Low-cost Space Research Articles

Dynamically redactable blockchain based on decentralized Chameleon hash

The immutability is a crucial property for blockchain applications, however, it also leads to problems such as the inability to revise illegal data on the blockchain and delete private data. Although redactable blockchains enable on-chain modification, they suffer from inefficiency and excessive centralization, the majority of redactable blockchain schemes ignore the difficult problems of traceability and consistency check. In this paper, we present a Dynamically Redactable Blockchain based on decentralized Chameleon hash (DRBC). Specifically, we propose an Identity-Based Decentralized Chameleon Hash (IDCH) and a Version-Based Transaction structure (VT) to realize the traceability of transaction modifications in a decentralized environment. Then, we propose an efficient block consistency check protocol based on the Bloom filter tree, which can realize the consistency check of transactions with extremely low time and space cost. Security analysis and experiment results demonstrate the reliability of DRBC and its significant advantages in a decentralized environment.

A Shining Example of Low-Cost Space Exploration: The Success of India's Space Program

A Shining Example of Low-Cost Space Exploration: The Success of India's Space Program

Simulation study on the damage behavior of tantalum target plates under high-velocity projectile impact

This study aims to explore the damage behavior of tantalum target plates under high-velocity projectile impact, addressing the threats of damage in the aerospace field due to debris and other factors. With the advent of low-cost space launches and large satellite projects, spacecraft such as space stations are facing increasingly severe collision risks. The research utilizes numerical simulation techniques, based on ANSYS/AUTODYN software and the Smoothed Particle Hydrodynamics (SPH) method, to simulate the impact process of projectiles of different velocities (1 ∼ 10 km/s) and materials (aluminum and steel) on tantalum target plates. The results are intended to provide theoretical support for the design of spacecraft protection structures and contribute data support for establishing a millimeter-level space debris impact database.

A Mesh Space Mapping Modeling Method with Mesh Deformation for Microwave Components.

In this study, a low-cost space mapping (SM) modeling method with mesh deformation is proposed for microwave components. In this approach, the coarse-mesh model with mesh deformation is developed as the coarse model, and the fine-mesh model is simulated as the fine model. The SM technique establishes the mapping relationship between the coarse-mesh model and the fine-mesh model. This approach enables us to combine the computational efficiency of the coarse model with the accuracy of the fine model. The automatic mesh deformation technology is embedded in the coarse model to avoid the discontinuous change in the electromagnetic response. The proposed model consisting of the coarse model and two mapping modules can represent the features of the fine model more accurately, and predict the electromagnetic response of microwave components quickly. The proposed mesh SM modeling technique is applied to the four-pole waveguide filter. The value for the training and test errors in the proposed model is less than 1%, which is lower than that for the ANN models and the existing SM models trained with the same data. Compared with HFSS software, the proposed model can save about 70% CPU time in predicting a set of 100 data. The results show that the proposed method achieves a good modeling accuracy and efficiency with few training data and a low computational cost.

A Megawatt-Scale Si/SiC Hybrid Multilevel Inverter for Electric Aircraft Propulsion Applications

This paper presents the design and development of a megawatt-scale medium-voltage (MV) hybrid inverter prototype to validate its feasibility and potentials for the electric propulsion on the next-generation electric aircraft system with an onboard MV dc distribution, e.g., 3 kV dc bus in this work. The proposed hybrid converter consists of a three-level active-neutral-point-clamped (ANPC) stage using 3.3 kV silicon IGBTs cascaded with an H-bridge stage using cost-effective 1.2 kV SiC MOSFETs in each phase. Comprehensive design and evaluation of the full-scale prototype are elaborated, including the low-inductance busbar design, converter architecture optimization and system integration. In addition, a low computational cost space vector modulation with common-mode voltage (CMV) reduction feature is proposed to fully exploit the benefits of SiC MOSFET in this hybrid topology. Extensive simulation and experimental results are provided to demonstrate the performance of each power stage and the full converter assembly in both the steady-state operation and variable frequency operations. Compared with the widely adopted IGBT based ANPC converter in MV applications, the proposed 7-L hybrid inverter system features higher power efficiency, reduced harmonics, higher dc voltage utilization, reduced CMV and lower dv/dt, while remains cost effective compared to the solution using MV SiC MOSFETs.

Shape Memory Polymer Composite Booms with Applications in Reel-Type Solar Arrays

Solar arrays are the primary energy source for spacecraft. Although traditional rigid solar arrays improve power supply, the quality increases proportionally. Hence, it is difficult to satisfy the requirements of high-power and low-cost space applications. In this study, a shape-memory polymer composite (SMPC) boom was designed, fabricated, and characterized for flexible reel-type solar arrays. The SMPC boom was fabricated from a smart material, a shape-memory polymer composite, whose mechanical properties were tested. Additionally, a mathematical model of the bending stiffness of the SMPC boom was developed, and the bending and buckling behaviors of the boom were further analyzed using the ABAQUS software. An SMPC boom was fabricated to demonstrate its shape memory characteristics, and the driving force of the booms with varying geometric parameters was investigated. We also designed and manufactured a reel-type solar array based on an SMPC boom and verified its self-deployment capability. The results indicated that the SMPC boom can be used as a deployable unit to roll out flexible solar arrays.

Computational Fluid Dynamics Analysis of the Kentucky Re-Entry Universal Payload System

The Kentucky Re-Entry Universal Payload System (KRUPS) is a low-cost space capsule that has been designed to collect flight data. This work focuses on computational fluid dynamics (CFD) simulations of the flow around the capsule at various altitudes along the trajectory path during Earth re-entry. CFD simulations are performed at altitudes of 60 and 40 km by accounting for thermochemical nonequilibrium and surface catalycity using current state-of-the-art hypersonic approaches. The flowfield at all altitudes exhibits significant thermal and chemical nonequilibrium with vibrational temperature lagging the translational temperature in the forebody and exceeding the translational temperature in the wake. Inclusion of surface catalycity influences the heat flux on the surface and the flow temperature in the boundary layer. The number density profiles of nitric oxide molecules and spectral emission computations using the line-by-line radiative solver NEQAIR indicate that higher emissions would occur at an altitude of 60 km in comparison to emissions at 40 km, and spectral intensity would be higher along the stagnation line despite high densities of NO near the edges of the capsule, and that emissions in the 100–400 nm wavelength range are dominant.

The Stability Analysis of a Tether for a Segmented Space Elevator

The space elevator system is a space tether system used to solve low-cost space transportation. Its high efficiency, large load and other characteristics have broad application prospects in the aerospace field. The stability analysis is the foundation of the space elevator system research. Based on the new segment space elevator system model, in this paper, the stability of the system at the equilibrium point is analyzed by Lyapunov stability theory; And based on the criterion that the change rate of the system restoring torque and the anchor point tension are greater than 0, the maximum offset angle of the system inside and outside the equatorial plane is analyzed. The results show that the segment space elevator is stable near the equilibrium point; The maximum deflection angle of the space elevator inside and outside the equatorial plane is related to the design stress of the anchor point; When the space elevator is offset outside the equatorial plane, it will only lose stability because the restoring torque reaches the maximum value; When the space elevator is offset in the equatorial plane, and due to the design stress of the anchor point is small, it will lose stability because the tensile force of the anchor point is reduced to 0, and when the design stress of the anchor point is large, it will lose stability because the recovery torque reaches the maximum value; The stability of the space elevator outside the equatorial plane is better than that in the equatorial plane.

Super-adiabatic temperature in homogenous ignition of CH4/O2/N2 mixtures

Methane-oxygen burning has promising application in future rocket engines used in low-cost space launch systems. In this study, the phenomenon of super-adiabatic temperature (SAT) in homogenous ignition process of methane-oxygen with and without nitrogen dilution is investigated. Simulations considering detailed chemistry are conducted for homogeneous ignition processes and premixed flames in CH4/O2/N2 mixtures. The objectives are to assess the effects of equivalence ratio, oxygen content in oxidizer, initial temperature and pressure on SAT and to identify the key elementary reactions involved in SAT for methane. It is found that the SAT changes non-monotonically with the equivalence ratio and there exists two regimes for SAT. The contribution of each elementary reaction to the post-ignition temperature decrement is quantified and the key reactions responsible for the occurrence of SAT are determined. It is found that the SAT in the homogenous ignition of CH4/O2/N2 mixtures is mainly caused by the endothermic dissociation reactions of H2O, H2, CO2 after thermal runaway. With the increase of initial temperature and oxygen content and decrease of pressure, the dissociation of H2O, H2 and CO2 becomes stronger and thereby SAT is larger. Moreover, the chemistry involved in the SAT for homogeneous ignition and premixed flames is compared. It is found that the same chemical kinetics is involved in the SAT for homogenous ignition process and premixed flames.

Embedding Tamper-Resistant, Publicly Verifiable Random Number Seeds in Permissionless Blockchain Systems

Many blockchain processes require pseudo-random numbers. This is especially true of blockchain consensus mechanisms that aim to fairly distribute the opportunity to propose new blocks between the participants in the system. The starting point for these processes is a source of randomness that participants cannot manipulate. This paper proposes two methods for embedding random number seeds in a blockchain data structure to serve as inputs to pseudo-random number generators. Because the output of a pseudo-random number generator depends deterministically on its seed, the properties of the seed are critical to the quality of the eventual pseudo-random number produced. Our protocol, B-Rand, embeds random number seeds that are <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">confidential</i> , <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">tamper-resistant</i> , <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">unpredictable</i> , <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">collision-resistant</i> , and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">publicly verifiable</i> as part of every transaction. These seeds may then be used by transaction owners to participate in processes in the blockchain system that require pseudo-random numbers. Both the Single Secret and Double Secret B-Rand protocols are highly scalable with low space and computational cost, and the worst case is linear in the number of transactions per block.

Siamese Network Based Multiscale Self-Supervised Heterogeneous Graph Representation Learning

Owing to label-free modeling of complex heterogeneity, self-supervised heterogeneous graph representation learning (SS-HGRL) has been widely studied in recent years. The goal of SS-HGRL is to design an unsupervised learning framework to represent complicated heterogeneous graph structures. However, based on contrastive learning, most existing methods of SS-HGRL require a large number of negative samples, which significantly increases the computation and memory costs. Furthermore, many methods cannot fully extract knowledge from a heterogeneous graph. To learn global and local information simultaneously at low time and space costs, we propose a novel Siamese Network based Multi-scale bootstrapping contrastive learning approach for Heterogeneous graphs (SNMH). Specifically, we first obtain views under the meta-path schema and the 1-hop relation type schema through dual-schema view generation. Then, we propose cross-schema and cross-view bootstrapping contrastive objectives to maximize the similarity of node representations between different schemas and views. By integrating and optimizing the above objectives, we can extract local and global information and eventually obtain the node representations for downstream tasks. To demonstrate the effectiveness of our model, we conduct experiments on several public datasets. Experimental results show that our model is superior to the state-of-the-art methods on the premise of lower time and space complexity. The source code and datasets are publicly available at https://github.com/lorisky1214/SNMH.

Small Satellites for Low-Cost Space Access: Launch, Deployment, Integration, and In-Space Logistics

Satellite launches have skyrocketed in recent years, as they become more affordable to smaller businesses in a variety of sectors. They no longer need as much space to construct it after using digital technology to considerably lower the size of its typical satellite communications payload. As a result, they relocated to a smaller space. A downsized payload may now fit on smaller satellites, providing them with more versatile and powerful communications capabilities that they may not have had before. Small satellites and CubeSats have transformed the space industry by providing an efficient alternative for cost-effective space launches as well as undertaking numerous technological demos, scientific research, Earth exploration, and other missions. Furthermore, since they are easier to design, construct, and launch than conventional satellites, these satellites are widely employed by commercial firms, government, military, and non-profit groups. In this article, we look at how the space industry has grown significantly over the years, resulting in a greater number of startups entering the market. Case studies on tiny satellite and CubeSat manufacturers as well as mission integrator firms are covered. This study also discusses how entrepreneurs may construct the CubeSat ecosystem by developing new methodologies and improved subsystems for the efficient operation of CubeSats. Finally, the article explores current trends as well as potential difficulties and advancements in tiny satellite and CubeSat technologies. This study makes it very evident that having private space enterprises is the only way for a nation to become a member of the global space economy. As a result, one of the country’s most significant responsibilities is to encourage private firms to participate in space operations.

Small Satellites for Low-Cost Space Access: Launch, Deployment, Integration, and In-Space Logistics

Satellite launches have skyrocketed in recent years, as they become more affordable to smaller businesses in a variety of sectors. They no longer need as much space to construct it after using digital technology to considerably lower the size of its typical satellite communications payload. As a result, they relocated to a smaller space. A downsized payload may now fit on smaller satellites, providing them with more versatile and powerful communications capabilities that they may not have had before. Small satellites and CubeSats have transformed the space industry by providing an efficient alternative for cost-effective space launches as well as undertaking numerous technological demos, scientific research, Earth exploration, and other missions. Furthermore, since they are easier to design, construct, and launch than conventional satellites, these satellites are widely employed by commercial firms, government, military, and non-profit groups. In this article, we look at how the space industry has grown significantly over the years, resulting in a greater number of startups entering the market. Case studies on tiny satellite and CubeSat manufacturers as well as mission integrator firms are covered. This study also discusses how entrepreneurs may construct the CubeSat ecosystem by developing new methodologies and improved subsystems for the efficient operation of CubeSats. Finally, the article explores current trends as well as potential difficulties and advancements in tiny satellite and CubeSat technologies. This study makes it very evident that having private space enterprises is the only way for a nation to become a member of the global space economy. As a result, one of the country’s most significant responsibilities is to encourage private firms to participate in space operations.

Application of Absolute Nodal Coordinate Formulation in Calculation of Space Elevator System

The space elevator system is a space tether system used to solve low-cost space transportation. Its high efficiency, large load, reusability and other characteristics have broad application prospects in the aerospace field. Most of the existing mechanical models are based on “chain-bar” and a lumped mass tether model, which cannot effectively reflect the flexible behaviour of the rope of space elevator system. To establish an accurate mechanical model, the gradient deficient beam elements of the absolute nodal coordinate formulation (ANCF) are used to build the mechanical model of the space elevator system. The universal gravitation and centrifugal force in the model are derived. The calculation results of the ANCF model are compared with the results of the finite element method (FEM) and lumped mass (LM) models. The results show that the calculation results of the ANCF method are not very different from the results of the FEM and LM models in the case of axial loading. In the case of lateral loading, the calculation results of the ANCF method are basically the same as the results of the FEM and LM models, but can better reflect the local flexible deformation of the space elevator rope, and have a better calculation stability than FEM. Under the same calculation accuracy, the ANCF method can use fewer elements, and the speed of convergence is faster than the FEM and LM models.

A stable strain gauge measurement method for monitoring in-situ stress

In-situ stress exists in all rock mass or structures, which is reflected in the deformation and failure of various underground or ground excavation in geotechnical engineering. In-situ widely used in the engineering practice, in-situ stress monitoring plays an important role in many aspects, such as mine development, slope support, and geological disaster prevention and control, etc. Strain gauge has been used to record rock deformation using Differential strain analysis (DSA), Hollow Inclusion Technique (CSIRO Cells), and other in-situ stress measurement techniques. Limited by the volume, cost, power, and connection scheme of the measuring instruments, the test data are always influenced by various immeasurable factors, such as bend of the measuring cable and change in the ambient temperature. Majority of the gauge measurement technologies are not suitable for in-situ stress monitoring because of the stability of strain gauge measurement is poor, limits the application range of the gauge measurement. A stable strain gauge measurement method can be used for medium to high-precision in-situ stress monitoring to serve various engineering developments. We made a new measurement scheme by using high-precision constant current with independent signal transmission channels to achieve a high stability and high-resolution strain gauge measurement circuit with low power consumption and space cost. The temperature drift is as low as 0.3 με/°C in 0°C–60°C temperature range at 8000 με strain input, which can achieve the measurement effect of the traditional desktop strain gauge in about 1/10th volume and very low cost. The error caused by the change of cable resistance is reduced to 1 ppm, and the error caused by the disconnection and reconnection is less than 1 με, which avoids the failures caused by various environmental factors in the monitoring process, and the installation distance of monitoring strain gauge can reach tens of meters. This creates conducive conditions for using traditional in-situ stress measurement technology with in-situ stress monitoring and establishes an efficient and low-cost in-situ stress monitoring system.

Icarus: In-situ monitoring of the surface degradation on a near-Sun asteroid

Icarus is a mission concept designed to record the activity of an asteroid during a close encounter with the Sun. The primary science goal of the mission is to unravel the nontrivial mechanism(s) that destroy asteroids on orbits with small perihelion distances. Understanding the destruction mechanism(s) allows us to constrain the bulk composition and interior structure of asteroids in general. The Icarus mission does not only aim to achieve its science goals but also functions as a technical demonstration of what a low-cost space mission can do. The proposed space segment will include a single spacecraft capable of surviving and operating in the harsh environment near the Sun. The spacecraft design relies on the heritage of missions such as Rosetta, MESSENGER, Parker Solar Probe, BepiColombo, and Solar Orbiter. The spacecraft will rendezvous with an asteroid during its perihelion passage and records the changes taking place on the asteroid’s surface. The primary scientific payload has to be capable of imaging the asteroid’s surface in high resolution using visual and near-infrared channels as well as collecting and analyzing particles that are ejected from the asteroid. The payload bay also allows for additional payloads relating to, for example, solar research. The Icarus spacecraft and the planned payloads have high technology readiness levels and the mission is aimed to fit the programmatic and cost constraints of the F1 mission (Comet Interceptor) by the European Space Agency. Considering the challenging nature of the Icarus trajectory and the fact that the next F-class mission opportunity (F2) is yet to be announced, we conclude that Icarus is feasible as an F-class mission when certain constraints such as a suitable launch configuration are met. A larger mission class, such as the M class by the European Space Agency, would be feasible in all circumstances.

A wireless communication scheme based on space- and frequency-division multiplexing using digital metasurfaces

Digitally programmable metasurfaces are of potential use in wireless multiplexing techniques because they can encode and transmit information without using traditional radio-frequency components such as antennas or mixers. Space–time-coding digital metasurfaces can, in particular, manipulate the propagation direction and harmonic power distribution of electromagnetic waves, making them suitable for space- and frequency-division multiplexing. However, while digital metasurfaces have been used for wireless communication, these systems could implement signal modulation only in the time domain. Here, we report a wireless communication scheme that uses space–time-coding digital metasurfaces to implement both space- and frequency-division multiplexing. By encoding space–time-coding matrices through multiple channels, digital messages can be directly transmitted to different users at different locations simultaneously, without the need for digital-to-analogue conversion and mixing processes. To illustrate this approach, we have built a dual-channel wireless communication system based on a two-bit space–time-coding digital metasurface and use it to transmit two different pictures to two users simultaneously in real time. Space–time-coding digital metasurfaces can be used to implement secure and low-cost space- and frequency-division multiplexing in a dual-channel wireless communication system.

Joint determination of rack configuration and shelf space allocation for a retailer

For brick-and-mortar retailers to be successful, it is critical for them to optimize their rack layout and product placement to draw the attention of shoppers. Recent studies show that racks placed at a non-90° angle along the shopper's path or rack heights positioned below a shopper's eye-height can provide improved visibility of products on those racks. While this can increase the likelihood of a shopper entering that aisle for an impulse purchase, the increase in floor space and restocking costs cannot be ignored. To address these tradeoffs, we propose the Joint Rack Configuration and Shelf Space Allocation (JRC-SSA) problem that jointly determines rack decisions (orientation and height) and product decisions (placement and number of locations) in order to maximize the retailer's impulse profit. We propose an optimization model for JRC-SSA and solve it using a Particle Swarm Optimization based algorithm. Results indicate that a retailer can realize up to 10.1% increase in profit through the JRC-SSA compared to a traditional 7 ft high rack placed at 90° orientation. Acute-angled racks appear to increase impulse profit over 90° racks at low space costs; shorter racks appear prominent for low restocking costs. We also notice that product location and allocation on the rack were altered substantially; high impulse products were often switched from the front to the back face (or vice-versa) to maintain high visibility in different rack orientations. Retailers can use these findings to redesign store sections for enhanced product visibility, which would not only increase their revenue, but also improve shopper experience.

CLEAN: Frequent pattern-based trajectory compression and computation on road networks

The volume of trajectory data has become tremendously huge in recent years. How to effectively and efficiently maintain and compute such trajectory data has become a challenging task. In this paper, we propose a trajectory spatial and temporal compression framework, namely CLEAN. The key of spatial compression is to mine meaningful trajectory frequent patterns on road network. By treating the mined patterns as dictionary items, the long trajectories have the chance to be encoded by shorter paths, thus leading to smaller space cost. And an error-bounded temporal compression is carefully designed on top of the identified spatial patterns for much low space cost. Meanwhile, the patterns are also utilized to improve the performance of two trajectory applications, range query and clustering, without decompression overhead. Extensive experiments on real trajectory datasets validate that CLEAN significantly outperforms existing state-of-art approaches in terms of spatial-temporal compression and trajectory applications.

Characteristic model and its applications in Mars aerocapture guidance

Mars exploration has been a hot spot around the world in the field of deep space exploration in recent years. Low-cost space transport is one of the key factors in space exploration and development, and aerodynamic assisted orbit change will reduce space vehicle design costs. Aerocapture is a form of aerodynamically assisted orbit shift, referring to the use of the aerodynamic force generated by the planetary atmosphere to minimize the energy of the orbit and the transfer of the hyperbolic orbit to the target orbit. There is only one opportunity to fulfill the aerocapture mission, and the criterion for reliability is very high. Because the aerocapture guidance and accuracy and robustness of the control are very poor, a smart and autonomous guidance system is required. The characteristic model-based guidance approach has a broad application potential and has high adaptability, robustness, and autonomy. The research status and progress of the theory of characteristic model and its application in Mars aerocapture guidance are reviewed, and the problems to be solved are put forward, which provides the basis for further research.