Space Dwarfs

Global Nominee

Space Dwarfs received a Global Nomination.

Solar System

Develop an approach for characterizing the composition of asteroid for mining potential and a process for mining different compositions. Explore a possible division of labor involving different types of vehicles (e.g. sensor units, drilling units, power gathering and distribution, extracted resources handling and transferring). Consider solutions for moving said asteroids between different orbits and/or consequently make periodical adjustments to keep them in place. Analyze how your idea would cope in some of the given scenarios or outline a scheme of your own.

Explanation

Introduction

Asteroid mining may be the only way to ever visit other planets or solar systems as a species; we can only take that much fuel to space, thus we need to get the rest while out there. Moreover, asteroids can sometimes be made of elements that are very rare and very expensive on Earth, making asteroid mining both a viable financial investment, and a necessary endeavour for the expansion and survival of humanity.

Background

We, the Space DwarFS team, developed and propose a process to choose exploitable asteroids and go there, study them, bring them or parts of them where we need them and either make fuel or get those precious ore back to earth.

The process starts with data gathering from afar. We utilize spectroscopy and other traditional techniques to estimate with significant certainty the asteroid’s properties, predominantly surface composition, mass and density. If the certainty is acceptable, we then send a small, relatively economic probe carrying an array of tools and equipment on the asteroid. This will include composition measurement and mapping tools to assist landing and later mining.

If the probe’s data confirms the required properties, (or if traditional techniques showed a very high degree of certainty for a particular asteroid) then a larger vehicle is send to the asteroid for processing and propulsion to bring the asteroid or pieces of one to a more desirable orbit. For asteroids composed of ice, this vehicle will include an electrolysis apparatus to separate oxygen and hydrogen and serve as a refuelling station for long missions. For asteroids containing precious materials the vehicle will carry mechanisms to remove and collect parts of the asteroid and send them to a decaying earth orbit, where they will be then de-orbited in pods with small thrusters and systems for soft landing to allow easier and safer retrieval.

GETTING THE DATA

Spectroscopy

Spectroscopy is a characterization method that allows to discover the composition of celestial bodies through the wavelengths they emit. The method allows to study far asteroids without the need to visit them with long and expensive missions.

Optical spectroscopy studies the visible light reflected of asteroids, identifying the surface characteristics; whereas gamma ray spectroscopy, although more complex and demanding, can study space rocks under the surface as well. These two methods allow for estimating with significant accuracy the composition of asteroids from afar; saving greatly on costs and time and allowing to sieve through the hundreds of thousands of potential asteroids.

Once we get there, we can use in-situ techniques to determine the composition with a high degree of accuracy. We propose the use of Laser-induced breakdown spectroscopy (LIBS) in combination with other techniques to collect data for this purpose.

Seismic data

Our probe will include an array of sensors to gather useful information from the targeted asteroid, one of these being a seismometric system. The idea is to measure propagating and reflecting mechanical waves within the asteroid to complement spectroscopic and LIBS data with information about the asteroid’s insides.

The basic implementation approach would be to deploy one or more micro-seismometers on the surface of a small body and then impact the body with a projectile or use explosive devices as an energy source (active seismology). This active seismology experiment would provide the seismic velocity of the interior across some number of ray paths. This implementation would present a low-risk, low-cost, opportunity to answer key questions about the asteroid’s internal structure, including voids, density and composition.

Where restrictions apply, seismic signals from natural sources such as meteoroid impacts and thermal cracking may serve as the energy source (passive seismology). Seismic sensors for such experiments could range from short period rugged passive seismic exploration sensors to MEMS high frequency sensors, engineered with high sensitivity to measure the expected low amplitude signals in the nearly zero mechanical noise of the environment.

The seismic signals can be contrasted with natural frequency predictive simulation data for the specific asteroid, and infer internal structure properties through analysing the potential differences. For small bodies it may be possible to get them to “ring” with relatively small sources and subsequently study the decay of the normal modes. Examining the normal mode oscillations of the Earth has proven to be very fruitful in yielding information about its internal structure historically, and in the Apollo 17 mission similar moon seismology data was obtained with geophones and explosive devices, as a precedence of the technology.

LANDING

To land on a space rock we must know where it is flat and solid, how it moves and rotates and what else is flying around. This is an ongoing challenge, as proven by the Philae lander mission outcomes. We propose the use of traditional image processing (i.e. earth and earth-orbit telescopes), on board image processing as today’s technology is now sufficiently developed and LiDAR for the final few hundred meters.

Image processing involves gathering a hi-resolution stereo photographic images of the asteroid and constructing a 3D model by analysing the differences between adjacent cameras as well as the contrasting shadows in respect to the light sources. Light Detection And Ranging or LiDAR, a technology used predominantly for high precision map making via sending and receiving the reflected laser off surfaces while considering the relative position of the probe from the target. Through implementation of modified LiDAR systems a precise 3D model of any asteroid can be recreated once we get there.

DATA ANALYSIS

In order to infer the composition of an asteroid, a new method is proposed. It is based on the valid assumption (as verified by the literature) that asteroids of the same type (e.g. Type M) have the similar composition of minerals and water (if any). The composition for a specific type can currently be provided by the Asterank API and the type is based on Tholen classification. In this approach, an algorithm is proposed to predict the type of an asteroid whose type is unknown to us. Briefly, the wavelength against (normalized) reflectance is considered. The range of approximately 0.5 to 1.2 microns is known to be relevant, which is part of near-infrared spectroscopy. In particular, the average signal of the waveform is evaluated and a ‘mean signal type’ is produced. This can be considered as the ‘training’ step of this naïve algorithm. Then this mean signal type is compared with the waveform of the asteroid, whose type is unknown. The comparison can be performed by subtracting the mean of the unknown signal and then by evaluating a distance/similarity metric, such as Sum of Squared Differences or Correlation. If it is ‘near’ enough (according to a threshold) then it is of the same type (e.g. Type M), otherwise it is not. So binary classification is achieved. If it is found to be an M asteroid, then it is known to contain nickel, iron and cobalt, according to Asterank. As a proof of concept, a part of the algorithm is implemented on MATLAB and can be found on the Github repository. Provided that datasets for every type exist, then a general multivariate classification can be performed instead of a binary, using one of the aforementioned distance/similarity metric, by taking the minimum distance (or maximum similarity). A threshold can still be used to identify asteroids that do not belong to any class/type.

A more sophisticated technique (e.g. using Machine Learning) could be applied, but this one is computational efficient in terms of time. For example, Principal Component Analysis (PCA) has been used in the past by Xu et al. 1995 (Icarus 115, 1-35). However, the main drawback of this newly proposed method is that currently, the only relevant data set with known types is the ‘EAR-A-I1092-2-MSPECTRA-V1.0’ with Spectra of M asteroids by Fornasier et al. (2010). So all the rest types (e.g. Type C, S, etc) are not available by NASA yet. However, a data set of some unknown types already exists and it is called ‘EAR-A-I0046-5-REDDYSPEC-V1.0’. It contains spectra of 40 near-Earth asteroids, obtained as part of Vishnu Reddy's Ph.D. dissertation at the University of North Dakota. Both data sets were acquired by the SpeX instrument located in Mauna Kea, Hawaii and they are available online at the NASA Planetary Data System.

MOVING THE ROCK

Anchoring

The lack of gravitational pull makes landing on an asteroid challenging to say the least. The probes can bounce off, parts and ore can fly away and ground friction is non-existent. The newly invented Jet Propulsion Lab Microspines is a technology developed to grip the uneven surface of asteroids using numerous sharp spines pulled with synthetic wires. The use of polymers and synthetics allows for lightweight yet strong anchoring that can decouple at will and move around. Our probes, thrusters and miners can utilize the JPL Microspines to safely anchor (or even move around!) on asteroids, and use traditional embedded anchors for tougher jobs like drilling.

Propulsion

Moving an asteroid around takes energy, and moving a fast, massive one takes a lot of it. Thankfully, we have years to do so, as near earth asteroid orbits are known well in advance; with relatively small pushes, gravitational assist from the sun, planets and moons we can manipulate their orbits and bring one where it’s easier to exploit, such as a far earth/moon orbit or even on the way to Mars. With its proven very high efficiency and specific impulse, as well as the recent Aerojet solar electric propulsion contract, we propose the use of electric propulsion (i.e. ion thrusters) to deorbit a small asteroid or fragments of one. Space charge problems can be mitigated by using the asteroid as a charge receiver.

GETTING THE STUFF

Fuel and water

For water (ice) asteroids, the “miner” will consist of an electrolysis system and three tanks to store hydrogen, oxygen and clean water respectively. The asteroid and attached asteroid will be placed in an orbit to facilitate refuelling of manned and unmanned missions, and powered by traditional photovoltaics used in the space industry.

Fracturing

Ore asteroids too large to move will need to be broken into more manageable parts; even the smaller ones might need to be separated into smaller segments to allow a manageable transfer to Earth. The use of traditional techniques such as sawing or grinding tend to be too heavy or simply impractical for space, and chemical extraction of minerals requires large and massive quantities of corrosive or erosive substances moved to the asteroid. We propose the use of explosive charges or expanding mechanisms implanted into the asteroid to controllably fracture it while engulfing fragments in a net-like device. This will require a drill for the bore hole, explosive charges, expanding mechanical or chemical systems to be inserted, the net to be deployed and the fracture to be performed.

Thermal Mineral Extraction

Solar Oven:
In the case of rich concentrations of fusible material, heat can be applied to melt or sublimate minerals directly. For asteroids within the solar system we can utilize large surface reflectors to bring the surface to melting temperatures and then collect minerals in containers. Alternatively, small nuclear reactors can produce sustained amounts of heat for this exact purpose. Lightweight, high heat resisting materials need to be further developed for this, as well as methods to use radiative cooling and asteroids as a heat sink.

Bringing it home

For transferring the ore from the asteroid to earth we propose the use of sphere-cone capsules, where the ore will be stored and then thrusters will bring the capsule to a decaying earth orbit. The capsules will use ablative tiles for the initial re-entry and parachutes once within the atmosphere.

THE FUTURE

Once we have a refuelling station outside the planet, we will be able to get everywhere within the solar system faster and much cheaper. Asteroid mining can become a highly profitable business, resulting in an exponential growth and opening access to once rare materials for everyday uses. Platinum electronics and gold wires can be the norm; luxury vacations to Venus a reality. Ore processing can be established in situ or in a bespoke space station, bringing us a step closer to self-sustainable space colonization.

Resources Used

LINKS

BIBLIOGRAPHY

Abell, Paul A. Near-IR reflectance spectroscopy of mainbelt and near-Earth objects: A study of their compositions, meteorite affinities, and source regions. 2003.
Bottke Jr, William F., David Vokrouhlický, David P. Rubincam, and David Nesvorný. "The Yarkovsky and YORP effects: Implications for asteroid dynamics." Annu. Rev. Earth Planet. Sci. 34 (2006): 157-191.
Xu, Shui, Richard P. Binzel, Thomas H. Burbine, and Schelte J. Bus. "Small main-belt asteroid spectroscopic survey: Initial results." Icarus 115, no. 1 (1995): 1-35.

DATASETS & APIs