In-Orbit Radiation Effects Monitoring on the UoSat Satellites

Since the summer of 1988, radiation effects, in particular single event upset (SEU) phenomena, have been monitored in the three mass semiconductor memory systems onboard the University of Surrey\u27s UoSAT-2 satellite, which is in a 700 km, near-polar low-Earth orbit. Almost 5000 events have now been logged by the spacecraft, and these have been assembled into a database for analysis by ground-based software. This software has allowed the SEU sensitivity of different device types to be analyzed, and the relative performance of the Mostek 4116, Texas 4416 NMOS DRAMs, the Toshiba TC5516, Harris 6564 and 6516, and the Hitachi 6264 and 6116 CMOS SRAMS, has been evaluated. The logs of in-orbit SEUs on UoSAT-2 have provided several interesting statistics, allowing direct comparison of static and dynamic RAMs ranging in capacity from 4 kilobits to 64 kilobits per chip. An unexpected result has been that none of the 288K bytes of 8-bit wide static RAM on UoSAT-2 have shown multiple-bit (per byte) upsets over the monitoring period. Also, the orbital analysis of UoSAT-2 SEUs shows an overwhelming concentration of events in the South Atlantic Anomaly for all device types. Further studies are now underway with the University of Surrey\u27s UoSAT-3 satellite. This spacecraft carries over 4M bytes of semiconductor memory as part of its store-and-forward communications payload, together with the Cosmic Particle / Total Dose Experiments (CPE / TDE), providing direct measurements of the space radiation environment

The SNAP-1 Machine Vision System

In June 2000, the Surrey Space Centre (SSC) and Surrey Satellite Technology Limited (SSTL) launched the remote inspection demonstrator nanosatellite, SNAP-1 . One of the primary mission objectives of this satellite was to image its companion microsatellite, Tsinghua-1, during the deployment phase of the launch. Later in the mission it is also planned that SNAP-1 will be manoeuvred back within visual range of Tsinghua-1, in order to carry out further imaging experiments whilst the satellites fly in formation. To fulfill its mission, SNAP-1 carries a powerful, innovative and highly integrated Machine Vision System (MVS). This consists of four ulta-minature CMOS video cameras, a software video digitiser, 8Mb of 70ns SRAM and a 220MHz StrongARM processor. The integration of these components provides a low cost, low power consumption, high reliability platform, with enough processing power to capture and process real-time video images. This will enable SNAP-1 to not only compress and return images back to Earth, but to perform high level computer vision functions such as optical target tracking, automatic pose and position estimation and on future SNAP missions perhaps even optically guided docking. This paper therefore details the design, performance and initial results from the SNAP-1 Machine Vision System

Novel techniques for the analysis of the TOA radiometric uncertainty

In the framework of the European Copernicus programme, the European Space Agency (ESA) has launched the Sentinel-2 (S2) Earth Observation (EO) mission which provides optical high spatial -resolution imagery over land and coastal areas. As part of this mission, a tool (named S2-RUT, from Sentinel-2 Radiometric Uncertainty Tool) estimates the radiometric uncertainties associated to each pixel using as input the top-of-atmosphere (TOA) reflectance factor images provided by ESA. The initial version of the tool has been implemented — code and user guide available1 — and integrated as part of the Sentinel Toolbox. The tool required the study of several radiometric uncertainty sources as well as the calculation and validation of the combined standard uncertainty in order to estimate the TOA reflectance factor uncertainty per pixel. Here we describe the recent research in order to accommodate novel uncertainty contributions to the TOA reflectance uncertainty estimates in future versions of the tool. The two contributions that we explore are the radiometric impact of the spectral knowledge and the uncertainty propagation of the resampling associated to the orthorectification process. The former is produced by the uncertainty associated to the spectral calibration as well as the spectral variations across the instrument focal plane and the instrument degradation. The latter results of the focal plane image propagation into the provided orthoimage. The uncertainty propagation depends on the radiance levels on the pixel neighbourhood and the pixel correlation in the temporal and spatial dimensions. Special effort has been made studying non-stable scenarios and the comparison with different interpolation method

Flight Results of the InflateSail Spacecraft and Future Applications of DragSails

The InflateSail CubeSat, designed and built at the Surrey Space Centre (SSC) at the University of Surrey, UK, for the Von Karman Institute (VKI), Belgium, is one of the technology demonstrators for the QB50 programme. The 3.2 kilogram InflateSail is “3U” in size and is equipped with a 1 metre long inflatable boom and a 10 square metre deployable drag sail. InflateSail\u27s primary goal is to demonstrate the effectiveness of using a drag sail in Low Earth Orbit (LEO) to dramatically increase the rate at which satellites lose altitude and re-enter the Earth\u27s atmosphere. InflateSail was launched on Friday 23rd June 2017 into a 505km Sun-synchronous orbit. Shortly after the satellite was inserted into its orbit, the satellite booted up and automatically started its successful deployment sequence and quickly started its decent. The spacecraft exhibited varying dynamic modes, capturing in-situ attitude data throughout the mission lifetime. The InflateSail spacecraft re-entered 72 days after launch. This paper describes the spacecraft and payload, and analyses the effect of payload deployment on its orbital trajectory. The boom/drag-sail technology developed by SSC will next be used on the RemoveDebris mission, which will demonstrate the applicability of the system to microsat deorbiting

Towards Robotic On-Orbit Assembly of Large Space Telescopes: Mission Architectures, Concepts, and Analyses

Over the next two decades, unprecedented astronomy missions could be enabled by space telescopes larger than the James Webb Space Telescope. Commercially, large aperture space-based imaging systems will enable a new generation of Earth Observation missions for both science and surveillance programs. However, launching and operating such large telescopes in the extreme space environment poses practical challenges. One of the key design challenges is that very large mirrors (i.e. apertures larger than 3m) cannot be monolithically manufactured and, instead, a segmented design must be utilized to achieve primary mirror sizes of up to 100m. Even if such large primary mirrors could be made, it is impossible to stow them in the fairings of current and planned launch vehicles, e.g., SpaceX’s Starship reportedly has a 9m fairing diameter. Though deployment of a segmented telescope via a folded-wing design (as done with the James Webb Space Telescope) is one approach to overcoming this volumetric challenge, it is considered unfeasible for large apertures such as the 25m telescope considered in this study. Parallel studies conducted by NASA indicate that robotic on-orbit assembly (OOA) of these observatories offers the possibility, surprisingly, of reduced cost and risk for smaller telescopes rather than deploying them from single launch vehicles but this is not proven. Thus, OOA of large aperture astronomical and Earth Observation telescopes is of particular interest to various space agencies and commercial entities. In a new partnership with Surrey Satellite Technology Limited and Airbus Defence and Space, the Surrey Space Centre is developing the capability for autonomous robotic OOA of large aperture segmented telescopes. This paper presents the concept of operation and mission analysis for OOA of a 25m aperture telescope operating in the visible waveband of the electromagnetic spectrum; telescopes of this size will be of much value as it would permit 1m spatial resolution of a location on Earth from geostationary orbit. Further, the conceptual evaluation of robotically assembling 2m and 5m telescopes will be addressed; these missions are envisaged as essential technology demonstration precursors to the 25m imaging system

MOST: A modified MLST typing tool based on short read sequencing

Multilocus sequence typing (MLST) is an effective method to describe bacterial populations. Conventionally, MLST involves Polymerase Chain Reaction (PCR) amplification of housekeeping genes followed by Sanger DNA sequencing. Public Health England (PHE) is in the process of replacing the conventional MLST methodology with a method based on short read sequence data derived from Whole Genome Sequencing (WGS). This paper reports the comparison of the reliability of MLST results derived from WGS data, comparing mapping and assembly-based approaches to conventional methods using 323 bacterial genomes of diverse species. The sensitivity of the two WGS based methods were further investigated with 26 mixed and 29 low coverage genomic data sets from Salmonella enteridis and Streptococcus pneumoniae. Of the 323 samples, 92.9% (n = 300), 97.5% (n = 315) and 99.7% (n = 322) full MLST profiles were derived by the conventional method, assembly- and mapping-based approaches, respectively. The concordance between samples that were typed by conventional (92.9%) and both WGS methods was 100%. From the 55 mixed and low coverage genomes, 89.1% (n = 49) and 67.3% (n = 37) full MLST profiles were derived from the mapping and assembly based approaches, respectively. In conclusion, deriving MLST from WGS data is more sensitive than the conventional method. When comparing WGS based methods, the mapping based approach was the most sensitive. In addition, the mapping based approach described here derives quality metrics, which are difficult to determine quantitatively using conventional and WGS-assembly based approaches