Low Earth Orbit Environment Research Articles

In Situ Measurement of Carbon Fibre/Polyether Ether Ketone Thermal Expansion in Low Earth Orbit

The low Earth orbit (LEO) environment exposes spacecraft to factors that can degrade the dimensional stability of the structure. Carbon Fibre/Polyether Ether Ketone (CF/PEEK) can limit such degradations. However, there are limited in-orbit data on the performance of CF/PEEK. Usage of small satellite as material science research platform can address such limitations. This paper discusses the design of a material science experiment termed material mission (MM) onboard Ten-Koh satellite, which allows in situ measurements of coefficient of thermal expansion (CTE) for CF/PEEK samples in LEO. Results from ground tests before launch demonstrated the feasibility of the MM design. Analysis of in-orbit data indicated that the CTE values exhibit a non-linear temperature dependence, and there was no shift in CTE values after four months. The acquired in-orbit data was consistent with previous ground tests and in-orbit data. The MM experiment provides data to verify the ground test of CF/PEEK performance in LEO. MM also proved the potential of small satellite as a platform for conducting meaningful material science experiments.

Development of Cycloaliphatic Epoxy-POSS Nanocomposite Matrices with Lambas Enhanced Resistance to Atomic Oxygen.

The preparation of ultra-thin CFRP laminates, which incorporate a cycloaliphatic epoxy resin reinforced with polyhedral oligomeric silsesquioxane (POSS) reagent nanofiller, using out-of-autoclave procedure is reported. The influence of the amount of POSS within the laminate on the mechanical properties and surface roughness of the laminates is analysed before and after exposure to atomic oxygen (AO) to simulate the effects of low Earth orbit (LEO). The addition of 5 wt% POSS to the base epoxy leads to an increase in both flexural strength and modulus, but these values begin to fall as the POSS content rises, possibly due to issues with agglomeration. The addition of POSS offers improved resistance against AO degradation with the laminates containing 20 wt% POSS demonstrating the lowest erosion yield (1.67 × 10−24 cm2/atom) after the equivalent of a period of 12 months in a simulated LEO environment. Exposure to AO promotes the formation of a silicon-rich coating layer on the surface of the laminate, which in turn reduces roughness and increases stiffness, as evidenced by measurements of flexural properties and spectral data after exposure.

First Optical Satellite Tracking Station (OSTS) at NRIAG-Egypt

In March 2019 the first dedicated of optical observation of space debris and artificial satellites (Optical Satellites Tracking Station (OSTS)) in Egypt has been performed by National Research Institute of Astronomy and Geophysics (NRIAG) at Kottamia Observatory. The 0.28 m Telescope is used for tracking and surveying debris and operational satellites at Low Earth Orbit (LEO), High ellipse orbit (HEO) and the Geosynchronous Earth Orbit (GEO). OSTS has also collaborated with International Scientific Optical Network (ISON) for optical observation. The necessary programs to control the telescope, camera and monitoring process are configured. Coordinate corrected metric data is provided with the time information. The system has validated and calibrated processing. The first results of the observations with image processing using Apex-2 software are presented. The optical observations using OSTS are being used to help characterize the debris environment in LEO, HEO and GEO to assist in the modeling projections for space debris database, real population and distribution, detection and orbital determination, and conjunction analysis between operational satellites and/or dangers debris.

Improved atomic oxygen erosion resistance of the carbon fibre–epoxy interface with polyhedral oligomeric silsesquioxane

Polyhedral oligomeric silsesquioxane (POSS) was grafted onto the surface of carbon fibres (CFs) to fabricate carbon fibre/epoxy (CF/EP) composites with improved interlaminar shear strength (ILSS) and atomic oxygen (AO) erosion resistance. POSS-CF was prepared by reacting amine groups on the pretreated CF surface with the POSS to form a continuous uniform layer of siloxane oligomers. X-Ray photoelectron spectroscopy, scanning electron microscopy and Fourier transform infrared spectroscopy demonstrated that POSS was successfully grafted onto the CF surface. The ILSS and AO erosion resistance of the POSS-treated CFs and CF-EP interface were improved because a SiO2 passivation layer formed with AO exposure, especially with POSS-EP0409. This is an effective solution for enhancing the interfacial bonding force and interfacial AO erosion resistance for the low-Earth orbit environment.

A low-frequency blind survey of the low Earth orbit environment using non-coherent passive radar with the Murchison widefield array

AbstractWe have extended our previous work to use the Murchison widefield array (MWA) as a non-coherent passive radar system in the FM frequency band, using terrestrial FM transmitters to illuminate objects in low Earth orbit (LEO) and the MWA as the sensitive receiving element for the radar return. We have implemented a blind detection algorithm that searches for these reflected signals in difference images constructed using standard interferometric imaging techniques. From a large-scale survey using 20 h of archived MWA observations, we detect 74 unique objects over multiple passes, demonstrating the MWA to be a valuable addition to the global Space Domain Awareness network. We detected objects with ranges up to 977 km and as small as$0.03$${\rm m}^2$radar cross section. We found that 30 objects were either non-operational satellites or upper-stage rocket body debris. Additionally, we also detected FM reflections from Geminid meteors and aircraft flying over the MWA. Most of the detections of objects in LEO were found to lie within the parameter space predicted by previous feasibility studies, verifying the performance of the MWA for this application. We have also used our survey to characterise these reflected signals from LEO objects as a source of radio frequency interference (RFI) that corrupts astronomical observations. This has allowed us to undertake an initial analysis of the impact of this RFI on the MWA and the future square kilometer array (SKA). As part of this analysis, we show that the standard MWA RFI flagging strategy misses most of this RFI and that this should be a careful consideration for the SKA.

Modeling and Thermal Analysis of a Moving Spacecraft Subject to Solar Radiation Effect

The impact of solar radiation on spacecraft can increase the cooling load, degrade the material properties of the structure and possibly lead to catastrophic failure of their missions. In this paper, we develop a computational model to investigate the effect of the exposure to solar radiation on the thermal distribution of a spacecraft with a cylindrical shape which is traveling in low earth orbit environment. This is obtained by the energy conservation between the heat conduction among the spacecraft, the heating from the solar radiation, and the radiative heat dissipation into the surroundings while accounting for the dynamics of the space vehicle (rotational motion). The model is solved numerically using the meshless collocation point method to evaluate the temperature variations under different operating conditions. The meshless method is based on approximating the unknown field function and their space derivatives, by using a set of nodes, sprinkled over the spatial domain of the spacecraft wall and functions with compact support. Meshless schemes bypass the use of conventional mesh configurations and require only clouds of points, without any prior knowledge on their connectivity. This would relieve the computational burden associated with mesh generation. The simulation results are found in good agreement with those reported in previously-published research works. The numerical results show that spinning the spacecraft at appropriate rates ensures low and uniform temperature distribution on the spacecraft, treated as thick-walled object of different geometries. Therefore, this would extend its lifetime and protect all on-board electronic equipment needed to accomplish its mission.

Specification of non-uniform residual stresses and tensile characteristic in laminated composite materials exposed to simulated space environment

In this study, the impact of the low earth orbit environment on multi-layered glass fiber reinforced polymer (GFRP) composites is analyzed in detail. The material responses are characterized through an assessment of residual stresses and mechanical property changes. To follow this aim, a thermal cycling condition was provided and composite samples were exposed to cyclic temperature variations with different number of thermal cycles. Then, the slitting method as an accurate semi-destructive technique was accomplished to characterize the non-uniform residual stresses through the depth of GFRP laminates. Additionally, tensile strength and mechanical properties were examined conducting tensile test. The results signified that residual stresses are reduced as the composites undergo temperature fluctuations. Finally, based on experimental results, a quadratic equation was proposed to predict the tensile strength of GFRPs exposed to thermal cycling condition. The proposed model was successfully verified and proved to be accurate with the error of less than 5%.

Resistance of nanoclay reinforced epoxy composites to hyperthermal atomic oxygen attack

Due to outstanding mechanical properties, heat resistance, and relatively facile production, nanoclay reinforced epoxy composites (NCRE composites) have been suggested as candidate materials for use on external surfaces of spacecraft residing in the low Earth orbit (LEO) environment. The resistance of the NCRE composites to bombardment by atomic oxygen (AO), a dominant component of the LEO environment, has been investigated. Four types of samples were used in this study. They were pure epoxy (0 wt% nanoclay content), and NCRE composites with different loadings of nanoclay—1 wt%, 2 wt%, and 4 wt%. Etch depths decreased with increasing nanoclay content, and for the 4 wt% samples it ranged from 28% to 37% compared to that of pure epoxy. X-ray photoelectron spectroscopy (XPS) indicates that after AO bombardment, relative area of C–C/C–H peak decreased, while the area of the C–O, ketones peaks increased, and the oxidation degree of surfaces increased. New carbon-related component carbonates were detected on nanoclay containing composite surfaces. Scanning electron microscopy indicates that aggregates formed on nanoclay-containing surfaces after AO bombardment. The sizes and densities of aggregates increased with nanoclay content. The combined erosion depths, XPS and SEM results indicate that although all the studied surfaces got eroded and oxidized after AO bombardment, the nanoclay containing composites showed better AO resistance compared to pure epoxy, because the produced aggregates on surface potentially act as a physical “shield”, effectively retarding parts of the surface from further AO etching.

Feasibility study of a proton fluence monitor for LEO-Nanosatellite missions based on displacement damage induced in GaAs-LED

High-energy protons trigger irreparable displacement damage (DD) in unbiased Gallium Arsenide (GaAs) Light-Emitting Diode GaAs-LED (GAL) . The DD is caused by non-ionizing-energy-loss (NIEL) process and results in reduction of light emission of the GAL when connected to a power source. Based on this finding a lightweight, low current consuming proton detector for space applications was developed. A commercial off the shelf (COTS) yellow GAL optically coupled to a Light-to-Frequency converter chip (LFC) made the basic assembly of the proposed proton detector. The device was calibrated using selected GAL samples irradiated with a 180 MeV proton beam from a proton-therapy medical cyclotron to 2, 10, 50, 100, 200 and 300 Gy dose levels. The light output of the GAL was measured with the detector assembly and presented as frequency (kHz). Protons of energy distribution between 100 keV to ∼500 MeV are trapped in the inner-shell of the Van Allen belt (VAB) surrounding the earth, whereas the intensity of trapped electrons (Emax ∼10 MeV) remains insignificant. The GAL light output data (frequency) was fitted with a second-degree polynomial function of imparted proton dose (∼ number of protons). The results were parameterized for widely used NASA radiation belt models AP8-Max and AP8-Min using the proton NIEL distribution in Gallium Arsenide (GaAs). Spacecrafts, in particular Nanosatellites operating in low earth orbit (LEO) environment are primarily exposed to those trapped protons in the VAB . Nanosatellites endure severe radiation exposure while passing through the South Atlantic Anomaly (SAA) region. The footprint, mass and average current consumption of the proton detector was 0.027 cm2, 0.28 g and 2.5 mA respectively. The highest detectable level proton fluence (protons⋅cm−2) was evaluated to be 1.17× 109 and 1.01× 109 for AP8-Max and AP8-Min models respectively. Hence the proposed GAL based radiation detector is only suited for proton fluence monitoring on board LEO-Nanosatellites (NanoSat) of short lifetime, usually 6–18 months.

MoS2-Au/Au multilayer lubrication film with better resistance to space environment

MoS2-Au/Au multilayer film was sputtered and exposed in low earth orbit environment aboard Chinese Shenzhou-7 manned spaceship to develop a solid film combining good lubricity and space-environment resistance together. The results revealed that space exposure caused the oxidation of MoS2-Au/Au multilayer film, but which was restricted into film surface. Importantly, the delaminating behavior was not observed from the space-exposed MoS2-Au/Au multilayer film, which was normal for other MoS2/metal multilayer film. As a result, the space-exposed MoS2-Au/Au multilayer film still exhibited a good lubricity (friction coefficients at ∼0.02–0.05), but a relatively high initial friction coefficient about 0.08 due to the surface oxidation. These results indicated that this multilayer lubrication film had a good capability resistant to space environment and potential application as solid lubricant in space technology.

Enhanced GEANT4 Monte Carlo simulations of the space radiation effects on the International Space Station and Apollo missions using high-performance computing environment

A significant challenge to current and future manned and/or unmanned space missions is due to deep space radiation. An improvement in more realistic (more accurate) simulation models in predicting the effects of radiation within the spacecraft is required, especially to better predict dose to astronauts, energy deposition within sensitive electronics, and effectiveness of radiation shielding for long-term space missions. The International Space Station provides an invaluable resource for long-term measurements of the radiation environment in Low Earth Orbit (LEO); however, the only manned missions with dosimetry data available beyond LEO are the Apollo missions. Thus the physiological effects and dosimetry for deep space missions are not well understood in planning extended missions. GEANT4, a Monte Carlo method, represents a powerful physics simulation tool to assess the effects of radiation transport through spacecraft. The newest version of GEANT4 supports multithreading and Message Passing Interface (MPI) allowing for much faster distributive processing of simulations, using a high-performance computing environment. This paper introduces a new simulation model and application using GEANT4 that greatly reduces computational time to hours instead of weeks without any post simulation processing based on high-performance computing. This paper also introduces a new set of GEANT4 computational detectors for calculating dose distribution, besides the historically used International Commission of Radiation Units simulation spheres. The computational detectors include a thermoluminescent detector, tissue equivalent proportional counter, and human phantom, along with additional new scorers to calculate dose equivalence based on the International Commission of Radiation Protection standards. This study presents GEANT4 simulations of the dose deposition for the International Space Station and the Apollo 11 and 14 missions, which replicate well the dose measurements during these missions. The simulations of both Apollo missions show consistent doses from galactic cosmic rays and radiation belts with a small variation in dose distribution across the Apollo capsule. The greatest contributor to radiation dose for both Apollo missions in the simulations came from galactic cosmic rays. Simulations of historical solar particle events during an Apollo missions show a solar particle event would not be fatal and below mission limits. These GEANT4 models also provides the values of the dose deposition and dose equivalent for various organs within a human phantom in the International Space Station and Apollo command module, which are developed for the first time using this GEANT4 based application.

Damage behavior of atomic oxygen on CVD SiC coating-modified carbon/carbon composite in low earth orbit environment

In this work, samples of carbon/carbon (C/C) and chemical vapor deposited (CVD) SiC-coated C/C samples were investigated to understand the AO damage mechanism in low Earth orbit (LEO) environment. The ground-based simulated atomic oxygen (AO) generator was employed. Results indicate that the CVD SiC coating exhibited improved radiation resistance properties against AO radiation as evidenced by a 16% better strength retention ratio, 60% less mass ablation, and increased strength stability. The magnitude of these influences affected the surface morphology, as observed by scanning electron microscopy (SEM) and surface resistance meter test results. The variations in the surface constituents were confirmed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) results. The main products left on surface after AO exposure are SiO2 and SiCxOy film. Additionally, Si atoms are found to be the preferential reacting element in the SiC coating, and this process is accompanied by graphite precipitation, grain growth, and crack necking. Also, the damage mechanism of the AO-exposed SiC coating was revealed and is discussed.

EXPOSE-R2 on the International Space Station (2014-2016): Results from the PSS and BOSS Astrobiology Experiments.

EXPOSE facilities were ESA multiuser facilities mounted outside the International Space Station for astrobiology experiments. Between 2008 and 2016, three series of experiments were conducted involving chemical and biological samples to test their resistance and evolution in the space environment in low Earth orbit. In this Astrobiology special collection, results from two experiments of the EXPOSE-R2 campaign (2014-2016) are presented: Biofilm Organisms Surfing Space (BOSS) relating to biology and Photochemistry on the Space Station (PSS) dealing with astrochemistry.

LEO Charging of the PICASSO Cubesat and Simulation of the Langmuir Probes Operation

The sweeping Langmuir probe (SLP) instrument is a payload of the European Space Agency's (ESA) in-orbit demonstrator PicoSatellite for Atmospheric and Space Science Observations (PICASSO) cubesat, measuring the plasma environment in a high-inclination low earth orbit (LEO) orbit. Because of the small size of the spacecraft (0.3 m × 0.1 m × 0.1 m), the spacecraft floating potential can significantly drift when sweeping the probe bias voltage, affecting the current-voltage characteristic from which plasma parameters are retrieved. In LEO, the spacecraft generally encounters a high-density, cold (less than 1 eV) plasma environment, but due to the high orbital inclination, PICASSO passes the auroral regions exposing the spacecraft to precipitating fluxes of hot (several kiloelectron volts) electrons with potentially harmful, high-level spacecraft charging as a result. To investigate the spacecraft charging and the in-orbit operation of the Langmuir probes in both of these regimes, simulations of PICASSO were carried out in Spacecraft Plasma Interaction System (SPIS). The conditions of the LEO plasma and the constraints imposed by the particle-in-cell (PIC) models on the mesh size make this type of plasma simulations a very challenging task.

5.2.5 Calibration of Detectors that Have Flown on Mir, ISS, Lunar Reconnaissance Orbiter, the Orion Spacecraft and the Mars Science Laboratory

A variety of radiation detectors and instruments have been deployed to characterize the radiation environment in low and high Earth orbit, lunar orbit, Mars orbit and on the surface of Mars. Here we discuss the testing and calibration of these detectors using HIMAC ion beams.

Radiation damage behavior of carbon/carbon composite in Low Earth Orbit environment

Abstract To understand the degradation behavior of Carbon/Carbon(C/C) composite in LEO radiation environment, groups of 2D-C/C composites samples were exposed to ground-based Low Earth Orbit(LEO) simulating facilities. The LEO radiating environment covers part of Van Allen inner belt, which contains atomic oxygen(AO) and high-energy proton radiating regions. These two kinds of radiating sources were arranged for simulating the real LEO radiating conditions regarding to the first orbit movement speed of serving space shuttles. Changes of micro-structure, mass loss, surface roughness, chemical construction and thermal physical properties after environmental assessment were analyzed and compared to understand the damage behavior of LEO radiation on C/C composite. It was found that AO is the main factor of mass loss in LEO radiating particles. The charged high-energy protons have an aggravating damage ability with energetic AO, damage situations of degree in orbit down process is more serious than in orbit rising process. The LEO radiation damage mechanisms of C/C composite are revealed and expounded either.

Comparison of the mechanical deterioration behavior of C/BMI composite under hygro-thermal or vacuum-thermal cycling

The effects of vacuum-thermal cycling and hygro-thermal cycling on the fiber/matrix interface characteristics of a carbon fiber reinforced bismaleimide (C/BMI) composite were investigated to assess the degradation behavior of the mechanical property of C/BMI composite in low earth orbit (LEO) and atmosphere environment. The feasibility of using one comprehensive accelerated test procedure capable of representing the LEO and atmosphere environmental effects simultaneously for the aerospace plane was explored for the first time. A simplified mathematical approach and the corresponding model was supplied firstly to prove the reliability and effectiveness of the widely-used SEM observation method in the assessment of fiber matrix interface properties. The dominating degradation mechanism of the C/BMI composites caused by vacuum-thermal cycling in LEO environment is the interfacial sliding induced by thermal stress, whereas the thermal oxidation and decomposition of the matrix is the main degradation mechanism after hygro-thermal cycling in atmosphere environment. Candidate composite materials for aerospace plane must be tested in atmosphere and LEO environments separately in the environmental simulation experiments before their application.

Small Satellites: A Threat for the Future Sustainability of Outer Space Exploration?

Sustainability is a very well-known issue in international environmental law, especially with regard to outer space activities and the related debris proliferation. Bearing in mind that outer space is a res communis area (i.e. outside the jurisdiction of any State), the present article discusses the need to re-think the concept of ‘exploration and use’ under the guidance of the sustainable development principle. In this context, special attention is given to the well-known threat posed by small satellites to the sustainability of the Low Earth Orbit environment and some proposals are made regarding the way forward.

Microstructure and properties of metallurgical bonding Mo/Pt/Ag laminated metal matrix composites

The Mo/Pt/Ag laminated metal matrix composites (LMMCs) have been used as interconnected materials of solar cell array of spacecraft at low-Earth orbit (LEO), where the interconnectors are vulnerable to the combined effects of atomic oxygen (AO) and thermal cycles. To enhance its resistance to LEO environment, the metallurgical bonding Mo/Pt/Ag LMMCs was prepared in this work with optimized processing parameters. During the process, the multiple calenderings and annealing at a protecting atmosphere were performed to improve the surface activity of Mo and Pt. Consequently, the expectant metallurgical bonding interfaces of Mo/Pt and Pt/Ag were successfully constructed through the atomic diffusion accelerated by the improvement of surface activity. Additionally, the resulting microstructure of the Mo/Pt interface was confirmed to be composed of MoPt and Mo3Pt alloy phases, and the Pt/Ag interface consisted of distorted and tangled Pt and Ag lattices. Besides, the interfacial type and the orientation relationships of constituent phases were determined. Lastly, the as-obtained Mo/Pt/Ag LMMCs is assessed to have good resistance to thermal fatigue and AO erosion by the thermal cycling and AO exposure experiments.

First results from the LUCID-Timepix spacecraft payload onboard the TechDemoSat-1 satellite in Low Earth Orbit

The Langton Ultimate Cosmic ray Intensity Detector (LUCID) is a payload onboard the satellite TechDemoSat-1, used to study the radiation environment in Low Earth Orbit (∼635 km). LUCID operated from 2014 to 2017, collecting over 2.1 million frames of radiation data from its five Timepix detectors on board. LUCID is one of the first uses of the Timepix detector technology in open space, with the data providing useful insight into the performance of this technology in new environments. It provides high-sensitivity imaging measurements of the mixed radiation field, with a wide dynamic range in terms of spectral response, particle type and direction. The data has been analysed using computing resources provided by GridPP, with a new machine learning algorithm that uses the Tensorflow framework. This algorithm provides a new approach to processing Medipix data, using a training set of human labelled tracks, providing greater particle classification accuracy than other algorithms. For managing the LUCID data, we have developed an online platform called Timepix Analysis Platform at School (TAPAS). This provides a swift and simple way for users to analyse data that they collect using Timepix detectors from both LUCID and other experiments. We also present some possible future uses of the LUCID data and Medipix detectors in space.