Patent Application
20210115693
The present invention relates to inflatable environments, and more particularly, an inflatable environment that is constructed with partial In-Situ Resource Utilization (ISRU) of planetary surface soil (regolith) combined with polymer foam.
Inflatable environments attempt to establish different meteorological conditions (e.g. pressure, temperature, humidity, radiation, solar radiation, etc.) between two physical volumes of space. Most of these environments are used for habitats of some kind, but may also be volumes of space set up for other uses such as processing, manufacturing, etc. Inflatable environments provide a transportable and rapid method of installing a volume package utilizing gas expansion. There are many designs of terrestrial inflatable systems, but there are also designs applicable to space use. The most notable designs for human-rated inflatable modules are TransHab or Bigelow Aerospace's “BA330”.
The term inflatable is also sometimes used to describe an airform, which is inflated to establish a formed structure, and then permanently rigidized by spraying a quick-hardening material (e.g. reaction polymers like polyurethanes) using a blowing agent (e.g. CO2/H2O). These are typically polyurethane foams with either closed cell (bubbles remain inside) or open cell (to allow air flow) properties. However, there is a desire for weight bearing materials, such as expandable foams, to be used on extraterrestrial bodies, such as the Moon, but where gravity differs from Earth (e.g. only ˜0.17 g for the moon).
Current technology of sprayable foams for space applications is best highlighted by the foam used on the NASA® Space Shuttle, which protected and insulated the external fuel tank. A special blend of polyurethane materials was developed by NASA®. The foam does not require adhesives. Further this foam self-adheres to the surface of the tank with sufficient strength to withstand the forces of a launch, as well as the extreme temperatures of cryogenics and launch. NASA® used three types of foam for the 1″ thick insulation (e.g., a polyurethane-BX-250 and two types of polyisocyanurates—NCFI 24-124 and NCFI 24-57). All three types were meant for thermal insulation and not for structural support.
There are other types of polyurethane blends that provide structural support under the rubric of geotechnical foams (e.g., NCFI “TerraThane” Polyurethanes). These spray foams have been used as substitute for backfill and void fills in stabilizing soil and concrete lifting. Depending on the application, the strength values, densities and reactivity profiles can be tailored.
Some polyurethane blends provide two desired properties (thermal insulation and waterproofing). For example, a product owned by Honeywell® (TerraStrong™) is used on army tents and provides combined protection for waterproofing, air and vapor control, thermal control and structural rigidity. Moreover, the underlying structural scaffold below the foam material can be removed and reused after the rigidization process is complete. Most of these materials have been designed for the meteorological variations found on Earth. Using the Moon as a non-Earth example, the harsh conditions prevailing on an inflatable environment, and more so if it is a human habitat, are severe temperature gradients (127C→173C), hard vacuum (affecting building material outgassing), micrometeorite impingement (can hit the moon at speeds up to ˜28 km/s), radiation (Sun and cosmic rays), solar wind (varies from 1010-1012 particles per cm−2s−1 sr−1) and lunar dust contamination.
Unlike on Earth where dust particles have been rounded as result of weathering, Lunar regolith is made up of fine yet abrasive shards capable of compromising plastics and fabrics. Inflatable environments for Earth applications and the polymeric materials used are designed to operate within a narrow variation of temperature, given the locality. The Earth's atmosphere moderates the weather and mitigates large temperature swings at a given locality. The moon, on the other hand, has no discernible atmosphere and has large temperature variations. Polymer properties have strong temperature dependences with density changes being the more prominent along with a low glass transition temperature.
Consequently, the design of an inflatable environment (or habitat) for extraterrestrial surfaces requires changes to the methodology from that of the assembly and materials used on Earth. Thus, an inflatable environment and construction methodology that maximizes ISRU, or use of local materials in the construction process, is the basis for the embodiments described herein.
Certain embodiments of the present invention may provide solutions to the problems and needs in the art that have not yet been fully identified, appreciated, or solved by current inflatable environment design and construction methods. Some embodiments generally pertain to Regishell, which is composed of unique material. In certain embodiments, Regishell is made from a combination of polymer foam waste, solvent and locally-sourced soil (e.g., regolith), and is employed in several environments. In one example, Regishell is used in an inflatable environment (or habitat) to conform to the shape of an inflated outer airform on a lunar surface or underneath the ground in a lunar vault.
In an embodiment, the inflatable environment conforms to a dome shaped airform on a planetary surface and is reinforced with Regishell.
In another embodiment, the inflatable environment conforms to the walls of a lava tube or man-made cave under the planetary surface utilizing Regishell.
In yet another embodiment, the inflatable environment conforms to a pre-constructed scaffolding or deployed structure reinforced with Regishell.
In yet a further embodiment, Regishell is used to create bricks with a mold or 3D printing technique, or applied directly on the surface to create foundations, launchpads, roads or tracks.
In order for the advantages of certain embodiments of the invention to be readily understood, a more particular description of the invention briefly described above will be rendered by reference to specific embodiments that are illustrated in the appended drawings. While it should be understood that these drawings depict only typical embodiments of the invention and are not therefore to be considered to be limiting of its scope, the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings, in which:
Some embodiments of the Regishell inflatable environment generally pertain to a commercially-supplied and deployed dome inflatable airform. For purposes of explanation, an airform may be defined as air-inflated and air-supported forms used for enabling construction of permanent monolithic dome structures, where “air” could be any gaseous substance, in some embodiments. For additive rigidity, thermal control and radiation protection, an inflated airform layer is hardened on site using a construction method utilizing “Regishell”. Regishell combines polymer foam in the form of beads, sheets, waste foam (as from equipment transport padding material), a solvent for melting the polymer, and local surface soil (e.g., regolith) materials.
In some embodiments, Regishell is applied to the interior (or inner layer) of the inflated airform to create the Regishell inflatable environment. Regishell is “sprayed” or applied as a “sandwich layer” to the inflated airform layer. When cured, a rigid structure is formed. The rigid structure may conform to the shape of the inflated external layer.
Below is a description of the layers within Regishell inflatable environment 100. For example, an inflatable airform layer 104 may be defined as material of an inflated airform, and may act as a base layer to separate the internal and external environments of Regishell inflatable environment 100. An initial layer 106 may be composed of Regishell (e.g., polymer and regolith), and may be applied to the inside of inflated airform layer 104 to stabilize Regishell inflatable environment 100. A reinforcement layer 108 is also used to strengthen Regishell inflatable environment 100, and may be composed of a combination of in-situ basalt fibers, which are created from sintered regolith, and Regishell. Inner layer 110 may be similar to that of initial layer 106. However, inner layer 110, which is composed of Regishell (e.g., polymer+regolith), is applied to the inside of reinforcement layer 108. External layer 112 is also composed of Regishell (e.g., polymer+regolith). It should be noted that additional additives for radiation protection may be applied to the outside of Regishell inflatable environment 100, in certain embodiments. Moreover, the ratio of polymer to regolith in the mixture between the external later 112 and inner layer 110 could be different.
It should be appreciated that Regishell is created when polymer is mixed with lunar regolith. Regishell may be applied to the interior of Regishell inflatable environment 100, i.e., applied to initial layer 106, allowing the interior of Regishell inflatable environment 100 to harden. As shown in
Reinforcement layer 108 may require a composite material made with basalt fiber extracted from the Lunar regolith and combined with the Regishell. This provides high strength reinforcement to one or more layers of Regishell inflatable environment 100.
When lunar regolith is preprocessed (mineral extraction), heated and cooled the lunar regolith produces basalt fibers needed for reinforcement layer 108. When controllably heated and cooled, gases and basalt glass composite material may be extracted from the lunar regolith. In some embodiments, basalt glass composite material combines three silicate minerals, i.e., plagioclase, pyroxene and olivine. Prior to cooling the basalt glass can then be further processed to form larger/longer fibers and then mixed with polymer-based Regishell, akin to glass and fiber composites on Earth.
Basalt is readily available on the moon but in 100-micron size particles. There is a technology developed on earth for fabricating basalt fibers (which have better physiochemical properties than fiberglass) and it is a one-stage process that includes crushing and melting (1500° C.), homogenization of basalt and extraction of fibers (via extrusion through small nozzles). The basalt is only heated once. These fibers can then be wound (fiber bundles) and then “woven” (if necessary). It should be appreciated that the above processes can be implemented via robotic action. The fibers or bundles of woven segments can then be mixed into the polyurethane materials for added strength and then applied to the apparatus as described above.
An example of a solvent is acetone, which reduces polymers like polystyrene (e.g., extruded polystyrene foam, similar to packing beads) into a slimy material. This slimy material can then be mixed with regolith without added heat. Other organic solvents may also work in some embodiments. Alternatively, heat may be used to melt the polymer foam material to enable mixing.
In some embodiments, process 200 may begin at 202 with adding Regolith in a gas sealable container. At 204, the Regolith is mechanically processed to minimize shard edges. For purposes of explanation, mechanically processed may be defined as the use of two mechanical surfaces that act to grind, break apart and shape the Regolith to enhance its use as a filler material for the polymer material, which acts as a matrix.
At 206, gas may be added to the processed Regolith at sub-Earth atmosphere pressure. Any type of gas could be used because it serves as a transfer vehicle for the mixture. A reactive gas (one that chemically reacts with the polymer or Regolith) could also be used but an inert gas would be the more preferred. In practicality, one should use gases that could be “mined” or extracted from the Regolith. For example, for lunar Regolith and using the data from the Apollo missions, upon heating, gases are dissipated along the following ratios, carbon is released mainly in the form of CO and CO2 (300-400 ppm) while nitrogen is released as N2 or NH3 (150-250 ppm). Sulfur is also released as SO2 and H2S (20-1300 ppm). If the habitat is for human environment, then the release of sulfur-based gas compounds should be minimized (toxic). Fortunately, these compounds are volatilized when the temperature is close to 1000 C. The nitrogen and carbon-based compounds come off at much lower temperatures. Consequently, there is a preprocess of excavating Regolith and distilling the gases to be used. However, it is also possible to bring inert gases from Earth (e.g. argon, nitrogen), and in certain embodiments, where there is an inflatable layer that forms the shape, it is possible to conceive of a robot that uses part of the gas within the inflated “balloon” as a high pressure propellant for dispensing material. In an alternative embodiment, heat may be applied on the processed Regolith to release gases. Depending on the embodiment, the heat applied is from heat focused sun radiation or from an electrical source. If the heat source is focused sun radiation, then it requires a curved shaped mirror (e.g. 1-2 m) that focusses the sun radiation into/onto the processed Regolith to heat it. The focused radiation would be on the “pipe” that contains the material. On the moon there is approximately 1.3 kW/m2 of solar power. A simple calculation can be done to show the power requirements. If a pipe of some length had an inner diameter such that the inner volume is 8 cubic inches, and assuming sandstone material on the inside and at a temperature of 20 C. Only 632 W of thermal energy would be needed and that for only 2 minutes to raise the sandstone temperature from 20 C to 300 C (well above the polymer melting temperatures. Consequently, a 1 m dia. solar concentrator operating at 50% efficiency could raise the temperature to levels necessary for the process described in
At 208, polymer is mixed into the regolith to form a binder. The mixing may be performed at a predetermined temperature sufficient for viscous fluid flow of the polymer. The polymer to regolith ratio may depend on the properties of the polymer. The key property is the viscosity of the polymer at the applied temperature. Less viscous material enables quicker mixing with the Regolith. At a given temperature, lower viscosity polymers tend to have lower molecular weight. Other relevant properties are to decrease the modulus (i.e., the slope of the stress-strain curve at zero strain), which happens with increasing temperature. In an embodiment, the “melt index” (a test established by the polymer thermoforming community as a quick test of flowability) can be used as a guide when a higher melt index number is needed. Other pertinent properties include, for example, heat capacity (amount of energy required to elevate polymer temperature) and less of an issue is the thermal conductivity (measure of energy transmission through the material). It should be noted that if heat was not applied in the previous step, then the polymer may be more of a solvent such as an acetone.
At 210, heat is maintained during application of the mixture to insure the composite material flows through the dispensing tool and only hardens when in contact with the desired build surface. The material should be dispensed at a rate that insures the removal of trapped gases prior to cooling/hardening. In some embodiments, if the regolith is going to be applied via a spray approach, compressible gas (e.g., CO2) is added to the Regishell. The compressible gas is a propellant that pushes the product out in the open and to the build location via free space air transfer. If the tool is operating as a direct-write build tool (layer by layer construction using a close-to-contact dispenser), then compressed gas may not be necessary. At 212, the regolith is cooled prior to applying a second layer. This process step is only valid if the construction is via layer-by-layer direct-write mode dispensing. The material is allowed to cool between layers to primarily remove trapped gases. It does not have to be cooled to the ambient temperatures, but just low enough that all trapped gases leave (only if gases were mixed into the Regishell).
Regishell Deployment
Depending on the embodiment, Regishell can be deployed numerous ways. For example, Regishell may be sprayed onto an airform or Regishell may be piped into a “sandwich” membrane layer of the airform. In another embodiment, Regishell may be directly applied to a lunar rock or surface (that will attach) or may be prepared as Regishell “bricks”, which are attached to a scaffold that has been deployed.
Spraying the Regishell
In some embodiments, process 300 may begin at 302 with adding compressible gas (e.g., CO2) to the compressor that contains the Regishell. At 304, using the compressor, the Regishell is sprayed onto the inflated airform layer at a high throughput force to form the initial layer. At 306, basalt material created for reinforcement is combined with the Regishell, so the combination may be applied to the reinforcement layer. At 308, additional Regishell is applied to the reinforcement layer as the inner layer, and at 310, additional Regishell (with protective additives) is applied to the external layer.
Process 600 may begin at 602 with preparing a scaffold surface, and at 604, making a mold that have the shape of holes for the scaffold. At 606, the mold is filled with a thin layer of either polymer beads or polymer “cookie sheet” layer. This may be considered as a sacrificial layer.
At 608, the Regishell is poured into the mold and allowed to cool so it can take shape of the mold. At 610, the mold is heated to locally melt the sacrificial layer to release the molded shape, and at 612, a pick-and-place robot is used to attached shaped “brick” into the scaffold holes. The use of the molded bricks also works for developing “roads” for wheeled robots. The brick-roads limit the generation of dust.
These embodiments and processes may be accomplished by robotic payloads delivered to the lunar surface ahead of human habitation. The robotic payloads may create initial infrastructure for astronaut crew sorties of short length. Once there is an interest in continuous and sustained presence on the planetary surface, robotic payloads could prepare a suitable surface to act as a foundation for deploying the Regishell inflatable environment.
A robotic precursor mission could also produce the basalt fibers needed for the reinforcement layer of the Regishell inflatable environments. A robotic precursor mission could deploy, assemble, and create material for the entire Regishell inflatable environment by robotic means, in preparation for crew to arrive.
Since the Regishell is a mixture of ISRU material and a polymer binder, one of ordinary skill in the art could imagine surfaces prepared using these special mixtures that will soften during daytime and harden at nighttime. Polystyrene for example will not melt at solar surface temperatures, but other polymers can be tailored to soften at solar surface temperatures. An additional embodiment of this concept is bricked roads that during the day would allow a leading mobile wheeled vehicle to generate a small depression (e.g. 1-2″) which then becomes a guide “track” for automated vehicles that follow it.
It will be readily understood that the components of various embodiments of the present invention, as generally described and illustrated in the figures herein, may be arranged and designed in a wide variety of different configurations. Thus, the detailed description of the embodiments, as represented in the attached figures, is not intended to limit the scope of the invention as claimed, but is merely representative of selected embodiments of the invention.
The features, structures, or characteristics of the invention described throughout this specification may be combined in any suitable manner in one or more embodiments. For example, reference throughout this specification to “certain embodiments,” “some embodiments,” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in certain embodiments,” “in some embodiment,” “in other embodiments,” or similar language throughout this specification do not necessarily all refer to the same group of embodiments and the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.
It should be noted that reference throughout this specification to features, advantages, or similar language does not imply that all of the features and advantages that may be realized with the present invention should be or are in any single embodiment of the invention. Rather, language referring to the features and advantages is understood to mean that a specific feature, advantage, or characteristic described in connection with an embodiment is included in at least one embodiment of the present invention. Thus, discussion of the features and advantages, and similar language, throughout this specification may, but do not necessarily, refer to the same embodiment.
Furthermore, the described features, advantages, and characteristics of the invention may be combined in any suitable manner in one or more embodiments. One skilled in the relevant art will recognize that the invention can be practiced without one or more of the specific features or advantages of a particular embodiment. In other instances, additional features and advantages may be recognized in certain embodiments that may not be present in all embodiments of the invention.
One having ordinary skill in the art will readily understand that the invention as discussed above may be practiced with steps in a different order, and/or with hardware elements in configurations which are different than those which are disclosed. Therefore, although the invention has been described based upon these preferred embodiments, it would be apparent to those of skill in the art that certain modifications, variations, and alternative constructions would be apparent, while remaining within the spirit and scope of the invention. In order to determine the metes and bounds of the invention, therefore, reference should be made to the appended claims.
