Material technologies for harsh space environment in Moon, and Mars missions

Rajesh Uppal September 15, 2022 Material, Nanotech, Space Comments Off on Material technologies for harsh space environment in Moon, and Mars missions 628 Views

There is global space race among countries to build Moon bases, harness it’s mineral resources and helium-3, fuel for future nuclear fusion power plants. Space agencies in US, China, Japan, Europe, Russia, Iran , Canada and a few private companies all hope to send people to the moon by as early as 2025. They’re talking about building bases, mining for natural resources, and studying the moon in unprecedented detail. A key figure at the European Space Agency says we must look at how we exploit the moon’s resources before it is too late, as missions begin surface mapping.

Space has now become another domain of warfare and becoming heavily militarized. U.S. government has finally designated space to be a legitimate domain of military operations and formed the U.S. Space Force which will operate in the near-Earth and cislunar domains like our current military operates in the domains of land, sea, and air. The U.S. Space Force must acquire responsive, routine, and reliable access to space — starting with launch systems optimize for reaching low Earth orbit (LEO). Many space analysts agree that this capability needs reusable launch vehicles (RLVs), not the current multi-stage, expendable vehicles.

A single-stage-to-orbit (or SSTO) vehicle reaches orbit from the surface of a body using only propellants and fluids and without expending tanks, engines, or other major hardware. The term usually, but not exclusively, refers to reusable vehicles. In the 1990s, NASA identified three critical technology needed to make an SSTO spacecraft achievable: (1) advanced composite materials; (2) altitude compensating engines; and (3) tri-propellant engines.

Materials are the enablers behind the structures, devices, vehicles, power, life support, propulsion, entry, and many other systems that Space agencies require to develop and use to fulfill their missions.

Materials and structures systems are essential to performing the functions required at virtually every stage of spaceflight operations in order to achieve specified mission objectives. Advanced manufacturing capabilities are required for significant improvements in cost, schedule, and overall performance.

New materials are needed to make lighter, stronger, faster, and safer space vehicles of the future. They must ensure that satellites and launchers work safely and well in extreme hot and cold conditions of space; amidst high pressure and protect crews from radiation hazards. They should also protect space vehicles from the impact of micrometeorites that may hit them.

Harsh Space Environment

From low Earth orbit to planetary bodies, space is a unique environment with atomic oxygen, radiation, high-speed impactors, and extreme temperature cycling.

Hardware exposed to space must withstand all aspects of the space environment. This includes vacuum, thermal cycling, charged particle radiation, ultraviolet radiation, and in some environments, plasma effects and atomic oxygen. Micrometeoroids and space debris particles may impact at high velocities. All of these may have significant effects on material properties either alone or in synergism.

Launching a spacecraft requires overcoming the Earth’s gravitational pull, but during the upward momentum of leaving the launching pad, the craft will experience up to three times the force of Earth’s gravity. Materials used on the spacecraft cannot break, bend or weaken under such effects. After the craft goes into orbit, the gravitational force drops to almost zero. This shift from high to no gravitational force can affect the integrity of low-grade materials or those not designed to withstand such stresses.

Spacecraft will experience internal and external forces. For example, the internal pressure from oxygen inside the International Space Station is 15 pounds per inch. The structure of the craft must stand up to this force from the inside in addition to retaining its shape from exterior pressures on it such as gravitational changes during launch. The hard vacuum of space with its pressures below 10−4 Pa (10−6 Torr) causes some materials to outgas, which in turn affects any spacecraft component with a line-of-sight to the emitting material.

Temperatures shift from high to low as an orbiting device moves into the sunlight or behind the Earth’s shadow. For example, NASA’s Orion spacecraft designed to travel outside the moon’s orbit will experience temperatures ranging from -101 to 288 degrees Celsius (-150 to 550 degrees Fahrenheit). Thermal cycling occurs as the spacecraft moves through sunlight and shadow while in orbit that can cause cracking, crazing, delamination, and other mechanical problems, particularly in assemblies where there is mismatch in the coefficient of thermal expansion.

Outside the protection of the Earth’s atmosphere, radiation levels increase. Charged particle radiation includes protons and electrons with a wide range of energies. Solar storms can drastically spike the radiation levels with little notice. Spacecraft operating in or outside the Van Allen belts are exposed to much greater radiation levels than those in low Earth orbit. Charged particle radiation, along with ultraviolet radiation can cause cross-linking (hardening) and chain scission (weakening) of polymers, darkening and color center formation in windows and optics, and single event upsets in electronics.

Plasma refers to the ionized molecules in the upper atmosphere that have been excited by interaction with ultraviolet radiation and are affected by the Earth’s magnetic field lines. Interaction with plasma and charged particles in the space environment contributes to the build-up of surface charge, especially in higher voltage systems. This surface charge can damage electronics, produce single-event upsets (SEU), trigger arcs in solar arrays or power systems, and cause dielectric breakdown of structure of surface coatings.

Atomic oxygen (AO) is produced when ultraviolet radiation reacts with molecular oxygen in the upper atmosphere. Currently only found in low Earth orbit between 100 and 1,000 km altitude, AO oxidizes metals, especially silver and osmium. AO reacts strongly with any material containing carbon, nitrogen, sulfur, and hydrogen bonds of 5 eV bond energy or less, meaning that most polymers react and erode away.

Over time, the number of defunct satellites still in orbit has increased. These shells create large amounts of space junk around the Earth, and any craft in orbit will experience several impacts from this refuse. Like the current satellites, older models had similarly durable constructions. So, their materials are robust and can create significant damage to new satellites that can’t withstand the impacts. In orbit, space junk is not the only problem for satellites. Meteors can reach speeds faster than bullets, 42 kilometers per second (26 miles per second). At these rates, even small space rocks can pierce a hole in a weak part of a satellite. Natural and human-made debris are real threats to any spacecraft, which is why testing impacts during material test programs should be an essential part of any orbiting spacecraft’s creation.

Vibrations may not occur in space, but spacecraft will experience much movement during and immediately after launch. Swept sine testing looks at how satellites handle a variety of vibration frequencies. By testing a range of motion on the materials, scientists can find weaknesses and correct them before the craft reaches orbit.

Material requirements

How will the fibers and fabrics perform there and what changes will be induced in the fiber materials? How should electronic fabrics be designed in order to meet the demands of aerospace applications? are some of the questions researchers are addressing.

Space puts all materials under severe stresses, allowing only the most robust products to survive. Testing materials for space is crucial to ensuring the devices that use them will last in the worst conditions known to humanity without a repair service anywhere in sight. Without testing, the efforts of putting satellites into orbit are for naught when the devices fail in the heat of the atmosphere or the cold of space

To understand the effects of space on different materials Kim de Groh, a senior materials research engineer at NASA’s Glenn Research Center in Cleveland, collects data from the Materials International Space Station Experiment (MISSE) missions. This past April de Groh sent 138 different material samples to the International Space Station as part of MISSE-9, which was successfully launched on SpaceX CRS-14 aboard a Dragon spacecraft. De Groh’s goal is to figure out how long these materials will last in outer space and to accomplish this goal she will study the effects atomic oxygen and radiation have on exposed polymers, composites and coatings.

The MISSE-9 samples will remain in space for one year, after which they will be returned to Earth for post-flight examination. The information gathered from this mission will allow de Groh to make more accurate predictions of materials and component lifetimes in space, and enable engineers to build longer-lasting vehicles for spaceflight.

Current state-of-the-art composite materials are not light/strong enough for crewed missions to Mars and beyond. Structural components of deep space vehicles require lighter/stronger materials for fuel efficiency. The NASA Space Technologies Research Institute (STRI) for Ultra-Strong Composites by Computational Design (US-COMP) is focused on developing a new generation of composites for this purpose. US-COMP is using computational simulation to drive the material design in an efficient manner.

Spacecraft Design and Materials Requirements

Various craft must be built to stand up to the extremes of space. Satellites, shuttles and even extravehicular mobility units (EMU) all need to have components that protect from impacts, pressure, radiation and temperature swings. Since these all need to withstand similar conditions with only the levels varying, testing for survivability overlaps for many types of spacecraft. In addition to the satellites or spacecraft , the equipment aboard them, including communications devices and cameras, need to have the durability to hold up to the same conditions.

Because the Orion will carry a human crew, the temperature inside the living and working quarters must remain a stable 25 degrees Celsius (77 degrees Fahrenheit). To accomplish this task, NASA will combine temperature controls and a thermal protection system to keep the astronauts inside safe. The temperatures become even more extreme upon reentry. Moving at a speed of 25,000 mph, the friction of the atmosphere will generate heat around the spacecraft up to 2,760 degrees Celsius (5,000 degrees Fahrenheit). The craft’s AVCOAT heat shields will protect the ship at their own expense. These single-use shields will disintegrate during reentry.

On the Orion, which will experience much more radiation than satellites in Earth’s orbit, several redundant systems will protect the craft and astronauts from radiation. Four computer systems will continue to check themselves throughout the journey. A separate backup computer will keep the spacecraft in operation should radiation cause the other four computers to fail. Astronauts will have a specially shielded storm shelter to retreat to in case of solar storms, and NASA is currently testing unique radiation-protective clothing that astronauts can quickly don to keep their organs safe from radiation damage.

Strength-to-weight ratio is usually the critical factor in choosing structural materials for spacecraft. Static and dynamic loads must be considered, along with thermal performance, corrosion protection, manufacturability, reparability, and cost. High strength alloys of aluminum, titanium, and stainless steel have been in common use for decades.

Aluminum-lithium alloys have 10% or more weight savings over standard aerospace aluminum alloys. For example, aluminum-lithium alloy was used in the Superlightweight Tank (SLWT) for the Space Shuttle, with a weight savings of 7,000 lbs. over the original External Tank.

“For space applications, weight is especially critical because every additional kilo costs about $10,000 to launch into Earth orbit,” explains Don Wantock, Product Portfolio Manager at Solvay’s Composite Materials. “The composites used in space structural applications, which are frequently polymers like epoxy combined with a carbon fiber reinforcement, often exhibit special characteristics for space use, but they do have a resemblance to the materials employed for aircraft manufacturing.”

Space structures that demand tight tolerances in coefficient of thermal expansion, such as telescope optical benches, are usually made of composite materials. A wide variety of fibers, including graphite, boron, fiberglass, aramids, and carbon are available, as are many polymer resin systems, including epoxy, phenolic, polyimide, and polysulfone. The fiber may be in tow, tape, sheet, or woven form for traditional polymer-matrix composites. Metal-matrix composites (MMCs) and ceramic-matrix composites (CMCs) may have particulate or fiber reinforcement, where the fiber can be continuous or discontinuous (chopped fibers or whiskers). These are used where high toughness is needed.

Individual materials need testing on the craft, and the systems require examination, too. For satellites, the batteries, fuel cells, solar panels, communication system, electrical components and antennas are few of the elements that require testing to ensure they will operate in concert correctly once the device reaches orbit.

Material requirements for ISRO future missions

Material costs alone are 85% of a launch vehicle. The remaining 15% includes the propellant, technology, labour, tracking and everything else. “Materials are the heart of any space programme. Without advancements in them we cannot keep it going.” A national effort is needed to develop and produce advanced materials to drive the future space programme, Indian Space Research Organisation (ISRO) chairman K. Sivan has said. He was delivering the 37th annual Brahm Prakash memorial lecture organised by the Indian Institute of Metals and the Indian Institute of Science.

Along with high propulsion systems for its launch vehicles, the ISRO is pursuing materials that have extraordinary properties, such as aluminium and beryllium alloys and carbon nanotubes. These are needed for the upcoming high-profile national missions such as the Human Space Programme (HSP), the Reusable Launch Vehicle (RLV), re-entering crew capsules, fuel-saving scramjet missions and the distant single-stage launchers. Locally made materials will also help to cut imports and also lower mission costs, Dr. Sivan said here.

“In recent years, ISRO has indigenised a large number of materials that are hard to get. This has reduced the import content from around 32% to 8% now. However, development of advanced materials such as carbon carbon composites and those for electronics is the immediate need of the space programme. A national effort is required in these two areas,” Dr. Sivan said.

Over the years, ISRO has localised maraging steel, many aluminium alloys, composites, chemicals, coatings and high temperature items. A hafnium-neobium has been produced to create a superalloy of columbium for advanced missions and needs to be produced on a large scale. ISRO is now looking for aluminium and beryllium alloys to make smaller structures; and carbon-carbon composites for the nose cone of the RLV; and carbon nanotubes for fuel tank systems and silica alternatives for thermal tiles. Next-generation semicryogenic launchers and electric propulsion systems of smaller future satellites need them.

“Lab-level R&D can produce small quantities of special materials. We want industry to come forward to produce them in large quantities,” told Dr. Sivan. A carbon fibre technology developed with National Aeronaticial Labs awaits a production partner.

Much of ISRO’s materials research is conducted at VSSC, the rocket development centre, with other centres chipping in. VSSC’s transfer of titanium sponge technology to Kerala Metals and Minerals Ltd is a major success story. Since 2015, it has erased ISRO’s import of 200-300 tonnes each year, bringing down the material’s cost and creating a surplus supply in the country.

Spacecraft materials

Kevlar is more frequently associated with its use in bulletproof garments for the military and police. This material has several properties that make it ideal for use in spacecraft. It has strength enough to resist bullets, making it perfect for standing up to impacts from meteors and space junk. Additionally, Kevlar weighs little compared to its durability. It also can experience extreme temperatures without damage to its structure or changing its form.

Another common material used in spacecraft is aluminum. Though itself, aluminum does not have the needed strength for space use, when combined with other metals into an alloy, its strength increases while maintaining its signature light weight. Aluminum alloy performs so well in impact testing that the International Space Station uses this material for its window shutters to keep debris from damaging the windows.

For the nose of the space shuttle that encountered temperatures over 1,260 degrees Celsius (2,300 degrees Fahrenheit), NASA used a reinforced carbon-carbon composite (RCC). Other areas of the space shuttle that experienced similarly hot temperatures used this composite. The benefit of RCC lies in its ability to give off heat applied directly to it as well as indirect heat. The warmth from nearby surfaces on the shuttle traveled to the RCC-covered parts, where the RCC would release the heat, helping the shuttle to cool down, similar to the way a radiator indirectly cools a car engine.

The process used to create RCC created cracks when the designers applied silicon carbide coating at high temperatures. However, when the temperatures around the shuttle rise, the cracks close. This changing of the material’s structure at various temperatures iterates how necessary testing the content is. Without thorough examination, a part made of RCC or similar composure may not perform as expected at elevated temperatures, causing the failure of the piece and the spacecraft it’s part of.

Thermal Protection materials

Thermal Protection Systems (TPS) protect spacecraft from extremely high temperatures and heating during all mission phases and are very often low-to-no-fault-tolerant, critical systems that constitute a significant mass fraction of spacecraft. TPS technologies require exotic materials and structures necessary for reentry and propulsion systems, and high-temperature sensors and electronics for health monitoring and communication through plasma during reentry.

Thermal protection materials are separate from thermal control materials in that thermal control materials are used to moderate on-orbit temperatures, and thermal protection materials are generally for higher temperatures, such as around engine exhaust or for reentry. These temperatures may reach 2,800 ºC (5,070 ºF). Heatshields may be made from reusable materials, such as tiles or ceramic-matrix composites, or one-time use materials, such as ablatives.

Reusable Surface Insulation

High-temperature reusable surface insulation (HRSI) has a black borosilicate glass coating, making this dark surface capable of standing up to the same high temperatures as the nose cone encountered. White parts of the shuttle have low-temperature reusable surface insulation (LRSI) and can only withstand lower temperatures, up to 649 degrees Celsius (1,200 degrees Fahrenheit). The white coloring allows for better control of temperatures inside the shuttle where the astronauts worked. NASA replaced the LRSI with advanced flexible, reusable surface insulation (ARSI). The space agency used ARSI for later shuttles Atlantis, Endeavor and Discovery. The application of this insulation reduced the cost of construction and the weight of the shuttle.

Nomex Felt

For the coldest areas of the shuttle that experienced temperatures no higher than 371 degrees Celsius (700 degrees Fahrenheit), NASA used reusable surface insulation made of coated Nomex felt. The middle and tail end of the craft in addition to the payload doors had this coating.

Thermal Glass

The space shuttles needed windows that would allow the astronauts to see out of clearly without allowing heat to pass through the material. Thermal glass proved the solution to protect the astronauts from both high and low temperatures around the windows and the pressures of space travel.

Silica

Silica cloth filled gaps on the space shuttle created by moving parts such as around the landing gear or the loading bay. Another part of the shuttle that used silica in its many forms included the RCC nose cone, which used sodium silicate to seal the cracks created during the coating process. NASA selected silica tiles for lower temperatures zones of the space shuttle, and shuttle builders used borosilicate glass coating for the HRSI portions of the ship.

In Nov 2020, MIT researchers sent samples of various high-tech fabrics, some with embedded sensors or electronics, to the International Space Station.

The white color of the International Space Station is actually a protective fabric material called Beta cloth, which is a Teflon-impregnated fiberglass designed to shield spacecraft and spacesuits from the harsh elements of low Earth orbit. For decades, these fabrics have remained electrically passive, despite offering large-area real estate on the exterior of space assets.

In Nov 2020 a team of MIT researchers sent samples of various high-tech fabrics, some with embedded sensors or electronics, to the International Space Station. The samples (unpowered for now) will be exposed to the space environment for a year in order to determine a baseline for how well these materials survive the harsh environment of low Earth orbit. The hope is that this work could lead to thermal blankets for spacecraft, that could act as sensitive detectors for impacting micrometeoroids and space debris. Ultimately, another goal is new smart fabrics that allow astronauts to feel touch right through their pressurized suits.

We imagine turning this spacecraft skin into an enormous space debris and micrometeoroid impact sensor. The samples that we worked with JAXA, the Japanese space agency, and Space BD to send to the International Space Station incorporate materials like charge-sensitive synthetic fur — an early concept — and vibration-sensitive fiber sensors — our project’s focus — into space-resilient fabrics. The resulting fabric may be useful for detecting cosmic dust of scientific interest, and for damage detection on spacecraft, said MIT’s multidisciplinary team, graduate students Juliana Cherston of the Media Lab, and Yuchen Sun of the Department of Chemistry, and postdoc Wei Yan of the Research Laboratory of Electronics and the Department of Materials Science and Engineering,

he fabric samples contain thermally drawn “acoustic” fibers developed with ISN funding that are capable of converting mechanical vibration energy into electric energy (via the piezoelectric effect). When micrometeoroids or space debris hit the fabric, the fabric vibrates, and the “acoustic” fiber generates an electrical signal. Thermally drawn multimaterial fibers have been developed by our research group at MIT for more than 20 years; what makes these acoustic fibers special is their exquisite sensitivity to mechanical vibrations. The fabric has been shown in ground facilities to detect and measure impact regardless of where the space dust impacted the surface of the fabric.

While our project’s main focus has been on augmenting fabrics used on the exterior of spacecraft, I also envision that future spacesuits will be electrically active and highly multifunctional. Textiles buried within the suit will be able monitor the health condition of astronauts in real time by interrogating physiological signals over large areas.

Fabrics may also serve as localized heating and cooling systems, radiation dosimeters, and efficient communications infrastructure (via fabric optics and acoustics). They may harvest solar energy as well as small amounts of energy from vibration, and store this energy in fiber batteries or supercapacitors, which would allow the system to be self-powered. Fabrics might even serve as part of an exoskeleton that assists astronauts in maneuvering on planetary bodies and in microgravity. One broad vision at play is to pack an enormous amount of function into space resilient textiles, creating an analogue of “Moore’s law” for space fabrics.

Recently, we have been venturing into the area of high-speed mechanics, testing novel materials spanning polymers, thin films, and nanoarchitected materials using a laser accelerator facility designed by our lab to impinge tiny particles on target surfaces at speeds exceeding 1 kilometer per second.

Chinese Scientists make material breakthrough that enables rockets to orbit longer

Chinese scientists have made a breakthrough in cryogenic rocket engine technology that can extend the orbital period of rockets from a few hours to 30 days, providing support for China’s future deep space exploration. Cryogenic rocket engines are specially designed to work at extremely low temperatures. They use non-toxic and non-polluting propellants, such as liquid hydrogen and liquid oxygen, which are more cost-efficient than others.

The engine has been widely used in domestic and foreign launch vehicles, including China’s Long March-5 and Long March-7 carrier rockets. However, most of these rockets can orbit only a few minutes or a few hours. An extended orbital period has puzzled the aerospace community for a long time. Scientists from the China Academy of Launch Vehicle Technology have developed two insulating materials that can reduce propellant evaporation loss and keep rockets in flight for longer than before. According to Zhang Shaohua, a member of the research team, a cryogenic rocket will face a severe thermal environment when it flies in orbit, which will cause lots of propellant evaporation, accelerate propellant loss and reduce the time in orbit.

“If a car keeps leaking oil, its range will inevitably be shortened,” said Zhang. In addition, when a rocket is flying, its engine will expel the exhaust gases to keep pressure balance in the propellant storage tank. However, under the microgravity environment in space, gas and liquid cryogenic propellant will be mixed, therefore, a large amount of liquid propellant will also be discharged during engine exhaust. One of the newly-developed materials is made of polyurethane foam, a chemical composition, which can increase the insulation capacity by more than 50 percent compared with traditional foam materials. The other one using variable density multilayer insulation also shows improved thermal performance, about 18 percent higher than traditional materials. The test results showed that with the two advanced materials, the daily evaporation of cryogenic propellant can be cut down from 2.5 percent to 0.5 percent, said Zhang. The material technology breakthrough realizes long-term storage of cryogenic propellant in orbit, proving its readiness for China’s future deep space exploration and long-distance space transportation, Zhang said.

Russian hi-tech hub creates ‘breakthrough’ composite material for space industry

Specialists of the Reshetnev Information Satellite Systems Company and scientists of the Skolkovo Science and Technology Institute (Skoltech) have developed a new technology of making composite materials that will allow designing light and firm panels for the space industry, the Skoltech press office reported.

“The joint experimental design work carried out by specialists of Skoltech and Information Satellite Systems has yielded a new technology of making a composite material – the honeycomb core made of aluminum foil. Honeycomb cored panels are widely used in space vehicles, aircraft-and ship-building, the furniture, automobile and other industries,” the Skoltech press office said in a statement.

The honeycomb core made of aluminum foil is referred to the category of composite materials that are very firm and light at the same time: the foil is just 23 micrometers thick while the honeycomb cell edge is 2.5 mm long. Skoltech engineers have developed equipment for making this honeycomb filler using laser technologies, the vision processing technology and modern automated systems. Overall, two types of the honeycomb filler have been developed under the project: for flat panels and for curvilinear (cylindrical, parabolic and other) load-carrying structures.

“The technical concept that has been developed and implemented is universal as it allows obtaining various types of the filler using the same equipment: with a flexible and hexagonal shape of the honeycomb cell [for curvilinear and flat structures, respectively]. In actual fact, the production of a new material has been created today, which opens new possibilities for implementing designers’ ideas for designing light and firm structures with the surface of the curve of the second order,” the statement says.

The conveyor for producing aluminum honeycombs has been launched at the Applied Mechanics Small Design Bureau (part of the Reshetnev Information Satellite Systems Company). Its production capacities will eventually suffice both to meet the Company’s requirements and provide other Roscosmos organizations with the high-quality material.

AFRL investigating space weather effects on satellite materials

The Air Force Research Laboratory, in partnership with several universities, has investigated the effects of space weather damage to polyimides, materials used extensively in spacecraft construction due to their high heat resistance. The researchers determined the previously unknown chemical and physical effects of electron bombardment in Earth’s magnetosphere on these polymers. Electrons trapped in the Earth’s magnetic field are the most damaging components of weather in the geosynchronous Earth orbit.

Polyimide films, such as Kapton, are used to construct spacecraft components, including flexible printed circuits, electronics, electronic packaging, wiring and thermal blankets. This material must endure the extreme and variable radiation conditions present in the operational environment for each spacecraft. Understanding the processes of radiation damage is a critical part of predicting the long-term behaviors of these products and improving their performance and operational longevity.

According to researchers, the stability of the polymer during and after radiation damage is a serious concern. While Kapton is extremely radiation resistant, it suffers serious performance degradation when exposed to the space environment. Normally flexible within a very broad temperature range that bridges -100 C to 250 C upon radiation exposure, the material turns brittle and loses its superior mechanical properties.A team of AFRL scientists at the Materials and Manufacturing Directorate and the Space Vehicles Directorate collaborated with a number of academic partners from Johns Hopkins University, Assurance Technology Corporation, Hunter College of the City University of New York and Pennsylvania State University to understand the damage caused by radiation.

The team discovered that when a Kapton sample is irradiated, it changes color from its normal orange-amber to red. This color change is indicative of electron-induced chemical changes in the material. After several hours of exposure to the atmosphere, the sample turns back to its original color. This “self-healing” effect is pronounced in the atmosphere and led the team to investigate what chemical alterations space-like radiation causes in Kapton.After thorough testing and modeling, it was discovered that while chemical bonds are broken throughout the material, the damage was localized on a few types of bonds. In other words, space radiation dose not break every chemical bond in the material and selectively leaves large pieces of the polymer unscathed.

This also implies that Kapton is not self-healing after irradiation as was first suggested when the color changed back to normal, but rather forms a new material with the pieces left behind after the damage. The team captured the effects of radiation damage using a modeling system called Reactive Force Field molecular dynamics known as Reaxff. The modeling system allows them to simulate the process in near real-world conditions. The researchers then correlate these modeling results to experimental characterization, including spectroscopy, thermo-mechanical testing and x-ray diffraction and scattering.

The interpretation of the modeling work combined with the experimental findings led to insights on how to improve the chemical structure of polyimides and create better radiation-hardened materials. Reaxff with its reactive force fields proves to be an efficient technique to predict the behavior of materials in extreme environments and provides a cost-effective screening tool for the most operational use of materials for extreme applications.These studies generated insight into improving the finest materials currently available for specialized applications. Preventing brittle behavior after irradiation may be avoided by adding additional flexible units into the polymer backbone and pathways that lead to better recombination and self-healing mechanisms.

This makes the backbone more rubber-like while retaining the high-temperature capabilities of Kapton after electron bombardment. Chemical bonds that are flexible enough could improve absorption of the incoming energy and turn it into heat rather than rupturing the bonds. Over the course of the collaboration, the team assembled all of the required modeling and evaluation expertise to move these goals closer to reality. “The modeling tool could be applied as a predictive tool for other systems that may be used in space or aerospace applications being irradiated by x-rays, gamma rays or electrons,” said Daniel Engelhart of Assurance Technology Corporation. “We are currently working on modeling more complex composite materials under extreme radiation environments.”

“We are also looking at materials which are currently explored as high temperature thermoplastic resins for advanced manufacturing processes,” said Hilmar Koerner of AFRL. These materials can be processed through an extruder and turned into a part, similar to 3D printing. Such materials have the potential to eventually replace Kapton, but are currently limited due to their high price. The team will continue to collaborate on improving the consistency and accuracy of these new theoretical models. The key enabler to solving this difficult problem is the large collaborative effort that was pulled together by AFRL and its partners.

Carbon nanotubes for space

Current and future space missions will push the limits of human exploration, taking astronauts further than ever before. A key safety issue throughout space travel stems from the continuous stream of damaging cosmic radiation that spacecraft are subjected to throughout their journey.

This radiation can damage or even destroy onboard electronics, causing data glitches, prompting vital computer systems to break down, and ultimately putting the mission in jeopardy and the safety of the crew at risk.

NASA has reported that these effects have caused incidents of communications and guidance issues, increased error rates, memory errors, and even spontaneous processor resets reported during solar events. New research reported in Oct 2021 by the American Chemical Society (ACS) in the ACS Nano journal has showcased the potential of carbon nanotubes to help address this issue, discussing how these nanotubes can be developed and configured to maintain their electrical properties and memory, even after being bombarded by significant amounts of radiation.

According to scientists from the Massachusetts Institute of Technology, single-walled CNTs might be the answer to that challenge. With support from the Air Force Research Laboratory in the USA, the researchers built memory chips based on field-effect transistors (FETs), where CNTs deposited on a silicon wafer served as a semiconducting layer.

The research focuses on the use of single-atom-thick carbon nanotubes’ potential to shield field-effect transistors from potentially damaging radiation, and the nanotubes’ capacity to improve the transistors’ energy efficiency versus standard silicon-based versions. Carbon nanotubes were deposited on a silicon wafer which functioned as the semiconducting layer in field-effect transistors. It was discovered that situating shields above and below the carbon nanotubes allowed the transistor’s electrical properties to be protected against incoming radiation up to 10 Mrad, much more than could be achieved via the use of most silicon-based radiation-tolerant electronics.

These memory chips were found to exhibit a similar X-ray radiation threshold to that of silicon-based SRAM devices.

In order to further evaluate the potential of these findings, a comparison was performed using a number of previous studies which had looked at the suitability of carbon nanotube field-effect transistors. This comparison with the literature confirmed that this work had yielded some of the most promising results thus far.

The researchers’ findings suggest that the use of double-shielded carbon nanotube field-effect transistors could lead to the development of next-generation electronics for space exploration, which are more resistant to radiation and therefore more likely to help keep equipment, electronics, and – most importantly – astronauts safe as they continue to explore space. The lifetime and distance of deep space missions are limited by the energy efficiency and robustness of the technology driving them.