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NASA NTRSDate not supplied

Heritage to Flight; The Test Program that Brought an Inflation System Back to Life for the Low Earth Orbit Flight Test of an Inflatable Decelerator (LOFTID)

Following the success of the Inflatable Reentry Vehicle Experiment-3 (IRVE-3) project, the Terrestrial Hypersonic Inflatable Aerodynamic Decelerator (HIAD) Orbital Reentry (THOR) project was stood up with a “built to print” Inflation System utilizing the IRVE-3 flight spares. When THOR was canceled, this Inflation System had already been tested and assembled, ready for use. Thus, when the Low Earth Orbit Flight Test of an Inflatable Decelerator (LOFTID) was spun up, the THOR system seemed like a good candidate to salvage flight ready hardware. There were, however, some key differences in the IRVE/THOR system and the LOFTID one. LOFTID’s HIAD was two times the size of IRVE for starters and would require much higher flows to accommodate inflating such an article within a specific timeframe. With new requirements and a tight schedule, the LOFTID Inflation team set to work to verify flight readiness under LOFTID conditions and eliminate the need to requalify new hardware. LOFTID, utilizing an Inflation System built primarily hardware from IRVE-3 spares, successfully flew in November of 2022. This paper will outline the mission differences, the test campaign used to prepare LOFTID’s Inflation System for flight, and some lessons learned in repurposing older hardware.

Inflation System↗
NASA NTRS1995

Low-Mass Inflation Systems for Inflatable Structures

The use of inflatable space structures has often been proposed for aerospace and planetary applications. Communication, power generation, and very-long-baseline interferometry are just three potential applications of inflatable technology. The success of inflatable structures depends on the development of an applications of inflatable technology. This paper describes two design studies performed to develop a low mass inflation system. The first study takes advantage of existing onboard propulsion gases to reduce the overall system mass. The second study assumes that there is no onboard propulsion system. Both studies employ advanced components developed for the Pluto fast flyby spacecraft to further reduce mass. The study examined four different types of systems: hydrazine, nitrogen and water, nitrogen, and xenon. This study shows that all of these systems can be built for a small space structure with masses lower than 0.5 kilograms.

Thunnissen, Daniel P.↗
NASA NTRS2000

Inflatable Structures Technology Handbook: Inflatable Habitats - Chapter 21

The technologies required to design, fabricate, and utilize an inflatable module for space applications has been demonstrated and proven by the TransHab team during the development phase of the program. Through testing and hands-on development several issues about inflatable space structures have been addressed , such as: ease of manufacturing, structural integrity, micrometeorite protection, folding , and vacuum deployment. The TransHab inflatable technology development program has proven that not only are inflatable structures a viable option, but they also offer significant advantages over conventional metallic structures.

Kennedy, Kriss J.↗
NASA NTRS2011

Inflation, Reionization, and All That: The Primordial Inflation Explorer

The Primordial Inflation Explorer is an Explorer-class mission to measure the gravity-wave signature of primordial inflation through its distinctive imprint on the linear polarization of the cosmic microwave background. PIXIE uses an innovative optical design to achieve background-limited sensitivity in 400 spectral channels spanning 2.5 decades in frequency from 30 GHz to 6 THz (1 cm to 50 micron wavelength). The principal science goal is the detection and characterization of linear polarization from an inflationary epoch in the early universe, with tensor-to-scalar ratio r less than l0^{-3) at 5 standard deviations. The rich PIXIE data set will also constrain physical processes ranging from Big Bang cosmology to the nature of the first stars to physical conditions within the interstellar medium of the Galaxy. I describe the PIXIE instrument and mission architecture needed to detect the inflationary signature using only 4 semiconductor bolometers.

Kogut, Alan J.↗
NASA NTRS2012

Inflation, Reionization, and All That: The Primordial Inflation Explorer

The Primordial Inflation Explorer is an Explorer-class mission to measure the gravity-wave signature of primordial inflation through its distinctive imprint on the linear polarization of the cosmic microwave background. PIXIE uses an innovative optical design to achieve background-limited sensitivity in 400 spectral channels spanning 2.5 decades in frequency from 30 GHz to 6 THz (1 cm to 50 micron wavelength). The principal science goal is the detection and characterization of linear polarization from an inflationary epoch in the early universe, with tensor-to-scalar ratio r < 10(exp -3) at 5 standard deviations. The rich PIXIE data set will also constrain physical processes ranging from Big Bang cosmology to the nature of the first stars to physical conditions within the interstellar medium of the Galaxy. I describe the PIXIE instrument and mission architecture needed to detect the inflationary signature using only 4 semiconductor bolometers.

Kogut, Alan J.↗
NASA NTRS1991

The inflation sector of extended inflation

In extended inflation, the inflationary era is brought to a close by the process of percolation of true vacuum bubbles produced in a first-order phase transition. This paper discusses several effects that might obtain if the universe undergoes an inflationary first-order phase transition.

Kolb, Edward W.↗
NASA NTRS2018

Development of an Inflatable Airlock for a Deep Space Gateway

Inflatable structures technology utilizes high-strength fabric materials and internal pressure to create a stiffened pressure vessel that can replace traditional metallic primary structure in a habitable spacecraft. The flexibility of fabric structures allows them to be compactly stowed for launch and expanded in space, providing significant launch volume savings. The unique construction and design flexibility of these structures can be customized for a variety of uses in space including landing bags, decelerators, long duration in-space and planetary surface habitats, and even airlocks. An airlock is often a required component of a crewed spacecraft to allow for maintenance and human exploration outside of the vehicle. Airlock designs in use today rely on complex hatches and seals connected by metallic walls. Recent developments towards the design of an inflatable airlock structure show feasibility and a significant launch volume savings over a traditional metallic design. This paper will provide a high-level summary of these projects and the current state-of-the-art in inflatable airlock development with additional references and detail about previous and on-going research, providing guidance for the design of a softgoods airlock system. The use of inflatables in space has been in development since the 1960’s for both habitats and airlocks. The first ever EVA was conducted by the USSR in 1965 using an inflatable airlock known as the Volga. This airlock was attached to the Voskhod 2 spacecraft and turned the vehicle into a dual chamber airlock. The airlock was successfully deployed, used and jettisoned after Alexey Leonov’s historic spacewalk. Additional work on human-rated inflatable structures was not continued until the late 1990’s when NASA-JSC led an effort to demonstrate these structures as feasible long-term pressurized elements with the TransHab project. The technology developed and pioneered during this project led to multiple patents and proven feasibility that inflatables could be used for large habitable structures. Following TransHab, Bigelow Aerospace continued the development of inflatable structures with technical support from NASA. This partnership eventually led to the successful flight certification, launch, attachment and deployment of the Bigelow Expandable Activities Module (BEAM) on the ISS in 2016. Inflatable and expandable airlock structures have undergone various detailed feasibility studies and testing for over 15 years, most notably with the Advanced Inflatable Airlock (AIA), Dual-Chamber Hybrid Inflatable Suitlock (DCIS), Minimalistic Advanced Soft Hatch (MASH), and Lightweight External Inflatable Airlock (LEIA). During this time, full-scale articles have been built and pressure-tested, and mock-ups and demonstrators have been constructed and evaluated. During the 2001-2003 timeframe, the AIA concept was matured through requirements development, conceptual design, subscale and full-scale engineering breadboards subjecting various test articles to deployment and pressure testing up to four times operating pressure. These tests proved the feasibility of successful deployment and structural integrity of an inflatable crewlock. Additional testing was performed in the ensuing years, as funding permitted, to further refine additional structural and deployment concepts and to understand the EVA crewmember interfaces, hatches and EVA support equipment interfaces that would be required for a fully functioning airlock. This work resulted in a refinement of the structural requirements and an accounting of the systems needed in an inflatable airlock. In 2014, the MASH project developed an ultra-lightweight airlock concept with a fabric hatch that utilized a unique pressure vessel shape to minimize structural loads around a linear seal. The concept uses an automated zipper-like seal that allows for crew egress/ingress. Most of the development work on the project thus far has focused on the design, analysis and testing of the primary structure and the zipper-like seal system is in the preliminary stages of development with a successful proof-of-concept test. As part of the 2017 LEIA effort, studies were conducted on EVA crewmember interfaces on the inside of an inflatable airlock. These efforts included the design of an internal secondary structure and placement of handholds and foot restraints to enable hatch opening, closing and translation through the airlock. Structural design, analysis and testing was completed on several secondary structure candidates. Crew interface testing was also completed using an inflatable crewlock mockup and the JSC Active Response Gravity Offload System (ARGOS) to simulate the movement of an EVA crewmember through an inflatable crewlock in microgravity. The results of these tests helped demonstrate the feasibility of utilizing an inflatable structure as an airlock and informed the required volume, hatch size, and configuration and location of translation aids for crewmembers in a microgravity crewlock. The ISS Quest airlock uses a dual-chamber design with isolated compartments known as the equipment-lock and the crewlock. The equipment-lock houses the Servicing, Performance and Checkout Equipment (SPCE) items (suit batteries, consumables, etc.) while the crewlock has limited internal hardware and is the nominally depressurized compartment during US EVAs. While inflatable dual chamber airlocks have been studied, the current state of the art emphasizes an inflatable crewlock-type structure attached to a rigid equipment-lock type or habitat structure. Since a large portion of the hardware in the equipment-lock are rigid components and connectors that are installed on the ground - and an inflatable structure does not achieve full structural capabilities until pressurized in space - a depressurized fabric structure cannot provide the capabilities of a full equipment-lock. The use of an inflatable as a crewlock, however, provides all the required capabilities for EVA operations in a small launch package that offers significant volume savings over a metallic crewlock. The functions of a traditional equipment lock, including the SPCE, could be provided by a spacecraft’s habitat module or node and not necessarily in a separate equipment lock. An inflatable crewlock would be attached to the vehicle and launched in a packed and compressed state, saving volume under the launch shroud and mass for the overall airlock element compared to a rigid crewlock. Work is currently underway to continue development of an inflatable airlock with a variety of focus areas including the consideration of crew-induced loads and interfaces, the design and development of an internal sub-structure to provide translation aids and restraints, the thermal considerations of a fabric shell depressurized during an EVA, the micrometeorite environment in deep space, and the packaging and deployment of an inflatable airlock.

Deep Space Exploration↗
NASA NTRS2005

Inflatable Re-Entry Vehicle Experiment (IRVE) Design Overview

Inflatable aeroshells offer several advantages over traditional rigid aeroshells for atmospheric entry. Inflatables offer increased payload volume fraction of the launch vehicle shroud and the possibility to deliver more payload mass to the surface for equivalent trajectory constraints. An inflatable s diameter is not constrained by the launch vehicle shroud. The resultant larger drag area can provide deceleration equivalent to a rigid system at higher atmospheric altitudes, thus offering access to higher landing sites. When stowed for launch and cruise, inflatable aeroshells allow access to the payload after the vehicle is integrated for launch and offer direct access to vehicle structure for structural attachment with the launch vehicle. They also offer an opportunity to eliminate system duplication between the cruise stage and entry vehicle. There are however several potential technical challenges for inflatable aeroshells. First and foremost is the fact that they are flexible structures. That flexibility could lead to unpredictable drag performance or an aerostructural dynamic instability. In addition, durability of large inflatable structures may limit their application. They are susceptible to puncture, a potentially catastrophic insult, from many possible sources. Finally, aerothermal heating during planetary entry poses a significant challenge to a thin membrane. NASA Langley Research Center and NASA's Wallops Flight Facility are jointly developing inflatable aeroshell technology for use on future NASA missions. The technology will be demonstrated in the Inflatable Re-entry Vehicle Experiment (IRVE). This paper will detail the development of the initial IRVE inflatable system to be launched on a Terrier/Orion sounding rocket in the fourth quarter of CY2005. The experiment will demonstrate achievable packaging efficiency of the inflatable aeroshell for launch, inflation, leak performance of the inflatable system throughout the flight regime, structural integrity when exposed to a relevant dynamic pressure and aerodynamic stability of the inflatable system. Structural integrity and structural response of the inflatable will be verified with photogrammetric measurements of the back side of the aeroshell in flight. Aerodynamic stability as well as drag performance will be verified with on board inertial measurements and radar tracking from multiple ground radar stations. The experiment will yield valuable information about zero-g vacuum deployment dynamics of the flexible inflatable structure with both inertial and photographic measurements. In addition to demonstrating inflatable technology, IRVE will validate structural, aerothermal, and trajectory modeling techniques for the inflatable. Structural response determined from photogrammetrics will validate structural models, skin temperature measurements and additional in-depth temperature measurements will validate material thermal performance models, and on board inertial measurements along with radar tracking from multiple ground radar stations will validate trajectory simulation models.

Hughes, Stephen J.↗
NASA NTRS2004

The Development of Large Inflatable Antenna for Deep-Space Communications

NASA/JPL's deep-space exploration program has been placing emphasis on reducing the mass and stowage volume of its spacecraft's high-gain and large-aperture antennas. To achieve these goals, the concept of deployable flat reflectarray antenna using an inflatable/thin-membrane structure was introduced at JPL several years ago. A reflectarray is a flat array antenna space-fed by a low-gain feed located at its focal point in a fashion similar to that of a parabolic reflector. The ref1ectarray's elements, using microstrip technology, can be printed onto a flat thin-membrane surface and are each uniquely designed to compensate for the different phase delays due to different path lengths from the feed. Although the reflectarray suffers from limited bandwidth (typically < 10%), it offers a more reliably deployed and maintained flat "natural" surface. A recent hardware development at JPL has demonstrated that a 0.2mm rms surface tolerance (l/50th of a wavelength) was achieved on a 3-meter Ka-band inflatable reflectarray. Another recent development, to combat the reflectarray's narrow band characteristic, demonstrated that dual-band performance, such as X- and Ka-bands, with an aperture efficiency of above 50 percent is achievable by the reflectarray antenna. To mechanically deploy the antenna, the reflectarray's thin membrane aperture surface is supported, tensioned and deployed by an inflatable tubular structure. There are several critical elements and challenging issues associated with the inflatable tube structure. First, the inflatable tube must be made rigidizable so that, once the tube is fully deployed in space, it rigidizes itself and the inflation system is no longer needed. In addition, if the tube is penetrated by small space debris, the tube will maintain its rigidity and not cause deformation to the antenna structure. To support large apertures (e.g. 10m or beyond) without causing any buckling to the small-diameter inflatable tube during vibration, the tube, in addition to rigidization, is also reinforced by circumferential thin blades, as well as axial blades. Second, a controlled deployment mechanism, such as by using Velcro strips, must also be implemented into the system so that, for very large structures, the long inflatable tubes can be deployed in a time-controlled fashion and not get tangled with each other. Third, the thermal analysis is another critical element and must be performed for the tube design in order to assure that the inflated tube, under extreme space thermal conditions, will not deform significantly. Finally, the dynamic vibration analysis must also be performed on the inflatable structure. This will investigate the response of the structure due to excitation introduced by the spacecraft maneuvering and thus determine any necessary damping. Several reflectarray antennas have been developed at JPL to demonstrate the technology. These include an earlier 1-meter X-band inflatable reflectarray, a 3-meter Ka-band inflatable reflectarray, a half-meter dual-band (X and Ka) reflectarray, and the current on-going 10-meter inflatable structure development. The detailed RF and mechanical descriptions of these antennas, as well as their performances, will be presented during the conference.

inflatable antenna↗
NASA NTRS2003

The development of inflatable array antennas

The deployable array antenna using an inflatable or thin-membrane structure has been identified as one of the enabling technologies to achieve low-mass, high packaging efficiency, low cost, and reliable deployment for future NASNJPL spacebome high-gain and large aperture antennas. Array antennas, when compared to parabolic reflectors, although suffering from limited bandwidth performance, offer wide-angle beam scanning capability and a more reliable flat “natural” aperture. To demonstrate the feasibility and capability of this low-mass array technology, three antenna concepts using inflatable and thin-membrane structures were initiated in 1997 at JPL and several breadboard units have been successfully developed. These three concepts are (1) the inflatable phased array, (2) the inflatable reflectarray, and (3) frame-supported thin membrane array antenna. All three concepts utilize the printed microstrip antenna technology. Although all three concepts will be briefly presented, this paper will discuss in more detail of the recent development of the second concept. The first concept of inflatable phased arrays that have been constructed are 3 to 5-meter size L-band dual-polarized synthetic aperture radar (SAR) arrays for Earth remote sensing application. They all consist of a rectangular configuration with inflatable cylindrical tubes that support and tension a multi-layer thin-membrane radiating aperture with microstrip patches and microstrip power divider lines. For the second concept, an inflatable reflectarray was developed for future deep-space telecom applications. It is a 3m Ka-band inflatable reflectarray (1.8 kg/m2). This reflectarray uses inflated torus tubes to support and tension a flat-membrane reflectarray surface. The reflectarray surface emulates a curved parabolic reflecting surface. However, because of its flat surface being a “natural surface”, it is much easier to achieve and more reliable to maintain the required surface tolerance than that of a curved parabola during long space flight. For the third concept, an L-band dual polarized SAR array with a 5m x 3m aperture and 2.5 kg/m2 of mass has recently been demonstrated. It consists of seven foldable panels each having a rectangular frame that supports a two-layer thinmembrane microstrip subarray aperture. Each frame is made of light-weight graphite composite material. The chief advantage of this deployable “frame” concept is that each frame is able to rigidly support an appropriate number of T/R modules and phase shifters to achieve the desired power distribution and beam scanning. Several technology challenges, such as the development of rigidizable inflatable tubes, a controlled deployment mechanism, thin-membrane thermal effects, a low-mass inflation system, membrane mounted T/R modules, means to counter surface tolerance issues, etc. are being investigated and will be discussed in the presentation. With foreseeable success in the development of these challenging areas, the inflatable/thin-membrane array antennas could be mature enough in a few years for actual space flight.

Lou, Michael↗
NASA NTRS2001

Advanced Structural and Inflatable Hybrid Spacecraft Module

An inflatable module comprising a structural core and an inflatable shell, wherein the inflatable shell is sealingly attached to the structural core. In its launch configuration, the wall thickness of the inflatable shell is collapsed by vacuum. Also in this configuration, the inflatable shell is collapsed and efficiently folded around the structural core. Upon deployment, the wall thickness of the inflatable shell is inflated; whereby the inflatable shell itself, is thereby inflated around the structural core, defining therein a large enclosed volume. A plurality of removable shelves are arranged interior to the structural core in the launch configuration. The structural core also includes at least one longeron that, in conjunction with the shelves, primarily constitute the rigid, strong, and lightweight load-bearing structure of the module during launch. The removable shelves are detachable from their arrangement in the launch configuration so that, when the module is in its deployed configuration and launch loads no longer exist, the shelves can be rearranged to provide a module interior arrangement suitable for human habitation and work. In the preferred embodiment, to provide efficiency in structural load paths and attachments, the shape of the inflatable shell is a cylinder with semi-toroidal ends.

Schneider, William C.↗
NASA NTRS2002

Structural Modeling of a Five-Meter Thin Film Inflatable Antenna/Concentrator

Inflatable structures have been the subject of renewed interest in recent years for space applications such as communications antennas, solar thermal propulsion, and space solar power. A major advantage of using inflatable structures in space is their extremely light weight. An obvious second advantage is on-orbit deployability and related space savings in the launch configuration. A recent technology demonstrator flight for inflatable structures was the Inflatable Antenna Experiment (IAE) that was deployed on orbit from the Shuttle Orbiter. Although difficulty was encountered in the inflation/deployment phase, the flight was successful overall and provided valuable experience in the use of such structures. Several papers on static structural analysis of inflated cylinders have been written, describing different techniques such as linear shell theory, and nonlinear and variational methods, but very little work had been done in dynamics of inflatable structures until recent years. In 1988 Leonard indicated that elastic beam bending modes could be utilized in approximating lower-order frequencies of inflatable beams. Main, et al. wrote a very significant 1995 paper describing results of modal tests of inflated cantilever beams and the determination of effective material properties. Changes in material properties for different pressures were also discussed, and the beam model was used in a more complex structure. The paper demonstrated that conventional finite element analysis packages could be very useful in the analysis of complex inflatable structures. The purposes of this paper are to discuss the methodology for dynamically characterizing a large 5-meter thin film inflatable reflector, and to discuss the test arrangement and results. Nonlinear finite element modal results are compared to modal test data. The work is significant and of considerable interest to researchers because of 1) the large size of the structure, making it useful for scaling studies, and 2) application of commercially available finite element software for modeling pressurized thin-film structures.

Smalley, Kurt B.↗
NASA NTRS2003

Inflatable Vessel and Method

An inflatable module comprising a structural core and an inflatable shell, wherein the inflatable shell is sealingly attached to the structural core. In its launch or pre-deployed configuration, the wall thickness of the inflatable shell is collapsed by vacuum. Also in this configuration, the inflatable shell is collapsed and efficiently folded around the structural core. Upon deployment, the wall thickness of the inflatable shell is inflated; whereby the inflatable shell itself, is thereby inflated around the structural core, defining therein a large enclosed volume. A plurality of removable shelves are arranged interior to the structural core in the launch configuration. The structural core also includes at least one longeron that, in conjunction with the shelves, primarily constitute the rigid, strong, and lightweight load-bearing structure of the module during launch. The removable shelves are detachable from their arrangement in the launch configuration so that, when the module is in its deployed configuration and launch loads no longer exist, the shelves can be rearranged to provide a module interior arrangement suitable for human habitation and work. In the preferred embodiment, to provide efficiency in structural load paths and attachments, the shape of the inflatable shell is a cylinder with semi-toroidal ends.

Raboin, Jasen L.↗
NASA NTRS2008

Damage Tolerance Testing of a NASA TransHab Derivative Woven Inflatable Module

Current options for Lunar habitat architecture include inflatable habitats and airlocks. Inflatable structures can have mass and volume advantages over conventional structures. Inflatable structures are perceived to carry additional risk because they are at a lower Technical Readiness Level (TRL) than conventional metallic structures. One of the risks associated with inflatable structures is understanding the tolerance to component damage and the resulting behavior of the system after the damage is introduced. The Damage Tolerance Test (DTT) is designed to study the structural integrity of an expandable structure during and subsequent to induced damage. The TransHab Project developed an experimental inflatable module developed at Johnson Space Center in the 1990's. The TransHab design was originally envisioned for use in Mars Transits but was also studied as a potential habitat for the International Space Station (ISS). The design of the TransHab module was based on a woven design using an Aramid fabric. Testing of this design demonstrated a high level of predictability and repeatability and good correlation with analytical predictions of stresses and deflections. Based on JSC's experience with the design and analysis of woven inflatable structures, the Damage Tolerance Test article was designed and fabricated using a woven design. The Damage Tolerance Test Article consists of a load bearing restraint layer, a bladder or gas barrier, and a structural metallic core. The test article restraint layer is fabricated from one inch wide Kevlar webbing that is woven in a basket weave pattern. Underneath the structural restraint layer is the bladder or gas barrier. For this test the bladder was required to maintain pressure for testing only and was not representative of a flight design. The bladder and structural restraint layer attach to the structural core of the module at steel bulkheads at each end. The two bulkheads are separated by a 10 foot center tube which provides the structural support for the module when in a non-inflated state as well as resists a portion of the axial load when pressurized. The longitudinal members of the structural restraint layer are attached to the bulkheads using a series of clevises that are bolted to the bulkheads. Strain gages are placed on the clevises that can measure change in load when the structural restraint is inflated. The test module is 88 inches in diameter and 120 inches in height. The objectives of the DTT are to (1) verify the structural integrity of the assembled and pressurized structure when a section of the structural restraint layer is cut by a foreign object, and (2) verify the load distribution of the structural restraint layer during pressurization, before and after the structural restraint layer is severed. For this test, a longitudinal structural restraint strap will be severed using a linear shape charge. The linear shape charge was designed specifically for this application to cut only a single longitudinal strap, while not damaging the bladder. An array of strain gages were located at the bulkhead mounted clevises where the longitudinal restraint layer straps are attached. The DTT article was inflated to 45 psig, 25% of the ultimate design pressure, and one of the one-inch wide longitudinal structural members was severed. Strain gage measurements of loading in an array of longitudinal straps were taken throughout pressurization of the module to 45 psig, before firing of the linear shape charge, and after firing of the shape charge and separation of the strap. During testing not only were the original objectives met but better than expected results occurred. This paper will discuss space inflatable structures, damage tolerance analysis, test results, and applicability to the Lunar architecture.

Edgecombe, John↗
NASA NTRS2009

Improved Method of Design for Folding Inflatable Shells

An improved method of designing complexly shaped inflatable shells to be assembled from gores was conceived for original application to the inflatable outer shell of a developmental habitable spacecraft module having a cylindrical mid-length section with toroidal end caps. The method is also applicable to inflatable shells of various shapes for terrestrial use. The method addresses problems associated with the assembly, folding, transport, and deployment of inflatable shells that may comprise multiple layers and have complex shapes that can include such doubly curved surfaces as toroids and spheres. One particularly difficult problem is that of mathematically defining fold lines on a gore pattern in a double- curvature region. Moreover, because the fold lines in a double-curvature region tend to be curved, there is a practical problem of how to implement the folds. Another problem is that of modifying the basic gore shapes and sizes for the various layers so that when they are folded as part of the integral structure, they do not mechanically interfere with each other at the fold lines. Heretofore, it has been a common practice to design an inflatable shell to be assembled in the deployed configuration, without regard for the need to fold it into compact form. Typically, the result has been that folding has been a difficult, time-consuming process resulting in a An improved method of designing complexly shaped inflatable shells to be assembled from gores was conceived for original application to the inflatable outer shell of a developmental habitable spacecraft module having a cylindrical mid-length section with toroidal end caps. The method is also applicable to inflatable shells of various shapes for terrestrial use. The method addresses problems associated with the assembly, folding, transport, and deployment of inflatable shells that may comprise multiple layers and have complex shapes that can include such doubly curved surfaces as toroids and spheres. One particularly difficult problem is that of mathematically defining fold lines on a gore pattern in a double- curvature region. Moreover, because the fold lines in a double-curvature region tend to be curved, there is a practical problem of how to implement the folds. Another problem is that of modifying the basic gore shapes and sizes for the various layers so that when they are folded as part of the integral structure, they do not mechanically interfere with each other at the fold lines. Heretofore, it has been a common practice to design an inflatable shell to be assembled in the deployed configuration, without regard for the need to fold it into compact form. Typically, the result has been that folding has been a difficult, time-consuming process resulting in a

Johnson, Christopher J.↗