Microsatellite Platform Research Articles

Research on multi-system software GNSS receiver of micro-satellite

介绍了卫星导航信号的构成及传统GPS (全球定位系统) 接收机的工作原理, 并将近年来受到广泛关注的软件无线电技术引入到GNSS (全球卫星导航系统) 接收领域, 形成了一种多系统兼容, 高度灵活, 可升级的GNSS 接收机新架构. 给出了满足小卫星平台需求的FPGA + DSP 的数字处理模块硬件架构以及接收机的软件参考结构. 论述了多系统软件无线电GNSS 接收机在小卫星平台中应用时存在的优势和不足, 以及在星载一体化小卫星中的应用前景.

HIGH POINTING ACCURACY WITH THE PICARD MICRO SATELLITE.

PICARD is a major scientific mission leaded by CNES which will contribute, through the observation of the Sun, to the identification of the Sun influence of the global Earth climate changes. The PICARD Attitude and Orbit Control Subsystem, discussed in this paper, is developed for CNES by ALCATEL ALENIA SPACE.The PICARD platform including the AOCS is based on the MYRIADE micro-satellite platform developed by the CNES, with the necessary adaptations to cope with the very severe pointing and stability requirements imposed by the payload.With respect to the generic MYRIADE AOCS, a dedicated Fine Pointing Mode has been introduced in addition to the Normal Mode. This Fine Pointing is based on a Sun Ecartometry Sensor developed specifically for that purpose and installed within the payload. The 2-axes information of the SES are fused with the output of a “classical” autonomous Star Tracker for providing a 3-axes attitude introduced in the control algorithms.On top of the Fine Pointing Mode, the ultimate pointing performance of the payload line of sight is achieve through a dedicated high-frequency control stage part of the telescope itself. This control stage is based on sun image detectors integrated in the focal plane of the telescope and on local piezoelectric actuators which act directly on the telescope primary mirror.The paper will present first the scientific mission objectives and the AOCS architecture. It will then focus on the specific satellite Fine Pointing Mode developed for PICARD, with a fine presentation of the Sun Ecartometry Sensor and the required data processing algorithms. Finally it will present the high frequency upper control stage which is decoupled from the platform attitude control and is integrated to the payload telescope.

Design of a quadrafilar helix antenna used on Alsat-1 S band transmitter

Alsat-1 is an enhanced micro-satellite platform, increased in mass and capability from the standard spacecraft of recent years. Larger solar panels provide more power, and increased accuracy in attitude determination and control allow more demanding payloads to be accommodated. Alsat-1 has flown a 32 m ground sampling distance tri-band multi-spectral CCD linear array imager. This payload is supported by 1 Gbyte of onboard memory storage, and is able to image an area of up to 600 km × 300 km . This obviously requires a high data rate (8 Mbps) for the return radio link to a ground station, as it is able to download the entire data storage in a single pass. This paper examines low Earth orbit (LEO) antenna requirements and design in the context of a real system, the Surrey Satellite Technology Limited (SSTL) advanced micro-satellite platform and puts forward designs for optimised antenna to match the advanced capability of the enhanced micro-satellite platform, the quadrafilar helix to downlink information to the ground with a constant value of link margin.

TopSat: low cost high-resolution imagery from space

TopSat is a mission to demonstrate the use of small low-cost platforms for high-resolution imaging and direct data dissemination to local users via the use of a fully mobile ground station. The main elements of the TopSat system are described including the high-performance imaging system, microsatellite platform, data-handling/downlink and ground station that will be used. Finally, the current status of the programme as of January 2003 is summarised.

A microsatellite platform for hot spot dedection

The main payload of the BIRD micro-satellite is the newly developed hot spot recognition system. Its a dual-channel instrument for middle and thermal infrared imagery based on cooled MCT line detectors. The miniaturisation by integrated detector/cooler assemblies provides a highly efficient design. Since the launch in October 2001 from SHAR/India the BIRD payload, claiming 30% of the BIRD mass of 92 kg, is fully operational. Among others forest fires (Australia), volcanoes (Etna, Chile) and burning coal mines (China) have been detected and their parameters like size, temperature and energy release could be determined. As the status of the payload system is satisfactorily it has a potential to be applied in new missions with the help of modern detector technology.

Experimental Evaluation of the Micro-Tech.-Sensor for Attitude and Orbit Determination

In the frame of ESA's Technology Flight Opportunity the MTS-AOMS sensor for autonomous attitude and orbit determination of satellites was flown on the Italian microsatellite platform MITA (Melf and Manhart, 2000). The system is characterized by a beamsplitter, which provides two non-collinear lines-of-sight so as to be used in a “sextant-mode”. The detector is based on active pixel technology.Additionally, the unit flown included a Magnetic Field Sensor (MFS) as well as an Angular Rate Sensor (ARS) in such a way that the sensors complement each other to form a multifunctional micro-systems-technology device for an attitude and orbit measurement system. The paper is concerned with an initial evaluation of performance based on various algorithms and experiments.

Second generation disaster-monitoring microsatellite platform

Earth Observation satellites have traditionally been expensive to develop and launch and, as a consequence, have been targeted to cover the diverse needs of a large user community. Many niche applications in remote sensing are not exploited to their full potential or operating on a profitable basis and, as a result, space-based Earth Observation has not yet made a similar impact into our everyday lives when compared with satellite communications. Small satellite technology however has come of age and Earth observation instrument technology has advanced to levels permitting high quality sensors to be flown on small inexpensive satellite platforms. Many examples of such missions have returned increasingly sophisticated imagery and have been well documented. As well as offering in-orbit ‘shutter control’ to small groups and specialist organisations, these satellites can be individually tailored to specific applications with custom sensors, filters, swath width, and Ground Sampling Distance. Surrey Satellite Technology Ltd. (SSTL) has been at the forefront of developing innovative Earth Observation missions for the past decade, using small satellites covering a mass range of 5kg to 300kg. Recent missions have demonstrated remote inspection, high quality multispectral imaging at Ground Sampling Distances (GSD) of 30m and panchromatic imaging at a GSD of 10m. Currently a disaster-monitoring network of five microsatellites is under construction by SSTL within an international partnership to capitalise on these small satellite capabilities. It will offer a system with a temporal resolution of daily global coverage providing rapid multi-spectral imagery of wide-swath 30m GSD to the disaster relief community. In order to expand the capabilities of such a network, Surrey is now developing a follow-on network based on a second-generation spacecraft platform, and a small satellite platform has been developed specifically to meet generic small satellite Earth Observation applications as part of a constellation. It allows the visible-band imaging network under development to be expanded to serve more advanced applications within disaster monitoring with sensors such as IR, ocean colour, hyperspectral, high resolution imagery, and even Synthetic Aperture Radar.