Space Mission Applications Research Articles

Ultra-thin perovskite solar cells with high specific power density based on colorless polyimide substrates

Ultra-thin perovskite solar cells (UTPSCs) have garnered significant attention for their high specific power and potential application in space missions. However, the efficiency of ultra-thin solar cells has been constrained by challenges in handling and fabricating them on the fragile ultra-thin substrates, leading to notable performance disparities compared to their rigid counterparts. Here, we present a novel method for fabricating efficient and stable ultra-thin flexible PSCs. By employing a polydimethylsiloxane (PDMS) buffer layer and controlling the imidization temperature of colorless polyimide (CPI), we prepared an ultra-thin CPI substrate with a thickness of 1–3 μm, which can be easily peeled off. This technique provides a heat-resistant ultra-thin substrate with a smooth surface for UTPSC fabrication. Additionally, the ultra-thin substrate exhibits superior thermal conductivity and more uniform temperature distribution compared to conventional flexible substrates. Ultimately, we achieve a 1.5 μm UTPSC with a power conversion efficiency of 22.13 % and an outstanding specific power density of 50 W/g, surpassing most existing solar cells. Remarkably, the UTPSCs demonstrate exceptional mechanical robustness, maintaining performance even under rigorous bending and twisting. Moreover, CPI exhibited better thermal expansion matching with perovskite and demonstrated enhanced stability under low-temperature conditions and thermal cycling, showing potential for space applications. Our approach of preparing ultra-thin CPI substrates offers an effective pathway for fabricating lightweight and highly flexible electronics.

The Challenges of Piezoelectric Actuators and Motors Application in a Space Environment

Piezoelectric actuators and motors are increasingly essential for space applications due to their precision, compactness, and efficiency. This review explores their advantages over traditional actuators, emphasizing their minimal electromagnetic interference, high responsiveness, and operational reliability in harsh space environments. This study highlights the challenges posed by space conditions such as vacuum, microgravity, extreme temperatures, and radiation, which require robust design and material considerations. A comprehensive review of missions using piezo actuators, including their operating principles, material advancements, and innovative designs tailored for space conditions. In addition, numerical calculations were performed by COMSOL Multiphysics 5.6 software with the aim of analyzing the impact of temperature variations typical of the low Earth orbit (LEO) on the electromechanical properties of the piezoelectric transducer. The results indicate significant variations in the characteristics of the resonant frequency, impedance, and phase frequency in a temperature range from −20 °C to 40 °C, emphasizing the importance of accounting for thermal effects in the design. The calculations show that advantages which are proposed by piezoelectric motion systems must be combined with adaptability to harsh environmental conditions and call for further research to enhance their robustness and performance for broader application in future space missions.

Application of Artificial Intelligence in Solar System Exploration and Beyond

Carl Sagan’s reflections emphasize the boundless potential awaiting humanity in space, regardless of our past achievements or failures. This optimistic view resonates with current space agencies, private space startups, and enthusiasts, all driven by the ambition to make humans a multiplanetary species. Key examples include Elon Musk’s goal to terraform Mars, despite skepticism from some scientists. Space exploration faces numerous challenges, such as dealing with space debris, unpredictable climates on other planets, and the complexities of missions like NASA’s attempts to land on Mars. Space missions confront obstacles in navigation, life detection, and sample testing. Astronauts also encounter physical and mental limitations due to the harsh conditions of space. Artificial Intelligence (AI) has emerged as a crucial tool in addressing these challenges. AI is categorized into supervised learning, unsupervised learning, and semi-supervised learning, with reinforcement learning being a distinct method used for autonomous applications. Neural networks, including convolutional and recurrent neural networks, mimic human behavior for tasks like image inspection and sequential data handling. Deep learning aids in complex pattern recognition, and natural language processing facilitates speech recognition and development. Expert systems enhance decision-making processes. This review explores various AI applications in space missions. AI technologies have been integral to recent missions such as the James Webb Space Telescope, which uses AI for object and galaxy inspection, and the ARTEMIS mission, which employs AI in designing new spacesuits. SpaceX leverages AI for reusable launch vehicles, while the European Space Agency (ESA) uses AI for autonomous spacecraft to cut mission costs. India plans to launch the AI-based Vyommitra robot in space and has utilized AI in the Chandrayaan mission for landing and navigation. Mars exploration benefits significantly from AI, given the planet’s unpredictable weather and cratered surface. AI technologies, like the OASIS system, aid in mission planning and rover navigation. AI also supports space agriculture research, as demonstrated by the UAE’s habitat design efforts. Beyond Mars, AI influences the exploration of asteroids and deep space. AI techniques, such as convolutional neural networks, assist in space dynamics calculations to predict asteroid trajectories and potential Earth impacts. AI has been employed in Voyager missions to seek extraterrestrial life and in the Hubble telescope for imaging exoplanets. AI enhances satellite communication and automates tasks on space stations, saving time and costs. Weather satellites, powered by AI, provide crucial alerts for natural disasters. Despite the challenges, AI offers promising solutions for advancing space exploration. The historical tendency to deem certain challenges insurmountable is gradually shifting, as past impossibilities, like human flight and space travel, have become historical milestones. This reinforces the importance of maintaining hope and persistence in the quest to explore space, as today's dreams may become tomorrow's history.

Multivariate Attention-Based Orbit Uncertainty Propagation and Orbit Determination Method for Earth–Jupiter Transfer

Current orbit uncertainty propagation (OUP) and orbit determination (OD) methods suffer from drawbacks related to high computational burden, limiting their applications in deep space missions. To this end, this paper proposes a multivariate attention-based method for efficient OUP and OD of Earth–Jupiter transfer. First, a neural network-based OD framework is utilized, in which the orbit propagation process in a traditional unscented transform (UT) and unscented Kalman filter (UKF) is replaced by the neural network. Then, the sample structure of training the neural network for the Earth–Jupiter transfer is discussed and designed. In addition, a method for efficiently generating a large number of samples for the Earth–Jupiter transfer is presented. Next, a multivariate attention-based neural network (MANN) is designed for orbit propagation, which shows better capacity in terms of accuracy and generalization than the deep neural network. Finally, the proposed method is successfully applied to solve the OD problem in an Earth–Jupiter transfer. Simulations show that the proposed method can obtain a similar estimation to the UKF while saving more than 90% of the computational cost.

Bounded impulse-control hovering formation in elliptical orbits

Satellite formation plays an important role in space missions such as on-orbit services and distributed space facilities. In these missions, hovering in a bounded range is one of the core tasks, but hovering technologies for the chief satellite in an elliptical orbit have been rarely investigated. Given the boundary constraints of relative motion between the chief and deputy satellites, this paper proposes two models for the design and control of hovering formation near an elliptical reference orbit through impulse: (1) the revisiting hovering formation model, which forces the deputy satellite to revisit the same relative position and maintains the formation via impulses; (2) the sequential-impulse-control hovering formation model, which uses a sequence of impulses to ensure the deputy satellite flies within the given boundary. Unlike the revisiting hovering formation model, this model does not require a fixed revisiting point, so the satellite’s trajectory is more flexible. The geometrical properties, formation maintenance strategy, and impulse-control solution for both models are investigated in detail. Finally, numerical simulations are conducted to verify the advantages of the proposed methods over other conventional methods, suggesting their wide applications in practical space missions.

LOCATIONS OF TRIANGULAR EQUILIBRIUM POINTS OF THE RESTRICTED THREE-BODY PROBLEM WITH POYNTING-ROBERTSON DRAG AND VARIABLE MASSES

The restricted three-body problem (R3BP) is a fascinating problem that has been receiving attentions of astronomers and scientists because of its vast implications in diverse scientific fields, including among others; celestial mechanics, galactic dynamics, chaos theory and molecular physics. In this paper, we examine the locations of the triangular equilibrium points of the R3BP with Poynting-Robertson (P-R) drag forces and variable masses. The primaries are assumed to vary under the unified Mestschersky law and their dynamics defined by the Gylden-Mestschersky equation, while the smaller primary is assumed to be a radiation emitter with P-R drag. The dynamical equations are obtained for both the non-autonomous with variable coefficients and autonomized system with constant coefficients. Further, the locations of the triangular points of the autonomized systems are obtained using perturbation method. It is seen that the positions are defined by the mass parameter, radiation pressure and P-R drag of the smaller primary. The triangular points of the non-autonomous equations are obtained with help of the Mestschersky transformation, and differ from those of the autonomized system due to a function of time. The equilibrium points have several applications in space missions, satellites constellations and station-keeping.

DEVELOPMENT AND QUALIFICATION OF CNT-CFRP COMPOSITE COMPONENTS FOR SPACE APPLICATIONS

Space payloads are required to be compact, to withstand harsh climatic conditions, and perform well over the duration of a mission. Advanced lightweight materials with low density, high strength, and high specific stiffness, such as carbon fiber reinforce polymers (CFRP), controlled expansion alloy (CE7), and kevlar composites are better suited for space hardware. Despite of having superior mechanical qualities, CFRP composites have limited range of applications due to their worse electrical and thermal conductivities. By adding nano-fillers to improve conductivity, CFRP can be used extensively. The most often employed conductive nano-fillers in CFRP composites are graphene and carbon nanotubes (CNTs). By creating CFRP composites with superior conductivities, the use of CFRP composites can be extended over large applications for space missions. Materials such as aluminum, kovar, invar, and other composites (non-conductive in nature) may be replaced by CFRP-CNT composites. It can be used for fabricating broad variety of satellite hard wares, including satellite panels, reflectors, feed horns, wave guides, carrier plates, electronic package boxes, and covers. Based on tests with different configurations, it was discovered that 0.5% SWCNT offered better mechanical and electrical properties. CNT-CFRP composites are used in the development of carrier plates and reflectors. This article primarily focuses on development of qualification test strategy and how it differs from traditional systems test plan. Results from test coupons and the product level tests were compared and analyzed. The results are acceptable and found better in comparison to their conventional counterparts.

REVIEW OF LOWER BODY NEGATIVE PRESSURE APPLICATIONS TO SIMULATE +GZ-INDUCED CARDIOVASCULAR STRAIN: RESEARCH HISTORY

Introduction: In the paper, a general overview of the development and applications of l ower body negative pressure ( LBNP) technology have been provided. The article also descr ibes the LBNP designs used to investigate the relationship between tolerance to negative pressure around the lower body and tolerance to acceleration (+Gz). Methods: A systematic review of the literature on the development and application of LBNP in the sc ope not limited to the time or geography framework was explored. Searches were performed using predefined keywords and filters for LBNP (e.g., aerospace, medicine, cardiovascular, space, acceleration, Gz ). Databases such as PubMed, IEEE Xplore, ScienceDire ct, and others relevant to this field of study were selected for the search. Results: The results of the review were organized by thematic categories (LBNP development, applications and use to s imulate +Gz induced cardiovascular strain ). Syntheses of the r esults are presented, highlighting key themes and insights. Discussion and Conclusion: T he use of LBNP to simulate cardiovascular strain, typically induced by positive G forces (+Gz) in fighter jet flight, has played an important role in our understanding of the cardiovascular response to gravitational forces. This knowledge not only benefits pilots, but also has wider implications for healthcare and working conditions where individuals may face similar physiological challenges. Although numerous reports su pport the development of LBNP for space mission applications, there is no evidence for the use of LBNP to simulate accelerations greater than +1 Gz over the past two decades. However, further research in this area is still warranted.

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.

Phytochemical evaluation of the fruits and green biomass of determinate-type sweet pepper (Capsicum annuum L. fasciculatum) grown in terrestrial bioregenerative life-support research facilities

ABSTRACT This study explores the potential feasibility of cultivating two determinate-type bell peppers, i.e. Hungarian Enigma Hot (HEH) and Hungarian Enigma Sweet (HES), in a ground bioregenerative life-support device. Fruits of the Hugarian Engima Sweet (HES) variety is advantageous for digestion due to it has thin cuticle and collenchyma at the same time the parenchyma of mesocarp of it is thin. β-carotene and caspanthin were the dominant carotenoids in both fruit varieties. Up to 55 tentative phytochemicals were not only in fruits but also in green juice processed from green leafy shoots. The green juice was also a rich source of protein (24–27% w/w) and a source of macro- and microelements. The findings of this study could hold valuable insights for the advancement of sustainable food production and resource utilization in space environments, with potential applications for long-duration space missions and beyond. Key policy highlight Two determinate-growth green pepper varieties with specific characteristics were grown in ground bioregenerative life-support research device Fruits of the Hugarian Engima Sweet (HES) variety is advantageous for digestion as it has thin cuticle and collenchyma at the same time the parenchyma of mesocarp is thin The green juice processed from green leafy shoots is a rich source of protein (24–27% w/w), luteins, flavonoids, phenolic acids and derivatives. With the change in color of the fruits from green to red, β-carotene and capanthin as carotenoids showed the greatest increase. Content of flavonoids and phenolic components, i.e. quercetin-3-O-d-glucopyranoside, rutin (quercetin-3-O-rutinoside), caffeic acid and ferulic acid showed a decreased trend during fruit ripening.

The “Effect of Marangoni Convection on Heat Transfer in Phase Change Materials” experiment

Present as well as future challenges of space exploration point to the need for improved thermal control systems. The “Effect of Marangoni Convection on Heat Transfer in Phase Change Materials” experiment, which is approved by ESA for execution on board the International Space Station, aims to contribute directly to current knowledge and basic understanding of heat and mass transport in phase change materials (PCMs) that incorporate a free surface in reduced gravity. The experiment will apply fixed temperatures to opposite ends of PCM samples held in cuboidal and cylindrical containers in order to drive controlled melting and solidification cycles that will be observed by means of optical cameras. The recorded images will be complemented by thermal measurements at key positions along the samples, which will allow different thermocapillary flow regimes to be distinguished according to their temporal dynamics. It is anticipated that thermal Marangoni (thermocapillary) convection will increase the heat transfer rate in these PCM devices by a significant factor (on the order of two or more) compared to melting governed by thermal diffusion (conduction). If the PCM designs prove robust, the experiment results can be expected to lead to substantial improvements in future designs for passive PCM applications in space missions.

Embracing robots in our lives [Editorial

Robotics has the power to change our lives by transforming manual jobs to autonomous ones, with increased economic growth and productivity. You may recall the surprising appearance of Sophia, the most advanced humanoid robot, which fluently interacted with people in 2016. We are eagerly waiting for Elon Musk’s Optimus to be available in 2027, a new humanoid robot that could be part of our everyday lives. NASA’s Robonaut 2 (or R2) was flown to the space station as part of STS-133 mission. A robot cooker is capable of large-scale, fully automatic cooking. In fact, robots are coming to our lives with applications in space missions, underwater exploration, agriculture and the food industry, medicine and health care, industrial automation and manufacturing, security, entertainment, search and rescue, and education. Robotics is a multidisciplinary and exciting research field that crosscuts computer science, electrical engineering, mechanical engineering, material science, etc.

Radiation damage in GaN/AlGaN and SiC electronic and photonic devices

The wide bandgap semiconductors SiC and GaN are commercialized for power electronics and for visible to UV light-emitting diodes in the case of the GaN/InGaN/AlGaN materials system. For power electronics applications, SiC MOSFETs (metal–oxide–semiconductor field effect transistors) and rectifiers and GaN/AlGaN HEMTs and vertical rectifiers provide more efficient switching at high-power levels than do Si devices and are now being used in electric vehicles and their charging infrastructure. These devices also have applications in more electric aircraft and space missions where high temperatures and extreme environments are involved. In this review, their inherent radiation hardness, defined as the tolerance to total doses, is compared to Si devices. This is higher for the wide bandgap semiconductors, due in part to their larger threshold energies for creating defects (atomic bond strength) and more importantly due to their high rates of defect recombination. However, it is now increasingly recognized that heavy-ion-induced catastrophic single-event burnout in SiC and GaN power devices commonly occurs at voltages ∼50% of the rated values. The onset of ion-induced leakage occurs above critical power dissipation within the epitaxial regions at high linear energy transfer rates and high applied biases. The amount of power dissipated along the ion track determines the extent of the leakage current degradation. The net result is the carriers produced along the ion track undergo impact ionization and thermal runaway. Light-emitting devices do not suffer from this mechanism since they are forward-biased. Strain has also recently been identified as a parameter that affects radiation susceptibility of the wide bandgap devices.

Optimizing transcranial magnetic stimulation for spaceflight applications

As space agencies aim to reach and build installations on Mars, the crews will face longer exposure to extreme environments that may compromise their health and performance. Transcranial magnetic stimulation (TMS) is a painless non-invasive brain stimulation technique that could support space exploration in multiple ways. However, changes in brain morphology previously observed after long-term space missions may impact the efficacy of this intervention. We investigated how to optimize TMS for spaceflight-associated brain changes. Magnetic resonance imaging T1-weighted scans were collected from 15 Roscosmos cosmonauts and 14 non-flyer participants before, after 6 months on the International Space Station, and at a 7-month follow-up. Using biophysical modeling, we show that TMS generates different modeled responses in specific brain regions after spaceflight in cosmonauts compared to the control group. Differences are related to spaceflight-induced structural brain changes, such as those impacting cerebrospinal fluid volume and distribution. We suggest solutions to individualize TMS to enhance its efficacy and precision for potential applications in long-duration space missions.

RF Systems on Chip and Mixed-Signal Front-End Devices: Game-Changing RF Technologies for Space Applications

Growing interest in the commercialization of space (NewSpace) is leading to increased acceptance of commercial off-the-shelf (COTS) electronics and thus enabling use in space of the latest technologies developed for terrestrial applications. This opens new capabilities for applications in space missions. RF communication via satellites has been established for decades; traditionally used for military applications, it is becoming increasingly important for commercial users. Today, global connectivity and access to the Internet has never been so important, and the demand for worldwide connectivity increases significantly each year. Space-based Internet access is especially important for areas with poor terrestrial infrastructure, such as Africa and Antarctica. There are already geostationary-Earth orbit (GEO)-stationary-located satellites available such as <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Inmarsat</i> or low-Earth orbit (LEO) satellite constellations like Iridium, which provide almost-global access to the Internet, but they are either very expensive or have low data rates and long latencies, so they are not very attractive. New solutions with high data rates, low latencies, and affordable fees are currently in development, such as StarLink, with its giga constellation <xref ref-type="bibr" rid="ref1" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">[1]</xref> , <xref ref-type="bibr" rid="ref2" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">[2]</xref> , and Amazon’s Project Kuiper <xref ref-type="bibr" rid="ref3" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">[3]</xref> , <xref ref-type="bibr" rid="ref4" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">[4]</xref> , <xref ref-type="bibr" rid="ref5" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">[5]</xref> . So it is true: there really has been a change in the market with the NewSpace Era. With NewSpace, or in other words, the commercialization of space, traditional space missions with high-quality assurance requirements, very long design and manufacturing times, and extraordinary costs may become obsolete at a certain point, at least when it comes to commercial services like satellite-based Internet access. To decrease the lead time and costs of such missions, satellite designers and manufacturers need to rely on commercially available electronics, namely, COTS devices, which are usually much cheaper and have better performance and shorter lead times compared to space-qualified parts. In terms of performance, COTS devices have great benefits over space-qualified parts simply because the design, development, and qualification processes for space parts are very complex and take years before they are qualified and available for the market. It is likely that state-of-the-art space-qualified parts are 10 years behind what we currently have available for terrestrial applications, such as for the automotive or industrial markets <xref ref-type="bibr" rid="ref6" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">[6]</xref> . One obvious reason is certainly that electronic parts manufacturers develop products for certain markets, and space is yet not one of the biggest or most attractive markets. But this has already started changing and big players such as Texas Instruments and Analog Devices are moving forward with the NewSpace wave and establishing ever-more products for commercial space applications. Truly, using state-of-the art electronics is not only of interest for the space-based Internet, there are also other space-related applications that can clearly benefit from using the latest technologies.

Thermal Stability of the Ferroelectric Properties in 100 nm-Thick Al0.72Sc0.28N.

The discovery of ferroelectricity in aluminum scandium nitride (Al1-xScxN) opens technological perspectives for harsh environments and space-related memory applications, considering the high-temperature stability of piezoelectricity in aluminum nitride. The ferroelectric and material properties of 100 nm-thick Al0.72Sc0.28N are studied up to 873 K, combining both electrical and in situ X-ray diffraction measurements as well as transmission electron microscopy and energy-dispersive X-ray spectroscopy. The present work demonstrates that Al0.72Sc0.28N can achieve high switching polarization and tunable coercive fields in a 375 K temperature range from room temperature up to 673 K. The degradation of the ferroelectric properties in the capacitors is observed above this temperature. Reduction of the effective top electrode area and consequent oxidation of the Al0.72Sc0.28N film are mainly responsible for this degradation. A slight variation of the Sc concentration is quantified across grain boundaries, even though its impact on the ferroelectric properties cannot be isolated from those brought by the top electrode deterioration and Al0.72Sc0.28N oxidation. The Curie temperature of Al0.72Sc0.28N is confirmed to be above 873 K, thus corroborating the promising thermal stability of this ferroelectric material. The present results further support the future adoption of Al1-xScxN in memory technologies for harsh environments like applications in space missions.

Spacecraft Proximity Maneuvering and Rendezvous With Collision Avoidance Based on Reinforcement Learning

The rapid development of the aerospace industry puts forward the urgent need for the evolution of autonomous spacecraft rendezvous technology, which has gained significant attention recently due to increased applications in various space missions. This article studies the relative position tracking problem of the autonomous spacecraft rendezvous under the requirement of collision avoidance. An exploration-adaptive deep deterministic policy gradient (DDPG) algorithm is proposed to train a definite control strategy for this mission. Similar to the DDPG algorithm, four neural networks are used in this method, where two of them are used to generate the deterministic policy, whereas the other two are used to score the obtained policy. Differently, adaptive noise is introduced to reduce the possibility of oscillations and divergences and to cut down the unnecessary computation by weakening the exploration of stabilization problems. In addition, in order to effectively and quickly adapt to some other similar scenarios, a metalearning-based idea is introduced by fine-tuning the prior strategy. Finally, two numerical simulations show that the trained control strategy can effectively avoid the oscillation phenomenon caused by the artificial potential function. Benefiting from this, the trained control strategy based on deep reinforcement learning technology can decrease the energy consumption by 16.44% during the close proximity phase, compared with the traditional artificial potential function method. Besides, after introducing the metalearning-based idea, a strategy available for some other perturbed scenarios can be trained in a relatively short period of time, which illustrates its adaptability.

Use of combined linear and nonlinear formalisms applied to the transport of protons and secondary electrons in a Monte Carlo code: Applications for space missions

A review of linear (dielectric theory) and nonlinear (binary collision theory) formalisms is proposed. The range of validity of both theories is discussed. The differential energy cross sections are fully detailed so that they are suitable for use in any Monte Carlo code. The use of the nonlinear formalism (and consequently the description of the differential cross sections) in a Monte Carlo code, such as GEANT4, is poorly addressed in the literature. In order to cover a very wide energy range, a combined model is discussed and implemented in GEANT4. Applications related to the space domain are studied, and the benefit of our combined model is investigated through a dedicated code devoted to the estimation of deposited energy in nanometric volumes.

Total ionization dose radiation tests results of the epoch timing system with sub-picosecond resolution and stability for its applications in space missions.

We report on the concept, design, and tests of a New Picosecond Event Timer (NPET) device and its response to the total ionizing dose. These radiation tests aimed to verify that the existing version of the NPET device may be used in space missions. The device was subjected to radiation of a total dose of 74 Gy provided by a 60Co source. The epoch timing part of the device was not detectably affected by the radiation dose. After the radiation dose, the epoch timing of single measurement resolution is better than 0.9ps with the overall timing stability characterized by Time Deviation being better than 5fs for averaging times of 100s. The completed device tests and results indicate the possibility of using the existing version of the New Pico Event Timing device electronics for a space mission in which the total radiation dose will not exceed 74 Gy value.

Enhanced Hole Transport in Ni/Y₂O₃/n-4H-SiC MOS for Self-Biased Radiation Detection

We report the fabrication of novel self-biased high resolution radiation detectors achieved in n-type 4H-SiC metal-oxide-semiconductor (MOS) devices. Vertical MOS structure has been realized by pulsed laser deposition of 40 nm Y <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> layer on 20 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> n-type 4H-SiC epilayer followed by sputter coating a nickel gate, which revealed a record-high hole diffusion length. The MOS device exhibited a remarkable radiation detection response to 5486 keV alpha particles with a charge collection efficiency of 82% and an energy resolution of 72 keV full width at half maximum (FWHM) at zero applied bias. The hole diffusion length has been calculated to be 56 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> using a drift-diffusion model. Such long hole diffusion length and a flat-band potential of 2.1 V, enabled to attain high efficiency and resolution in the self-biased mode. Band energy calculations indicated that the presence of Y <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> layer may have neutralized the hole traps usually present in a metal-4H-SiC interface thereby substantially improving the hole transport. Such high performing self-biased radiation detectors fabricated on 4H-SiC are intended for applications in harsh environment space missions, wherein carrying detector power supplies as a payload becomes a critical logistic issue. The present study opens the high potential of other wide bandgap semiconductors as self-biased MOS devices as well.