Low Earth Orbit CubeSat Research Articles

Calibration of RADMON radiation monitor onboard Aalto-1 CubeSat

RADMON is a small radiation monitor designed and assembled by students of University of Turku and University of Helsinki. It is flown on-board Aalto-1, a 3-unit CubeSat in low Earth orbit at about 500 km altitude. The detector unit of the instrument consists of two detectors, a Si solid-state detector and a CsI(Tl) scintillator, and utilizes the ΔE-E technique to determine the total energy and species of each particle hitting the detector. We present the results of the on-ground and in-flight calibration campaigns of the instrument, as well as the characterization of its response through extensive simulations within the Geant4 framework. The overall energy calibration margin achieved is about 5%. The full instrument response to protons and electrons is presented and the issue of proton contamination of the electron channels is quantified and discussed.

Temperature Sensor Assisted Lifetime Enhancement of Satellite Embedded Systems via Multi-Core Task Mapping and DVFS.

Recently, thanks to the miniaturization and high performance of commercial-off-the-shelf (COTS) computer systems, small satellites get popular. However, due to the very expensive launching cost, it is critical to reduce the physical size and weight of the satellite systems such as cube satellites (CubeSats), making it infeasible to install high capacity batteries or solar panels. Thus, the low-power design is one of the most critical issues in the design of such systems. In addition, as satellites make a periodic revolution around the Earth in a vacuum, their operating temperature varies greatly. For instance, in a low earth orbit (LEO) CubeSats, the temperatures vary from 30 to −30 degrees Celsius, resulting in a big thermal cycle (TC) in the electronic parts that is known to be one of the most critical reliability threats. Moreover, such LEO CubeSats are not fully protected by active thermal control and thermal insulation due to the cost, volume, and weight problems. In this paper, we propose to utilize temperature sensors to maximize the lifetime reliability of the LEO satellite systems via multi-core mapping and dynamic voltage and frequency scaling (DVFS) under power constraint. As conventional reliability enhancement techniques primarily focus on reducing the temperature, it may cause enlarged TCs, making them even less reliable. On the contrary, we try to maintain the TC optimal in terms of reliability with respect to the given power constraint. Experimental evaluation shows that the proposed technique improves the expected lifetime of the satellite embedded systems by up to 8.03 times in the simulation of Nvidia’s Jetson TK1.

Design of a Reduced SpaceFibre Interface: An Enabling Technology for Low-Cost Spacecraft High-Speed Data-Handling

SpaceFibre is an upcoming on-board high-speed communication protocol for space applications. It has been developed in collaboration with the European Space Agency to answer the growing data-rate requirement of satellite payloads such as Synthetic Aperture Radars or hyper-spectral imagers. SpaceFibre offers a complete set of features (i.e., Fault Detection, Isolation and Recovery, and Quality of Service) that guarantees robust communication at the price of higher complexity. This article proposes an innovative modified implementation of the SpaceFibre standard: R-SpaceFibre. It has been designed to reduce hardware resources while keeping high data-rate capability and flow control. Attention is given to the trade-off between Data link layer complexity reduction and protocol features. The proposed protocol is particularly suitable in scenarios where very low bit error rate is foreseen and data integrity is not critical, for example in imaging instruments. The main advantage is a reduction of more than 40% of logical resources required per single interface. R-SpaceFibre may be a suitable solution for several applications, such as low earth orbit CubeSats, which have strict requirements in terms of available logic resources, mass, volume and cost, and more relaxed constraints in terms of upset immunity.

Design and validation of an adaptive CubeSat transmitter system

CubeSat in low earth orbit (LEO) primarily uses an amateur radio-band transmitter with a fixed specification. Nevertheless, the LEO satellite does not have an orbital velocity that equates to one sidereal day. Therefore, the ground station antenna views the satellite at different elevation angles which result in varied propagation path lengths. In this paper, an adaptive transmitter is designed to optimise the LEO satellite communication link and overcome the variability of the propagation path length issue due to different ground station elevation angles. A satellite communication link and operation analyses are performed to identify the relationship between the variation of the elevation angle so as to determine the optimum signal-to-noise ratio (SNR), improve data rate and increase the power efficiency of an adaptive link. Based on the results, a model is developed to control the adaptive configuration. The SNR and power consumption performance of the developed transmitter is compared with commercial transmitters. The results indicate that the transmitter output power is adjustable from 0.5 W to 1 W, and the data rate is selectable between 9600 bps and 19,200 bps. Compared to other CubeSat transmitters, the developed adaptive transmitter demonstrates more than 20% improvement in terms of SNR optimisation, additional throughput and power reduction.

Can We Estimate Air Density of the Thermosphere with CubeSats?

The measurement of air density in the Earth’s thermosphere has a wide range of scientific applications from space weather to upper atmosphere dynamics, but also technical applications from satellite control to predictions of atmospheric reentry of space debris. This study models the torques applying on a three-unit CubeSat in low Earth orbit to infer the capability of such platforms to measure the air density along their orbit. Realistic noise levels of available CubeSat components are used, and sensitivity to the various noise sources is presented. The precise knowledge of the spacecraft attitude, angular acceleration, residual magnetic dipole, and center of gravity is critical to allow proper air density retrieval. Winds in the thermosphere also have a significant impact on the thermosphere density retrieval, suggesting that this parameter can also be constrained. Attitude control is not necessary if the attitude itself is properly known. The application to the EntrySat CubeSat predicts that such retrieval is possible at altitudes lower than 200 km with errors lower than 30%. The air density retrieval from CubeSat platforms will open new capabilities to infer upper atmosphere dynamics.

Location awareness method for spot beam emitters

As more and more spacecraft launched into the space, the probability of radiofrequency (RF) interference raises and the burden of RF spectrum management increases as well. The monitoring of global RF beam information and identifying of spot beam emitters location can effectively obtain space data resources, which will do great help for mitigating global RF interference and optimising space spectrum resources. This study proposes a novel location awareness method for spot beam emitters based on the nanosatellite platform. The proposed method identifies the position of spot beam emitters on a global scale by flying a low earth orbit CubeSat constellation through the coverage of the spot beams. The properties such as geometry, the target motion equation, the measurement process, and the Particle Filter equations are all addressed with respect to the location methods. The authors illustrate a realistic scenario simulated within the Systems Tool Kit, in which CubeSats receive signals from the spot beam emitters. The scenario shows that their location awareness method proposed in this study is available and efficient.

Inter-Satellite Communication for LEO CubeSat Network: QoS Parameters and Feasibility of Massive MIMO

This paper evaluates inter-satellite communication for a low earth orbit CubeSat network. This paper consists of two parts: determination and estimation of quality of service (QoS) parameters and evaluation of the feasibility of a Massive Multiple Input Multiple Output (MIMO) system for inter-satellite links. CubeSats are low-cost and small satellites that were initially designed by students during the educational process but are now launched for conducting space research and for commercial use. Recently, some companies and research studies promoted CubeSats to build a wireless communication networks for different proposes, such as earth observation, weather forecasting, providing access to the internet, internet of things and machine to machine services. The main distinguishing features of a CubeSat network include low-cost and fast deployment with a consequent advantage: the possibility to build a large network (hundreds of spacecraft) with limited resources. However, due to the limited size and function of CubeSats, the feasibility of a CubeSat network with inter-satellite links is debatable. In this paper, we investigate the QoS parameters for an inter-satellite link and factors affecting it. The theoretical design with a constructive drawing of massive MIMO has been made. The possibility and time duration of inter-satellite communication has been calculated for three different cases using real data and including Massive MIMO. The simulation of orbit movements for groups of CubeSats has been made. The correlation between relative positions of satellites in orbits, parameters of communication channels and the QoS was determined. The feasibility of massive MIMO for CubeSat communications has been estimated. Based on simulation results, suggestions and possible technical and non-technical solutions were highlighted together with future studies and simulations.

A parallel electrostatic Particle-in-Cell method on unstructured tetrahedral grids for large-scale bounded collisionless plasma simulations

An unstructured electrostatic Particle-In-Cell (EUPIC) method is developed on arbitrary tetrahedral grids for simulation of plasmas bounded by arbitrary geometries. The electric potential in EUPIC is obtained on cell vertices from a finite volume Multi-Point Flux Approximation of Gauss' law using the indirect dual cell with Dirichlet, Neumann and external circuit boundary conditions. The resulting matrix equation for the nodal potential is solved with a restarted generalized minimal residual method (GMRES) and an ILU(0) preconditioner algorithm, parallelized using a combination of node coloring and level scheduling approaches. The electric field on vertices is obtained using the gradient theorem applied to the indirect dual cell. The algorithms for injection, particle loading, particle motion, and particle tracking are parallelized for unstructured tetrahedral grids. The algorithms for the potential solver, electric field evaluation, loading, scatter-gather algorithms are verified using analytic solutions for test cases subject to Laplace and Poisson equations. Grid sensitivity analysis examines the L2 and L∞ norms of the relative error in potential, field, and charge density as a function of edge-averaged and volume-averaged cell size. Analysis shows second order of convergence for the potential and first order of convergence for the electric field and charge density. Temporal sensitivity analysis is performed and the momentum and energy conservation properties of the particle integrators in EUPIC are examined. The effects of cell size and timestep on heating, slowing-down and the deflection times are quantified. The heating, slowing-down and the deflection times are found to be almost linearly dependent on number of particles per cell. EUPIC simulations of current collection by cylindrical Langmuir probes in collisionless plasmas show good comparison with previous experimentally validated numerical results. These simulations were also used in a parallelization efficiency investigation. Results show that the EUPIC has efficiency of more than 80% when the simulation is performed on a single CPU from a non-uniform memory access node and the efficiency is decreasing as the number of threads further increases. The EUPIC is applied to the simulation of the multi-species plasma flow over a geometrically complex CubeSat in Low Earth Orbit. The EUPIC potential and flowfield distribution around the CubeSat exhibit features that are consistent with previous simulations over simpler geometrical bodies.

Erratum to: Thermal deformation of 3U CubeSat in low Earth orbit

Erratum to: Thermal deformation of 3U CubeSat in low Earth orbit

Thermal deformation of 3U CubeSat in low Earth orbit

The impact of uneven heating on a satellite structure in low Earth orbit has been considered using the example of 3U CubeSat. The calculations showed that the thermal deformation of CubeSat structure in orbit caused a deviation between normals to opposite small satellite sides of about 0.03°. Such a deviation is commensurate with the required satellite pointing accuracy approximately 0.1° necessary for satellite laser communication. It means that to solve similar problems in the CubeSat designing that require such or better CubeSat pointing accuracy, it is necessary to take into account the expected satellite structure thermal deformation.

Applications of fracture mechanics to quantitative accelerated life testing of plastic encapsulated microelectronics

Accelerated testing must address the failure mechanisms active within the devices undergoing tests in order to assess lifetimes in a meaningful way. The assumption of constant temperature, thermally activated lifetime, based upon the Arrhenius assumptions, does not always provide the necessary understanding to interpret accelerated tests in microelectronics. Plastic encapsulants, dielectric polymers, and underfill materials are subject to delamination and cracking with thermal cycling. Crack propagation during use environment exposure, drives the potential for failure of microelectronic devices and is therefore a necessary focal point in qualification and life testing. This paper reviews the available research in the application of fracture mechanics to this class of problems in microelectronics including relevant test data. In addition, useful acceleration factor models are derived for polymer crack propagation based on principles of linear elastic fracture mechanics. Further, a simple approach to estimating the minimum temperature cycling ranges, necessary to propagate a crack, is also presented. Finally, a methodology of applying acceleration factors to develop testing plans is shown, with an example in spaceflight for a cubesat in low Earth orbit. Overall, this is a paper that shows a useful and appropriate process for creating physics of failure based life testing for delamination and cracking failures in microelectronic polymers in a temperature cycling environment.

Model predictive and reallocation problem for CubeSat fault recovery and attitude control

Abstract In recent years, thanks to the increase of the know-how on machine-learning techniques and the advance of the computational capabilities of on-board processing, expensive computing algorithms, such as Model Predictive Control, have begun to spread in space applications even on small on-board processor. The paper presents an algorithm for an optimal fault recovery of a 3U CubeSat, developed in MathWorks Matlab & Simulink environment. This algorithm involves optimization techniques aiming at obtaining the optimal recovery solution, and involves a Model Predictive Control approach for the attitude control. The simulated system is a CubeSat in Low Earth Orbit: the attitude control is performed with three magnetic torquers and a single reaction wheel. The simulation neglects the errors in the attitude determination of the satellite, and focuses on the recovery approach and control method. The optimal recovery approach takes advantage of the properties of magnetic actuation, which gives the possibility of the redistribution of the control action when a fault occurs on a single magnetic torquer, even in absence of redundant actuators. In addition, the paper presents the results of the implementation of Model Predictive approach to control the attitude of the satellite.

Space base laser torque applied on LEO satellites of various geometries at satellite’s closest approach

In light of using laser power in space applications, the motivation of this paper is to use a space based solar pumped laser to produce a torque on LEO satellites of various shapes. It is assumed that there is a space station that fires laser beam toward the satellite so the beam spreading due to diffraction is considered to be the dominant effect on the laser beam propagation. The laser torque is calculated at the point of closest approach between the space station and some sun synchronous low Earth orbit cubesats. The numerical application shows that space based laser torque has a significant contribution on the LEO cubesats. It has a maximum value in the order of 10−8Nm which is comparable with the residual magnetic moment. However, it has a minimum value in the order 10−11Nm which is comparable with the aerodynamic and gravity gradient torque. Consequently, space based laser torque can be used as an active attitude control system.

Ground Base Laser Torque Applied on LEO Satellites of Various Geometries

This paper is devoted to investigate the feasibility of using a medium power ground-based laser to produce a torque on LEO satellites of various shapes. The laser intensity delivered to a satellite is calculated using a simple model of laser propagation in which a standard atmospheric condition and linear atmospheric interaction mechanism is assumed. The laser force is formulated using a geocentric equatorial system in which the Earth is an oblate spheroid. The torque is formulated for a cylindrical satellite, spherical satellites and for satellites of complex shape. The torque algorithm is implemented for some sun synchronous low Earth orbit cubesats. Based on satellites perigee height, the results demonstrate that laser torque affecting on a cubesat has a maximum value in the order of 10 -9 which is comparable with that of solar radiation. However, it has a minimum value in the order of 10 -10 which is comparable with that of gravity gradient. Moreover, the results clarify the dependency of the laser torque on the orbital eccentricity. As the orbit becomes more circular it will experience less torque. So, we can conclude that the ground based laser torque has a significant contribution on the low Earth orbit cubesats. It can be adjusted to obtain the required control torque and it can be used as an active attitude control system for cubesats.