Spacecraft In Low Earth Orbit Research Articles

Highly flexible porous indium-tin-oxide coating with enhanced atomic oxygen and electrostatic discharge resistance

Polyimides (PI) are commonly used in spacecraft in low Earth orbit (LEO) due to their flexibility. However, they are susceptible to erosion caused by atomic oxygen (AO) and electrostatic discharge (ESD) induced by plasma in the harsh LEO environment. Indium-tin-oxide (ITO), owing to its excellent electrostatic and AO resistance, has emerged as the most promising inorganic protective coating for PI in LEO applications. But the inherent rigidity of ITO and the high-temperature annealing process commonly required for synthesis make it challenging to employ ITO as flexible polymer substrates. In this work, we have synthesized the porous ITO layer with a low-temperature (≤150 °C) method and combined it with layer double hydroxides (LDHs) to enhance the flexibility, AO resistance, and ESD protection of the coating. The porous ITO in combination with LDHs layers effectively improve the flexibility (after 20,000 bending cycles without failure problem), AO resistance (erosion yield down to -0.102 × 10−26 cm3/atom under an exposure dose of 5.22 × 1021 atoms/cm2) and ESD resistance properties (sheet resistance around 202 kΩ/sq). The synthesis method proposed avoids the high-temperature annealing and the residual stress effect on the coating's flexibility. This work provides an efficient approach to realizing flexible and protective coating on polymers for long-lasting spacecraft electronic devices in low Earth orbit.

Modelling an Ion Thruster for a Small Spacecraft in Very Low Earth Orbit

A gridded ion thruster running on two different propellants (Xenon and Iodine) and sited within a 3U CubeSat satellite, is modelled in a Low-Earth-Orbit (altitude 400 km), using a Particle-in-Cell approach. Charged exchange collisions cause a plume backflow, which results in erosion or contamination of external spacecraft surfaces. In particular, this research is motivated by evaluating the risks to solar panel arrays from plume backflow. At low altitudes there is a wide range of ambient species able to interact electrostatically with the ion plume. In particular one must consider the plasma potential of the incoming particle flux at the solid boundaries as well as a sheath comparison and the temperature of the solar panel surfaces. This enables evaluation of the effect of temperature on the charged exchange region. A Particle-in-Cell is used, with a hybrid approach where electrons are treated as a fluid and the propellant as kinetic particles. Our results compare surface ablation for two propellants, focusing on solar panel arrays which are considered to be especially vulnerable to the backflow of ions from the plume expansion. It is found that the flux of incoming particles increases for lower satellite surface temperatures. Furthermore, Xenon results in having a lower overall effect on the sensitivity of the particle flux in comparison to Iodine.

A simplified geospace model for satellite design

This study introduced a simplified, integrated computational model to estimate the drag coefficient and surface charging within the plasma wake of Low Earth Orbit (LEO) spacecraft influenced by various solar activities. The model constituted four core modules: a solver for the solar wind-magnetosphere interaction, a magnetosphere-ionosphere coupling for electric field mapping, an ionization model for the F-layer of the ionosphere, and an estimation model for excess satellite drag and plasma wake size. The initial module adopted a simplified 1D ideal Magnetohydrodynamic (MHD) model while incorporating magnetosphere-ionosphere interactions to derive electric field data near Earth’s boundary. A simplified ionospheric model for the F-layer was implemented to compute the O+ and electron densities. Subsequently, the spacecraft drag coefficient and the plasma wake size were determined for varying solar wind speed inputs corresponding to quiet, intense, and extreme space weather conditions. In the case of extreme conditions with a solar wind speed of 1000 km/s, the results indicated that the excess satellite drag coefficient and plasma wake size increased to around ten percent.

Developing a novel battery management algorithm with energy budget calculation for low Earth orbit (LEO) spacecraft

Developing a novel battery management algorithm with energy budget calculation for low Earth orbit (LEO) spacecraft

Variability and distribution of nighttime equatorial to mid latitude ionospheric irregularities and vertical plasma drift observed by FORMOSAT-5 Advanced Ionospheric Probe in-situ measurements from 2017 – 2020

Irregularities in ionospheric plasma distribution can result in severe scintillation and disruption to the radio frequencies utilized for satellite communications and navigation. In the low and mid latitudes, these irregularities can include Equatorial Plasma Bubbles (EPBs) and Travelling Ionospheric Disturbances (TIDs). EPBs are irregularities manifesting in low latitude nighttime ionosphere plasma density that can extend along magnetic field lines with zonal scales on the order of 100 km or less, while TIDs are propagating wave disturbances. High frequency in-situ measurements of ionospheric plasma aboard spacecraft in Low Earth Orbit (LEO) are a direct measurement of irregularities in plasma density and are therefore valuable for resolving EPB and TID occurrences, variability, and relation to other ionospheric parameters that are believed to play a driving role in the formation of such irregularities. In this study, we utilize observations taken over a three-year period between 2017 and 2020 by the Advanced Ionospheric Probe (AIP) carried aboard the FORMOSAT-5 satellite to examine the spatial, seasonal, and interannual variability of equatorial to mid latitude ionospheric irregularities and vertical ion drift during this time. AIP provides in-situ measurements of ion density and vertical ion drift in the equatorial to mid latitude ionosphere at approximately 720 km altitude with local times between 22:00 – 23:00 local time. Our global scale results resolve distinct and inter-annually recurrent seasonal patterns in the distribution of nighttime ionospheric irregularities and vertical plasma drift during this time. Elevated occurrences of ion density irregularities are resolved along the Equatorial Ionization Anomaly (EIA) latitudes, while notable occurrences with variability consistent with EPBs also observed along the low and equatorial magnetic latitudes. Zonal variability of equatorial irregularities consistent with the signatures of nonmigrating atmospheric tides are observed. It is also notable that the occurrences and geographic distribution of ion density irregularities showed a considerable level of interannual variability, especially at mid latitudes over the South Atlantic and Southern African sectors, which showed much higher levels of irregularities in 2017–––2018, compared to 2019 and 2020. In comparison, the spatial and interannual variation of the co-located vertical ion drifts were much more consistent during the years examined, indicating that the driver for the observed interannual variability in ion density irregularities cannot be attributed to the vertical ion drift at the same time and location of the observations. This highlights the need for in-situ instruments distributed across multiple satellites in different local time zones.

An on‐orbit calibration method for time delay of inter‐satellite link transponder in tracking and data relay satellite

AbstractThe tracking and data relay satellite (TDRS) in geosynchronous orbit (GEO) can provide ranging and communication services for user spacecraft in low Earth orbit (LEO) through the inter‐satellite link (ISL). The time delay of TDRS ISL transponder in orbit differs from its pre‐launch state and changes due to the complex space environment, adding significant errors to the user spacecraft's orbit determination based on four‐way ranging data. The authors have developed a calibration system and proposed an efficient on‐orbit calibration method for the ISL transponder's time delay in TDRS. Experimental results demonstrate the effectiveness of the authors’ method, and the RMS of calibration residuals is less than 0.5 m.

Impact of the South Atlantic Anomaly on radiation exposure at flight altitudes during solar minimum

The South Atlantic Anomaly (SAA) is a geographical region over the South Atlantic Ocean where the inner Van Allen radiation belt extends down particularly close to Earth. This leads to highly increased levels of ionizing radiation and related impacts on spacecraft in Low Earth Orbits, e.g., correspondingly increased radiation exposure of astronauts and electronic components on the International Space Station. According to an urban legend, the SAA is also supposed to affect the radiation field in the atmosphere even down to the altitudes of civil aviation. In order to identify and quantify any additional contributions to the omnipresent radiation exposure due to the Galactic Cosmic Radiation at flight altitudes, comprehensive measurements were performed crossing the geographical region of the SAA at an altitude of 13 km in a unique flight mission—Atlantic Kiss. No indication of increased radiation exposure was found.

Carbon Nanocomposites in Aerospace Technology: A Way to Protect Low-Orbit Satellites.

Recent advancements in space technology and reduced launching cost led companies, defence and government organisations to turn their attention to low Earth orbit (LEO) and very low Earth orbit (VLEO) satellites, for they offer significant advantages over other types of spacecraft and present an attractive solution for observation, communication and other tasks. However, keeping satellites in LEO and VLEO presents a unique set of challenges, in addition to those typically associated with exposure to space environment such as damage from space debris, thermal fluctuations, radiation and thermal management in vacuum. The structural and functional elements of LEO and especially VLEO satellites are significantly affected by residual atmosphere and, in particular, atomic oxygen (AO). At VLEO, the remaining atmosphere is dense enough to create significant drag and quicky de-orbit satellites; thus, thrusters are needed to keep them on a stable orbit. Atomic oxygen-induced material erosion is another key challenge to overcome during the design phase of LEO and VLEO spacecraft. This review covered the corrosion interactions between the satellites and the low orbit environment, and how it can be minimised through the use of carbon-based nanomaterials and their composites. The review also discussed key mechanisms and challenges underpinning material design and fabrication, and it outlined the current research in this area.

The atomic oxygen resistant study of a transparent polyimide film containing phosphorus and fluorine

As ideal packaging materials for solar cells of low-Earth orbit (LEO) spacecraft, polyimide (PI) films have to withstand various harsh space environment. Here, we investigate the atomic oxygen (AO)-resistant property of a transparent PI film with side diphenylphosphine oxide and trifluoromethyl. After exposed under AO (1.3 × 1020 atoms·cm−2), most excellent properties of the PI film can be maintained except for partial loss of transmittance. Its erosion yield is 0.56 × 10−24 cm3·atom−1, only 18.7% as that of Kapton film at the same condition. To understand the damage mechanism, the surface and bulk performances of the AO exposed PI film were systematically investigated and compared with those of the prinstine PI film. The results indicate that the relative concentration of phosphorus and oxygen near to the AO exposed surface of the PI film increases, which means the formation of a phosphate passivation layer. The thickness of phosphate passivation layer is about 200 nm with the content of PO3− decreasing in vertical direction of itself, which can reduce the further erosion of the PI film by AO. Such PI films containing P and F are much more AO resistant and expected a candidate as packaging material for LEO spacecraft.

LEO Satellite Navigation Based on Optical Measurements of a Cooperative Constellation

Autonomous, anti-jamming, and high-precision satellite navigation are of great importance to current and future space technologies. This paper proposes a cooperative constellation navigation system for low Earth orbit (LEO) satellites that use only the optical measurements of cooperative satellites. Based on photometry, an optical transmission link model of the system is built. With the pixel coordinates of the cooperative satellites on the optical images, the line of sight (LoS) vectors of the cooperative satellites with respect to the LEO spacecraft are first calculated, and a single-point positioning method based on the LoS vectors’ inner products is proposed. The single-point positioning results are then fed into a least square batch filter to estimate a high-precision spacecraft orbit. Simulations are conducted to evaluate the potential navigation accuracy. With a cooperative satellite ephemeris error of 100 m and an optical measurement noise level of 5 arcsecs, position accuracies of single-point positioning and dynamic orbit determination in the order of hundreds of meters and eight meters, respectively, are realized. In addition, the influences of the orbital altitude of the cooperative constellation, the ephemeris error of the cooperative satellite, the noise level of the optical measurements, and the Earth’s gravitational model on navigation accuracy are investigated via comparative simulations.

Long-term atomic oxygen resistant polyimide films containing carborane nanocage structure in the main chains

High-temperature durable polymer films with long-term atomic oxygen (AO) resistant capabilities are highly desired for the development of spacecraft with long-servicing lifetimes in low earth orbit (LEO). The relatively poor AO resistance of conventional polyimide (Kapton® H) film severely limited its applications in LEO spacecraft. In this work, carborane nanocage rich in boron element was introduced into polyimide molecular chain to prolong the atomic oxygen resistance life of polyimide film. A series of carborane-containing polyimide (CBPI) nanocomposite films with ultrahigh AO resistance have been prepared by casting precursor polyamic acid (PAA) solution on a glass plate, followed by thermal imidization at several elevated temperatures. The AO exposure experiments were tested in a ground-based AO effects simulation facility in our laboratory with the filament discharge and bound of magnetic field. Incorporation of carborane nanocage structure apparently improved the thermal stability and AO resistance of the PI nanocomposite films. The CBPI-50 film exhibited the lowest AO average erosion yield (Es) of 2.3 × 10−25 cm3·atom−1 under AO exposure with a fluence of 3.33 × 1020 atoms·cm−2, which is more than one order of magnitude lower than the reference Kapton® H film. The protective mechanism of CBPI nanocomposite films during AO exposure was proposed.

Space radiation induced failure rate calculation method using energy deposition probability function for high-voltage semiconductor device

With the development of modern space technology, it is necessary to use onboard high voltage power systems to supply increased electric power demand. High-voltage semiconductor devices are the critical components in the system. According to the increase in the power system bus voltage, malfunction of high voltage power semiconductor devices due to space radiation becomes the most critical issue for designing the system. What we need to reduce the risk is failure rate calculation for the high-voltage semiconductors used in the system and selecting appropriate devices and the bus voltage. This risk can be reduced by calculating the probability of damage caused by space radiation for high-voltage semiconductor devices. In this study, the energy deposition probability function of a silicon semiconductor device has been developed in a more comprehensive way using the Geant4 simulation toolkit. This method makes it possible to calculate the safe operating voltage of any semiconductor device in space depending on the shape, size, applied voltage, doping concentration, and space radiation flux. Furthermore, using this comprehensive method for defining the safe threshold applied voltage of a high-voltage PiN diode of spacecraft in low earth orbit and compared it to a reference. Data availabilityThe raw/processed data required to reproduce these findings cannot be shared at this time as the data also forms part of an ongoing study.

Spacecraft attitude estimation under attitude tracking maneuver during close-proximity operations

This paper presents a real-time relative three-axis attitude estimation using a camera and two gyros under momentum changes during close-proximity operations. The camera sensor provides quaternion measurements that relate the body frame of the deputy spacecraft with respect to the body frame of the chief spacecraft. The quaternion measurements are coupled with gyro measurements and attitude dynamics model in a multiplicative extended Kalman filter to determine relative attitude and gyro biases under momentum changes. The relative quaternion kinematics is augmented with spacecraft relative motion dynamics to represent the filter process dynamics. The quaternion measurements from a camera sensor and inertial measurement units (IMU) are utilized to the filter measurement model. The fault-tolerant attitude controller actuated by four reaction wheels, which has no unwinding problem is used for attitude tracking maneuvers during close-proximity operations in the presence of external disturbances, uncertain inertia parameter and actuator faults. This controller is combined with the extended Kalman filter to filter noisy measurements and to estimate gyro biases, which leads to a full-state feedback control system. Numerical simulations are performed to verify the effectiveness of the attitude estimation and control systems of the spacecraft with four reaction wheels during close-proximity operations of spacecraft in low-Earth orbit.

Laser Vibrometry-Based Precise Measurement of Tape-Shaped Tethers Damping Ratio Toward Space Applications

To mitigate the growing problem of space debris, current international guidelines require spacecraft in Low Earth Orbit (LEO) to implement post-mission disposal strategies to be deorbited within 25 years from the end of their operative life. Electrodynamic tethers are an effective and promising option for deorbiting as they do not require fuel consumption. However, the success of this new technology also depends on the dynamic stability of thin tape-shaped tethers during both deployment and deorbiting phases. This is where precise measurement of damping characteristics of thin tape-shaped tethers comes in. This paper presents an innovative experimental setup and analysis methods for precisely measuring the damping ratio of a thin (thickness 50 microns) tape-shaped tether made of PEEK intended for use in electrodynamic tethers applications. To capture longitudinal oscillations during dynamic tests, we employed a laser vibrometer and explored four different methods of experimental data analysis, comparing and describing them in detail in the paper. We also conducted an uncertainty analysis in line with ISO GUM. The experimental results show good agreement among the four methods used to estimate the damping ratio with the most precise method involving nonlinear regression applied to all the experimental data. A Monte Carlo analysis was carried out considering the most significant sources of uncertainty. The smallest uncertainty interval is ±1% of the estimated damping ratio, with a 95% confidence level, using this method.

A method for high-precision time transfer between low earth orbit spacecraft and Beidou satellite and its preliminary test verification

A method for high-precision time transfer between low earth orbit spacecraft and Beidou satellite and its preliminary test verification

Development of risk assessment technology for small spacecraft based on a space weather heat map

This study focuses on the development and implementation of a specialized technology to address the challenges posed by space weather on the performance and operational reliability of small spacecraft, particularly CubeSats and nanosatellites in Low Earth Orbit (LEO). The research emphasizes the importance of data acquisition, processing, and visualization of energy particle fluxes in near-Earth space, with a web application demonstrating visualization of average electron values in a heat map format. The proposed technology, in conjunction with space weather prediction methods, allows for quick response to adverse conditions, contributing to increased longevity and operational efficiency of small spacecraft. In the absence of comprehensive protection systems, the research suggests simple organizational methods as an effective approach for risk mitigation and reliability improvement, applicable even to spacecraft already in orbit.

On the Role of ULF Waves in the Spatial and Temporal Periodicity of Energetic Electron Precipitation

AbstractEnergetic electron precipitation to the Earth's atmosphere is a key process controlling radiation belt dynamics and magnetosphere‐ionosphere coupling. One of the main drivers of precipitation is electron resonant scattering by whistler‐mode waves. Low‐altitude observations of such precipitation often reveal quasi‐periodicity in the ultra‐low‐frequency (ULF) range associated with whistler‐mode waves, causally linked to ULF‐modulated equatorial electron flux and its anisotropy. Conjunctions between ground‐based instruments and equatorial spacecraft show that low‐altitude precipitation concurrent with equatorial whistler‐mode waves also exhibits a spatial periodicity as a function of latitude over a large spatial region. Whether this spatial periodicity might also be due to magnetospheric ULF waves spatially modulating electron fluxes and whistler‐mode chorus has not been previously addressed due to a lack of conjunctions between equatorial spacecraft, low earth orbit spacecraft, and ground‐based instruments. To examine this question, we combine ground‐based and equatorial observations magnetically conjugate to observations of precipitation at the low‐altitude, polar‐orbiting CubeSats Electron Losses and Fields Investigation‐A and ‐B. As they sequentially cross the outer radiation belt with a temporal separation of minutes to tens of minutes, they can easily reveal the spatial quasi‐periodicity of electron precipitation. Our combined data sets confirm that ULF waves may modulate whistler‐mode wave generation within a large magnetic local time and L‐shell domain in the equatorial magnetosphere, and thus lead to significant aggregate energetic electron precipitation exhibiting both temporal and spatial periodicity. Our results suggest that the coupling between ULF and whistler‐mode waves is important for outer radiation belt dynamics.

Demonstration of 100 Gbps coherent free-space optical communications at LEO tracking rates

Free-space optical communications are poised to alleviate the data-flow bottleneck experienced by spacecraft as traditional radio frequencies reach their practical limit. While enabling orders-of-magnitude gains in data rates, optical signals impose much stricter pointing requirements and are strongly affected by atmospheric turbulence. Coherent detection methods, which capitalize fully on the available degrees of freedom to maximize data capacity, have the added complication of needing to couple the received signal into single-mode fiber. In this paper we present results from a coherent 1550 nm link across turbulent atmosphere between a deployable optical terminal and a drone-mounted retroreflector. Through 10 Hz machine vision optical tracking with nested 200 Hz tip/tilt adaptive optics stabilisation, we corrected for pointing errors and atmospheric turbulence to maintain robust single mode fiber coupling, resulting in an uninterrupted 100 Gbps optical data link while tracking at angular rates of up to 1.5 deg/s, equivalent to that of spacecraft in low earth orbit. With the greater data capacity of coherent communications and compatibility with extant fiber-based technologies being demonstrated across static links, ground-to-low earth orbit links of Terabits per second can ultimately be achieved with capable ground stations.

DMSP Poynting Flux: Data Processing and Inter-Spacecraft Comparisons.

Poynting flux (PF) calculated from low Earth orbit spacecraft in situ ion drift and magnetic field measurements is an important measure of energy exchange between the magnetosphere and ionosphere. Defense Meteorological Satellite Program (DMSP) spacecraft provide an extensive back‐catalog of ion drift and magnetic perturbation measurements, from which quasi‐steady PF could be calculated. However, since DMSP are operations‐focused spacecraft, data must be carefully preprocessed for research use. We describe an automated approach for calculating earthward PF focusing on pre‐processing and quality control. We produce a PF data set using nine satellite‐years of DMSP F15, F16, and F18 observations. To validate our process we inter‐compare PF from different spacecraft using more than 2,000 magnetic conjunction events. We find no serious systematic differences. We further describe and apply an equal‐area binning technique to obtain average spatial patterns of PF, magnetic perturbation, electric field and ion drift velocity. We perform our analysis using all components of electric and magnetic field and comment on the adverse consequences of the typical single‐electric‐field‐component DMSP PF approximation on inter‐spacecraft agreement. Including full‐field components significantly increases the relative strength of near‐cusp PF and increases the integrated high‐latitude PF by ∼25%.

Improved Wear Resistance and Environmental Adaptability of a Polysiloxane/Molybdenum Disulfide Composite Lubricating Coating Using Polyhedral Oligomeric Silsesquioxane.

Polysiloxane/molybdenum disulfide (MoS2) composite lubricating coatings that are used in low-earth orbit spacecraft have high resistance to atomic oxygen attack and outstanding vacuum tribological properties. However, their atmospheric environment wear resistance and adaptability under high humidity are poor. In this paper, octa-aminophenyl T8-polyhedral oligomeric silsesquioxane (NH2-POSS) was used to enhance their atmospheric wear resistance and environmental adaptability to increase the protection of polysiloxane lubricating coatings for spacecraft. In this study, the effect of NH2-POSS on the mechanical properties of a polysiloxane coating and the tribological properties of the POSS-enhanced polysiloxane/MoS2 lubricating coating were investigated and the mechanism of NH2-POSS enhancement was discussed. Results showed that the addition of NH2-POSS markedly improved the hardness and elastic modulus of the polysiloxane coatings by increasing the crosslink density of the polysiloxanes and nanofiller effect of POSS. Among them, 6 wt% NH2-POSS can reduce the wear rate of the lubricating coating by 25%. In addition, this study also explores the adaptability of polysiloxane/MoS2 lubricating coatings in a high-humidity environment and an atomic oxygen irradiation environment, which provides a reference for further optimization of polysiloxane lubricating coatings.