May 20, 2024

Are Chemical Rockets or Solar Sails Better to Return Resources from Asteroids?

When responding to these types of theoretical questions, it is necessary to enforce limits on the answers. Billions of asteroids exist in the solar system, so its more reasonable to only look at those known as Near Earth Asteroids (NEAs).
So they broke the area around Earth down into generalized orbital parameters– semi-major axis eccentricity, disposition, and distance. With those three criteria, it is much easier to get a handle on what a general transfer orbit would appear like to a provided asteroid in that region of area, some of which would be rather near Earth on its orbital path..

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If and when we ever get an asteroid mining market off the ground, one of the most important choices to be made in the structure of any asteroid mining mission would be how to get the resources back to where all of our other facilities is– someplace around the Earth. That decision generally will focus on one of 2 propulsion methodologies– chemical rockets, such as those we currently use to get us into space in the first place, or solar sails, which, while slower and not able to get us into orbit, dont need any fuel.

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If and when we ever get an asteroid mining market off the ground, one of the most important choices to be made in the structure of any asteroid mining mission would be how to get the resources back to where all of our other infrastructure is– someplace around the Earth. Billions of asteroids exist in the solar system, so its more realistic to only look at those known as Near Earth Asteroids (NEAs). Other restraints were also necessary– such as determining just the cost and advantage of transferring material back from the asteroid, not the mining of the asteroid itself. Volatiles, such as water, have actually been a focal point of asteroid mining conversations, as they form the basis of rocket fuel that would be needed to explore farther into the solar system and cost a lot of money to bring up from Earth itself. When the earnings surpasses the cost of the mission, the NPV turns positive, which, in this case, indicates whether a mission to an asteroid in that location would be worth it.

To make that decision, the authors utilized a technique called a genetic algorithm to fix an optimization problem. Basically, they provided the algorithm a bunch of parameters, such as the orbital mechanics, masses of the spacecraft, and the amount of volatiles told the algorithm and returned to optimize the critical NPV worth. The algorithms result was really clear– solar sails have positive NPVs for a larger range of areas located in near-Earth area.
Mainly this was because of some weak points in chemical rockets. They had to utilize some of their provided material to get back to GEO. And, while the time for their transfer orbit was much shorter, another factor of the NPV, the discount rate, which decreases the amount of expected value of a resource the farther in the future it is offered, doesnt take enough out of the worth of that which the solar sail can bring back that would make it on par with the chemical rocket.
There were still some locations of near-Earth space that even solar sails were not profitable in, so the authors suggest that future asteroid miners look at asteroids in the specific regions they call out as potentially profitable if they are trying to find their first major mining site. In addition, the scientists made some modifications to their original standard objectives structure, such as stopping at a Lunar Gateway, including a 2nd trip, and running a series of variable simulations, called Monte Carlo simulations, that would test the level to which these different plans paid.

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Other restrictions were also necessary– such as determining only the expense and advantage of transferring product back from the asteroid, not the mining of the asteroid itself. Getting the mining devices there and set up was considered beyond the scope of this paper. There needed to be a wait time at the asteroid itself so the return objective might have time to equip up on the material it would be bring.
That material, in this calculation, was volatiles. Volatiles, such as water, have been a centerpiece of asteroid mining conversations, as they form the basis of rocket fuel that would be required to check out farther into the planetary system and cost a lot of money to raise from Earth itself. Furthermore, chemical rockets can then utilize some of those volatiles as their own fuel to make their method back to the Earth system.
A couple of more constraints formed, consisting of sending out the volatiles back to geostationary orbit (GEO), some assumptions about launch costs based on the forecasted costs of Starship, and identifying that necessary metric of financial studies– the net present value (NPV). NPV is the outcome that the options would be judged on and based upon various calculated elements. These would include a range of expenses, such as launch cost, development cost, producing cost, and functional expense. The income would be calculated based on the anticipated value of the volatiles provided to orbit. When the profits exceeds the cost of the mission, the NPV turns positive, which, in this case, suggests whether a mission to an asteroid because area would be worth it.

The volatiles returned from the asteroid would be utilized for orbital refueling, as described in this UT video.
Overall, while there are possibly rewarding targets for each type of propulsion system, it appears that solar sails are clearly the winner between the 2. Now its up to those who hope to build the very first asteroid mining empire to listen.
Learn More: Vergaaij et al.– Economic Assessment of High-Thrust and Solar-Sail Propulsion for Near-Earth Asteroid MiningUT– What Is A Solar Sail?UT– How do you Keep a Solar Sail Stable?UT– A brand-new Kind of Solar Sail Could let us Explore Difficult Places to Reach in the Solar System.
Lead Image: Artists depiction of an asteroid field.Credit: NASA/ JPL/ Caltech.
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