Alex da Silva Curiel

Stand-alone spacecraft attitude determination using real flight GPS data from UOSAT-12

Abstract This paper presents the results of an experimental attitude determination system employing GPS (Global Positioning System), using phase difference data logged in orbit on the UoSAT-12 minisatellite, which was launched in 1999. The basics of GPS attitude determination are described, and two attitude determination algorithms are described and compared: one based on least squares estimation, and the other based on Kalman Filtering. The algorithm developed for resolving integer ambiguities in the carrier phase differences is tested to achieve instantaneous attitude from a set of only four measurements collected from two antenna baselines. A quaternion estimator based on a standard extended Kalman filter (qEKF) uses all GPS measurements to enable continued attitude determination taking into account the spacecraft dynamics. The attitude information derived from on-board magnetometers and a horizon sensor is used to evaluate the results of GPS attitude determination. Most recently, the LSQ attitude algorithms have been demonstrated in orbit and compared with the qEKF method.

Earthquake science research with a microsatellite

Reliable, repeatable earthquake forecast is a subject surrounded by controversy and scepticism. What is clear is that reliable forecast would be a critical tool for effective earthquake disaster management. It is proposed that satellites and ground–based facilities may detect earthquake precursors in the ionosphere a few hours or days before the main shock. A low–cost 100 kg class satellite carrying a topside sounder is proposed, to make systematic measurements over seismically active zones. The mission aims to confirm or refute the hypothesis of ionospheric earthquake precursors, define the reliability and reproducibility, and enable further scientific understanding of their mechanisms.

Second generation disaster-monitoring microsatellite platform

Abstract 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.

First Year in Orbit – Results from the Beijing-1 Operational High Resolution Small Satellite

The Beijing-1 high-resolution spacecraft was launched in late 2005, and since its launch, the spacecraft has been commissioned and has started routine operations. The small spacecraft represents the highest GSD achieved for any spacecraft of such mass and size, yet is designed as a tool to provide high duty cycle commercial operational services.

ALSAT-1 First Year in Orbit

The role of satellites in medium and high-resolution reconnaissance of the Earth has been well demonstrated in recent years through missions such as Landsat, SPOT, IKONOS, EROS, ImageSat and Quickbird. Medium resolution data products have added significantly to Earth science, but commercial markets have concentrated on enhancing resolution. The markets for such high-resolution data products are well served, and are likely to become more competitive with further planned high-resolution missions. The small satellite sector has concentrated on reducing the cost of specialised data products that are ill served by current missions, and on the development of systems providing niche services. One such area where smaller satellites can provide a distinct advantage is in meeting the needs for higher temporal resolution, as this typically requires multiple satellites to operate as a constellation. Such a system has been discussed widely in the disaster monitoring community, Surrey is currently engaged in launching its first constellation to provide daily global coverage at moderate resolution in three spectral bands, as part of a system to provide global disaster monitoring. The first spacecraft in this Disaster Monitoring Constellation (DMC), ALSAT-1, was launched in late 2002. The programme employs novel models for international collaboration, and demonstrates how small satellite missions can be employed in emerging applications. This paper provides an overview of the DMC programme, details the ALSAT-1 spacecraft and payload, and provides the first in-orbit mission results from ALSAT-1. The paper also addresses the future of the programme, and an update of the second DMC launch due in August 2003. The latest results of the 3rd DMC Consortium meeting will also be reviewed.