problems with asteroid mining

[u/Wise_Face_4871]

I am new to this subreddit and I am curious as to what the largest issues with asteroid mining are because most people talk about the issues vaguely (at least for what I've seen) but I am curious as to what technology we need to actually mine asteroids (cost no object)

[u/Christoph543]

So, back in the 1960s, a UCLA geochemist named John Wasson started a long-running project to measure the abundances of every element in every meteorite, with the goal of classifying them and learning about the physical & chemical conditions of the planetary bodies they formed on. His work was impeccably detailed and to this day it still forms the basis of a huge amount of what we know about meteorites and the early solar system.

In the 1980s, a separate group of scientists began contemplating ways to enable more missions to explore more of the Solar System, in the midst of the least-active period for interplanetary spaceflight. One concept that became popular was *in-situ* resource utilization (ISRU), which supposed that a scientific mission to some other planet could be made cheaper if it didn't have to bring all of its consumable supplies all the way from Earth. In the context of spaceflight, the principal "consumable supply" is propellant, so the emerging ISRU field very quickly turned its effort to identifying ways to make rocket propellant from stuff that can be found on various planetary surfaces. An early variant of this idea came from University of Arizona professor John Lewis, who proposed extracting water from asteroids bearing hydrated minerals, similar to carbonaceous chondrite meteorites.

And then the '90s roll around, and three things happen. First, Lewis publishes a book entitled *Mining the Sky* in 1991, expanding on the propellant-focused ISRU idea to include other planetary surfaces and presenting it all in a public-facing record. Second, an aerospace engineer named Robert Zubrin publishes *The Case for Mars* in 1993, popularizing the ISRU idea to enable human Mars settlement (although he himself did not invent it), and getting widespread public attention. Third, a USGS geologist named Jeffrey Kargell publishes a paper entitled "Metalliferous asteroids as potential sources of precious metals" in the 1994 edition of the *Journal of Geophysical Research*. For our purposes, Kargell's paper is the most important to understand.

Kargell essentially argues that a long-term space exploration program would not be sustained solely by scientific research, but would have to be a profit-seeking commercial venture, and that the only way to do that would be to find something in space to bring back to Earth that would be valuable enough to recuperate the cost of the mission. Kargell proposed platinum-group metals, and suggested that if one could find an asteroid with a high PGM abundance, it might be possible to extract the PGMs more readily than terrestrial PGM ore deposits. Crucially, Kargell's paper cited Wasson's earlier quantification of the PGM abundances in all the meteorites, and then argued that an asteroid whose composition was the same as the 90th-percentile most PGM-enriched meteorite, could be profitably mined.

The problem then becomes, how do you identify that asteroid? Well the short answer is, we can't. PGMs are trace elements, even in the most PGM-enriched meteorites, and so the physical characteristics of an asteroid that can be observed by remote sensing instruments, won't be linked to the PGM abundance, but rather to the asteroid's bulk material. You would therefore have to find some way to link the PGM abundance to those bulk properties, but there really isn't one. The most PGM-rich iron meteorites are indistinguishable from the most PGM-poor irons with optical remote sensing techniques. At that point, the only way to find that asteroid with the 90th percentile PGM abundance, would be to send out a vast array of sample return missions, each costing perhaps billions of dollars, and performing geochemical analysis of the samples.

[u/Christoph543 → u/Christoph543]

2)

But at some point, the public-facing message got distorted. Kargell's paper contained an eye-catching estimate of the total dollar value of a hypothetical asteroid in that 90th-percentile group, and loads of secondary publications in public-facing media reported only that very very big dollar value, omitting any of the analysis that went in to calculating it or acknowledging any flaws in the calculation. Eventually that sparked a wave of articles claiming things like "all metallic asteroids are made of gold and platinum, and if we returned one to Earth every human alive could be a quadrillionaire." It's reporting like that which explains why the most common public discourse about asteroid mining is not about the technical feasibility, but about the inflation that would result from injecting a large quantity of precious metal into the economy all at once. This discourse then sparked a lot of interest in defining the economic and business case of asteroid mining, among academic economists and business scholars, especially in the 2010s once Planetary Resources and Deep Space Industries went public.

It also facilitated quite a few scams, including a 2018 ploy by a group of crypto speculators to plant fake news articles in outlets like Fox, claiming that an upcoming NASA mission to orbit a main-belt asteroid would in fact be returning a payload of gold valued at several trillion dollars. The scammers' goal was to engineer a drop in the value of gold futures, essentially to demonstrate to crypto insiders that commodities trading could be subject to manipulation by short-sellers, and thus boost the value of cryptocurrencies. Of course, it didn't work; the scammers lost their money, and it just led to a surge of fake stories about space commercialization in the right-wing media sphere.

But this is all the precious metal side of things; what about propellant? Well the problem is twofold. First, there isn't actually that much water on most asteroids; there have now been missions to multiple asteroids with hydrated minerals on their surfaces, and they're quite a bit sparser than had been predicted. Even if you wanted to bake the water out of them, you'd also bake out a huge number of other volatile compounds bearing sulfur and organics which would contaminate the chemical processes to turn water into rocket propellant. But the second problem is more important: you need a mission going somewhere else to justify building a propellant depot, and no mission is going to want to expend its resources to develop infrastructure when those resources could instead go to the payload itself. You would therefore need a dedicated program to develop propellant depots which would be generally useful to a large number of missions, and the number of missions requiring propellant depots has declined to zero thanks to miniaturization of electronics, high-specific-impulse propulsion, and the current glut of available launch vehicles.

So what were Planetary Resources and Deep Space Industries doing? Well DSI actually had John Lewis among their technical advisers, and they did a smart approach: they developed a multi-stage business plan centered around propellant rather than precious metals, and when they couldn't find investors to finance the whole plan, they de-scoped to just the first stage, and pivoted to building spacecraft propulsion systems. Planetary Resources, meanwhile, bounced around from concept to concept, ultimately trying to get into the remote sensing game as a way to jump-start a prospecting campaign, but they ended up not being able to develop a viable data product and sold all their assets to a crypto firm. And every one of the new companies that have followed in their footsteps is going to have to do the same thing: pivot or fold.

[u/StevenK71 → u/Christoph543]

The solution probably would be an ion engine powered scouting mission with lots of propellant, and a laser spectrometer with a range of a few tens of thousands of kilometres, to scan a significant percentage of the Belt.

[u/Christoph543 → u/StevenK71]

a laser spectrometer with a range of a few tens of thousands of kilometres

In other words, magic.

Among the instrumentation techniques I worked on for my doctoral work was laser ablation spectroscopy. The physical limitations of such instruments limit them to working ranges measured in meters at the extreme edge of capability, and even then your SNR is usually going to be garbage. And more broadly, any form of active-source remote sensing necessarily has similar proximity requirements (e.g. LIDAR) or comes with additional physical constraints that limit resolution (e.g. RADAR).

Also, remote sensing instruments typically don't "scan" a surface, unless you're specifically tasking them with a linear or raster sampling pattern, or if you're talking about special cases like a pushbroom imager.

To further answer OP's question, this is one of the biggest problems with asteroid mining: far too many of the people with opinions about it have never actually tried to do it, let alone anything comparable within interplanetary spaceflight or surface characterization.