Surrey Satellite Technology Research Articles

Performance analysis of power conditioning and distribution module for microsatellite applications

Abstract Algeria’s micro-satellite, Alsat-1b, was successfully launched into a 680 km low Earth orbit onboard a PSLV-C35 rocket from Sriharikota, South India, on September 26, 2016. The spacecraft was conceived, built and launched as part of an 18-month technology transfer programme between Algeria’s Algerian Space Agency (ASAL) and the United Kingdom’s Surrey Satellite Technology Limited (SSTL). This document details the Power Conditioning and Distribution Module’s (PCM-PDM) design and performance in orbit, critical component of a satellite electrical power system, responsible for converting, regulating and distributing power to various subsystems and payloads. The PCM-PDM developed and produced by SSTL was subjected to rigorous testing simulating harsh space conditions to assess its performance. The results of this comprehensive analysis indicate that the module can effectively withstand extreme environmental factors and function optimally in challenging settings. The analysis focused on the PCM-PDM’s ability to provide reliable and efficient power conditioning and distribution to the satellite, including its load management capabilities, overcurrent protection, protection against undervoltage and critical mode operations. The results of the performance analysis showed that the PCM-PDM met the required specifications and demonstrated reliable and efficient operation in different modes of the satellite’s mission. The study highlights the importance of careful design and rigorous testing of the PCM-PDM to ensure the reliable and efficient operation of the satellite and its payloads.

ANALYSIS OF NOVASAR-1 S-BAND DATA IN DEVELOPING AN ALTERNATIVE LAND COVER MAPPING

Abstract. The Advanced Science and Technology Institute of the Department of Science and Technology (DOST-ASTI), through its Synthetic Aperture Radar and Automatic Identification System (SARwAIS) Project, has gained access to S-Band SAR images acquired by the NovaSAR-1 satellite of UK’s Surrey Satellite Technology Ltd. (SSTL) To help maximize the utility of these images especially in the aspect of terrain-related applications, their viability as potential alternatives to datasets like optical satellite images and other SAR images in characterizing land cover types was evaluated. Statistical analyses on the backscatter values from the tri-polarization ScanSAR datasets using Multivariate Analysis of Variance (MANOVA) and its corresponding post-hoc tests showed that there is a significant difference on the mean backscatter values at 0.05 level of significance. Moreover, Tukey’s honestly significant difference (Tukey’s HSD) test determined which pairs contribute to the significant difference. Using the Random Forest algorithm resulted in an accuracy of 66.93% without further optimization and/or reduction in the number of land covers being classified. Despite the relatively unremarkable accuracy score, it still showed potential for data augmentation with optical satellites for land cover mapping and other terrain-related applications.

AUGMENTING THE PHILIPPINES’ DOST-ASTI’S POTENTIAL FLOOD EXTENTS MAPPING SERVICE WITH S-BAND NOVASAR-1 IMAGES

Abstract. The Philippines’ Advanced Science and Technology Institute under the Department of Science and Technology (DOST-ASTI) has developed an AI-based and near real-time flood extent mapping service that utilizes C-Band Sentinel-1 SAR images. However, this method is limited by the availability of the Sentinel-1 images during flooding events. To address this issue, the institute, through its SARwAIS Project, utilized the S-Band NovaSAR-1 satellite, which was designed and launched by Surrey Satellite Technology, Ltd. With a 10% share to NovaSAR-1’s imaging capacity, the country can task image acquisitions that could help augment the Sentinel-1 datasets. Successfully captured images are prepared using the institute’s developed pre-processing workflow. Afterwards, a thresholding method, adopted from UN-SPIDER’s recommended practices for flood mapping, is employed to identify potentially flooded areas from these images. Generated products are then assessed to determine their relative accuracy in detecting potential floods. Satisfactory products are then distributed to relevant disaster management agencies and are also published in the agency’s social media page for further information dissemination. Python scripts were then developed to automate the established workflows, which were initially done manually. These scripts also help expedite the generation of flood maps especially when processing multiple SAR images. The acquisition and utilization of NovaSAR-1 images substantially help the country address the gaps on the availability of workable data for a more informative disaster response especially during flooding events.

Investigation of the aberrant record from bus GPS receiver onboard FORMOSAT-7/COSMIC-2 satellite constellation in low Earth orbit

Investigation of the aberrant record from bus GPS receiver onboard FORMOSAT-7/COSMIC-2 satellite constellation in low Earth orbit

Active debris removal: A review and case study on LEOPARD Phase 0-A mission

Active debris removal: A review and case study on LEOPARD Phase 0-A mission

Ground and flight tests of AlSat-1B butane propulsion system

On September 26, 2016 Algerian Space Agency launched AlSat-1B, the second in a series of medium resolution earth observation satellites mission. AlSat-1B electro-thermal propulsion system follows the classic design principle that has been used on previous SSTL-100 missions. With a total dry weight of 5.17 kg, the system is filled with 2.35 L self-pressurized butane. The thruster assembly is designed to use 15 W (at 28 V) redundant heater elements, it is designed to have an average mission thrust of 50 mN. With a warm up time of 10 min, the temperature of the butane will be increased by over 250 °C. This is the equivalent of about 35% gain in specific impulse over ambient temperature butane. The spacecraft dry weigh at launch site was 107 kg, the propulsion system is designed to provide at least 19 m/s Delta-v to meet the spacecraft's mission requirement. To investigate the system readiness for flight, a series of performance tests have been completed at the Surrey Satellite Technology Ltd laboratories (United Kingdom), Satellite Development Centre (Algeria) and Satish Dhawan Space Centre rocket launch site (India), the results of these tests as well as initial flight test results are presented in this paper.

Power System Design and Performance for Low Earth Orbit Spacecraft

On the September 26, 2016, Algeria's enhanced micro-satellite Alsat-1B was launched into a 680-km low Earth orbit onboard a PSLV-C35 rocket from Sriharikota near the metropolis of Chennai (South India). The spacecraft was designed, manufactured, and launched as an 18-month long technology transfer program between the Algerian Space Agency (ASAL), Algeria and Surrey Satellite Technology Limited (SSTL), U.K. This article describes the design and in-orbit performance of the power system and the design of the Alsat-1B high-efficiency solar power system used to charge AEA Battery System Ltd and Société des Accumulateurs Fixes et de Traction Lithium-ion batteries. The solar power system described in this article is deployed on many satellites including Alsat-1b, which was launched from a heritage SSTL power system. It was implemented with a conventional pulsewidth modulator (PWM) duty cycle ratio control method to design and build a solar battery charger. Maximum power point tracking (MPPT) was used to maximize the output power, irrespective of the temperature of the solar arrays and irradiation conditions. The simulation results achieved by using Orcad/Pspice programs are in good agreement with the experimental results. These results demonstrate the reliability and validity of the implemented MPPT technique. The battery charger prototype was tested and the results obtained provided conclusions on the conditions of permanent control on the battery charger.

Towards Deep Simulations of LEO Satellite Links Based-on Saratoga

Satellites, in low earth orbit, are increasingly deployed in last years. They are used as well various space missions and mostly in remote sensing missions. Despite this growing interest and the large number of deployed satellites, each space mission has its own requirements according the purposed activities. Engineers are called-upon to develop new codes, algorithms, and to bring changes to the manufacturer’s technology. Initially, the new developed features are implemented on test-beds for the assessment purposes, however, emulation platforms are expensive and their implementation time consuming. Simulation models give the first try out and overcome some issues by giving an agility for a wide range of experimentations in short time, while having a lower cost. In this context, we present a contribution on the widely used simulator by scientific researcher community NS-2. The contribution consists to model the wireless communications between satellites and ground stations based-on SSTL (Surrey Satellite Technology Ltd) technology. We present the setting-up of additional physical layer modules required to model the radio links in space missions and antenna features; we describe, in addition, the developed module to model the Saratoga transfer protocol as an application layer. Evaluation of the developed modules on NS-2 is performed by simulations and comparisons to the referenced simulator in space industry STK and the realistic data collected from the operational mission Alsat-1B.

Stability Evaluation of the SDRE Technique based on Java in a CubeSat Attitude and Orbit Control Subsystem

In 2013, the STRaND (University of Surrey and Surrey Satellite Technology Ltd) and the PhoneSat (NASA) programs attracted the attention of the aerospace community applying commercial off-the-shelf smartphones in CubeSats. Both programs deployed CubeSats using smartphones based on Google's Android, in which application development is mainly based on Java programming language. Some of these CubeSats had actuators, e.g., STRaND-1 had three reaction wheels mounted in an orthogonal configuration to provide three-axis control, whereas PhoneSat 2.0 beta had magnetorquers to de-tumble the spacecraft. Taking into account a CubeSat that runs Android operating system (based on a smartphone), it is natural to evaluate the attitude and orbit control subsystem (AOCS) based on Java. Elsewhere, we shown State-Dependent Riccati Equation (SDRE) is a feasible non-linear control technique that can be applied in such CubeSats using Java. Moreover, we shown, through simulation using a Monte Carlo perturbation model, SDRE provides better performance than the PID controller, a linear control technique. In this paper, we tackle the next fundamental problem: stability. We evaluate stability from two perspectives: (1) parametric uncertainty of the inertia tensor and (2) a Monte Carlo perturbation model based on a uniform attitude probability distribution. Through the combination of these two perspectives, we grasp the stability properties of SDRE in a broader sense. In order to handle the uncertainty appropriately, we combine SDRE with H∞. The Nanosatellite Constellation for Environmental Data Collection (CONASAT), a CubeSat from the Brazilian National Institute for Space Research (INPE), provided the nominal parameters for the simulations. The initial results of the simulations shown that the SDRE controller is stable to ± 20% uncertainty in the inertia tensor for attitudes uniformly distributed and angular velocity up to 0.15 radians/second.

EARTH OBSERVATION APPLICATIONS FOR GOAL 14: IMPROVING MARITIME DOMAIN AWARENESS USING SYNTHETIC APERTURE RADAR IMAGING WITH AUTOMATIC IDENTIFICATION SYSTEM IN THE PHILIPPINES

Abstract. The Philippines has acquired access to the NovaSAR-1 satellite developed by Surrey Satellite Technology, Ltd. (SSTL) for the implementation of its project Synthetic Aperture Radar (SAR) and Automatic Identification System (AIS) for Innovative Terrestrial Monitoring and Maritime Surveillance, which will provide simultaneous S-band SAR imaging with AIS data for applications targeted on improving maritime domain awareness. The country has inherent challenges in this field due to its archipelagic nature, with earth observation seen as a potential solution as it provides an immediate and wide coverage over designated priority areas. This contributes toward achieving Sustainable Development Goal 14: Life Below Water by providing objective information in support of data-driven decision and policymaking, closing knowledge gaps in monitoring Philippine waters.

Remote Sensing of Forest Biomass Using GNSS Reflectometry

In this study, the capability of Global Navigation Satellite System Reflectometry in evaluating forest biomass from space has been investigated by using data coming from the TechDemoSat-1 (TDS-1) mission of Surrey Satellite Technology Ltd. and from the Cyclone Satellite System (CyGNSS) mission of NASA. The analysis has been first conducted using TDS-1 data on a local scale, by selecting five test areas located in different parts of the Earth's surface. The areas were chosen as examples of various forest coverages, including equatorial and boreal forests. Then, the analysis has been extended by using CyGNSS to a global scale, including any type of forest coverage. The peak of the Delay Doppler Map calibrated to retrieve an “equivalent” reflectivity has been exploited for this investigation and its sensitivity to forest parameters has been evaluated by a direct comparison with vegetation optical depth (VOD) derived from the Soil Moisture Active Passive L-band radiometer, with a pantropical aboveground biomass (AGB) map and then with a tree height (H) global map derived from the Geoscience Laser Altimeter System installed on-board the ICEsat satellite. The sensitivity analysis confirmed the decreasing trend of the observed equivalent reflectivity for increasing biomass, with correlation coefficients 0.31 ≤ R ≤ 0.54 depending on the target parameter (VOD, AGB, or H) and on the considered dataset (local or global). These correlations were not sufficient to retrieve the target parameters by simple inversion of the direct relationships. The retrieval has been therefore based on Artificial Neural Networks making it possible to add other inputs (e.g., the incidence angle, the signal to noise ratio, and the lat/lon information in case of global maps) to the algorithm. Although not directly correlated to the biomass, these inputs helped in improving the retrieval accuracy. The algorithm was tested on both the selected areas and globally, showing a promising ability to retrieve the target parameter, either AGB or H, with correlation coefficients R ≃ 0.8.

Topology Optimization for Additive Manufacturing as an Enabler for Light Weight Flight Hardware

Three case studies utilizing topology optimization and Additive Manufacturing for the development of space flight hardware are described. The Additive Manufacturing (AM) modality that was used in this work is powder bed laser based fusion. The case studies correspond to the redesign and manufacture of two heritage parts for a Surrey Satellite Technology LTD (SSTL) Technology Demonstrator Space Mission that are currently functioning in orbit (case studies 1 and 2), and a system of five components for the SpaceIL’s lunar launch vehicle planned for launch in the near future (case study 3). In each case, the nominal or heritage part has undergone topology optimization, incorporating the AM manufacturing constraints that include: minimization of support structures, ability to remove unsintered powder, and minimization of heat transfer jumps that will cause artifact warpage. To this end the topology optimization exercise must be coupled to the Additive Manufacturing build direction, and steps are incorporated to integrate the AM constraints. After design verification by successfully passing a Finite Element Analysis routine, the components have been fabricated and the AM artifacts and in-process testing coupons have undergone verification and qualification testing in order to deliver structural components that are suitable for their respective missions.

Additive Manufacturing of Lightweight, Optimized, Metallic Components Suitable for Space Flight

A holistic process flow designed and implemented for additive manufacturing of topology-optimized metallic components suitable for use on satellites is described and demonstrated with two components that are part of the Surrey Satellite Technology, Ltd. technology mission. The holistic process flow begins with part selection and includes topology optimization, finite element analysis verification, additive manufacturing, and an aggressive mechanical and material testing campaign. The case studies used in this work include a camera bracket and a satellite panel insert. Both parts were fabricated under the guidelines of the holistic process flow in a total of eight weeks from concept to verification for flight. The process flow includes verification feedback loops in the design stage and the manufacturing stage. The aggressive testing campaign that is the last step in the process flow is included in order to guarantee the mechanical fidelity of the additively manufactured, produced components intended for flight approval and to demonstrate that the project specifications are met.

Full simulation of the LUCID experiment in the Low Earth Orbit radiation environment

The Langton Ultimate Cosmic ray Intensity Detector (LUCID) experiment is a satellite-based device that uses five Timepix hybrid silicon pixel detectors to make measurements of the radiation environment at an altitude of approximately 630 km, i.e. in Low Earth Orbit (LEO) . The experiment launched aboard Surrey Satellite Technology Limited's (SSTL's) TechDemoSat-1 on Tuesday the 8th of July 2014. The Timepix detectors, developed by the Medipix2 Collaboration, are arranged to form the five sides of a cube enclosed by a 0.7 mm thick aluminium covering, and are operated in Time-over-Threshold (ToT) mode to allow the flux, energy and directionality of incident ionising radiation to be measured. To understand the expected detector performance with respect to these measurements, the LUCID experiment has been modelled using the Allpix software package, a generic simulation toolkit for silicon pixel detectors built upon the GEANT4 framework. The work presented here summarises studies completed using the GridPP Collaboration's computing grid infrastructure to perform the simulations, store the resultant datasets, and share that data with the LUCID Collaboration. The analysis of these datasets has given an indication of the expected performance in differing space radiation environments (for example, during passes of the polar regions or the South Atlantic Anomaly), and has allowed the LUCID Collaboration to prepare for when data is transmitted back to Earth in late 2014.

Integrated Semiempirical Methodology for Microvibration Prediction

In this paper, a full methodology to deal with microvibration predictions onboard satellites is described. Two important aspects are tackled: 1) the characterization of the sources with a pragmatic procedure that allows integrating into the algorithm the full effect of the sources, including their dynamic coupling with the satellite structure; 2) the modeling of the transfer function source receivers with a technique named in this paper as the Craig–Bampton stochastic method, which allows prediction of a nominal response and variations due to structural uncertainties as accurate as full Monte Carlo simulations but at a fraction of the computational effort. The paper then includes a statistical study of the data from the structural dynamic testing of the five identical craft of the Rapid-Eye constellation to set the magnitude of the uncertainties that should be applied in the analysis. Finally, the computational procedure is applied to the new high-resolution satellite SSTL-300-S1 and the predictions compared with the experimental results retrieved during the physical microvibration testing of the satellite, which was carried out at the Surrey Satellite Technology Limited facilities in the United Kingdom.

Simulation and analysis of the LUCID experiment in the Low Earth Orbit radiation environment

The Langton Ultimate Cosmic ray Intensity Detector (LUCID) experiment is a satellite-based device that will use five Timepix hybrid silicon pixel detectors to make measurements of the radiation environment at an altitude of approximately 635 km, i.e. in Low Earth Orbit (LEO). The experiment is due to launch aboard Surrey Satellite Technology Limited's (SSTL's) TechDemoSat-1 in 2014. The Timepix detectors, developed by the Medipix Collaboration, are arranged to form the five sides of a cube enclosed by a 0.7 mm thick aluminium "dome", and will be operated in Time-over-Threshold mode to allow the flux, energy and directionality of incident ionising radiation to be measured. To estimate the anticipated data rates with respect to these measurements, the LUCID experiment has been modelled using the GEANT4 software framework. As an input to these simulations, SPENVIS, ESA's Space Environment information system, was used to obtain the estimated flux of trapped protons and electrons in TechDemoSat-1's orbit with NASA's AP-8 and AE-8 models. A web portal, LUCIDITY, was developeded to allow school students from the LUCID Collaboration to manage SPENVIS flux spectra and GEANT4 input cards. The initial results reported here confirm that the LUCID's data transmission allowance is sufficient, and further work applying the techniques to more specific space radiation environments with a more sophisticated simulation is proposed.

The Micro Radiation Environment Monitor (MuREM) and SSTL Radiation Monitor (SSTL RM) on TechDemoSat-1

Two new miniaturized scientific radiation monitoring payloads are presented prior to their first flight on the TechDemoSat-1 Spacecraft. They are capable of monitoring the space radiation environment and its effects on radiation-sensitive devices. Micro radaion environment monitor (MuREM) and Surrey Satellite Technology radiation monitor (SSTL RM) carry RADFET dosimeters, dose-rate-sensitive photodiodes, and p-i-n diode particle detectors. SSTL RM is also connected to external RADFET sensors placed around the spacecraft, while MuREM carries a radiation effects payload consisting of COTS devices that will be monitored while exposed to the space radiation environment.

Satellite expertise overhead

The UK space industry is booming. No sooner did Guildford-based Surrey Satellite Technology Ltd unveil its new 3,700 m2 satellite clean-room facility, than the European Commission chose the company to assemble the next batch of eight Galileo satellite navigation payloads adding to the 14 that it is already building.

Design and validation of inverse optimisation software for the attitude control of microsatellites

Design and validation of inverse optimisation software for the attitude control of microsatellites

Experience with Delay‐Tolerant Networking from orbit

Abstract We describe the first use from space of the Bundle Protocol for Delay‐Tolerant Networking (DTN) and lessons learned from experiments made and experience gained with this protocol. The Disaster Monitoring Constellation (DMC), constructed by Surrey Satellite Technology Ltd (SSTL), is a multiple‐satellite Earth‐imaging low‐Earth‐orbit sensor network in which recorded image swaths are stored onboard each satellite and later downloaded from the satellite payloads to a ground station. Store‐and‐forward of images with capture and later download gives each satellite the characteristics of a node in a disruption‐tolerant network. Originally developed for the ‘Interplanetary Internet,’ DTNs are now under investigation in an Internet Research Task Force (IRTF) DTN research group (RG), which has developed a ‘bundle’ architecture and protocol. The DMC is technically advanced in its adoption of the Internet Protocol (IP) for its imaging payloads and for satellite command and control, based around reuse of commercial networking and link protocols. These satellites' use of IP has enabled earlier experiments with the Cisco router in Low Earth Orbit (CLEO) onboard the constellation's UK‐DMC satellite. Earth images are downloaded from the satellites using a custom IP‐based high‐speed transfer protocol developed by SSTL, Saratoga, which tolerates unusual link environments. Saratoga has been documented in the Internet Engineering Task Force (IETF) for wider adoption. We experiment with the use of DTNRG bundle concepts onboard the UK‐DMC satellite, by examining how Saratoga can be used as a DTN ‘convergence layer’ to carry the DTNRG Bundle Protocol, so that sensor images can be delivered to ground stations and beyond as bundles. Our practical experience with the first successful use of the DTNRG Bundle Protocol in a space environment gives us insights into the design of the Bundle Protocol and enables us to identify issues that must be addressed before wider deployment of the Bundle Protocol. Published in 2010 by John Wiley & Sons, Ltd.