1. Introduction
Because of the valuable assets that asteroids possess, the examination of asteroids for forthcoming excavation intentions has garnered significant focus [
1,
2,
3,
4]. For these operations, one must contemplate the following: (i) the spacecraft rendezvous and navigation phase, during which precise management of the spacecraft’s dynamics is necessary while the spacecraft traverses the proximity of the asteroid being apprehended, (ii) the asteroid apprehension phase, and (iii) the optical excavation phase [
1].
Although rendezvous assignment and docking [
1], spacecraft rendezvous and close-range maneuvering [
1,
5,
6], and spacecraft direction in rendezvous assignments [
1,
7] have been extensively explored in the literature, asteroid excavation without digging (optical excavation) has not been extensively examined. To tackle this void, the primary aim of this document is to model, design, simulate, and test experimentally a high-strength and high-temperature resistant composite structure material for in-space optical excavation (asteroid excavation). In other words, this paper consists of (i) modeling and designing a composite material at the polymer and atomic/molecular levels, (ii) investigating the mechanical performance (high strength) of the composite material at the polymer and atomic/molecular levels for in-space optical mining, (iii) investigating thermal performance (high-temperature resistant) at the polymer and atomic/molecular levels of the composite material for in-space optical mining, and iv) experimental testing of the composite material.
The objective of the mechanical performance investigation of the material designed and modeled at the polymer level is to figure out the best combinations of materials suitable for use in space asteroid mining (optical mining). For this paper, we only show the modeling and simulations of a composite structure material made up of Nomex (outer layer), Kevlar (supporting layer), and Spirooxazine-Doped PANI film (core layer).
It is important to mention that multiple combinations made up of the following were modeled and simulated in COMSOL: Nomex, Kevlar, Aerogel, carbon epoxy, Glass vinylester, Kapton, polyvinyl chloride (PVC) foam, Polyethylene Terephthalate (PET), Polyamide (Nylon), Polyimide, Aluminized mylar, PTFE (Teflon), Polypropylene, Silica aerogel, high-temperature fabrics, carbon/carbon composite. Based on the listed materials, the combination of Nomex/Kevlar/Spirooxazine-Doped PANI film stands out as the best combination to be considered as a high-strength composite structure material for in-space optical mining.
The objective of the thermal investigation is to determine if the selected composite material (material made up of Nomex, Kevlar, and Spirooxazine-Doped PANI film) based on the mechanical performance investigation is suitable for optical mining (asteroid mining).
To examine the thermal efficiency of the composite material designed and modeled at the polymer level, a simulated trial was established using COMSOL. Within this setup, a laser heats a composite consisting of Nomex, Kevlar, and Spirooxazine-Doped PANI film. The laser moves both inward and outward radially as time progresses, while the composite material rotates on its platform [
8]. Initially, for the examination of the mechanical aspects of the composite material modeled and designed at the polymer level, the analysis contrasted the following frequently utilized techniques [
9]: (i) an equivalent solitary layer principle [
8], employing first-order shear deformation theory (ESLFSDT) [
8], (ii) layerwise elasticity theory [
8], and (iii) a multiple-model approach [
8]. It is noteworthy that these identical methodologies were applied and fully described in detail in our previously published article [
8].
Next, for the thermal analysis of the composite material modeled and designed at the polymer level, the composite material fabricated and simulated mechanically (mechanical characteristics simulations) underwent heating from a laser that traverses radially inward and outward over time, while the composite itself rotates on its platform [
8]. The transient thermal reaction of the composite was acquired by modeling the incoming heat flux from the laser as a spatially distributed heat source on the surface [
8]. The mean, peak, and nadir temperatures, alongside the utmost temperature disparity across the composite, were recorded at each computational increment [
8]. The temperature dispersion throughout the entire composite material was documented at specified intervals of output time. It is noteworthy that this identical approach was employed in our previously published manuscript [
8].
Fourthly, for the experimental investigation of the composite material modeled and designed at the polymer level, a thin PANI layer was successfully synthesized via electrochemical polymerization on a flexible substrate [
10]. The quantitative analysis of colorimetric [
10], optical [
10], and structural evolution [
10], alongside the EC properties of the electrodeposited PANI film [
10], were meticulously examined across various potentials [
10]. The Raman spectra delineate the underlying mechanisms driving the observed color alterations in response to external stimuli [
10]. The synthesized film underwent scrutiny using a diverse array of characterization techniques [
10], including scanning electron microscopy (SEM) [
10], colorimetric analyses [
10], UV-vis spectroscopy [
10], Raman spectroscopy [
10], and cyclic voltammetry [
10]. It is pertinent to note that this identical methodology [
10] was applied and fully described in detail in our previously published manuscript [
10]. The contributions of these methodologies to understanding the following properties of the PANI film were described in detail in our published manuscripts [
10]: surface morphology, electrochemical dynamics, and molecular structural evolution [
10].
Following the initial design, modeling, and testing of the composite material at the polymer level, we advanced our approach by designing, modeling, and simulating a novel composite material composed of Nomex, Kevlar, and Spirooxazine-Doped Polyaniline (PANI) at the atomic and molecular levels. In this refined process, we meticulously considered constraints such as chemical structure, bonding, and physical interactions, including Van der Waals forces, to ensure an accurate representation of the material’s behavior.
As part of our design concept, the composite material was engineered with interwoven or layered Nomex and Kevlar polymer chains, creating a robust and flexible network. A thin film of Spirooxazine-Doped PANI was then strategically deposited onto this composite network, enhancing its functional properties through the incorporation of photochromic and conductive features. Subsequent simulations of the composite material were conducted, and the results were rigorously compared to those obtained from earlier modeling and simulations performed at the polymer level. This comparative analysis allowed us to validate the material’s performance and optimize its structural and functional characteristics for potential applications in advanced technological fields.
The uniqueness and contributions of this endeavor are delineated as follows: (i) pioneering material advancement for in-space optical mining application. This initiative introduces an original composite material endowed with outstanding high-strength and high-temperature resistance tailored explicitly for in-space optical mining. The development of this material may encompass groundbreaking amalgamations of polymers, ceramics, or alternative cutting-edge materials. (ii) Fusion of composite material with optical mining systems. This initiative showcases the formulation of simulation models that seamlessly integrate the composite material into the overarching optical mining framework. This entails deliberations on the material’s interaction with mining apparatuses, energy reservoirs, and other constituent elements to optimize the entire mining continuum. (iii) Thermal regulation solutions for the optical mining milieu. This endeavor unveils innovative remedies for thermal regulation in environments characterized by elevated temperatures encountered during optical mining. This encompasses simulations demonstrating the material’s adeptness in heat dissipation or resistance to thermal deterioration, thus ensuring the robustness and endurance of mining paraphernalia. (iv) Understanding material dynamics in the space environment. Noteworthy emphasis is placed on the distinctive challenges posed by the space milieu, such as microgravity and vacuum conditions. This initiative contributes to comprehending how the material reacts in these conditions and its ability to endure or adapt to the rigors of space mining. (v) Assessment of the material’s impact on resource efficiency and sustainability in space missions. This entails considerations of recycling, reusability, and decreased reliance on earth-derived resources for space expeditions. (vi) Fostering interdisciplinary collaboration. This endeavor fosters synergies among researchers from diverse domains, including materials science, aerospace engineering, optics, and mining engineering. This interdisciplinary synergy can furnish holistic insights into the challenges and prospects linked with in-space optical mining. (vii) Advancing future space exploration. This undertaking enriches the broader domain of space exploration by furnishing solutions for resource extraction and utilization in space, vital for sustainable and enduring human presence beyond Earth. (viii) This empirical exploration enhances our comprehension of the Spirooxazine-Doped PANI film structure and the electrochemical and correlated optical attributes, thereby offering deeper insight into dual-function EC charge storage polymers and other energy-related functional materials.
The outcomes of the mechanical and thermal explorations evince that the composite material comprising Nomex, Kevlar, and Spirooxazine-Doped PANI film manifests potential as a high-strength and high-temperature resistant composite structural material for in-space optical mining endeavors.
3. Model Development of the Composite Material at the Atomic and Molecular Levels: Design and Development of a New Composite Material Made Up of Nomex, Kevlar, and Spirooxazine-Doped PANI
3.1. Considerations for the Development of the Composite Material
Given that the objective is to create a material for in-space optical mining applications, we aimed to develop a composite consisting of Nomex, Kevlar, and a photochromic material specifically designed for asteroid mining.
The photochromic material will replace the PANI thin film used in our previous work, as documented in our published article [
8]. This material must be capable of changing color upon exposure to sunlight, enhancing the functionality of the composite.
Key considerations for this development include the following. (i) Integration: The photochromic material must be seamlessly integrated into the composite without compromising the mechanical properties of Kevlar and Nomex, maintaining their inherent strength and durability. (ii) Stability: The photochromic material must withstand the extreme conditions of space, including radiation, temperature fluctuations, and vacuum environments, to ensure long-term stability and performance. (iii) Reversibility: The photochromic change should be reversible, allowing for multiple cycles of color change in response to sunlight exposure, which is critical for the dynamic conditions of space. (iv) Performance: The selected photochromic material should enhance the composite’s suitability for in-space asteroid mining, leveraging the strengths of Nomex and Kevlar to provide a robust and versatile solution.
After extensive investigations and simulations, Spirooxazine-Doped PANI emerged as the optimal choice. This material is renowned for its ability to change color under sunlight exposure and its durability and stability in harsh environments.
By replacing the PANI thin film with Spirooxazine-Doped PANI, the resulting composite material—comprising Nomex/Kevlar reinforced with a Spirooxazine-Doped PANI thin film—will benefit from enhanced physical interactions and hydrogen bonding, defined as follows:
(1) Physical Interaction: The Nomex and Kevlar fibers will be interwoven to form a strong, three-dimensional network. The Spirooxazine-Doped PANI thin film will be deposited onto this network, potentially through methods like spin-coating or vapor deposition. The PANI film will conform to the surface of the fibers, creating a physical entanglement.
(2) Hydrogen Bonding: There’s a possibility for hydrogen bonding between the Nomex/Kevlar and Spirooxazine-Doped PANI. The amine groups (NH2) in PANI can form hydrogen bonds with the oxygen atoms (C=O) in the amide bonds of Nomex/Kevlar. Additionally, Spirooxazine molecules might interact with both the PANI backbone and the fibers, potentially forming additional bonding sites. These hydrogen bonds, though weak individually, can collectively contribute to a stronger interface among the components.
3.2. Differences between Spirooxazine-Doped PANI Thin Film and PANI Thin Film: Tools That Lead to the Selection of the Photochromic Material
(1) Structure and Properties of the Polyaniline (PANI) Thin Film: This section presents the chemical structure, conductivity, and color change properties.
Chemical Structure: PANI is a conducting polymer with repeating units of benzene rings connected by amine groups.
Conductivity: PANI’s electrical conductivity can be adjusted by doping with acids, making it suitable for various electronic applications.
Color Change: PANI exhibits electrochromic properties, meaning it can change color when an electrical voltage is applied. However, its response to light (photochromism) is limited.
(2) Structure and Properties of the Spirooxazine-Doped PANI Thin Film: This section presents the chemical structure, conductivity, and color change properties.
Chemical Structure: This composite material includes PANI doped with Spirooxazine molecules, which are photochromic compounds.
Conductivity: The incorporation of Spirooxazine may slightly affect the conductivity of PANI but generally maintains its conductive properties.
Color Change: Spirooxazine is a photochromic compound that undergoes a reversible transformation between two forms when exposed to UV light and visible light, resulting in a color change.
(3) Electronic Structure Differences: This section presents the electronic structure differences between the Spirooxazine-Doped PANI thin film and the PANI thin film.
PANI: The electronic structure of PANI involves π − π∗ transitions within the benzene rings and the lone pair electrons on the nitrogen atoms, which contribute to its conductivity and electrochromic properties.
Spirooxazine-Doped PANI: The presence of Spirooxazine introduces additional electronic states and transitions. Spirooxazine has a closed form and an open form, with different electronic structures. The closed form is typically colorless, while the open form, induced by UV light, is colored because of the extended conjugation system that alters its electronic absorption spectrum.
3.3. Advantages of Spirooxazine-Doped PANI Over PANI in Color Change: Tools That Lead to Selecting the Photochromic Material
(1) Photochromic Response: This section presents the photochromic response of o PANI vs. Spirooxazine-Doped PANI.
PANI: Limited photochromic properties; primarily changes color through electrochromism when voltage is applied.
Spirooxazine-Doped PANI: Exhibits strong photochromic properties due to Spirooxazine molecules. When exposed to sunlight (UV light), Spirooxazine undergoes a structural change, causing a significant color change. This process is reversible, and the material returns to its original color when the UV light is removed.
(2) Reversibility and Speed: This section presents the reversibility and speed of PANI vs. Spirooxazine-Doped PANI.
PANI: Electrochromic changes can be reversible but require an external voltage. The speed of the color change depends on the applied voltage and the doping level.
Spirooxazine-Doped PANI: The photochromic color change in Spirooxazine-Doped PANI is typically fast and reversible upon exposure to UV light and visible light. This allows for quick and repeatable color changes with sunlight exposure.
(3) Sensitivity to Light: This section presents the sensitivity to light of PANI Vs. Spirooxazine-Doped PANI.
PANI: Limited sensitivity to light, primarily responds to electrical stimuli.
Spirooxazine-Doped PANI: High sensitivity to UV light due to Spirooxazine. The color change can be triggered directly by sunlight, making it ideal for applications where visual indicators of light exposure are needed.
3.4. Design
(1) Nomex Structure: This section presents the chemical structure and atomic bonds and explains how the structure of Nomex can be represented visually.
Atomic-Level View of Nomex: Imagine long, chain-like molecules where aromatic rings (benzene rings) are linked by amide bonds (-C(=O)-NH-). The aromatic rings are arranged in a relatively stiff, rod-like structure.
Chemical Structure: Nomex (Poly(meta-phenylene isophthalamide)) is an aramid polymer consisting of meta-phenylene rings connected by isophthalamide units.
Atomic Bonds (or bonding): The atomic bonds consist of (i) phenylene rings, which are hexagonal rings made of carbon atoms, connected by alternating single and double bonds, (ii) amide groups, which are rings connected by amide linkages (-CONH-), forming hydrogen bonds with neighboring polymer chains, and (iii) hydrogen bonds, which are interactions among hydrogen atoms of the amide groups, and the oxygen atoms of other amide groups provide thermal stability and flame resistance.
Visual Representation: The Nomex structure shows meta-phenylene rings connected by isophthalamide units with hydrogen bonds among amide groups.
Figure 1 shows the atomic-level view of the designed Nomex structure, as shown in
Figure 2. These figures show meta-phenylene rings connected by isophthalamide units with hydrogen bonds among amide groups. This illustration highlights the hexagonal rings made of carbon atoms, connected by alternating single and double bonds, and the amide linkages (-CONH-).
(2) Kevlar Structure: This section presents the chemical structure and atomic bonds and explains how the structure of Kevlar can be represented visually.
Atomic-Level View of Kevlar: Similar to Nomex, Kevlar has long chains with aromatic rings linked by amide bonds. However, the arrangement of the chains in Kevlar is more crystalline and rigid, contributing to its higher strength.
Chemical Structure: Kevlar (Poly(paraphenylene terephthalamide)) is another aramid polymer consisting of para-phenylene rings connected by terephthalamide units.
Atomic Bonds (or bonding): The atomic bonds consist of (i) phenylene rings, which are hexagonal rings made of carbon atoms, connected by alternating single and double bonds, (ii) amide groups, which are rings connected by amide linkages (-CONH-), forming extensive hydrogen bonds among polymer chains, and (iii) hydrogen bonds, which are strong interactions among hydrogen atoms of amide the groups, and the oxygen atoms of other amide groups contribute to Kevlar’s high tensile strength and stiffness.
Visual Representation: The structure of Kevlar shows para-phenylene rings connected by terephthalamide units with an extensive hydrogen bonding network.
Figure 3 shows the atomic-level view of the designed Kevlar structure, as shown in
Figure 4. These figures show para-phenylene rings connected by terephthalamide units with an extensive hydrogen bonding network. This illustration highlights the hexagonal rings made of carbon atoms, connected by alternating single and double bonds, and the amide linkages (-CONH-).
(3) Spirooxazine-Doped PANI Thin Film: This section presents the chemical structure and the atomic bonds and explains how Spirooxazine-Doped PANI can be represented visually.
Atomic-Level View of the Polyaniline (PANI) thin film:
Imagine a network of interconnected aniline rings (benzene rings with an attached amine group -NH2). The bonding among these rings involves alternating single and double bonds, allowing for the movement of electrons along the chain and contributing to conductivity.
Atomic-Level View of Spirooxazine-Doped PANI: Imagine a network of interconnected aniline rings (benzene rings with an attached amine group -NH2). The bonding among these rings involves alternating single and double bonds, allowing for the movement of electrons along the chain and contributing to conductivity. Incorporated within this network are Spirooxazine molecules, which are photochromic compounds. These Spirooxazine molecules are bonded to the Polyaniline chains, potentially through interactions with the amine groups or the aromatic rings, creating points where the Spirooxazine can influence the electronic properties of the PANI, such as by altering its conductivity or optical properties in response to light.
Below is the atomic-level view of Spirooxazine-Doped Polyaniline (PANI), showing a network of interconnected aniline rings with alternating single and double bonds, along with incorporated Spirooxazine molecules bonded to Polyaniline chains. This illustration highlights the interactions between Spirooxazine and PANI, influencing its electronic and optical properties. The second image shows the Polyaniline backbone with incorporated Spirooxazine molecules and highlights the interaction points where Spirooxazine molecules are bonded to the Polyaniline chain
Chemical Structure: PANI (Polyaniline) is a conducting polymer with repeating units of benzene rings (C6H4) connected by amine (NH) groups. Spirooxazine molecules are incorporated into the PANI matrix. • Atomic Bonds (or bonding): The atomic bonds consist of (i) benzene rings, which are hexagonal rings made of carbon atoms, connected by alternating single and double bonds, (ii) amine groups, which are benzene rings connected by amine groups, allowing for interactions with other materials, and (iii) Spirooxazine interactions, in which Spirooxazine molecules interact with PANI chains, potentially through the amine groups or aromatic rings, modifying the conductivity and optical properties of PANI.
Visual Representation: The figures provided above (
Figure 5) show the designed Spirooxazine-Doped PANI structure with benzene rings connected by amine groups and Spirooxazine molecules interacting with the PANI matrix.
(4) Composite Material Made Up of Nomex, Kevlar, and Spirooxazine-Doped PANI: This section presents the design concept and bonding and how the composite material can be represented visually.
Design Concept: The composite is designed with interwoven or layered Nomex and Kevlar polymer chains. The Spirooxazine-Doped PANI thin film is deposited onto the network composite material made up of Nomex and Kevlar.
Bonding and Interactions: The bonding consists of (i) hydrogen bonds between the amide groups of Nomex and Kevlar, as well as between these groups and the Spirooxazine-Doped PANI thin film, and (ii) Van der Waals interactions, which are additional interactions between the Spirooxazine-Doped PANI film and the Nomex/Kevlar network that enhance the composite’s properties.
Visual Representation: The composite structure in
Figure 6 shows interwoven Nomex and Kevlar units with a Spirooxazine-Doped PANI thin film deposited onto the network, illustrating hydrogen bonds and other interactions among the materials.
Figure 6 shows the atomic-level view of the composite structure made up of Nomex, Kevlar, and the Spirooxazine-Doped Polyaniline (PANI) thin film. This illustration shows Nomex and Kevlar fibers interwoven to form a strong, three-dimensional network with the Spirooxazine-Doped PANI thin film deposited onto the network. It highlights the physical entanglement and potential hydrogen bonding between the amine groups (NH2) in PANI and the oxygen atoms (C=O) in the amide bonds of Nomex/Kevlar, along with the interaction between Spirooxazine molecules and both the PANI backbone and the fibers. The image highlights the hydrogen bonding and structural features of each material, as well as their interactions in the composite structure.
6. Conclusions
This study simulated the mechanical and thermal behaviors of a composite material consisting of Nomex, Kevlar, and Spirooxazine-Doped PANI film at both the polymer and atomic/molecular levels. Experimental testing was performed in a laboratory on a sample manufactured from the composite material designed and modeled at the polymer level.
Initially, this study illustrated the modeling of a composite structure composed of Nomex, Kevlar, and Spirooxazine-Doped PANI film. Three modeling techniques, layerwise theory, equivalent single layer (ESL) theory, and a multiple-model method, were employed. Modal and frequency–response analyses were conducted, comparing the multiple-model method with traditional layerwise and ESL theories in terms of performance and accuracy, including the through-thickness stress distribution. The results indicate the multiple-model method is the optimal choice for accuracy and performance in modeling composite structures.
The combination of Nomex, Kevlar, and Spirooxazine-Doped PANI film is identified as optimal for in-space optical mining applications.
Secondly, the composite material made up of Nomex, Kevlar, and Spirooxazine-Doped PANI film was modeled and simulated to determine its mechanical strength and response to laser heating as performed similarly in our previously published article. The transient thermal response of the material to radial laser heating was obtained, with peak, average, and minimum temperatures computed. Thermodynamics simulations indicate suitability for high-temperature resistant composite material in-space optical mining applications.
Thirdly, experimental investigations on the electrodeposited PANI film’s colorimetric and electrochromic characteristics were conducted [
10]. Cyclic voltammetry tests reveal ion-diffusion dominant processes in electrochromism [
10]. Significant transitions between benzene and quinone phases are observed in Raman spectra of PANI [
10]. Infrared camera testing demonstrates the PANI film’s capacity to block infrared radiation, indicating potential applications in satellite thermal management and military camouflage [
10].
Overall, the PANI film exhibits desirable properties for incorporation into composite materials for in-space optical mining applications, promising mechanical strength, thermal stability, and optical responsiveness [
10].
In summary, our simulations suggest the composite material made up of Nomex, Kevlar, and Spirooxazine-Doped PANI film material is suitable for high-strength, high-temperature resistant composite material for in-space optical mining applications.