Single Event Upset Error Protection for Solid State Data Memory on Microsatellites

Many microsatellite missions rely upon large arrays of CMOS static RAM for data storage. Even a satellite with strict power and volume limitations can carry several Mbytes of SRAM. Experience has shown that these memory arrays are useful for scientific data collection image storage, store and- forward message switching and spacecraft telemetry monitoring. This paper describes the authors\u27 design and implementation of error protection codes which protect large CMOS RAM arrays from radiation-induced single event upsets

Pose Estimation of Target Satellite for Proximity Operations

Close-proximity operations are increasingly a topic of interest, where satellites manoeuvre within a very small distance of other spacecraft. A high degree of accuracy is required in estimating the relative position and orientation of the other spacecraft, in order to conduct such manoeuvres safely. Traditionally, active systems such as radar or more recently Differential GPS have been used for relative position estimation, yet these give little information on the orientation of the other satellite. Passive imaging can provide a large amount of information on the location and orientation of the Target, with high spatial resolution. Imaging requires only low-powered cameras, which can be made available on a wider range of satellites, and does not require any functionality from the other spacecraft. A robust autonomous close-range relative orientation and location (pose) estimation system is proposed, based on computer vision. Using a single image, and utilising knowledge of the Target spacecraft, an estimation of the Target’s six relative rotation and translation parameters are found from a distance in the order of 10 metres. Such position and rotation estimates over time will allow relative orbit parameter estimation, and enable close-proximity operations such as docking and remote inspection

A Novel Method for Achieving SAR Imaging with a Pair of Micro-Satellites by Means of a Bi-Static Configuration

There is increasing interest in the potential capabilities and applications of micro -satellites in the field of Earth-observation (EO). Passive optical imaging is now well established on such platforms, however, an active imaging payload - a synthetic aperture radar (SAR) - would appear to be insupportable, due to its size, complexity and high -power requirements. A major driver of these requirements is that traditional SAR systems use backscatter - which is necessarily weak from most terrain types. If the forward scattered energy could be gathered, then the transmit-power requirements could drop significantly. We therefore propose a novel method by which two micro-satellites fly in formation to accomplish a SAR mission bi-statically. The transmitting satellite will be the “master”, with the receiver satellite “slaved” off it by means of a synchronization signal. The satellites image a swath of 30 km, at a ground resolution of 30 m from 700 km altitude. Our constellation geometry can image anywhere in a pre-selected latitude band, and requires minimal orbit-control resources. The viewing configuration resolves the left-right ambiguity that occurs in near nadir pointing bi-static radar. Applications to a polar ice-monitoring mission are discussed, although with minor changes any location on Earth can be viewed

Low-Cost Dual-Band Circularly Polarized Switched-Beam Array for Global Navigation Satellite System

This paper presents the design and development of a dual-band switched-beam microstrip array for global navigation satellite system (GNSS) applications such as ocean reflectometry and remote sensing. In contrast to the traditional Butler matrix, a simple, low cost, broadband and low insertion loss beam switching feed network is proposed, designed and integrated with a dual band antenna array to achieve continuous beam coverage of ±25° around the boresight at the L1 (1.575 GHz) and L2 (1.227 GHz) bands. To reduce the cost, microstrip lines and PIN diode based switches are employed. The proposed switched-beam network is then integrated with dual-band step-shorted annular ring (S-SAR) antenna elements in order to produce a fully integrated compact-sized switched-beam array. Antenna simulation results show that the switched-beam array achieves a maximum gain of 12 dBic at the L1 band and 10 dBic at the L2 band. In order to validate the concept, a scaled down prototype of the simulated design is fabricated and measured. The prototype operates at twice of the original design frequency, i.e., 3.15 GHz and 2.454 GHz and the measured results confirm that the integrated array achieves beam switching and good performance at both bands

Passive SAR Satellite System (PASSAT): airborne demonstrator and first results

This paper presents the development and execution of an airborne experimental campaign as part of the continuing investigation of a passive Synthetic Aperture Radar using digital television broadcasting stations as illuminators of opportunity, and micro-/nano-satellite receivers in Low Earth Orbit. For the flight experiments, a hardware demonstrator was developed that utilised two receiving antennas, allowing both cross-correlation and auto-correlation range compression schemes, and was mounted to an airborne platform to image stationary rural areas up to 50 km from the transmitter. This paper presents the first image results of these experiments as well as initial analysis of image formation aspects including, range compression scheme and effects on the image quality of the signal to noise on the reference channel

Geographical and temporal distribution of SARS-CoV-2 clades in the WHO European Region, January to June 2020

We show the distribution of SARS-CoV-2 genetic clades over time and between countries and outline potential genomic surveillance objectives. We applied three available genomic nomenclature systems for SARS-CoV-2 to all sequence data from the WHO European Region available during the COVID-19 pandemic until 10 July 2020. We highlight the importance of real-time sequencing and data dissemination in a pandemic situation. We provide a comparison of the nomenclatures and lay a foundation for future European genomic surveillance of SARS-CoV-2.Peer reviewe

Single event effects in commercial memory devices in the space radiation environment

SIGLEAvailable from British Library Document Supply Centre-DSC:DXN008561 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Utilising the EyasSAT concept in space systems engineering courses at the University of Surrey

EyasSAT is a revolutionary concept in space systems engineering education. Up until now, space systems engineering has been typically conducted behind the cloak of clean rooms protecting intellectual property by a select few individuals with millions of dollars at stake. To the