Low Earth Orbit Environment Research Articles

The LUCID-Timepix spacecraft payload and the CERN@school educational programme

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. The data has been analysed using computing resources provided by GridPP, with a novel machine learning algorithm. 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 school based Timepix projects. These projects constitute a secondary school programme 'CERN@school' that give a framework for novel implementations of conventional classroom experiments using Timepix, as well as letting students contribute to large international scientific collaborations and devise their own research projects.

The Solar Particle Event on 10 September 2017 as observed onboard the International Space Station (ISS)

AbstractThe nominal radiation environment in low Earth orbit, especially for the International Space Station (ISS), is dominated by two sources. The first is galactic cosmic radiation, which is modulated by the interplanetary and the Earth's magnetic fields, and the second is trapped radiation in the form of the Van Allen belts. The trapped radiation inside the ISS is mostly due to protons of the inner radiation belt. In addition to these sources sporadic solar particle events (SPEs) can produce high doses inside and outside the ISS, depending on the intensity and energy spectrum of the event. Before 2017, the last SPE observed inside the ISS with relevant radiation detectors occurred in May 2012. Even though we are currently approaching the next solar minimum, an SPE was observed in September 2017, which was (a) a ground‐level enhancement, (b) measured with various radiation detector systems onboard the ISS, and (c) observed on the surface of Mars. This paper gives an overview of the 10 September 2017 SPE measured with the DOSIS 3D‐DOSTEL and the ISS‐RAD (Radiation Assessment Detector) instruments, both located at this time in close proximity to each other in the Columbus Laboratory of the ISS. The additional dose received during the SPE was 146.2 μGy in Si as measured by ISS‐RAD and 67.8 μGy in Si as measured by the DOSIS 3D‐DOSTEL instruments. In comparison, the dose measured on the surface of Mars with the Mars Science Laboratory‐RAD instrument accounted to 418 μGy in Si.

A neutral wind instrument for nano-satellite platforms.

Here we describe the first neutral wind sensor developed specifically for use on resource limited nano-satellite platforms. The instrument is a next generation redesign of the ram wind sensor flown on the Communications/Navigation Outage Forecasting System satellite for measurements of neutral velocity, temperature, and composition. Results of subsystem tests in vacuum conditions show low-power operation, promising design, and good resolution of measured parameters over the operational pressure and energy ranges expected in the low Earth orbit 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.

Space debris collision probability analysis for proposed global broadband constellations

Fragmentation events, caused by the collision of two objects in space, have been a significant source of space debris objects over a cumulative five decades of space activity. Current proposals by different commercial entities aim to launch constellations comprising thousands of satellites in Low Earth Orbit (LEO), which would result in an increase of more than five times the number of currently active satellites in a region where debris objects are most concentrated. The Inter-Agency Space Debris Coordination Committee (IADC) has already recognized the potential influence of large constellations on the LEO environment and the subsequent need to assess whether current mitigation guidelines will be adequate moving forward. Given developments for such constellations are already underway, independent research efforts ahead of any revision to current IADC guidelines could be of great value not only to the organizations involved in their operation, but also to policymakers and existing space users. This paper evaluates the probability of collisions for mega-constellations operating in the current LEO debris environment under best and worst-case implementation of current mitigation guidelines. Simulation studies are performed using the European Space Agency's (ESA) MASTER-2009 debris evolutionary model, and the specifications of the proposed OneWeb and SpaceX constellations as example mega-constellations. Multiple scenarios are then tested to assess mitigation measures and their ability to minimize the probability of fragmentation events and the creation of new debris in LEO.

The effect of simulated space radiation on the N-glycosylation of human immunoglobulin G1.

On a roundtrip to Mars, astronauts are expectedly exposed to an approximate amount of radiation that exceeds the lifetime limits on Earth. This elevated radiation dose is mainly due to Galactic Cosmic Rays and Solar Particle Events. Specific patterns of the N-glycosylation of human Igs have already been associated with various ailments such as autoimmune diseases, malignant transformation, chronic inflammation, and ageing. The focus of our work was to investigate the effect of low-energy proton irradiation on the IgG N-glycosylation profile with the goal if disease associated changes could be detected during space travel and not altered by space radiation. Two ionization sources were used during the experiments, a Van de Graaff generator for the irradiation of solidified hIgG samples in vacuum, and a Tandetron accelerator to irradiate hIgG samples in aqueous solution form. Structural carbohydrate analysis was accomplished by CE with laser induced fluorescent detection to determine the effects of simulated space radiation on N-glycosylation of hIgG1 samples. Our results revealed that even several thousand times higher radiation doses that of astronauts can suffer during long duration missions beyond the shielding environment of Low Earth Orbit, no changes were observed in hIgG1 N-glycosylation. Consequently, changes in N-linked carbohydrate profile of IgG1 can be used as molecular diagnostic tools in space.

A LiF and BeO TLD based microdosimeter for space radiation risk assessment of astronauts

The ratio of thermoluminescence glow curve area of BeO and LiF dosimeters was found to be proportional to average LET and quality factor (Q) of impinging mixed radiations. Using this phenomenon and widely available Thermoluminescence Dosimeter TLD-700 (7LiF: Mg,Ti) and BeO (Thermolux 995) chips a TLD-Microdosimeter (LiBe-14) emulating a much larger gas-filled Tissue Equivalent Proportional Counter (TEPC) was developed. The TEPC is an essential device of space radiation dosimetry widely used by international space agencies. The LiBe-14 is capable of assessing the LETTissue (5–300 keV/μm), quality factor Q (1–30) and associated dose equivalent H (0.1–1000 mSv) of any mixed radiation fields of interest, including space radiations predominant in Low Earth Orbit (LEO) environment. The TLD microdosimeter was calibrated using the secondary radiation fields produced by bombarding a 25 cm × 25 cm × 35 cm polystyrene phantom with 81, 119, 150, 177, 201 and 231 MeV protons from a Proton Therapy Medical Cyclotron. The TLD pair (BeO/LiF) was attached to the TEPC and placed lateral to the proton beam. The characteristics of space radiation inside the spacecraft are complex. Hence, personal dosimetry of astronauts in the space habitat is performed using “multi-element” dosimeters made of different types of TLD and CR-39 plastic nuclear track detector (PNTD). The TLD and PNTD are used to assess the sparsely (low LET) and densely (high LET) ionising radiation component respectively. This report elucidates the feasibility of LiBe-14 microdosimeter for the estimation of overall dose equivalent and “risk of exposure induced death” (REID) of astronauts working in LEO space stations.

Sensitivity analysis of launch activities in Low Earth Orbit

This work aims to investigate the response of the low Earth orbit environment to the change in number and distribution of new launches and to understand the effects of the size and post-mission lifetime of a large constellation of spacecraft. The analysis presented in this paper were carried out using MISSD, Model for Investigating control Strategies for Space Debris, a multi-shell, and multi-species source-sink statistical model able to simulate the injection, removal and interaction of six type of objects up to an altitude of 2000 km. The results suggest that multiple regions experience a sensible increment in the orbital density when slightly increasing the launch activity for the next 200 years. Recently, many private companies expressed their interest in putting large constellations of satellites at 1100–1300 km altitude. However, results show that the launch of just six additional spacecraft per year in this region increased the spatial density by an amount equal to the projection over 200 years of today's most crowded region. Results also show that the increase in the orbital population and collision risk caused by the presence of large constellations could be mitigated using a high level of post-mission disposal compliance, reliable deorbit mechanisms and reducing thepost-mission lifetime to 5 years.

Diagnosing low earth orbit satellite anomalies using NOAA-15 electron data associated with geomagnetic perturbations

A satellite placed in space is constantly affected by the space environment, resulting in various impacts from temporary faults to permanent failures depending on factors such as satellite orbit, solar and geomagnetic activities, satellite local time, and satellite construction material. Anomaly events commonly occur during periods of high geomagnetic activity that also trigger plasma variation in the low Earth orbit (LEO) environment. In this study, we diagnosed anomalies in LEO satellites using electron data from the Medium Energy Proton and Electron Detector onboard the National Oceanic and Atmospheric Administration (NOAA)-15 satellite. In addition, we analyzed the fluctuation of electron flux in association with geomagnetic disturbances 3 days before and after the anomaly day. We selected 20 LEO anomaly cases registered in the Satellite News Digest database for the years 2000–2008. Satellite local time, an important parameter for anomaly diagnosis, was determined using propagated two-line element data in the SGP4 simplified general perturbation model to calculate the longitude of the ascending node of the satellite through the position and velocity vectors. The results showed that the majority of LEO satellite anomalies are linked to low-energy electron fluxes of 30–100 keV and magnetic perturbations that had a higher correlation coefficient (~ 90%) on the day of the anomaly. The mean local time calculation for the anomaly day with respect to the nighttime migration of energetic electrons revealed that the majority of anomalies (65%) occurred on the night side of Earth during the dusk-to-dawn sector of magnetic local time.

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.

Combustion Synthesis Technology for a Sustainable Settlement Overnight

Space technology has been developed for frontier exploration not only in low-earth orbit environment but also beyond the earth orbit to the Moon and Mars, where material resources might be strongly restricted and almost impossible to be resupplied from the earth for distant and long-term missions performance toward “long-stays of humans in space”. For performing such long-term space explorations, none would be enough to develop technologies with resources only from the earth; it should be required to utilize resources on other places with different nature of the earth, i.e., in-situ resource utilization. One of important challenges of lunar in-situ resource utilization is thermal control of spacecraft on lunar surface for long-lunar durations. Such thermal control under “long-term field operation” would be solved by “thermal wadis” studied as a part of sustainable researches on overnight survivals such as lunar-night. The resources such as metal oxides that exist on planets or satellites could be refined, and utilized as a supply of heat energy, where combustion synthesis can stand as a hopeful technology for such requirements. The combustion synthesis technology is mainly characterized with generation of high-temperature, spontaneous propagation of reaction, rapid synthesis and high operability under various influences with centrifugal-force, low-gravity and high vacuum. These concepts, technologies and hardware would be applicable to both the Moon and Mars, and these capabilities might achieve the maximum benefits of in-situ resource utilization with the aid of combustion synthesis applications. The present paper mainly concerns the combustion synthesis technologies for sustainable lunar overnight survivals by focusing on “potential precursor synthesis and formation”, “in-situ resource utilization in extreme environments” and “exergy loss minimization with efficient energy conversion”.

High-Performance Embedded Computing in Space: Evaluation of Platforms for Vision-Based Navigation

Vision-based navigation has become increasingly important in a variety of space applications for enhancing autonomy and dependability. Future missions, such as active debris removal for remediating the low Earth orbit environment, will rely on novel high-performance avionics to support advanced image processing algorithms with substantial workloads. However, when designing new avionics architectures, constraints relating to the use of electronics in space present great challenges, further exacerbated by the need for significantly faster processing compared to conventional space-grade central processing units. With the long-term goal of designing high-performance embedded computers for space, in this paper, an extended study and tradeoff analysis of a diverse set of computing platforms and architectures (i.e., central processing units, multicore digital signal processors, graphics processing units, and field-programmable gate arrays) are performed with radiation-hardened and commercial off-the-shelf technology. Overall, the study involves more than 30 devices and 10 benchmarks, which are selected after exploring the algorithms and specifications required for vision-based navigation. The present analysis combines literature survey and in-house development/testing to derive a sizable consistent picture of all possible solutions. Among others, the results show that certain 28 nm system-on-chip devices perform faster than space-grade and embedded central processing units by 1–3 orders of magnitude, while consuming less than 10 W. Field-programmable gate array platforms provide the highest performance per watt ratio.

A simple strategy to tailor the microstructure and wear-resistance of sputtered WS2 films

Sputtered WS2 films can be modified by adding some amount of hetero-elements to overcome the porous columnar microstructure and thereby to enhance the wear resistance. However, the recession of tribological properties of WS2-hetero-element composite films in low earth orbit environment would be a potential danger because most hetero-elements succumbed to oxidation by atomic oxygen. Herein, by altering deposition argon pressure to adjust the plasmas bombard function on growing WS2 film, the characteristic porous microstructure disappeared. At the optimization condition, the sputtered WS2 film exhibited a dense microstructure, high ratio of S to W, and thereby much better wear-resistance. However, the excessive bombardment would result in the prominent loss of S atoms in WS2 film and the deterioration of tribological properties.

The detection of ultra-relativistic electrons in low Earth orbit

Aims. To better understand the radiation environment in low Earth orbit (LEO), the analysis of in-situ observations of a variety of particles, at different atmospheric heights, and in a wide range of energies, is needed. Methods. We present an analysis of energetic particles, indirectly detected by the large yield radiometer (LYRA) instrument on board ESA's project for on-board autonomy 2 (PROBA2) satellite as background signal. Combining energetic particle telescope (EPT) observations with LYRA data for an overlapping period of time, we identified these particles as electrons with an energy range of 2 to 8 MeV. Results. The observed events are strongly correlated to geo-magnetic activity and appear even during modest disturbances. They are also well confined geographically within the L = 4–6 McIlwain zone, which makes it possible to identify their source. Conclusions. Although highly energetic particles are commonly perturbing data acquisition of space instruments, we show in this work that ultra-relativistic electrons with energies in the range of 2–8 MeV are detected only at high latitudes, while not present in the South Atlantic Anomaly region.

Polybenzimidazole (PBI) film coating for improved hypervelocity impact energy absorption for space applications

This paper deals with how the use of Polybenzimidazole (PBI) as a film coating over conventional composite designs could help improve the hypervelocity impact ballistic performance of the system. PBI coated composite samples were studied for resistance to Low Earth Orbit environment conditions like high vacuum, thermal cycling, Atomic Oxygen and Ultraviolet Radiation in a simulation facility. It was observed that the PBI coated composites reduced mass loss and surface erosion compared to the non-coated samples after LEO exposure. Hypervelocity impact experiments were conducted on the PBI coated composites for impact velocities between 2.5 to 3 km/s. The experiments showed that the PBI film coating significantly increased the energy absorption of the composite system. The effect of thickness increase as a result of the film application on energy absorption was also found to be negligible confirming the effectiveness of PBI coating as a hypervelocity shield.

Performance Analysis of Sensor Systems for Space Situational Awareness

With increased human activity in space, the risk of re-entry and collision between space objects is constantly increasing. Hence, the need for space situational awareness (SSA) programs has been acknowledged by many experienced space agencies. Optical and radar sensors, which enable the surveillance and tracking of space objects, are the most important technical components of SSA systems. In particular, combinations of radar systems and optical sensor networks play an outstanding role in SSA programs. At present, Korea operates the optical wide field patrol network (OWL-Net), the only optical system for tracking space objects. However, due to their dependence on weather conditions and observation time, it is not reasonable to use optical systems alone for SSA initiatives, as they have limited operational availability. Therefore, the strategies for developing radar systems should be considered for an efficient SSA system using currently available technology. The purpose of this paper is to analyze the performance of a radar system in detecting and tracking space objects. With the radar system investigated, the minimum sensitivity is defined as detection of a 1-m2 radar cross section (RCS) at an altitude of 2,000 km, with operating frequencies in the L, S, C, X or Ku-band. The results of power budget analysis showed that the maximum detection range of 2,000 km, which includes the low earth orbit (LEO) environment, can be achieved with a transmission power of 900 kW, transmit and receive antenna gains of 40 dB and 43 dB, respectively, a pulse width of 2 ms, and a signal processing gain of 13.3 dB, at a frequency of 1.3 GHz. We defined the key parameters of the radar following a performance analysis of the system. This research can thus provide guidelines for the conceptual design of radar systems for national SSA initiatives.

English

In the presented study, by applying analytical methods and using experimental data, equations are achieved to predict the fatigue life of unidirectional carbon fiber/epoxy composite (UCFEC) that is applied in aerospace structures. The experimental data used to obtain these equations are achieved by low earth orbit (LEO) environment simulation experiment and other experiments. By employing convex curves analytical method, some equations to predict the fatigue life of unidirectional carbon fiber/epoxy composite in LEO are achieved. Then, by inspiration of convex curves method, steady-linear method to predict the fatigue life of unidirectional carbon fiber/epoxy composite on Mars is proposed. Furthermore, the results of convex curves method have proved that the main factor causing fracture of UCFEC in vacuum thermal cycles is the degradation of inter laminar shear strength between the carbon fiber and epoxy. Finally, the results obtained by these methods are compared with the results from other experiments of composite materials. The comparison showed that the results of this study seem acceptable. Key words: Fatigue life prediction, unidirectional carbon fiber, composite, earth orbit, Mars.

Analysis of atomic oxygen and ultraviolet exposure effects on cycloaliphatic epoxy resins reinforced with octa-functional POSS

In this study, novel nanocomposites were created by incorporation of Silsesquioxane containing eight glycidylether groups (octa-POSS) into a cycloaliphatic epoxy cured by an anhydride. The developed resin system, with different nanoparticle concentrations, was used on the outer layers of an ultra-thin CFRP structure in order to provide better environmental resistance to the environment of low Earth orbit (LEO) which was tested in a ground-simulation facility. The developed resins were subjected to space-like degrading factors and their response to corrosion, radiation and elevated temperatures was monitored by mass loss, together with measuring changes in surface chemistry (ATR-FTIR), functionality development (contact angle measurement and XPS), roughness (scanning laser microscopy) and morphology (SEM). The influence of increasing octa-POSS content on thermo-mechanical properties was measured with DMTA and the strength and modulus of elasticity were determined by flexural test. The addition of octa-POSS in any loading improves the environmental resistance, however, the most significant retention of mass and mechanical and surface properties after space-like exposure was observed in the 20 wt% octa-POSS reinforced cycloaliphatic epoxy. The results presented here may contribute to the development of novel class of nanocomposites which can offer an extended service life in LEO.

Effect of large constellations on lifetime of satellites in low earth orbits

A 2010 study found, assuming business-as-usual satellite operations and replenishment activities, that for large satellites operating in the low Earth orbit (LEO) regime, a mean lifetime reduction over the next 50 years of ∼13% might be expected (i.e., a satellite with a mean lifetime of 10 years in a no-debris environment would see a reduction of 1.3 years in an environment that included space debris), with much of this reduction coming from degradation of solar panels by small, un-trackable debris. Since 2010, proposals have been put forward that would add thousands of new satellites to the LEO environment within the next few years, many more than the number projected in the 2010 study.The current study reexamines the earlier prediction by assuming that over 5000 new small satellites are operating in high LEO orbits, consistent with proposals announced by commercial companies. As with the 2010 study, this projection includes the effects of collisions of both tracked objects, objects greater than 10 cm in LEO, and small debris down to 1 mm—a size that the 2010 study showed could “sandblast” and reduce the power output of solar panels—and adds changes in the debris environment due to the previously un-modeled new satellites colliding in their constellations and with other objects as they undergo constellation replenishment activities.Primary results are that satellites being disposed from or added to the new constellations and debris associated with collisions involving these objects could potentially double the reduction in the mean operational lifetime of satellites operating in LEO. As in the 2010 study, the degradation of solar panels due to small debris impacts is a significant factor in this degradation, with the mean lifetime reduction increasing from the 13% predicted in the earlier study to as much as 60% in some cases (i.e., a large satellite with a mean lifetime of 20 years in a no-debris environment could have its mean lifetime reduced by as much as 12 years). Results suggest that minimizing collisions during replenishment activities and making solar panels and space hardware more resilient to small debris impacts will be increasingly important in the future.

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.