Spacecraft In Orbit Research Articles

Development of a hybrid screen channel liquid acquisition device for reliable microgravity transfer of cryogenic fluids

Refueling spacecraft in orbit offers potential benefits to future extended duration missions including increased spacecraft payload capacity and reduced launch cost. However, a key challenge for refueling cryogenic propellants in microgravity conditions is the acquisition of vapor-free liquid propellants from an in-orbit supply tank. This is especially true when the required liquid flow rate is high but residual liquid in the tank must be minimal. Vane-type Propellant Management Devices (PMDs) excel in stabilizing and distributing liquid, but are more susceptible to gas ingestion, and generally only perform well at lower flow rates and/or under favorable acceleration gradients. Screen channel PMDs do not stabilize and distribute the liquid as well, but are less susceptible to gas ingestion, and perform well at higher flow rates and/or under adverse accelerations. Screened channel LADs appear to hold many advantages for a flight cryogenic system with high demand flow rate, however there are currently no flight cryogenic fluid-based screen channel LADs. To address this need, Creare has been working with NASA Glenn to develop a hybrid Liquid Acquisition Device (LAD) for cryogenic propellants consisting of screened channels with attached guide vanes, and a screened sump. Creare’s design forms the flow channel from screen material itself, allowing much higher acquisition surface area per unit volume as compared to existing designs. The screened channel LAD and screened sump are assembled by Creare’s advanced laser welding processes to reliably maintain the pore structure of the screen adjacent to the bonding joints. After completing a series of fabrication trials to validate the reliability and repeatability of the approach, a prototype screen channel was fabricated, and its performance was characterized in LN2 outflow. Results were found to be consistent with single-phase CFD predictions of this geometry for a partially exposed screen channel. Two-phase CFD analysis was conducted to evaluate the performance of the guide vanes in favorably distributing liquid to enhance expulsion efficiency. Preliminary structural analysis was performed on representative geometry for the LAD assembly to assess stresses of the under 5 g acceleration. Using this screen channel geometry and overall design approach, Creare assembled a laboratory-scale hybrid LAD with four parallel gallery arms, a screened sump, and guide vanes. The assembly has been installed in a large dewar for preliminary evaluation in LN2. This unit is planned for delivery to NASA for follow-on investigations using liquid hydrogen.

Communication-Aware Orbit Design for Small Spacecraft Swarms Around Small Bodies

Exploration of small Solar System bodies has traditionally been performed by monolithic spacecraft carrying several science instruments. However, instruments often cannot be operated simultaneously due to requirements including viewing angle, illumination, power, and data constraints. This has motivated interest in architectures in which a swarm of small spacecraft, each carrying one instrument, studies a small body after being deployed by a carrier spacecraft; such architectures hold promise to yield significant improvements in mission efficiency, increased data quality, and reduced mission duration. A key difficulty is the selection of orbits for the spacecraft, which must satisfy not only instrument requirements but also communication and data storage constraints. To address this, we propose a novel gradient-based optimization algorithm that simultaneously optimizes spacecraft orbits, observations, and communications; the approach captures instrument requirements, communication bandwidth, and memory usage, and it accommodates irregular gravity field models and surface geometries. Numerical simulations of a six-spacecraft swarm studying the 433 Eros asteroid show that the approach results in a 67.9% increase in data returned as compared to a communication-agnostic approach. Collectively, these results enable system designers to quickly assess the end-to-end performance of multispacecraft constellations, and represent a first step toward communication-aware design of multispacecraft missions for small Solar System body exploration.

Porous silica coating with excellent atomic oxygen protection performance and flexibility

With the rapid development of spacecrafts in the low earth orbit (LEO), the protection requirements of polyimide (PI) surface against atomic oxygen (AO) erosion had been highlighted. Inorganic coatings trended to crack and peel off due to stress, which limited their application on flexible polymer surfaces. Different from the conventional idea of using dense inorganic coatings to develop AO resistance, in this work, APTES ((3-aminopropyl) triethoxysilane) -modified silica coatings with porous structure have successfully removed the influence of stress and increased the adsorption of AO and adhesion. As a result, the porous silica coating exhibited excellent AO protection performance (low erosion of 1.18 × 10−26 cm3 atom−1), good flexibility (no damage or crack on the surface after bending), and enhanced PI substrate-adhesion. The results of first-principles calculations and experiments indicate that the structure with large surface area and small pore volume is able to adsorb AO and reduce the erosion. This study proposed a new solution of adopting non-dense structure and a novel AO protection mechanism of porous coatings, which expands the application of inorganic coatings for AO protection.

Orbital distances and options for small body satellites in Non-Keplerian orbits dominated by solar radiation pressure

We offer a comprehensive description for the dynamics of a spacecraft affected by solar radiation pressure (SRP) orbiting a small body. Constrains are given for regions, in which stable motion is possible. For short and long time scales two different analytical frameworks are summarized and applied. (1) For time scales well below one heliocentric revolution we examine the “static” case, involving SRP fixed in both magnitude and direction. We demonstrate a closed-form solution for quasi terminator orbits using parabolic coordinates. (2) Next, we study the “dynamic” case where the asteroid is in an eccentric orbit about the Sun, involving changing solar aspect angle and distance. To solve this Augmented Hill Three-Body Problem (AH3BP), SRP effects are averaged over the anomaly of the orbiter. From this approximation we derive constrains for Sun-synchronous orbits in size and eccentricity. The findings of the analysis (1) and (2) are then applied to small- and medium-sized spacecraft orbiting specific asteroids, comets, dwarf planets and (for comparison) planets. We consider ranges of orbiter mass and surface area exposed to the Sun, as well as small body parameters, including mass and orbit. We show the resulting constrains on orbit size as well as parameters of Sun-synchronous orbits and frozen orbits in tables. While terminator orbits may only vary in size, quasi terminator orbits can cover wide regions best described in the parabolic coordinates of case (1). This region has four parameters for our orbit options. As alternative application for orbit stability we calculate constraints on orbit and particle sizes for dust particles. Numerical integration is used to validate the resilience of these solutions to further perturbation by third bodies or the small body's non-spherical shape. • We estimated orbital distances for spacecrafts in Sun-synchronous orbits around 9 small bodies. • Orbital shapes deviate greatly from Keplerian conic sections due to solar radiation pressure. • Quasi-terminator orbit dynamics are confined and described by up to four parabolas. • For orbiting dust a frozen state is assumed, limits to orbital sizes are given. • Numeric simulations add perturbing effects and validate predictions about orbit stability.

Decoupled and coupled moons’ ephemerides estimation strategies application to the JUICE mission

When reconstructing natural satellites' ephemerides from space missions' tracking data, the dynamics of the spacecraft and natural bodies are often solved for separately, in a decoupled manner. Alternatively, the ephemeris generation and spacecraft orbit determination can be performed concurrently. This method directly maps the available data set to the estimated parameters' covariances while fully accounting for all dynamical couplings. It thus provides a statistically consistent solution to the estimation problem, whereas this is not directly ensured with the decoupled strategy. For the Galilean moons in particular, the JUICE mission provides a unique, although challenging, opportunity for ephemerides improvement. For such a dynamically coupled problem, choosing between the two state estimation strategies will be influential. This paper quantifies the Galilean moons' state uncertainties attainable when applying a coupled estimation strategy to simulated JUICE data, and discusses the challenges that remain to be addressed to achieve such a coupled solution from real observations. We first provide a detailed, explicit formulation for the coupled approach, which was still missing in the literature although already used in past studies. We then assessed the relative performances of the two ephemerides generation techniques for the JUICE test case. To this end, we used both decoupled and coupled models on simulated JUICE radiometric data. We compared the resulting covariances for the Galilean moons' states, and showed that the decoupled approach yields slightly lower formal errors for the moons' tangential positions. However, the coupled model can reduce the state uncertainties by more than one order of magnitude in the radial direction ( i.e. towards the central body). It also proved more sensitive to the dynamical coupling between Io, Europa and Ganymede, allowing the state solutions for the first two moons to fully benefit from JUICE orbital phase around Ganymede. On the other hand, we showed that the choice of state estimation methods does not strongly affect the moons' gravity field determination. Many issues still remain to be solved before a concurrent estimation strategy can be successfully applied, especially to reconstruct the moons’ dynamics over long timescales. Nonetheless, our analysis highlights promising ephemerides improvements and thus motivates future efforts to reach a coupled state solution for the Galilean moons.

Flashover of insulation materials induced by electrostatic electromagnetic pulse

PurposeThe purpose of this paper is to research the induced flashover laws of different insulation materials under electrostatic electromagnetic pulse, and the induced flashover characteristics of different electrode structures are further explored.Design/methodology/approachAccording to standard IEC 61000–4-2, an experimental system of electrostatic electromagnetic pulse flashover for insulation materials is established. The induction flashover laws of polytetrafluoroethylene, epoxy resin and polymethyl methacrylate surface-mounted finger electrodes under the different intensity of electrostatic electromagnetic pulse are researched. The influence of the finger electrode, needle–needle electrode and needle–plate electrode on insulation flashover was compared. Secondary electron emission avalanche (SEEA) and field superposition theory are used to analyze the experimental results of electrostatic electromagnetic pulse induced flashover.FindingsThe larger the dielectric strength of insulation materials, the more difficult flashover occurs on the surface. The field superposition enhances collision ionization between electrons and gas molecules, which leads to the insulation materials surface induced flashover easily by electrostatic electromagnetic pulse. The sharper the electrode shapes on the insulation materials surface, the stronger the electric field intensity at the cathode triple junction, more initial electrons are excited to form the discharge channel, which easily leads to flashover on the surface of the insulating material.Originality/valueThe proposed field superposition combined with the SEEA method provides a new study perspective and enables a more rational, comprehensive analysis of electrostatic electromagnetic pulse induced flashover of insulation materials. The work of this paper can provide a reference for the safety protection of spacecraft in orbit under a strong electromagnetic field environment, increase the service life of spacecraft and improve the reliability of spacecraft’s safe operation in orbit. It provides a basis for the selection of insulation materials for equipment under the different intensities of the external electromagnetic environment.

Analysis and Demonstration of First Cross-Support Interferometry Tracking in China Mars Mission

Delta-Differential One-Way Ranging (DeltaDOR) is widely used in deep spacecraft navigation, and cross support could enhance navigation accuracy with more interferometry baselines and longer baseline. In China Mars mission Tianwen-1, formal joint cross-support interferometry tracking between China Satellite Launch and TT&C General (CLTC) and European Space Operations Center (ESOC) under commercial contract was conducted around the critical stages of the mission, such as Mars orbit insertion. Cross-support interferometry is a new challenge to CLTC, as the correlator for routine DeltaDOR measurements do not fit for cross support, because of observable definition, blind station clock searching, and so on. This paper discusses the new method and algorithm adopted in joint cross support, especially for spacecraft tone signal processing and clock estimation when correlating with the data of two stations from different agencies. Results of the cross-support interferometry tracking activities are also analyzed. Observables from CLTC and ESOC are consistent with each other, and the difference in observables is in the order of tens of ps. All the baselines are induced to evaluate the accuracy of the spacecraft orbit determined and predicted by CLTC, and the DeltaDOR residuals have a root-mean-square (RMS) better than 0.5 ns (the goal is 1 ns), which could enhance the confidence of the orbit accuracy and the effectiveness of control parameters during critical orbit operation.

A Persistent Avian Formation on a South-Facing Slope, along the Northwest Rim of the Argyre Basin of Mars

This is an examination of an avian-shaped feature that rests below a network of cellular structures found on a mound within the Argyre Basin of Mars. The area examined is located near 48.0° south and 55.1° west. A set of four supportive images provided by the Mars Global Surveyor and Mars Reconnaissance Orbiter spacecraft show the feature is persistent over a period of more than 20 years. The images reveal defining aspects of this avian feature, including a head, beak, body, eye, legs, feet, toes, wing, and feathers. When taken together, these components induce the visual impression of an avian-shaped formation that exhibits a unique set of proportional features. The claim of artificial construction is offered and the geoscientist author will examine natural mechanisms that could contribute to the creation of this feature and the testimony of three veterinarians will provide a critical analysis of the avian features. A terrestrial comparison of aesthetic and iconographic motifs is investigated. The request for further study and additional images of these structural components are also encouraged.

Autonomous orbit determination for satellite formations using relative sensing: Observability analysis and optimization

Orbit determination of spacecraft in orbit has been mostly dependent on either GNSS satellite signals or ground station telemetry. Both methods present their limitations, however: GNSS signals can only be used effectively in earth orbit, and ground-based orbit determination presents an inherent latency that increases with the Earth–spacecraft distance. For spacecraft flying formations, an alternative method of orbit determination, independent of external signals, consists in the observation of the spacecraft’s position with respect to the central body through the relative positioning history of the spacecraft within the formation. In this paper, the potential of the relative positioning method is demonstrated in the context of the SunRISE mission, and compared with the mission’s previously proposed orbit determination methods. An optimization study is then made to find the optimal placement of a new spacecraft in the formation so as to maximize the positioning accuracy of the system. Finally, the possibility of removing part of the system’s relative bearing measurements while maintaining its observability is also studied. The resulting system is found to be observable, but ill-conditioned.

Design & development of X-ray Solar Monitor (XSM) filter wheel drive mechanism with self hold down feature for chandrayaan-2 orbiter

Onboard Chandrayaan-2 Orbiter, an X-ray Solar Monitor (XSM) instrument was flown for the measurement of intensity of solar X-rays within energy band of 1–15 keV. To achieve this, an active filter wheel drive mechanism is used to control the energy of the solar flares falling onto the detector by flipping the filter wheel. During normal flares, the filter wheel is steered to open position whereas during very large solar flares, a beryllium filter is positioned below the detector to reduce the incident solar energy. An in-built flare detection logic operates the mechanism in real-time when the threshold value of solar flares is crossed. The mechanism also has an additional calibration source which regularly calibrates the instrument.The filter wheel drive mechanism is developed as a compact, miniaturized system without requiring any hold-down thereby reducing the mass and design complications. The self-balanced filter wheel is designed by the ingenious usage of dead weights such that center of gravity of the wheel passes through the rotation axis. Together with the back-driving torque of the motor, the tendency of the wheel to jitter during launch is reduced, thus avoiding a separate hold down mechanism. An additional gripping force is ensured between the filter wheel and the motor shaft by using a grub screw. One end of the filter wheel shaft is supported at the base plate through a DU bush to reduce friction during filter wheel’s rotation and the other end is connected to the motor shaft. A novel Optical Sensor based wheel position feedback system is also developed for the position indication during pre and post dynamic tests.In this paper, the design details of the XSM Filter wheel mechanism along with its analysis and hardware performance evaluation during theintegrated tests with the Chandrayaan-2 Orbiter spacecraft is presented.

Broadband Energization of Superthermal Electrons in Jupiter’s Inner Magnetosphere

AbstractThe Juno spacecraft in a polar orbit around Jupiter has observed broadband electron energization signatures at high latitudes (Mauk et al., 2017, https://doi.org/10.1038/nature23648). We investigate the origin of this energization by simulating the propagation of dispersive Alfvén waves from the Io plasma torus to high latitudes. These waves may be triggered by mechanisms such as the moon‐magnetosphere interaction or inflows from radial transport. We build on the initial hybrid gyrofluid‐kinetic electron simulation of Damiano et al. (2019, https://doi.org/10.1029/2018gl081219) to further quantify electron energization by Alfvénic waves, and investigate this process as a local source mechanism for observed broadband superthermal electron populations. We find that the magnitude of energization increases with the wave amplitude, while decreasing the radial wavelength reduces the high‐latitude wave and particle energy flux. Over the examined range of initial conditions we successfully generate broadband electron populations consistent with Juno observations (Mauk et al., 2017, http://doi.org/10.1038/nature23648; Szalay et al., 2018, https://doi.org/10.1029/2018je005752), that contribute to both precipitating populations and those that form trans‐hemispheric beams. Our energized electron distributions are consistent with observed superthermal populations critical for the torus energy budget (Bagenal & Delamere, 2011, https://doi.org/10.1029/2010ja016294) and Io‐related auroral emission.

Quasi‐Periodic Whistler Mode Emission in the Plasmasphere as Observed by the DSX Spacecraft

AbstractWe describe the quasi‐periodic (QP) whistler‐mode emissions found in the plasmasphere as detected by electric and magnetic instrumentation onboard the Demonstration and Science Experiments (DSX) spacecraft in medium Earth orbit. Over the course of the nearly 2‐year mission, at least 45 episodes of whistler mode QP emissions were detected by the Broad Band Receiver (BBR) onboard DSX. Episodes of QP emissions were identified by discrete events having a clear unambiguous periodic nature as detected by both the electric antennae and search coil magnetic sensors in the BBR survey data at 30 s temporal resolution. Most of the QP episodes occurred in a frequency range between 1 and 4 kHz, in a band previously identified by Van Allen Probes and Cluster investigators. However, episodes were also detected by DSX at higher frequencies ‐ events in these episodes extending all the way to 15 kHz. We present our findings on these unusual high frequency events in the presentation herein. Specifically, these high frequency QP episodes tended to be observed near dawn/dusk when the spacecraft was at relatively high magnetic latitudes and on magnetic L‐shells between 3 and 5. Another unusual feature of these episodes is that individual up‐drifting events making up the episode were found to sometimes occur concurrently in time: The high frequency portion of one up‐drifting “polliwog‐shaped” event overlapped in time with the low frequency portion of the subsequent event. This behavior of the QP emissions has not been previously emphasized and we consider how this temporal concurrence relates to the source processes.

Jupiter's Low-Altitude Auroral Zones: Fields, Particles, Plasma Waves, and Density Depletions.

The Juno spacecraft's polar orbits have enabled direct sampling of Jupiter's low‐altitude auroral field lines. While various data sets have identified unique features over Jupiter's main aurora, they are yet to be analyzed altogether to determine how they can be reconciled and fit into the bigger picture of Jupiter's auroral generation mechanisms. Jupiter's main aurora has been classified into distinct “zones”, based on repeatable signatures found in energetic electron and proton spectra. We combine fields, particles, and plasma wave data sets to analyze Zone‐I and Zone‐II, which are suggested to carry upward and downward field‐aligned currents, respectively. We find Zone‐I to have well‐defined boundaries across all data sets. H+ and/or H3 + cyclotron waves are commonly observed in Zone‐I in the presence of energetic upward H+ beams and downward energetic electron beams. Zone‐II, on the other hand, does not have a clear poleward boundary with the polar cap, and its signatures are more sporadic. Large‐amplitude solitary waves, which are reminiscent of those ubiquitous in Earth's downward current region, are a key feature of Zone‐II. Alfvénic fluctuations are most prominent in the diffuse aurora and are repeatedly found to diminish in Zone‐I and Zone‐II, likely due to dissipation, at higher altitudes, to energize auroral electrons. Finally, we identify significant electron density depletions, by up to 2 orders of magnitude, in Zone‐I, and discuss their important implications for the development of parallel potentials, Alfvénic dissipation, and radio wave generation.

Modeling efforts for multi-mission science

AbstractThe Solar Orbiter spacecraft, launched in February 2020, is equipped with both remote-sensing (RS) and in-situ (IS) instruments to record novel and unprecedented measurements of the solar atmosphere and the inner heliosphere. To take full advantage of these new datasets, we have developed tools and techniques to facilitate multi-instrument and multi-spacecraft studies. In particular the yet inaccessible low solar corona below 2 R⊙ can only be observed remotely and techniques must be used to retrieve coronal plasma properties in time and in 3-D space. These properties are useful to drive numerical models and test the different theories proposed to describe the fundamental processes of the solar atmosphere. In addition, the last decades of research have shown that the coupling between the solar corona and the heliosphere is most efficiently studied by combining RS with IS data. During one of the last Solar Orbiter remote sensing windows (March 2022), planned for the Solar Orbiter instruments, we ran complex observation campaigns to maximize the likelihood of linking IS data to their source region near the Sun, by directing some RS instruments to specific targets on the solar disk just days before data acquisition. We show how it is possible to achieve these results directed to improve our understanding of how heliospheric probes connect magnetically to the solar disk.

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.

In-depth investigation of low-energy proton irradiation effect on the structural and photoresponse properties of ε-Ga2O3 thin films

Ga2O3 possesses an ultra-wide bandgap (∼4.9 eV) and an extremely large breakdown field strength (∼8 MV/cm), which promises extraordinary application potential in power electronics and ultraviolet optoelectronics. With the demand for highly durable devices in harsh environments such as in low earth orbit spacecraft, in-depth understanding of the particle radiation effect on the structural and performance degradation of the device is desired. In this work, we employ 150 keV low energy proton with intensity up to 5 × 1015 dose to irradiate the epitaxial ε-Ga2O3 thin films. The characterization of the structural and optical properties shows no detectable variations in lattice structure and optical transmission. In addition, with increasing irradiation dosage, a decrease of Ga3+ population and an increase of the concentration of oxygen vacancies are confirmed by X-ray photoemission spectroscopy. Photoresponse measurements further illustrate that, despite of a mild degradation in the photodetector performance, the device still shows a high photoresponsivity of 2.52 × 10-3 A/W and a large photo-to-dark current ratio over 103. Our work reveals that ε-Ga2O3 exhibits excellent radiation hardness under low-energy proton irradiation conditions and highlights the potential for operational optoelectronics in extreme environment.

Q-SAT for atmosphere and gravity field detection: Design, mission and preliminary results

Q-SAT, a small spherical satellite designed and developed by Tsinghua university, was successfully launched on Aug 6, 2020 at Jiuquan satellite launch center in China. The mission of Q-Sat is the joint measurement of long-wavelength Earth gravity field and upper atmosphere density, which is of great significance for improving spacecraft orbit prediction and promoting the development of satellite gravity measurement technology. The satellite is designed in spherical shape innovatively and deploys high dynamic dual-frequency GPS as the main payload. On-orbit data shows that the atmospheric density detection precision is in the order of 10−14kg/m3 and the gravity recovery precision achieves the level of 30 orders. All mission success criteria and objectives were achieved. This paper presents the design, space mission, key technologies, science capabilities and preliminary results of the satellite.

Selection of time-dependent worst-case thermal environmental conditions for Low Earth Orbit spacecrafts

When facing the thermal analysis of a Low Earth Orbit satellite, selecting the worst-case orbit where the minimum and maximum temperatures are reached is essential for ensuring the success of the mission. Typical orbits have a non-constant Solar Beta Angle throughout the year providing a wide range of orbits with different heat loads and eclipses. It is possible to focus the analysis on a single orbit configuration by a rough analysis using a simple model. In order to achieve this, every potential orbit with their corresponding thermal environmental parameters must be analysed based on real data. The direct solar radiation, the albedo and the Earth Outgoing Longwave Radiation (OLR) characterize the thermal environment to be taken into account. However, their values have a wide variability which depend on many parameters. Based on the characteristics of the orbit and the system thermo-optical properties and characteristic time, it is possible to obtain particularized profiles of albedo and OLR that would lead the system to its maximum and minimum temperatures. The conventional criteria, which is studied here in depth, provides two constant values of albedo and OLR as the hot and cold worst-cases. This is suitable for massive system or cases in which the characteristics times of the system are high. For lighter elements or low characteristic times, temperatures throughout the orbit deviate considerably from the real behaviour. In contrast, the methodology here proposed provides a time-dependant profile that allows for the determination of a system temperature response closer to the real one, together with the potential minimum and maximum temperatures of the orbit, in order to optimize the design and avoid the oversizing.

Evolution of the performance monitoring techniques for solar arrays of the service module Zvezda within the ISS Russian segment over the course of its orbital flight

The paper discusses issues involved in mission control of the International Space Station (ISS), in particular, specific aspects of monitoring and evaluating the status of Power Supply Systems (PSS) and solar arrays (SA) as their components. Power budget simulations use as their initial computational parameter the current SA performance, which is determined on the basis of a special performance evaluation mode. The obtained data make it possible to take into account the spaceflight factors resulting in performance degradation. Besides that, when using the SA performance evaluation mode as a method for periodically checking the SA status, the more accurate determination of the actual SA performance involves taking into account the shadowing of the photovoltaic cells, the effect of the light reflected off the Earth surface, and current generation resulting from illumination of both the front and the back surfaces of the SA. The paper presents the results of space experiment Albedo carried out onboard the Russian Segment (RS) of the ISS, which included development of techniques for taking into account the above factors when simulating the PSS power budget for the Service Module (SM) Zvezda. Developed as a result of carrying out the space experiment was a procedure for determining SA performance and simulating the power input from the ISS RS SM SA taking into account the Earth albedo; recommendations were made for the orbital spacecraft PSS control modes taking into account the possibility of power generation from the Earth outgoing light flux. Based on the results of testing the developed computational schemes for evaluating the SA performance and simulations of incoming power that take into account the Earth albedo, substantiated values were obtained for the proposed reference parameter for evaluating the ISS RS SM SA. The developed procedure provides the most accurate performance evaluation for both front and back surfaces of the SA. Computational schemes for predicting incoming power proposed within the framework of the procedure make it possible to give highly accurate predictions of incoming power using precise simulations of light flux coming from Earth, as well as to determine the contribution of variable components into the SA performance determined during a periodic SA performance estimate.