Distributed processing of a fractal array beamformer

Fractals have been proven as potential candidates for satellite flying formations, where its different elements represent a thinned array. The distributed and low power nature of the nodes in this network motivates distributed processing when using such an array as a beamformer. This paper proposes such initial idea, and demonstrates that benefits such as strictly limited local processing capability independent of the array’s dimension and local calibration can be bought at the expense of a slightly increased overall cost

Impact of a purina fractal array geometry on beamforming performance and complexity

This paper investigates the possible benefits of using a Purina fractal array for beamforming, since this particular fractal has recently been suggested as the flight formation for a fractionated space craft. We analyse the beam pattern created by this, and define power concentration as measure of focussing the main beam of a multi-dimensional array. Using this performance metric and the computation cost of the array, a comparison to full lattice arrays is made. We quantify the significant benefits of the Purina array offered over a full lattice array of same complexity particularly at lower frequencies, and the complexity advantages over full lattice arrays of same aperture, particularly if energy is to be concentrated within a small angular spread

Payload Testing of a Weak Coherent Pulse Quantum Key Distribution Module for the Responsive Operations on Key Services (ROKS) Mission

Quantum Key Distribution (QKD) missions currently in development for space are expanding in number due to the increasing need for more secure means of encryption combined with the range limitations of terrestrial QKD. Most of these new missions are using smaller satellites to test their payloads. The ROKS (Responsive Operations for Key Services) mission is one such mission. It will utilize a 6U CubeSat bus and is set to launch in Q4 2022. A breadboard model of a 785nm weak coherent pulse quantum source module designed for ROKS, named JADE, was tested within a lab testbench environment with the mission’s systems represented by breadboard models with equivalent components. JADE’s optical module was miniaturized to be compatible with the limited payload volumes of these small classes of satellites. Lab-based testbench characterization of JADE’s ability to emit quantum pulses with four polarization states that propagate through the beam steering system for analysis by a receiver box was demonstrated. Future work will focus on further shrinking the JADE module down to less than 1/3U size, increasing the interoperability of the module with standard interfaces for both CubeSats and SmallSats, and adding further capabilities and full environmental testing qualification to JADE

Responsive Operations for Key Services (ROKS): A Modular, Low SWaP Quantum Communications Payload

Quantum key distribution (QKD) is a theoretically proven future-proof secure encryption method that inherits its security from fundamental physical principles. With a proof-of-concept QKD payload having flown on the Micius satellite since 2016, efforts have intensified globally. Craft Prospect, working with a number of UK organisations, has been focused on miniaturising the technologies that enable QKD so that they may be used in smaller platforms including nanosatellites. The significant reduction of size, and therefore the cost of launching quantum communication technologies either on a dedicated platform or hosted as part of a larger optical communications will improve potential access to quantum encryption on a relatively quick timescale. The Responsive Operations for Key Services (ROKS) mission seeks to be among the first to send a QKD payload on a CubeSat into low Earth orbit, demonstrating the capabilities of newly developed modular quantum technologies. The ROKS payload comprises a quantum source module that supplies photons randomly in any of four linear polarisation states fed from a quantum random number generator; an acquisition, pointing, and tracking system to fine-tune alignment of the quantum source beam with an optical ground station; an imager that will detect cloud cover autonomously; and an onboard computer that controls and monitors the other modules, which manages the payload and assures the overall performance and security of the system. Each of these modules have been developed with low Size, Weight and Power (SWaP) for CubeSats, but with interoperability in mind for other satellite form factors. We present each of the listed components, together with the initial test results from our test bench and the performance of our protoflight models prior to initial integration with the 6U CubeSat platform systems. The completed ROKS payload will be ready for flight at the end of 2022, with various modular components already being baselined for flight and integrated into third party communication missions

Communications for CubeSat networks and fractionalised spacecraft

The use of low-cost CubeSats in the context of satellite formation flying appears favourable due to their small size, relatively low launch cost, short development cycle and utilisation of commercial off the shelf components. However, the task of managing complex formations using a large number of satellites in Earth orbit is not a trivial one, and is further exacerbated by low-power and processing constraints in CubeSats. With this in mind, a Field Programmable Gate Array (FPGA) based system has been developed to provide next generation on-board computing capability.;The features and functionality provided by this on-board computer, as well as the steps taken to ensure reliability, including design processes and mitigation techniques are presented in this work and compared to state of the art technology.Coupling reliable formation flying capabilities with the possibility of producing complex patterns using spacecraft will enable the potential of grouping a number of antenna elements into a cooperative structure. The key point in the exploitation of formation flying techniques for the deployment of an antenna array is that the performance of a homogeneous pattern of array elements can be matched or surpassed by fractal geometries.;This thesis analyses the Purina fractal array when utilised for beamforming. A new metric termed power concentration is introduced, which assesses the power dissipated within a cone aligned with the array's look direction, i.e. an assessment how much of the radiated power will reach a specific foot print. Using this metric the performance for beamformers of varying complexity can be compared, independent of the number of sensor elements used to form the array and across a range of frequencies. Furthermore the robustness of the array with respect to element displacement and failure is investigated.;The fractionated nature of such a satellite network and the low-power nature of the nodes motivates distributed processing when using such an array as a beamformer. By mirroring the fractal structure in the processing architecture, the proposed idea demonstrates that benefits such as strictly limited local processing capability independent of the array's dimension and local calibration can be bought at the expense of a slightly increased overall cost.The use of low-cost CubeSats in the context of satellite formation flying appears favourable due to their small size, relatively low launch cost, short development cycle and utilisation of commercial off the shelf components. However, the task of managing complex formations using a large number of satellites in Earth orbit is not a trivial one, and is further exacerbated by low-power and processing constraints in CubeSats. With this in mind, a Field Programmable Gate Array (FPGA) based system has been developed to provide next generation on-board computing capability.;The features and functionality provided by this on-board computer, as well as the steps taken to ensure reliability, including design processes and mitigation techniques are presented in this work and compared to state of the art technology.Coupling reliable formation flying capabilities with the possibility of producing complex patterns using spacecraft will enable the potential of grouping a number of antenna elements into a cooperative structure. The key point in the exploitation of formation flying techniques for the deployment of an antenna array is that the performance of a homogeneous pattern of array elements can be matched or surpassed by fractal geometries.;This thesis analyses the Purina fractal array when utilised for beamforming. A new metric termed power concentration is introduced, which assesses the power dissipated within a cone aligned with the array's look direction, i.e. an assessment how much of the radiated power will reach a specific foot print. Using this metric the performance for beamformers of varying complexity can be compared, independent of the number of sensor elements used to form the array and across a range of frequencies. Furthermore the robustness of the array with respect to element displacement and failure is investigated.;The fractionated nature of such a satellite network and the low-power nature of the nodes motivates distributed processing when using such an array as a beamformer. By mirroring the fractal structure in the processing architecture, the proposed idea demonstrates that benefits such as strictly limited local processing capability independent of the array's dimension and local calibration can be bought at the expense of a slightly increased overall cost

Enabling and exploiting self-similar central symmetry formations

In this work a formation flying based architecture is presented within the context of a distributed antenna array. An artificial potential function method is used to control the formation whereby deviation from an all-to-all interaction scheme and swarm shaping are enabled through a self-similar connection network. Introduction of an asymmetric term in the potential function formulation results in the emergence of structures with a central symmetry. The connection network then groups these identical structures through a hierarchical scheme. This produces a fractal shape which is considered for the first time as a distributed antenna array exploiting the recursive arrangement of its elements to augment performance. A 5-element Purina fractal is used as the base formation which is then replicated a number of times increasing the antenna-array aperture and resulting in a highly directional beam from a relatively low number of elements. Justifications are provided in support of the claimed benefits for distributed antenna arrays exploiting fractal geometries. The formation deployment is simulated in Earth orbit together with analytical proofs completing the arguments aimed to demonstrate feasibility of the concept and the advantages provided by grouping antenna elements into coherent structures