Near-Earth Resources: Short-Term Limitations with Interstellar Consequences

Author: James Schwartz, Ph.D., Fairmount Lecturer, Wichita State University

Abstract Background: There is a tendency of space mining advocates to focus on, e.g., total near-Earth asteroid (NEA) resource inventories, suggesting a picture that the resources of near-Earth space are (nearly) limitless, and that we needn’t worry about how (or how much or often) these resources are exploited and used.

Abstract Objectives: I will present evidence undermining the “limitless” perspective on NEAs and lunar resources. Focusing on water in particular, I will show that when important practical limitations are taken into consideration (e.g., delta-V requirements; asteroid distributions; launch windows; etc.), the easily accessible near-Earth resource pool appears quite small. Since these resources are (for all practical purposes) non-renewable, the ways in which they are used over the short term will affect our ability to satisfy longer-term goals, including our ability to provision interstellar missions.

Abstract Methods: Data is gathered from the planetary science literature describing NEA and lunar resource availability, focusing on publications discussing resources as energetically accessible as the Moon. This data will be used to provide a practical perspective on the (surprisingly limited) quantity of easily accessible space resources, and what this means for interstellar travel.

Abstract Results: There are multiple ways to filter the NEA population for accessibility, and several are discussed. One estimate, which looks at water-rich NEAs with a return delta-V equal to lunar escape velocity, suggests there is perhaps 8×10^11 kg water among this population. An estimate of water ice deposits in the bases of lunar polar craters comes to 3×10^12 kg. Altogether this water would form a sphere of about 2 km in diameter, which is hardly a limitless quantity of water to use for drinking, hydroponics, propellant, etc. It must also be kept in mind that only small quantities of this total will be available at any given time, given the orbital dynamics of the NEA population.

Abstract Conclusions: Unless some portion of our early spoils is reserved for the expansion of spaceflight capabilities, more energetically distance resources pools will remain out of reach, significantly impairing our ability to provision interstellar missions. Thus, the fate of interstellar exploration depends on the way that space mining conducted and regulated.