Low Earth Orbit Microsatellite Research Articles

An Attitude Adaptive Integral Sliding Mode Control Algorithm with Disturbance Observer for Microsatellites to Track High-Speed Moving Targets

Gaze tracking of high-speed moving targets is a novel application mode for low Earth orbit microsatellites. In this mode, small satellites are equipped with high-resolution, narrow-field-of-view video cameras for stable gaze-tracking imaging of high-speed moving targets. This paper proposes a high-precision attitude adaptive integral sliding mode control method with a feedforward compensation disturbance observer to enhance the capability of a microsatellite attitude control system for gaze tracking of high-speed moving targets. Specifically, first, we present the attitude control system model for microsatellites and the calculation method for the desired attitude of target tracking based on image feedback. Then, an adaptive integral sliding mode attitude control algorithm with a feedforward compensation disturbance observer, which meets the requirements of high-precision tracking control, is designed. The developed algorithm utilizes the disturbance observer to observe the friction torque of the flywheel and compensates for it through feedforward control. It also employs the adaptive integral sliding mode control algorithm to reduce the impact of uncertain disturbances, decrease the steady-state error of the system, and enhance attitude control precision. Simulation experiments demonstrated that the designed disturbance observer can successfully observe the frictional disturbance torque of the flywheel. The attitude Euler angle control precision for high-speed moving target tracking reached 0.03°, and the angular velocity control precision reached 0.005°/s, validating the effectiveness of the proposed approach.

Research on Hopping Routing of Periodic Multiorbit LEO Satellites

In recent years, the low Earth orbit microsatellite network technology has experienced rapid development due to its advantages of low latency, low cost, and short development cycles. However, building an efficient and reliable satellite network routing system faces many challenges due to the characteristics of satellite networks, such as fast‐changing topology, large variations in link latency, higher probabilities of node and link failures, and limited resources. Routing algorithms have a significant impact on intersatellite communication and have become a research hotspot. The current mainstream algorithms focus on reducing information propagation delays between satellites to enable faster transmission. However, many satellite networks, such as meteorological observation satellite networks, are not sensitive to propagation delays but emphasize reducing hardware costs, especially for the receiving and transmitting signal systems of satellites. This means minimizing the single‐step signal transmission distance of satellites. This article proposes a routing algorithm based on time slot planning and the shortest path step length. Experimental simulation results demonstrate that this algorithm significantly reduces the step length of signal transmission and lowers hardware costs.

Thermal Design and Analysis of a Low Earth Orbit Micro-Satellite

The need for space missions is ever growing with the complexity of problems encountered, requiring experiments at different physical conditions. The cost and other factors experienced in each of the space missions are soaring, irrespective of the entanglements of these missions. Micro and Nano satellites have paved way in this regard, as they are cheap, feasible and provide a platform for new technologies to be tested and validated in space which can then be extended to larger satellites for enhanced applications. Orbital harsh conditions make thermal system design very big challenge to satisfy the different operation conditions required per satellite components. Thermal Control system (TCS) analysis of Hyper-Spectral Remote Sensing Micro-Satellite is crucial in its conceptual design phase. The thermal system design concept of the Micro-Satellite may be passive or active system working on a non-hermetic platform. Satellite thermal system shall provide suitable temperature envelop allow components to work in full performance. It consumes daily average power about 45 W. Battery is the most critical component because of its capacity sensitivity to temperature changes.

Impacts of laser cooling for low earth orbit observation satellites: An analysis in terms of size, weight and power

Laser cooling in solids is a breakthrough technology allowing vibration-free cooling down to a temperature of 100 K in a miniaturized way. It appears as a promising technology to improve future observation satellites performances e.g. in SWIR and NIR domains.In this paper, integration of a laser cooler onboard an observation satellite is studied for the first time. Our study focuses on size, weight and power (SWaP) criteria, at both satellite payload and platform levels. Its goal is to assess the interest of using an optical cryocooler over a mechanical cryocooler for low earth orbit (LEO) infrared observation missions.A preliminary space-borne laser cooler (LC) architecture is proposed. It is composed of two parts. The first part is the cooling head, based on state-of-the-art cooling crystals 10%Yb:YLF and an astigmatic multipass cavity. The second part is the cryocooler opto-electronics, based on redundant laser diodes and fiber coupled to the cooling head. The cooling power is estimated for a small focal plane, taking into account the thermal load of an infrared detector and the parasitic heat fluxes inside the cryostat. The required optical and electrical powers of the laser cooler are then estimated considering the crystal efficiency, the thermal link losses and the opto-electronics efficiency.Assuming a 5-year long LEO microsatellite mission, the sizing of the electrical power systems (PCDU, solar array, batteries) and thermal control systems (heatpipes, radiators) is performed. An additional mass margin is added to take mechanical support structures into account. At the end, payload and platform masses and volumes are summed respectively to obtain a SWaP balance at satellite level, representative of the overall impact of a laser cooler. The study is repeated for the case of a Miniature Pulse Tube Cooler (MPTC) architecture under the same mission and platform assumptions. Finally, the two architectures are compared. It is shown that even if the power requirement of a laser cooler is high, the reduction of mass and internal volume makes it possible for small satellite payloads.

Microsatellite attitude determination based on skylight polarization and geomagnetic measurement

A new attitude determination method based on skylight polarization sensors and magnetometers is proposed for microsatellites in the low earth orbits. First, a two-channel polarization sensor is developed to measure skylight polarization and obtain the solar direction information. Second, the measurement model of the polarization sensor and three-axis magnetometer are derived. Finally, with the satellite attitude equation as the state equation, an extended Kalman filter is developed to estimate the satellite attitude. Simulation results manifested the feasibility of using polarization sensors and magnetometers to determine the attitude information of low earth orbit microsatellite.

A low-energy sensitive compact gamma-ray detector based on LaBr3 and SiPM for GECAM

The Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) project is the planned Chinese space telescope for detecting the X- and gamma-ray. It consists of two micro-satellites in low earth orbit with the advantages of instantaneous full-sky coverage. Due to the limitation of size, weight and power consumption of micro-satellites, silicon photomultipliers (SiPMs) are used to replace the photomultiplier tubes (PMTs) to assemble a novel gamma-ray detector. A prototype of a SiPM array with LaBr3 crystal is built and tested, and it shows a high detection efficiency (70% at 5.9 keV) and an acceptable uniformity. The low energy X-ray of 5.9 keV can be detected by single channel readout circuit, and the energy resolution are 125% (FWHM) at 5.9 keV, 6.5% at 662 keV and 3.5% at 1332 keV . The design and the performance of the detector are discussed in this paper.

Thermal Subsystem Operational Times Analysis for Ubiquitous Small Satellites Relay in LEO

The success of the satellite subsystems engineering depends on the optimal design, modeling, simulation, and validation of the deliverables of the conceptual and mission design objectives. This paper presents the operational times analysis of the thermal control subsystem onboard a 97-kg microsatellite in low-Earth orbit during an eclipse period. Power-storing, communication downlink and uplink, payload processing, and thermal control overpower modes were implemented for a communication mission under worst-case orbital patterns. An embedded digital temperature and lighting controller circuitry was designed and practically validated to effect a desired logic. For an average eclipse period of 34.4 mins, the operational times of the thermal subsystem at altitudes of 400 km, 500 km, and 600 km are 38.6 mins, 38.1 mins, and 37.7 mins respectively. Moreover, the thermal control subsystem simulation reveals that reducing the operational times of non-thermal control subsystems during the eclipse period by 50 % can result in an operational factor of safety of over 1.5. At least 10 dB data link transmission margin can be achieved. The reported findings show that the operational times of spacecraft subsystems overpower modes can be reconfigured in orbit to reliably sustain the operating conditions of the capability-based satellite components for ubiquitous communication.

Propulsion options for very low Earth orbit microsatellites

The growing competitiveness in the commercial space market has raised the interest in operating small spacecraft at very low altitudes. To make this feasible, the space industry has started developing propulsion options tailored specifically to these platforms. This paper presents a review of emerging micropropulsion technologies and evaluates their applicability to microsatellite missions in the altitude range 250–500km. The results of the proposed analysis are demonstrated on two different remote sensing applications.

Controlling the Electric Potential of the Low-Earth Orbit Microsatellite in Ionosphere Observation via Langmuir Probe

Using a Langmuir probe mounted on a large satellite is a general method to directly measure ionosphere’s plasma characteristics, such as electron temperature and electron density. Microsatellites are also being planned to be used for this task due to their apparent advantages, such as low-cost and short development time. However, the deployment of Langmuir probe on a microsatellite faces with a problem that the satellite’s electric potential fluctuates significantly as the plasma’s currents are fed to a satellite’s conducting surface which is not much larger than that of the probe. This in turn adversely affects the accuracy of the observation results. In this paper, a technique exploiting an electron gun is proposed to stabilize this fluctuation. The technique is tested in a space chamber and the obtained results are shown to demonstrate the effective controlling of the satellite electric potential.

A Liability and Insurance Regime for Space Debris Mitigation

ABSTRACTConcerns about the threat that space debris pose to satellites are expected to increase as the number of mostly non-maneuverable microsatellites in low-Earth orbit grows. International guidelines developed to mitigate the risk from space debris are frequently not followed, however, and may not be able to cope with the dramatic growth expected in the number of satellites. Moreover, the current legal framework is unable to determine who is liable for losses in an on-orbital collision. A space surveillance data-sharing committee is proposed to solve this liability problem. Under the proposed liability rules, satellite operators would be liable for the debris they create and insurance companies would cover such a risk, creating a new financial incentive for operators to adopt space debris mitigation guidelines.

A Microsatellite Reaction Wheel Based on a Fuzzy Logic Controller for the Attitude Control System

Current interest in small satellites lies in the feasibility of achieving specific but limited objectives, by necessity, small satellites technology requires simple control schemes. In this paper, we present a fuzzy logic controller, as an attempt to replace the classical proportional derivative (PD) controller that is widely used in the spacecraft attitude determination control system (ADCS). The fuzzy logic controller is implemented on the Z axis (yaw) closed loop reaction wheel of a low earth orbit microsatellite with a gravity gradient stabilization. The yaw axis is pointed toward earth. We mention here that, when the spacecraft is not in the imaging mode, it starts spinning along the yaw axis to keep it within thermal limits. So that, in this axis the spacecraft is either in the imaging mode (freeze mode) or barbeque mode (BBQ mode).

Microsatellite Attitude Determination and Control Subsystem Design and Implementation: Software-in-the-Loop Approach

The paper describes the development of a microsatellite attitude determination and control subsystem (ADCS) and verification of its functionality by software-in-the-loop (SIL) method. The role of ADCS is to provide attitude control functions, including the de-tumbling and stabilizing the satellite angular velocity, and as well as estimating the orbit and attitude information during the satellite operation. In Taiwan, Air Force Institute of Technology (AFIT), dedicating for students to design experimental low earth orbit micro-satellite, called AFITsat. For AFITsat, the operation of the ADCS consists of three modes which are initialization mode, detumbling mode, and normal mode, respectively. During the initialization mode, ADCS collects the early orbit measurement data from various sensors so that the data can be downlinked to the ground station for further analysis. As particularly emphasized in this paper, during the detumbling mode, ADCS implements the thrusters in plus-wide modulation control method to decrease the satellite angular velocity. ADCS provides the attitude determination function for the estimation of the satellite state, during normal mode. The three modes of microsatellite adopted Kalman filter algorithm estimate microsatellite attitude. This paper will discuss using the SIL validation ADCS function and verify its feasibility.

Estimation and Analysis of Two-Line Elements for Small Satellites

This paper presents an assessment of two-line element sets for one nano- and two micro-satellites in low Earth orbit. Both the publicly available element sets issued by the North American Aerospace Defense Command and element sets estimated from GPS tracking data are assessed. The nanosatellite, which carries an intermittently operated dual-frequency GPS receiver, presents one of the first opportunities to assess two-line-element accuracy for an object measuring only using precise reference orbits. The larger satellites provide continuous GPS coverage as well as insight into the impact of maneuvers and formation flying on two-line element sets. It is found that, overall, the North American Aerospace Defense Command two-line element sets provide reliable position information accurate to a few kilometers for small satellites in low Earth orbit and that, with an arc length similar to the North American Aerospace Defense Command, two-line elements estimated from continuous GPS data or even intermittent GPS data collected sufficiently often can improve the spread of five-day along-track propagation errors from 10 km down to 2 km for a nanosatellite.

Space Technology 5 multipoint observations of transpolar arc-related field-aligned currents

[1] We present two transpolar arc events where for the first time we are able to analyze changes in field-aligned currents associated with high-latitude transpolar auroral arcs on time scales of a few minutes. This is accomplished through the use of highly accurate multipoint magnetic field measurements provided by the Space Technology 5 mission, which consists of three microsatellites in low-Earth orbit. In the first event we examine measurements of an arc that is part of a highly dynamic auroral pattern, that of a hook-shaped arc. In the second event, a more stable dusk oval-aligned arc is analyzed. These events illustrate the dynamic nature of arc formation and show the usefulness of high-resolution multipoint measurements. Minimum variance analysis is used to determine the appropriateness of the infinite current sheet approximation and to calculate arc alignment angles which are then compared with those estimated from UV images or precipitating particle data.

Performance Analysis of Anti-Interference Wireless Packet Networks for LEO Micro-Satellite with Adaptive Nulling Antenna Array

Information integrity is key to successful operations in intricacy environments in the future, especially when strong interferences exist. This paper presents the design of a novel wireless packet network receiver system for Low Earth Orbit ( LEO) micro-satellites with adaptive nulling antenna arrays. It uses three types of interference suppression in cascade: namely spread spectrum, adaptive array nulling, and transform domain filtering. This paper proposes a pilot channel-aided method in order to make full advantage of this arrangement, and analyzes its throughput and delay performance using the Markov chain model. Our results show that this method can achieve excellent delay and through put performance: When the number of array antenna is 8, its through put increase relative to the standard Slot-ALOHA protocol is 125%.

Wheel Attitude Cancellation Thruster Torque of LEO Microsatellite during Orbital Maintenance

A cold gas propulsion system is used for orbital maintenance on board microsatellite. Cold gas thrusters are the simplest way of achieving thrust. A microsatellite could be a part of the constellation and to maintain a daily coverage, it will be equipped with a propulsion system for an orbit control. A constellation of several microsatellites could be launched and put at the allocate position in the orbit. To do this, the satellites need few months to be in their final position. A propulsion system is used, among other things, to maintain the satellite at its nominal position. The wheels (reaction/momentum) will be used to dump the thruster disturbances caused by misalignment. This study describes the wheel attitude damping thruster disturbances of Low Earth Orbit (LEO) microsatellite for orbit maintenance with the following points: 1) Attitude dynamics, 2) External disturbances, 3) Magnetic wheel control, 4) Simulation results will be presented to evaluate the performance and design objectives. © 2006 Asian Network for Scientific Information.

A Feasibility Study of Commercial Laminated Lithium-Ion Polymer Cells for Space Applications: Endurance Testing for Space Environment

Lithium-ion polymer cells are expected to provide power storage in microsatellites due to their high energy density, high voltage, and high flexibility in configuration. Our previous work demonstrated the excellent life performance of polymer electrolyte (PE)-type lithium-ion polymer cells in a vacuum. In this work, we determine whether this type of cell cycles normally in a space environment. We conducted endurance testing for γ-ray radiation and vibration of the PE cells, simulating a microsatellite launch. The γ-ray radiation testing revealed that these cells have excellent resistance to γ-ray exposure in simulated low-Earth-orbit (LEO) and geostationary-Earth-orbit (GEO) environments. Vibration testing in an ultrahigh vacuum demonstrated that the cells could endure a microsatellite launch when fastened only with aluminum tape. During this testing, we did not detect any gas components associated with cell solvents. The promising results led us to conclude that PE cells can store power well for an LEO or GEO microsatellite.

Small Mobile Ground Terminal Design for a Microsatellite Data Collection System

Many developing countries with the help of developed ones have gained space technologies experience by building and launching microsatellites which involve affordable costs. Apart from technology transfer, different applications could be achieved using a LEO (low earth orbit) microsatellite over large areas where other communication systems are lacking. The use of a single LEO microsatellite for data collection implies a complex hardware and software architectures of the ground terminals especially when they are designed to be small, lightweight and economical. The ground terminal proposed in this paper is a small, assembled device that incorporates a microcontroller, RAM, Flash memory, Real Time Clock, OEM GPS board, AFSK modem, backup lithium battery, and a transceiver. Its built-in software handles all functions involved in collecting, packaging, and transmitting the various data to the microsatellite. A satellite visibility calculation algorithm, developed in assembly language, makes the terminal intelligent without the need of a PC which makes other available commercial terminals heavy and difficult to carry. The small terminal can be mounted on any mobile or fixed platform to accomplish missions such as data collection from remote sites or mobile automatic position reporting. The connected sensors or GPS are sampled at regular time intervals and data stored in memory. Once the satellite comes into range, the gathered data is packetized and transmitted. The terminal can even be connected to any text editing device for messaging. This paper describes the hardware and software solutions achieved to develop a small, very low cost and automatic ground terminal for use with a single microsatellite data collection system.

The Topsat satellite

This paper discusses the Topsat satellite, currently being built by a partnership between DERA Space, Rutherford Appleton Laboratory, Surrey Satellite Technology Ltd and InfoTerra Ltd (Formerly NRSC). Topsat will have the capability to provide imagery at 25m panchromatic and 5m colour resolution, direct to the user at a mobile ground station, from a 125kg microsatellite in low Earth orbit. Its low‐cost philosophy includes wide use of commercial off‐the‐shelf components and the goal of a one‐year mission life.

UoSAT-12 minisatellite for high performance earth observation at low cost

Surrey Satellite Technology Ltd (SSTL) at the University of Surrey (UK) has pioneered cost-effective satellite engineering techniques for smaller, faster and cheaper satellites to provide affordable access to space. SSTL has designed, built, launched and operated a series of twelve 50 kg microsatellites in low Earth orbit which carry a wide range of satellite communications, space science, remote sensing and in-orbit technology demonstration payloads—for both civil and military applications. Eight of SSTL’s microsatellites have carried CCD Earth imaging cameras, coupled with powerful onboard processing computers which have demonstrated the capability of this new generation of low-cost, rapid-response, modern small satellites. SSTL has recently developed an advanced 250 kg minisatellite platform to meet the needs of future low-cost Earth observation and remote sensing applications. With enhanced payload mass and volume, attitude stability and communications capabilities, this new platform will support more sophisticated payloads than the minimalist microsatellites. The experimental UoSAT-12 mission, to be launched into LEO in 1997, will carry high resolution and multispectral remote sensing payloads to demonstrate imaging not currently practicable on existing microsatellites. This paper reviews the design and characteristics of the UoSAT-12 imaging payloads which include multispectral cameras providing 40 m ground resolution with an 80 km swath width, and a panchromatic imaging instrument providing 10 m resolution. The trade-off between linear pushbroom sensors and area CCD cameras, and the role of on-board processing for automatic image processing is presented. These techniques enable small, low-cost minisatellites to approach the performance of conventional Earth observation satellites—but at a fraction of the cost. This pioneering work by Surrey on advanced microsatellites and minisatellites has resulted in imaging missions that can respond rapidly to customer requirements, which are affordable to a far wider community of individual commercial or governmental organizations, and which provide emerging space nations with an independent Earth observation capability.