would look like to a given asteroid in this region of space, some of which would be quite close to Earth on its orbital path.
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Other limitations were also necessary, such as calculating only the cost and benefit of the transfer of material from the asteroid, not the extraction of the asteroid itself. Getting the mining equipment there and installing it was considered beyond the scope of this document. In addition, there had to be a waiting time on the asteroid itself so that the return mission could have time to stock up on the material it would carry.
This material, in this calculation, was volatile. Volatiles, such as water, have been a focal point of discussions about asteroid mining, as they form the basis of the rocket fuel that would be needed to explore beyond the solar system and cost a lot of money to extract from the Earth itself. Additionally, chemical rockets can use some of these volatiles as their own fuel to return to the Earth system.
A few more constraints were set, including sending the volatiles into Geostationary Orbit (GEO), making some assumptions about launch costs based on projected Starship costs, and determining that all-important economic metric : the net present value (NPV). ). The NPV is the result by which the solutions would be judged and it would be based on various calculated factors. These would include a variety of costs such as launch cost, development cost, manufacturing cost and operating cost. Revenue would be calculated based on the expected value of the volatiles delivered into orbit. When the revenue exceeds the cost of the mission, the NPV becomes positive, which in this case indicates whether a mission to an asteroid in that area would be worthwhile.
To make this determination, the authors used a technique called a genetic algorithm to solve an optimization problem. Essentially, they gave the algorithm a bunch of parameters, such as orbital mechanics, spacecraft masses, and the amount of volatiles returned and told the algorithm to optimize the all-important NPV value. The result of the algorithm was very clear: solar sails have positive NPVs for a wider variety of areas located in near-Earth space.
This was mainly due to some weaknesses in chemical rockets. They had to use some of the delivered material to get back to GEO. And while the time for its transfer orbit was shorter, another factor in NPV, the discount rate, which reduces the amount of expected value of a resource the further into the future it is sold, did not take enough of the value. of what the solar sail can return that would do it at the height of the chemical rocket.
There were still some areas of near-Earth space where even solar sails weren’t profitable, so the authors suggest future asteroid miners look at asteroids in specific regions they say are potentially profitable if they are looking for their first major mining site. . In addition, the researchers made some modifications to the structure of their original baseline missions, including stopping at a lunar gateway, adding a second trip, and running a series of variable simulations, known as Monte simulations Carlo, which would test the extent to which these different schemes were profitable.
Volatiles returned from the asteroid would be used for orbital refueling, as described in this UT video.
Both adding a second trip and stopping at Lunar Gateway instead of GEO added significant value to each type of mission architecture. Monte Carlo simulations also showed that their profitability was consistent with slight input costs and output revenue variations. Overall, while there are potentially profitable targets for each type of propulsion system, solar sails seem to be the clear winner between the two. Now it’s their turn to listen to those hoping to build the first asteroid mining empire.
More information: Vergaaij et al. – Economic evaluation of high thrust and solar sail propulsion for near-Earth asteroid miningUT – What is a solar sail? UT – How does a solar sail stay stable? to reach the Solar System
Main image: An artist’s rendering of an asteroid field. Credits: NASA/JPL/Caltech
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