Low Earth Orbit Space Environment Research Articles

High-efficiency radiation attenuation shields of polymer composites for the low earth orbit space environment – multilayer shielding simulation system-based investigations

The polymer/metal hybrids have been used as a solution for the mitigation of ionizing radiation in space for sensitive electronics components, particularly for a proton-rich Low Earth Orbit (LEO) environment. Consequently, radiation attenuation analysis of polymer/metal hybrid composites has been investigated. Radiation attenuation analysis has been performed using online GEANT4 (simulation toolkit) and the Multilayer Shielding Simulation System (MULASSIS) for the LEO space environment. The shielding potential of polymers, such as poly(dimethyl siloxane), poly(methyl methacrylate), polyurethane and ultra-high molecular weight polyethylene, were analyzed with optimized compositions. It was observed that the pristine PDMS attenuated relatively more radiations than other polymer matrices. For modelling of hybrid radiation material composition, PDMS and carbon fibre fabric-derived composite laminates along with metal sheets (Aluminum Al, Tantalum Ta or Tungsten W) were used to analyze hybrid compositions. Here, hybrid composition performance was analyzed as a function of various areal densities. Analyzed polymer laminate/metal hybrid compositions performed better to attenuate LEO radiations up to 42.29%, compared to conventional Al (areal densities of 0.2–1.0 g/cm2). The maximum magnitude of attenuation was found at an areal density of 1.0 g/cm2 for Ta and W metal composition (39.44% and 42.29%, respectively), and so performed better than Al metal. Improved attenuation ratios of the hybrid compositions revealed that the hybrid laminate/metal shields can replace conventional Al shields towards LEO space radiations.

Incremental learning-based optimal design of BFN kernel for online spacecraft disturbance rejection control

Low earth orbit (LEO) space environment is glutted with unknown and uncertain disturbance, which impede the regular operation and dynamic stability of spacecraft. In recent decades, Basis Function Network (BFN) has attracted much attention benefiting from its potential adaptability for unknown dynamic disturbance. However, it also suffers from the shortcomings of parameter drift, under fitting and long time consuming, which restricts its applications in practical space missions. This paper proposes a new online network reconstruction algorithm, which enables BFN a better excitation effect and more rapid response with less time consumption. The algorithm selects less but more relevant basis functions than routine neural network to approximate the disturbance, which consequently helps to achieve a better characterization effect. Two BFN selection strategies based on iterative learning and batch learning are proposed to further increase the efficiency of online network reconstruction. Detailed theoretical derivation proves the feasibility of the new algorithm. Numerical simulation of a real space station shows that the algorithm has strong adaptability and time efficiency under the interference of structural uncertainty.

High performance Li-, Na-, and K-ion storage in electrically conducting coordination polymers.

Coordination polymers (CPs) made of redox-active organic moieties and metal ions emerge as an important class of electroactive materials for battery applications. However, the design and synthesis of high voltage alkali-cation reservoir anionic CPs remains challenging, hindering their practical applications. Herein, we report a family of electrically conducting alkali-cation reservoir CPs with the general formula of A2-TM-PTtSA (wherein A = Li+, Na+, or K+; TM = Fe2+, Co2+, or Mn2+; and PTtSA = benzene-1,2,4,5-tetra-methylsulfonamide). The incorporation of transition metal centers not only enables intrinsic high electrical conductivity, but also shows an impressive redox potential increase of as high as 1 V as compared to A4-PTtSA analogues, resulting in a class of organometallic cathode materials with a high average redox potential of 2.95–3.25 V for Li-, Na- and K-ion batteries. A detailed structure – composition – physicochemical properties – performance correlation study is provided relying on experimental and computational analysis. The best performing candidate shows excellent rate capability (86% of the nominal capacity retained at 10C rate), remarkable cycling stability (96.5% after 1000 cycles), outstanding tolerance to low carbon content (5 wt%), high mass loading (50 mg cm−2), and extreme utilisation conditions of low earth orbit space environment tests. The significance of the disclosed alkali-ion reservoir cathodes is further emphasized by utilizing conventional Li-host graphite anode for full cell assembly, attaining a record voltage of 3 V in an organic cathode Li-ion proof-of-concept cell.

ADEO: the European commercial passive de-orbit subsystem family enabling space debris mitigation

The ADEO subsystem is a scalable drag augmentation device that uses the residual Earth atmosphere present in Low Earth Orbit (LEO) to passively de-orbit of satellites between 1 and 2000 kg. For the de-orbit maneuvre, a large surface is deployed which multiplies the drag effective surface of the satellite significantly. Thereby the drag force is increased as well causing accelerated decay in orbit altitude. Advantageous about a drag augmentation device is that it does not require any active steering and can be designed for passive attitude stabilization thereby making it applicable for non-operational, tumbling spacecrafts as well. The ADEO subsystem consists of four deployable booms that span four sail segments in a planar shaped configuration. While the sails are made of an aluminum-coated polyimide foil, its coating thickness was chosen such that it provides sufficient protection from the LEO space environment. The current activity commenced in August 2018 is going to provide a fully qualified Protoflight Model (PFM) for a follow-up “In Orbit Demonstration” (IOD) in 2021/2022 (ADEO is selected as payload on the European Commission IOD/IOV satellite programme). In May 2020, the team passed the Manufacturing Readiness Review (MRR). An extensive Breadboarding- and Engineering Model campaign including life tests had already been carried out in 2019. The first ADEO-L PFM consists of a 5 m x 5 m dragsail deployed under control of own onboard electronics. Optionally, ADEO-L systems can be equipped with a so-called “watchdog routine” inside the electronics which is able to recognize the point in time when the satellite has come to the end of its life circle. With the help of an on-board battery the sail will be deployed automatically after a certain time in orbit. Operating like this, ADEO-L can be truly called “100% passive”, a “CleanGreen Space Mission”. First commercial candidate missions to be targeted after the successful EC-IOD mission were already identified by Airbus DS (DE) and QinetiQ (BE).

Space Qualification of Ultrafast Laser‐Written Integrated Waveguide Optics

AbstractSatellite‐based quantum technologies represent a possible route for extending the achievable range of quantum communication, allowing the construction of worldwide quantum networks without quantum repeaters. In space missions, however, the volume available for the instrumentation is limited, and footprint is a crucial specification of the devices that can be employed. Integrated optics could be highly beneficial in this sense, as it allows for the miniaturization of different functionalities in small and monolithic photonic circuits. This article reports on qualification of waveguides fabricated in glass by femtosecond laser micromachining for their use in a low Earth orbit space environment. In particular, different laser‐written integrated devices, such as straight waveguides, directional couplers, and Mach–Zehnder interferometers, are exposed to suitable proton and γ‐ray irradiation. This experiment shows that no significant changes have been induced to their characteristics and performances by the radiation exposure. These results, combined with the high compatibility of laser‐written optical circuits to quantum communication applications, pave the way for the use of laser‐written integrated photonic components in future satellite missions.

The effect of atomic oxygen flux and impact energy on the damage of spacecraft metals

High-energy atomic impacts represent one of the biggest threats to material performance in both the low earth orbit (LEO) and deep space environment. However, while significant test data exists for LEO atomic oxygen (AO) collisions, further research is needed on the effect of high-energy collisions that can potentially occur in deeper space. As such, this study investigated using the ReaxFF force field in molecular dynamics to simulate the impact of atomic oxygen on two common spacecraft metals, silver and aluminum. This study used a Wigner-Seitz defect analysis to track the damage evolution of the remaining substrate during impact. Results indicated that for both silver and aluminum the number of defects and depth of damage increased linearly with impact energy. While silver was shown to have a higher erosion yield than aluminum, its substrate formed less defects at all impact energies considered. The source of this discrepancy was attributed to the lower energy needed to form vacancies in aluminum as compared to silver. Our results show that while erosion is certainly an important parameter in measuring the damage to a material by high-energy impacts, it is not sufficient to describe the amount of damage and state of the remaining substrate. Overall, this study demonstrates the potential for molecular dynamics simulations to be used to compare material performance and degradation in harsh deep space environments where testing may not be possible.

POSS enhanced 3D graphene - Polyimide film for atomic oxygen endurance in Low Earth Orbit space environment

Recently, 3D-graphene infused polyimide (3DC/PI) films have shown to be an effective protection coating for electrostatic discharge in spacecraft. However, these films are not suitable for Low Earth Orbit (LEO) due to atomic oxygen (AO) erosion. Here, we used Polyhedral Oligomeric Silsesquioxane (POSS) to enhance the AO durability of 3D-C/PI films. Three different ways of adding POSS to the composite films were studied with ground-based AO exposure. For all infusion approaches, their electrical conductivity behaviour is well preserved and the presence of POSS results in reduced AO erosion yield. Of all the methods studied here, incorporating POSS directly into PI results in the lowest erosion yield of 4.67 × 10−25 cm3/O-atom (one order of magnitude lower than that of Kapton). Adding POSS to PI, extends the durability of the composite film beyond 10 years, making it an ideal protective material for long term mission in LEO.

Characterization of simulated low earth orbit space environment effects on acid-spun carbon nanotube yarns

The purpose of this study is to quantify the detrimental effects of atomic oxygen and ultraviolet (UV) C radiation on the mechanical properties, electrical conductivity, and piezoresistive effect of acid-spun carbon nanotube (CNT) yarns. Monotonic tensile tests with in-situ electrical resistance measurements were performed on pristine and exposed yarns to determine the effects of the atomic oxygen and UVC exposures on the yarn’s material properties. Both type of exposures were performed under vacuum to simulate space environment conditions. The CNT yarns’ mechanical properties did not change significantly after being exposed to UV radiation, but were significantly degraded by the atomic oxygen exposure. The electrical conductivity of the yarn was not significantly affected by either exposure. The piezoresistive effect did not significantly change due to atomic oxygen exposure, but was significantly enhanced as a result of the UV exposure. Scanning electron microscopy revealed significant erosion due to atomic oxygen exposure, but the UV exposure did not significantly change the appearance of the yarn’s external surface. Raman spectroscopy showed that both exposure types induced significant structural disorder in the surface level CNTs. Focused ion beam milling of a UVC exposed yarn revealed that the depth of the induced disorder was very shallow.

Resilient Graphene Ultrathin Flat Lens in Aerospace, Chemical, and Biological Harsh Environments.

The development of ultrathin flat lenses has revolutionized the lens technologies and holds great promise for miniaturizing the conventional lens system in integrated photonic applications. In certain applications, the lenses are required to operate in harsh and/or extreme environments, for example aerospace, chemical, and biological environments. Under such circumstances, it is critical that the ultrathin flat lenses can be resilient and preserve their outstanding performance. However, the majority of the demonstrated ultrathin flat lenses are based on metal or semiconductor materials that have poor chemical, thermal, and UV stability, which limit their applications. Herein, we experimentally demonstrate a graphene ultrathin flat lens that can be applied in harsh environments for different applications, including a low Earth orbit space environment, strong corrosive chemical environments (pH = 0 and pH = 14), and biochemical environment. The graphene lenses have extraordinary environmental stability and can maintain a high level of structural integrity and outstanding focusing performance under different test conditions. Thus, it opens tremendous practical application opportunities for ultrathin flat lenses.

Hollow silica nanosphere/polyimide composite films for enhanced transparency and atomic oxygen resistance

Abstract In the low Earth orbit (LEO) space, transparent polyimide (PI) films with high transmittance and strong resistance to atomic oxygen (AO) are pursued for providing effective protection and energy harvesting for novel lightweight solar arrays in spacecraft. In this work, hollow silica nanospheres (HSNs) were inlaid in transparent PI films for the formation of an HSN/PI composite structure, where the HSNs were first generated by a solution-based removal of organic templates from PAA-silica core-shell nanospheres, free from common high-temperature treatments, and then transferred to PI substrates. The HSN/PI composite structures resulted in the higher transmittance and stronger resistance to AO than did the pristine PI: the composite flexible films showed an average transmittance of 92.43% at broad wavelengths (400–1600 nm) and an AO erosion yield of 4.67 × 10−26 cm3/atom after an AO exposure of 6.05 × 1020 atoms/cm2, which were superior to those of the pristine PI (90.80% and 1.33 × 10−24 cm3/atom, respectively). Simultaneous realization of antireflective (AR), AO resistant, and mechanically robust PI composite flexible films provides new solutions to traditional AR patterned AO-resistant PIs and insights into the multifunctionalization of PIs in the LEO space environment.

Mechanically Robust Atomic Oxygen-Resistant Coatings Capable of Autonomously Healing Damage in Low Earth Orbit Space Environment.

Polymeric materials used in spacecraft require to be protected with an atomic oxygen (AO)-resistant layer because AO can degrade these polymers when spacecraft serves in low earth orbit (LEO) environment. However, mechanical damage on AO-resistant coatings can expose the underlying polymers to AO erosion, shortening their service life. In this study, the fabrication of durable AO-resistant coatings that are capable of autonomously healing mechanical damage under LEO environment is presented. The self-healing AO-resistant coatings are comprised of 2-ureido-4[1H]-pyrimidinone (UPy)-functionalized polyhedral oligomeric silsesquioxane (POSS) (denoted as UPy-POSS) that forms hydrogen-bonded three-dimensional supramolecular polymers. The UPy-POSS supramolecular polymers can be conveniently deposited on polyimides by a hot pressing process. The UPy-POSS polymeric coatings are mechanically robust, thermally stable, and transparent and have a strong adhesion toward polyimides to endure repeated bending/unbending treatments and thermal cycling. The UPy-POSS polymeric coatings exhibit excellent AO attack resistance because of the formation of epidermal SiO2 layer after AO exposure. Due to the reversibility of the quadruple hydrogen bonds between UPy motifs, the UPy-POSS polymeric coatings can rapidly heal mechanical damage such as cracks at 80 °C or under LEO environment to restore their original AO-resistant function.

Responses of TMDs-metals composite films to atomic oxygen exposure

To clarify the ability of reactive metals alloyed transition metal disulfides (TMDs) films resistant to low-earth-orbit (LEO) space exposure, the MoS2-16 at. % Ag film was sputtered and exposed in long-term atomic oxygen (AO) environment. Results revealed the MoS2-Ag composite film could be severely oxidized by the AO irradiation. The 2H-MoSxOy matrix was severely oxidized to MoO3 and MoO2, and the alloyed Ag was partially oxidized to Ag2O. The volume expansion from the oxidation of Ag to Ag2O was responsible for the cracking and thereby severe oxidation of brittle 2H-MoSxOy platelets in the composite film. Furthermore, the re-growth of Ag induced by the AO irradiation was also observed in the initial stage of AO irradiation. Due to the oxidization, the film morphology was changed from the characteristic dentrite-like surface for the non-irradiated film to the terrace-like one for the irradiated film and eventually to the chrysanthemum-like one as increasing the AO fluence. Wear tests revealed that the wear resistance of MoS2 film in vacuum environment could be significantly improved. However, the wear resistance of MoS2-Ag composite film was obviously deteriorated because of the severe oxidation from the AO irradiation. The wear life of MoS2-Ag composite film was sharply reduced from ∼7.6 × 105 cycles before the AO irradiation to ∼4.9 × 104 cycles after the AO irradiation of 5.6 × 1026 atoms∙m−2. These results indicated that for the selection of solid lubricants in LEO space environment, the reactive metals alloyed TMDs films should be excluded as possible as to eliminate potential risks.

Response of MoS2-Sb2O3 film to low-earth-orbit space environment

Many failures and anomalies of spacecrafts originated from space environmental factors. Meanwhile, MoS2 based films have been widely used in space technology as solid lubricants. In this paper, the compact MoS2-Sb2O3 composite film was rf-sputtered and exposed in low earth orbit (LEO) environment, which was aboard the exterior of Shenzhou-7 Manned Spaceship (SZMS-7). The results revealed that the space exposure effect on MoS2-Sb2O3 composite film mainly exhibited the oxidation at the film surface layer less than 3.5 nm. No severe oxidation and cracking phenomena were observed from the space-exposed MoS2-Sb2O3 composite film, which was normal for many space materials. Namely, the MoS2-Sb2O3 composite film exhibited a better capability resistant to LEO space environment.

Enhanced resistance to atomic oxygen of OG POSS/epoxy nanocomposites

Atomic oxygen (AO) in the low Earth orbit (LEO) space is critical to polymer matrix composites. AO strikes the surfaces of materials with sufficient energy to break chemical bonds. In this study, to solve the problem of undercutting of polymer matrix composite by AO, an octaglycidyldimethylsilyl (OG) polyhedral oligomeric silsesquioxane (POSS)/epoxy nanocomposite was proposed to improve the resistance of epoxy to AO. OG POSS/epoxy nanocomposites were fabricated and AO exposure test was carried out to confirm the improvement of resistance to AO. Consequently, it was observed that OG POSS increased the resistance of epoxy to AO. Compared with neat epoxy, OG POSS/epoxy nanocomposite containing 10 wt% OG POSS exhibited a reduction of 67% in mass loss by AO. OG POSS could be readily adapted to epoxy without a complex homogenization process. Therefore, this technology will be an effective way to help epoxy matrix composites survive in severe LEO space environments.

The degradation behavior of C/C composites in high-energy atomic oxygen

In low earth orbit (LEO), spacecraft, space structure and other applications encounter a degradation problem induced by the impact of atomic oxygen (AO) in the space environment. C/C composites (C/Cs), which are widely applied to different applications in space systems, were tested to study the irradiation and bombardment effects of LEO space environment on the composites. The degradation was analyzed in the aspect of mass loss, morphology and flexural strength and thermal conductivity properties. Results show that the specimens are bombarded by high-speed AO with high activity during AO irradiation test. The flexural strength of C/C composites after AO irradiation test for 24 h (AO24, 150.4 MPa) is decreased by 25.8% than C/Cs (202.7 MPa). The coefficients of thermal conductivity of C/Cs after AO irradiation show an increase. Carbon fibers and pyrolytic carbon (PyC) were also exposed to AO irradiation test. Results show that the denudation rate of PyC is slower than that of C/C composites and carbon fiber. Besides, the denudation of carbon fiber (form crisscrossed ravine) is most serious. PyC shows the least damage. This work may provide not only the influence of AO irradiation on C/Cs but the protection of C/Cs from AO irradiation.

Response of RF-sputtered MoS2 composite films to LEO space environment

The rf-sputtered MoS2-Au composite films were exposed in real low earth orbit (LEO) space environment by a space environment exposure device (SEED) aboard China Shenzhou-7 manned spaceship. The ability of the composite films resistant to atomic oxygen (AO) was investigated using X-ray photoelectron spectroscope (XPS), X-ray diffraction (XRD) and field emission scanning electron microscope (FESEM) equipped with an X-ray energy dispersive spectroscopy (EDS). The results showed that the microstructure of the composite film was densified because the growth of MoS2 platelets was suppressed to some content due to the addition of Au, although it was still characterized by a typical dendrite-like morphology. No obvious change in the morphology, phase structure, element composition and friction property was observed from the space exposed and non-exposed composite films, indicating that the composite film exhibited a better anti-oxidation ability as exposed in LEO environment. The improved anti-oxidation ability was attributed to the more compact microstructure and a passivation effect that the dangling bonds at the edge planes of MoS2 platelets were probably occupied by the partial doping atoms.

CVD nano-coating of carbon composites for space materials atomic oxygen shielding

Abstract: The present work analyzes the possibility to employ carbon nanostructures as a basic material to prevent the erosion effects of atomic oxygen suffered by the carbon fiber reinforced polymeric material used in low earth orbit space environment. The application of thin protecting coatings to base materials is a widely used method for preventing the atomic oxygen induced erosion, and thus degradation. The generic purpose is to integrate carbon nanostructures onto carbon composites surface in order to develop the basic substrate of advanced nanocomposite for atomic oxygen protection. The final goal is the characterization of carbon nanostructures-reinforced carbon composites by means of on-ground atomic oxygen simulation facility, with the future objective to assess and optimize the process of carbon-multiscale advanced composites production. With such an aim, a wide investigation on the methane chemical vapor deposition (CVD) over catalyzed carbon fiber-based substrates has been carried out. The as grown nanostructures have been analyzed in terms of morphology, as well as regarding the main features of the resulting growth (yield, purity, homogeneity, coating uniformity, etc.) and the influence of the deposition route operating parameters (catalyst typology, gas flowing rate, growth time/temperature, etc.). A high degree of reproducibility in terms of the relationship between the carbon deposit type/yield and the main process variables (catalyst and protocol) has been thus obtained. Finally, atomic oxygen ground tests have been conducted in order to evaluate the coating process effectiveness. The on-ground test in atomic oxygen environment, with respect to the performances of the reference carbon composites (in terms of total mass loss and atomic oxygen rate of erosion), showed a worsening for the disordered carbon deposit, while an intriguing improvement was achieved by the high-yield carbon nano-filaments deposition.

Effect of thermocycling on the microstructure of Ti-6Al-4V alloy in simulated low Earth orbit space environment

The study of material damage and its physical mechanisms, the deep understanding of material performance degradation processes, and the improvement of key materials and devices used in a space environment are undoubtedly of critical scientific importance. This work investigated the mechanical properties and microstructures of the Ti-6Al-4V alloy subjected to thermocycling in a simulated low Earth orbit (LEO) space environment by using microhardness tests, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The results revealed an initial increase in hardness with the number of cycles, followed by a subsequent decrease. After 300 thermal cycles, many cavities were formed at the two-phase interface of the Ti-6Al-4V alloy. The dominating structures were transformed into dislocation cell substructures of larger size. After 500 cycles, the central structures in the sample were subgrains evolving by dislocation cells, as well as intragranular twins and jogs structures. The relationship between microstructural evolution and thermal fatigue in LEO space environment was discussed, which may help predict the fatigue damage of materials.

The effects of low earth orbit atomic oxygen on the properties of Polytetrafluoroethylene

Polymers are widely used in space systems as the structural materials. The low earth orbit (LEO) space environment includes hazards such as atomic oxygen. Exposure of polymeric materials to atomic oxygen results in destructive effects on the chemical, electrical, thermal, optical and mechanical properties as well as surface degradation. In the present work, the effects of atomic oxygen on the mechanical, thermal, and optical properties of Polytetrafluoroethylene film have been investigated. The atomic oxygen density was calculated by SPENVIS tool. After the atomic oxygen exposure by using radio-frequency (RF) plasma source, the appearance of the samples changed, and the mass of the samples reduced because of outgassing. The results of thermal analysis showed that atomic oxygen flux does not affect thermal degradation of samples regarding TGA diagrams. By increasing the atomic oxygen flux, the amount of absorbance increased showing that atomic oxygen had damaged the surface of Polytetrafluoroethylene, and it had oxidized the surface of the polymer.

Effect of AO/UV/RD exposure on spaceborne diffusers: a comparative experiment.

The environmental measuring instrument (EMI) is a nadir-viewing wide-field imaging spectrometer, which adopts spaceborne diffusers in in-flight calibration systems, including an aluminum diffuser and a quartz volume diffuser. Spaceborne diffusers, are the key components of in-flight calibration systems, and are used to introduce sunlight into the EMI. Hemispheric reflectance and bidirectional reflectance distribution function were experimentally measured to analyze spaceborne diffuser performance. Radiation exposure experiments on atomic oxygen, UV, and radiation dose of the spaceborne diffusers were performed at ground level because the EMI works in low Earth orbit space environments. Effects of radiation exposure on spaceborne diffusers were discussed in detail. Protective methods were introduced to reduce the effects of the space environment, and an in-orbit monitoring method was also proposed.