Small Satellites In Low Earth Orbit Research Articles

Fast Reconfiguration Maneuvers of a Micro-satellite Constellation Based on a Hybrid Rocket Engine

In this work, the formation flight of the CubeSat cluster RODiO (Radar for Earth Observation by synthetic aperture DIstributed on a cluster of CubeSats equipped with high-technology micro-propellers for new Operative services) with respect to a small satellite in LEO (Low Earth Orbit) has been analyzed. RODiO is an innovative mission concept funded by the Italian Space Agency (ASI) in the context of the Alcor program. The small satellite is equipped with an antenna that allows it to function as a transmitter, whereas RODiO functions as a receiver. The extension of the virtual SAR (Synthetic Aperture Radar) antenna can be achieved by establishing an along-track baseline performing an orbital coplanar maneuver. Another interesting scenario is the possibility to create a cross-track baseline performing an inclination change maneuver. Such formation reconfiguration maneuvers can be achieved in relatively short times only by use of a high-thrust propulsion system, i.e., based on conventional chemical technologies. From the study of maneuvers, it is possible to identify the required ∆V (order of magnitude of 10 m/s), which represents an input parameter for the design of propulsion system. Among the different kinds of propulsion systems, a Hybrid Rocket Engine was chosen. Based on the previous experience acquired by Department of Industrial Engineering (University of Naples Federico II), the preliminary design of the thrust chamber for a Hybrid Rocket Engine based on Hydrogen Peroxide (91 wt%) of the 10 N-class could be carried out, whose dimensions meet the compactness requirements of the CubeSat (1.5 U, 2 kg).

Federated Learning in Satellite Constellations

Federated learning (FL) has recently emerged as a distributed machine learning paradigm for systems with limited and intermittent connectivity. This paper presents the new context brought to FL by satellite constellations, where the connectivity patterns are significantly different from the ones observed in conventional terrestrial FL. The focus is on large constellations in low Earth orbit (LEO), where each satellites participates in a data-driven FL task using a locally stored dataset. This scenario is motivated by the trend towards mega constellations of interconnected small satellites in LEO and the integration of artificial intelligence in satellites. We propose a classification of satellite FL based on the communication capabilities of the satellites, the constellation design, and the location of the parameter server. A comprehensive overview of the current state-of-the-art in this field is provided and the unique challenges and opportunities of satellite FL are discussed. Finally, we outline several open research directions for FL in satellite constellations and present some future perspectives on this topic.

Satellite to buoy IoT communications in the Arctic Ocean

Internet of things (IoT), to Arctic Ocean areas using Low Earth Orbit (LEO) satellites for communication to and from sensor units on the sea, has become increasingly important. It is challenging to close the link budget from a buoy on sea to a LEO satellite due to restrictions on the availability of power in such installations. Phenomena as scattering from the sea surface and small-scale fading, ionospheric scintillations, diffraction loss at low elevation angles, and power availability in small LEO satellites and models for analysis are described. It is of great importance to have a radio wave propagation model that accurately predicts path loss between an installation on the sea and a LEO satellite taking all loss mechanisms into account. In this paper, a path-loss model for satellite to buoy communications over the sea is described. In this model, maritime propagation phenomena in the radio link include free space loss, scintillation loss caused by the ionosphere, diffraction loss at low elevation angle, and scattering at the sea surface depending on the wave height and small-scale fading. Furthermore, a buoy on the sea surface with strong angular movement will cause a varying receive signal level depending on the antenna diagram. These phenomena are assessed. A link budget for the frequencies 433, 868, and 3,400 MHz is calculated for a LEO satellite at a height of 800 km.

A 7 m × 1.5 m Aperture Parabolic Cylinder Deployable Mesh Reflector Antenna for Next-Generation Satellite Synthetic Aperture Radar

A high priority next-generation satellite remote sensing mission necessitates a lightweight deployable antenna that can fit in the package of low-Earth orbit small satellites. In this work, we present the development of a 7 m×1.5 m aperture C-Band parabolic cylinder mesh reflector along with a 1×32 element linear patch array feed. The detailed and tailored mechanical design, full-wave analysis, and measurements of the reflector are elaborated. The reflector is constructed with a mesh surface with unique deployment mechanisms for weight reduction and stowage. The linear microstrip patch array feed is designed with a lightweight honeycomb substrate and is used for the breadboard testing of the parabolic cylinder reflector. The antenna achieved the desired surface accuracy and a measured gain of 42.06 dBi at 5.357 GHz, with half-power beamwidths of 0.52° and 2.35° in the two principal planes.

Reliable and Low-Overhead Clustering in LEO Small Satellite Networks

Low earth orbit (LEO) small satellites have attracted great interests in civilian and military applications due to their low cost and high service performance. However, the enormous scale and high dynamism of small satellites pose challenges to network flexibility and scalability. Therefore, the hierarchical satellite network structure is introduced as an effective approach to enhance the satellite network capabilities further. In this regard, small satellites’ clustering is of fundamental importance for designing such a hierarchical structure. Satellite clusters are always prone to instability due to unpredictable link failures and frequent topology changes. In this article, we study the small satellite clustering problem of jointly optimizing the cluster reliability and the network management overhead. A coalition game-theoretic framework is introduced to obtain low computational complexity by adopting the clustering-decision-making process in an automated and fully distributed fashion. A distributed coalition formation algorithm based on the optimization of reliability and management overhead is developed for the clustering problem. Finally, extensive simulations have been conducted, and the results show that our proposed clustering scheme is able to produce better results than the baseline schemes.

A Community-Driven Approach to Democratize Access to Satellite Ground Stations

If you were to launch a small satellite in Low-Earth Orbit (LEO) today, the cost of installing/renting ground stations around the world to maintain global coverage is likely to rival the satellite launch costs. While satellite launch costs for small players have reduced significantly due to the emergence of ride sharing programs operated by both public and private organizations, access to ground station infrastructure is still a luxury due to the immense cost and form factor of the components involved, which need to be installed in a large, elevated area free from any obstructions.

Improved Single-Frequency Kinematic Orbit Determination Strategy of Small LEO Satellite with the Sun-Pointing Attitude Mode

Kinematic orbit determination (KOD) of low earth orbit (LEO) satellites only using single-frequency global navigation satellite system (GNSS) data is a suitable solution for space applications demanding meter-level orbit precision. For some small LEO satellites with the sun-pointing attitude mode, the rotation of the GNSS antenna radiation pattern changes the observation noise characteristics. Since the rotation angle information of the antenna plane may not be available for most low-cost missions, the true elevation cannot be computed and a general elevation-dependent weighting model remains invalid for the onboard GNSS observations. Furthermore, the low-stability GNSS receiver clock oscillator of the LEO satellite at high speeds makes single-frequency cycle slip detection ineffective and difficult since the clock steering events occur frequently. In this study, we investigated the improved KOD strategy to improve the performance of orbit solution using single-frequency GPS and BeiDou navigation satellite system (BDS) observations collected from the Luojia-1A satellite. The weighting model based on exponential function and signal strength is proposed according to the analysis of satellite attitude impact, and a joint single-frequency detection algorithm of receiver clock jump and cycle slip is investigated as well. Based on the GPS/BDS-combined KOD results, it is demonstrated that the clock jump and cycle slip can be properly detected and observations can be effectively utilized with the proposed weighting model considering satellite attitude, which significantly improves the availability and accuracy of orbit solution. The number of available epochs is increased by 12.9% benefitting from this strategy. The orbital root mean square (RMS) precision improvements in the radial, along-track, and cross-track directions are 22.1%, 16.4%, and 6.5%, respectively. Combining BDS observations also contributes to orbit precision improvement, which reaches up to 28.8%.

POD of small LEO satellites based on precise real-time MADOCA and SBAS-aided PPP corrections

For real-time precise orbit determination (POD) of low earth orbit (LEO) satellites, high-accuracy global navigation satellite system (GNSS) orbit and clock products are necessary in real time. Recently, the Japanese multi-GNSS advanced demonstration of orbit and clock analysis precise point positioning (PPP) service and the new generation of the Australian/New Zealand satellite-based augmentation system (SBAS)-aided PPP service provide free and precise GNSS products that are directly broadcast through the navigation and geostationary earth orbit satellites, respectively. With the high quality of both products shown in this study, a 3D accuracy of centimeters can be achieved in the post-processing mode for the reduced-dynamic orbits of small LEO satellites having a duty cycle down to 40% and at sub-dm to dm level for the kinematic orbits. The results show a promising future for high-accuracy real-time POD onboard LEO satellites benefiting from the precise free-of-charge PPP corrections broadcast by navigation systems or SBAS.

E-CGR: Energy-Aware Contact Graph Routing Over Nanosatellite Networks

Satellite constellations are envisioned as meaningful transport networks to forward data throughout the world, both as a solution for areas where there are no other telecommunication infrastructures or as a backup solution to support the terrestrial network. Low Earth Orbit (LEO) satellites are the most appealing for this purpose due to the achievable performance keeping low design and deployment costs. Mega-constellation made of thousands of small LEO satellites are planned to be employed to cover the entire Earth's surface. However, smaller is the size and weight of satellites, higher are the technological challenges and stricter are the hardware constraints which affect the data forwarding process and have to be taken into account. Energy is one of them. Telecommunication hardware energy consumption is considerable, especially in case of high traffic volumes, while energy storage capacity and battery recharge rate are limited due to the small battery size and solar panel surface area, respectively. In this paper, we propose a novel energy-aware routing algorithm based on the Contact Graph Routing (CGR) called E-CGR. E-CGR exploits static and known a priori information about contacts to compute routing paths from sources to destinations which are then “validated” and “confirmed” from the energy viewpoint.

A flexible LEO satellite modem with Ka‐band RF frontend for a data relay satellite system

SummaryFrom a geostationary Earth orbit (GEO) satellite's perspective, a low Earth orbit (LEO) satellite is visible on more than half of its orbit. Albeit the free‐space loss of an inter‐satellite link is much higher than the one of a direct ground link, considerable data rates and download volumes can be achieved. In this paper, we describe the system architecture of an integrated approach for a data relay satellite system and the development of LEO satellite and ground station modems. The approach allows serving several small and inexpensive LEO satellites at the same time both with low rate telemetry/telecommand links and with high rate download of sensor data.

LEO Small-Satellite Constellations for 5G and Beyond-5G Communications

The next frontier towards truly ubiquitous connectivity is the use of Low Earth Orbit (LEO) small-satellite constellations to support 5G and Beyond-5G (B5G) networks. Besides enhanced mobile broadband (eMBB) and massive machine-type communications (mMTC), LEO constellations can support ultra-reliable communications (URC) with relaxed latency requirements of a few tens of milliseconds. Small-satellite impairments and the use of low orbits pose major challenges to the design and performance of these networks, but also open new innovation opportunities. This paper provides a comprehensive overview of the physical and logical links, along with the essential architectural and technological components that enable the full integration of LEO constellations into 5G and B5G systems. Furthermore, we characterize and compare each physical link category and explore novel techniques to maximize the achievable data rates.

A steerable dielectric resonator antenna array with isoflux radiation pattern

AbstractA dielectric resonator antenna array is presented which is intended for use as an integrated solar panel antenna on low Earth orbit small satellites, such as CubeSats. This array has a back‐to‐back Yagi‐Uda topology and can steer its beam ensuring a constant flux density at a satellite ground station. This isoflux gain profile is formed by the envelope of the steered beams which are controlled using a single digital phase shifter. The array achieved a beam steering limit of ±66° with a measured maximum gain of 11.4 dBi.

Investigation of Estimation Methods for Time-varying Residual Magnetic Moment

Generally, the dominant attitude disturbance source for the low Earth orbit small satellites is the residual magnetic moment (RMM). The RMM should be estimated and compensated in orbit to increase the attitude estimation and control accuracy. Although the estimator is usually built with the assumption that these parameters are constant, the RMM changes with sudden shifts caused by the variations in the onboard electrical current. The estimator should quickly track these unobserved parameters in case of change and perform accurate estimation for the rest of the procedure. In this paper, we investigate applicability of the existing estimators, such as the particle filter, for the RMM estimation. We present the initial results for an extended Kalman particle filter (EKPF) based method which may be useful for improving the estimation accuracy and tracking capability.

소형인공위성용 리튬이온 배터리시스템의 신뢰성 확보을 위한 우주인증시험

본 논문에서는 저궤도 소형인공위성에서 위성의 각 부에 전원을 공급하기 위한 리튬이온 배터리 시스템의 신뢰성 확보를 위해 수행한 우주인증시험들의 결과를 나타내었다. 리튬이온 배터리 시스템의 신뢰성을 검증하기 위하여 구조해적, 성능시험, 우주 및 발사환경에서의 환경시험 등을 수행하였다. 모든 해석 및 시험 결과가 요구조건에 만족함을 보임으로써 리튬이온 배터리를 적용한 소형인공위성의 신뢰성을 검증하고 제고할 수 있었다. This paper introduces the lithium ion battery system for LEO(Low Earth Orbit) small satellites. This study proves the reliability of lithium ion batteries applying to the space application. The specifications for lithium ion battery unit are proposed to supply power to the satellite and the overall mechanical design including structural simulation to confirm the reliability of the lithium ion BMS(Battery Management System) under the space environment and launching conditions. The results of structural simulation, functional tests, and space environmental tests show the lithium ion battery system is space qualified. Space qualification of the small satellite battery system to secure reliability of BMS and lithium ion batteries lend credibility for using lithium ion batteries in space application.

An Implementation of Predictive Functional Control for Image-Based Satellite Attitude Control

This paper presents an implementation of predictive functional control for image- based satellite attitude control. The approach considers Low Earth Orbit small satellites equipped with an on-board camera for interactive Earth observation. The control goal is to keep a target on the Earth surface in the satellite's camera field of view during orbiting of the satellite above the target. The control error is given in the image frame, therefore in-image interaction with the system is possible. Two types of control problems are considered: target tracking and oriented-target tracking. The system contains a delay that is taken into account in development of the predictive control law. The control problem is solved in the framework of predictive functional control that is based on the kinematic model of the satellite attitude. The presented control algorithm is validated in simulation environment.

Experimental Missions in <em>W</em>-Band: A Small LEO Satellite Approach

W-band (75-110 GHz) is proposed nowadays as a valuable alternative to intensively-exploited Ku- and Ka-bands for high-speed transmission over satellite networks. In such a framework, some experiments are being carried out, which are targeted to verify the feasibility of exploitation of W-band for broadband service deployment. From a theoretical viewpoint, the large bandwidth availability and the scarce amount of interference typical of W-band should guarantee high capacities. Nevertheless, many crucial aspects are still to be carefully investigated, e.g., signal propagation issues, RF impairments, choice of modulation and coding, efficient antenna design, etc. In this paper, an overview is made on the low Earth orbit (LEO) nano-satellite mission in-orbit key-test and validation of W-band (IKNOW). IKNOW mission is an ongoing advanced feasibility study part of an Italian Space Agency Project, named W-band analysis and verification (WAVE), coordinated by the Department of Electronic Engineering, University of Rome ldquoTor Vergatardquo. The main objective of the IKNOW mission is to tackle some of the unexplored critical aspects concerning W-band satellite transmission. In such a perspective, IKNOW should be regarded as a ldquopilot mission,rdquo whose results will be used for a first uplink-downlink satellite channel characterization, in-orbit validation of W-band technology, and space qualification processes. This paper is focused on the research work carried out in a preliminary phase of the IKNOW study and will also consider a number of elements related to the mission configuration, payload architecture, link analysis, potential RF impairment factors, and atmospheric effects. Proposed analysis and preliminary results shown can provide to interested readers the basic guidelines that will drive the practical implementation of IKNOW mission, as well as the most relevant issues to be faced by future developers of W-band missions using small LEO satellites.

Mechanical fatigue and spectrum analysis of small-satellite structure

Mechanical fatigue due to environmental loads and spectrum analysis due to launch loads of the primary structure of a low cost, low-earth orbit small satellite intended for earth observation missions are presented. The payload of the satellite under consideration is a precise optical unit to image the earth’s surface having a mass of 45 kg. 3-D Finite Element Model for the satellite structure is generated by applying substructure method. Modal analysis is required to determine natural frequencies of the satellite and define its mode shape. Then, ranking of mode shapes according to specific constraint is performed. Harmonic analysis at resonance frequencies with the highest ranking is done and cumulative fatigue damage analysis is performed. Spectrum analysis is performed for Small Sat structure to verify the satellite structure reliability under all dynamic random vibration loads applied during transportation and launch cases.

A real time low complexity codec for use in low Earth orbit small satellite missions

A single-board computer system created specifically to meet the demands of a new generation of small satellite missions has been designed, built and tested at Surrey Satellite Technology Limited (SSTL). The satellite onboard computer is an MPC8260 based system that was originally developed for use onboard the first Algerian satellite (Alsat-1). For the secure transaction of data between the central processing unit (CPU) of the onboard computer and its local random access memory (RAM), the program memory has been designed with triple modular redundancy (TMR), which is a hardware implementation that includes replicated memory circuits and voting logic to detect and correct a faulty value. TMR error correction technique allows single correction of one error bit per stored word. For computers on board a satellite, there is however a definite risk of two error bits occurring within one byte of stored data. In this paper, a real time low complexity codec for use in low earth orbit small satellite missions is presented and implemented in field programmable gate array (FPGA) technology. The proposed device is transparent to the routine transfer of data between the CPU and its local RAM. A simple method of decoding is adopted that allows considerable simplification of the codec with a low complexity.

The LEOSTAR platform design and validation

Matra Marconi Space (MMS) has designed a new generation of platforms for Low Earth Orbit small satellites: the LEOSTAR family. The key characteristics of the LEOSTAR platform, namely manoeuvring capability, pointing accuracy, high performance localisation, spacecraft stability and enhanced autonomy, make it perfectly adapted to high performance Observation missions. After an overview of the LEOSTAR concept, this paper presents the main performances of the LEOSTAR platform as fully confirmed and validated by the avionics tests campaign.

Impact of the “faster better cheaper” requirements for satellites components/subsystems on SEP organistion and processes

In the early 90′s, SEP environment in the satellites business quickly evolved from agencies funded programs (ESA, CNES, government) to a situation in which SEP has numerous private customers and where agencies behave as private companies i.e. opening world-wide competition, requesting high involvement of SEP in non recurring funding. SEP quickly reacted to face this challenge by improving not only their products but also the way these products are developed and produced. A new organization of SEP/DPES unit (around 200 people) was set up end 1994, with project oriented guidelines such as streamlining the hierarchical levels in order to increase personals implication and motivation, favoring flexible project organizations to the previous somewhat rigid matrix organization, enforcing commercial/marketing structure to the new customers. Highly motivated slim teams were constituted around each project, picking up expert partners inside SEP/DPES departments. Project partners proved to plead in an efficient manner with their own management on the behalf of the projects they were implied in. Eventually, this organization helped, of course with other progress actions, to a global performance improvement of SEP/DPES. Improved development processes were put into practice in 1995 among which design to cost, carefully decided internal preliminary studies, long term agreements with preferred subcontractors. SEP/DPES ISO.9001 certification (mid-1998) which gives evidence of the satisfactory status of SEP/DPES PA system already helps to avoid to costly comply with numerous project tailored P.A. requirements. New products were developed/qualified since the mid-90′s, on SEP funding (at least partial, sometimes total), following the here before described processes and organization. Among SEP/DPES newly developed products, three examples are more thoroughly discussed. In the field of electrical propulsion where SEP/DPES has gained expertise in since the 60′s, new developments started in the early 90′s in Hall propulsion through numerous partnership with Russian, American and Italian companies and/or universities. A mature knowledge of Hall thruster functioning and technologies helped SEP to recently complete a successful qualification of their first Hall thruster. “PPS 1350” which will be in flight aboard STENTOR French technological satellite in year 2000. A cost reduction research of this new product was held in parallel to the PPS 1350 qualification, taking into account all the lessons learnt during PPS 1350 development. Its major outputs are the numerous simplifications that were found leading to dramatic cost reductions without impairing thruster performances (reliability was even improved). This improved thruster is today very favorably considered by several primes for small low earth orbit satellites. Hydrazine propulsion is an other example. In this field, which SEP decided in 1996 to accompany their customers in their move from large traditional satellites (SPOT/ERS family) to smaller, cheaper ones. To do so, SEP proposed a monolithic propulsion subsystem (patented design) in which all usual propulsion subsystem assembly devices (piping, supports, brackets…) are avoided, components being directly mounted on the propellant tank. Significant costs reduction could be offered to customers thanks to this innovation. Along with the hydrazine propulsion, SEP also modernised their solar array drive mechanisms the SEPTA's® — SEPTA 31 was qualified end 1998 and will have its maiden flight aboard CNES/ALCATEL JASONI small earth observation satellite. In summary, SEP had to make important changes in order to adapt to the market evolution, which occurred in the early 90's. There efforts implied as well organization as processes as products. First outputs are significant cost reduction; in line will the objectives. First hardware of this new generation will fly in year 2000.