With the extensive cost reductions associated with small satellites, low Earth orbit missions are increasingly becoming popular, mostly with universities and the New-Space industry. However, a persistent limitation associated with the smallest satellites is the significant reduction in energy resources that each satellite has at its disposal. This limitation poses a challenge when using advanced communication systems, particularly those employing advanced forward error correction such as low-density parity check (LDPC) codes. To conserve the high computational energy required to decode such codes, we propose a novel early termination stopping criterion for LDPC decoders that is based on detecting the periodicity of syndrome weight oscillations. The technique is independent of the operating signal-to-noise ratio and results in reductions better than 80%, in the computational energy expended on a well-known bit-flipping decoding algorithm. Real world results are presented using an ARM-based microcontroller.
A circular planar array composed of four equilat-eral triangle patch antennas with a common triangular ground plane is proposed. The array is a building block for a geodesic dome phased array antenna (GDPAA) based on an icosahedron structure, primarily intended for use in the UHF amateur satel-lite band of 435-438 MHz. Due to the relatively long wavelength of this band, a novel design for a low-cost GDPAA with a reduced footprint is proposed. It is found that if individual ele-ments are placed in a circular lattice, the footprint is reduced and the overall array performance and antenna isolation are improved.
As far as tech trends go, smaller is almost always better. The team behind the University of Malta’s first ever PocketQube satellite agree— except when it comes to their ambitions. Cassi Camilleri speaks to Dr Ing. Marc Azzopardi, Darren Cachia, and Jonathan Camilleri to determine how work is progressing ahead of their 2018 space launch.
The University of Malta Astronics research group (ASTREA) has been developing a family of low cost PocketQube (PQ) picosatellites, with the smallest having a total mass of under 250 g and dimensions of a 5 cm cube. These satellites will be launched in low meta-stable orbits where an electric propulsion system will be required to maintain the orbit and perform other orbital manoeuvres. The Pulsed Plasma Thruster (PPT) is a promising technology for creating such miniaturised propulsion systems. However, scaling down this technology to fit inside PQs presents new challenges. Hence, different configurations of the coaxial PPT with reliable integrated ignition mechanisms are being developed as part of this project. This paper describes the overall mission feasibility of using PPT technology to reduce a 𝟓𝟎𝟎 𝐠 2p PQ’s orbit decay at an altitude of 𝟓𝟎𝟎 𝐤𝐦. Two PPT configurations with carbonisation mitigation efforts having a total discharge energy of 𝟎.𝟑𝟑𝟖 𝐉 per pulse were developed and an analysis of the PPT PQ subsystems is provided. The results include the developed PPT PQ, a simulation of the electric field strength of the two PPT configurations, and the plasma plume generated by the thrusters.
Modelling, simulating and testing the on-orbit thermal behaviour of a pico-satellite before launch is critical to ensure component reliability and performance. Due to small thermal inertia and hence small time constant, a pico-satellite may undergo larger temperature swings than those experienced by larger satellites. Weight, size and power limitations are especially restrictive in pico-satellites and limit thermal control to passive systems such as controlling conduction and radiation heat transfer paths. A lumped parameter thermal model was developed to study the on-orbit thermal response of the UoMBSat-1 PocketQube, Malta’s first pico-satellite project. A numerical finite element model is presented in order to test and validate the thermal model and passive thermal control. Small satellites are usually launched on rockets as piggyback satellites; therefore, orbit parameters are rarely known in the early stages of the project and various launch opportunities would need to be evaluated and compared. This paper presents a parametric analysis where the effects of orbit parameters, such as altitude and beta angle, on the thermal response are evaluated. We show that by controlling the surface finish and beta angle, it is possible to place a pico-satellite in a thermal regime that is suitable for typical electronic components, and batteries.
Space weather refers to “conditions on the Sun and in the solar wind, magnetosphere, ionosphere, and the thermosphere that can influence the performance and reliability of space-borne and ground-based technological systems and can endanger human life or health” [National Space Weather Program, 1995]. Of particular interest are the effects caused by the ionosphere, which is an ionised region of the upper atmosphere, ranging from approximately 90 to 1500 km. The ionosphere can degrade the performance of many radio systems; these include satellite navigation systems (i.e. GPS), satellite communications and space based radar. Measurements of the electron density in the ionosphere can be used to improve empirical ionospheric models or as inputs into assimilative ionospheric models, thereby permitting the development of better techniques to mitigate the impact of the ionosphere on radio systems. Ground-based radar systems may be used to make measurements of the bottom-side of the ionosphere (i.e. below the height of the peak density), and GPS provides a means of making integrated measurements of total electron content between a satellite and a receiver. However, for measurements of the top-side of the ionosphere, satellite based instrumentation is required. A radio frequency ionospheric impedance probe (ImP) is being developed by the Space Environment and Radio Engineering group at the University of Birmingham, UK, to provide in-situ measurements of the top-side electron density. ImP will measure this density by exciting an antenna embedded in the ionosphere – the frequencies at which the antenna resonates can then be used to estimate the electron density. ImP can be hosted on a dedicated very small spacecraft, such as a PocketQube. A PocketQube is a small spacecraft typically measuring 5x5x5 cm. Alternatively, it could be hosted as a secondary payload on a larger platform, such as a CubeSat or larger. Effective ionospheric measurements will require several ImPs to be installed on satellite constellations to provide measurements with high spatial and temporal resolution. A PocketQube platform is being developed by the Astrionics group at the University of Malta, with a target of launching a complete spacecraft with an ImP in March 2018. The platform is being developed to meet the design constraints imposed by ImP. ImP requires both orbital positioning data and attitude determination, which is to be provided by the platform. ImP measurements also require a magnetically clean environment as it is susceptible to local magnetic fields. This poster paper will describe the principle of operation behind ImP, as well as the design of the instrument itself. It will also describe the challenges involved in designing a versatile PocketQube spacecraft architecture that can accommodate a scientific payload.
Since the advent of CubeSat spacecraft, universities and private entities have been successfully designing and launching satellites at a fraction of the traditional cost. These satellites still accommodate useful scientific payloads. Another recently established satellite format is the PocketQube (PQ)-one eighth the size of a CubeSat – with the aim of further reducing launching costs. However, this brings with it the challenge of working with substantially smaller power, mass and volume budgets. Accurate ionospheric modelling requires the use of electron density measurements at the topside of the ionosphere which could be obtained via distributed in-situ sensing. This makes a low cost PQ constellation ideal for this application. In order to assess the feasibility of the PQ format, a preliminary study was conducted about the design of a PQ technology demonstrator capable of carrying a scientific payload. In this paper, the design approaches are discussed, keeping in mind the design budget restrictions as well as the constraints imposed by the ionospheric sensor.