An Asteroid Regolith Database for ISRU

Abstract

We have developed the first database of asteroid regolith properties: fifty asteroids so far, to aid space resource utilisation workers. The physical parameters: grain density, grain size, near surface bulk density and porosity are provided of a collection of the asteroids. The strength of our method is that it combines three types of information: 1) spacecraft-based, in-situ data, 2) laboratory-based meteorite samples, and 3) telescopic, remote data, such as from polarisation-- the joint usage which amplifies the success and the probability of gaining new information. The database is also uniquely robust, due to its large number of crosschecks for the database's regolith parameters. Theoretical studies provide additional crosschecks. See Figure 1. A critical perspective is the assignment of the spatial scales where the bulk density and porosity of an asteroid is related to the average density and porosity of its constituent rocks, which is further distinguished from the average density of the mineral assemblages within the rocks.

Introduction

In-space resource utilisation will provide an extension of our SpaceShip Earth to include space infrastructures for, and of, our robots that are orbiting the Earth and traveling beyond. With such space resources, we can service, recycle, or build anew, without the limitations of carrying the resources from the Earth. Telecommuncations, Earth observations, planetary research, extraterrestrial life explorations, are just a few examples, which can be implemented cheaper and more efficiently using resources in space.

Despite the asteroid mining industry’s shift to smaller companies since 2018, it is no longer a question of  ‘if’ but of ‘when’.  The endeavour of the in-space utilisation of asteroid resources have several attractive features over their lunar and Martian counterparts, in that their low gravity, large quantities,and tiny sizes lead to different legal regimes for their utilisation and hence are more attractive for private funders to build in space with these resources.

The derived products for the asteroid regolith properties are currently following this flowchart:

Figure 1: Flowchart of the methodology of the Asteroid Regolith Database.

Meteorite Samples as Proxies?

One particular goal and feature of the Asteroid Regolith Database (ARD)'s robust strengths, is the use of proxies in lieu of asteroid samples to determine an asteroid regolith's porosity. This year, we sought to answer the following question before we can trust that meteorites can indeed be porosity proxies: Are meteorites already compressed in porosity before they enter the Earth’s atmosphere?

Empirical Support:

How to use such a Meteorite Proxy in the ARD:

• IF data for an asteroid is missing or sparse, but is linked to a meteorite analog, then one can compare the measured meteorite porosity of the analog material with the inferred bulk density of the material, to deduce density of the regolith grain.
• Thermal conductivity meteorite lab data additionally provides information to derive asteroid regolith particle sizes and particle porosity and crosschecks.
• However, IF the assumption is not valid, then one can still fit a functional form rearranging the thermal inertia equation, ρ = Γ²/(kc_p) and keeping track of scales (ρ_rock, ρ_grain, φ_rock, etc., for example: ρ_rock = (1−φ_rock)ρ_grain  and proceed. 
• IF one assumes that it’s valid to match meteoritic thermal inertia versus porosity data to its asteroidal counterpart, then one can relate regolith parameters, to derive a functional form that relates thermal inertia and porosity. Such an assumption will allow one to fill in possible gaps in data, to help mitigate any lack of thermal inertia data to derive porosities for the asteroid regolith database.

• In either case, we will have a function form that provides a Γ versus porosity relationship when we do not have thermal inertia data. The estimates of the accuracy will need to include the laboratory data acquisition errors along with the model fitting errors.

Summary and Conclusions

We have 50 asteroids thus far in our Asteroid Regolith Database. See the TREX website for the list: https://trex.psi.edu/ 

Upon investigating the meteorite proxy question, our Conclusions point to a clear need for more meteorite samples, measured in SEM in consistent ways.

Acknowledgements

The ARD has been supported, in part, by several funding organisations: (Vaivode): the University of Latvia Institute of Astronomy small research projects funding, and (Graps):  the NASA Toolbox for Research and Exploration (TREX) project, which is a node of NASA’s Solar System Exploration Research Virtual Institute 2016 (SSERVI16) Cooperative Agreement (NNH16ZDA001N).