This chapter outlines the benefits of Galileo for future satellite missions. In this context, it will address the Galileo services, signals and frequencies. Further, aspects of interoperability with other GNSS and their potential impact on space applications will he discussed.

Oil layer and surface roughness of steel strip are measured on line with equipment that has been adapted to withstand the severe environment of a cold rolling mill. The system ensures the effective lubrication of the strip and it displays roughness data all along the coil. This makes it possible to optimize the rolling process on-line and it affords comprehensive information on the strip properties.

JAESat is a joint micro-satellite project between Queensland University of Technology (QUT), Australian Space Research Institute (ASRI) and other national and international partners including the Australian Cooperative Research Centre for Satellite Systems (CRCSS), Kayser-Threde GmbH, Aerospace Concepts and Auspace who will contribute to this project. The JAESat micro-satellite project is an educational and GNSS technology demonstration mission. The main objectives of the JAESat mission are the design and development of a micro-satellite in order to educate and train students and also to generate a platform in space for technology demonstration and conduction of research on a low-cost basis. The main payload on-board JAESat will be a GPS receiver called SPARx (SPace Applications Receiver), developed by the Queensland University of Technology for attitude and orbit determination. In addition to the GPS based attitude sensor, a star sensor will be on-board JAESat for attitude determination. JAESat will be three-axis stabilized based on a zero-momentum approach using magnetic coil actuators. This paper will outline the Attitude Control System (ACS) concept for JAESat including: subsystem configuration and components, performance requirements, control mode definition, attitude dynamic modeling, control law development, and attitude determination concept. Performance of the JAESat ACS is predicted via simulations using a comprehensive ACS model developed in Matlab Simulink.

JAESat is a joint micro-satellite project between Queensland University of Technology (QUT), Australian Space Research Institute (ASRI) and other national and international partners, i.e. Australian Cooperative Research Centre for Satellite Systems (CRCSS), Kayser-Threde GmbH, Aerospace Concepts and Auspace who contributed to this project. The JAESat project is conducted under the leadership of the Queensland University of Technology.The JAESat micro-satellite project is an educational and GNSS technology demonstration mission. The main objectives of the JAESat mission are the design and development of a micro satellite in order to educate and train students and also to generate a platform in space for technology demonstration and conduction of research on a low cost basis. The main payload onboard of JAESat will be a GPS receiver called SPARx (SPace Applications Receiver), developed by the Queensland University of Technology for Attitude and onboard Orbit determination. In addition to the GPS based attitude sensor, also a Star Sensor will be onboard of JAESat for attitude determination. This paper will outline the JAESat Orbit and Attitude Determination concept and discuss results based on conducted tests and simulations related to functionality and performance.

The Joint Australian Engineering Satellite (JaeSat) is a micro satellite being developed under the management of the Australian Space Research Institute (ASRI). However, currently a project management responsibility transfer from ASRI to the Queensland University of Technology (QUT) and a possible participation/cooperation from the Australian Cooperative Research Center (CRCSS) is under negotiation. JaeSat will be launched by a Ukraine rocket called Dnepr. The orbit will be a Low Earth Orbit (LEO) with an altitude of 800 km and an inclination around 98 deg. This paper will provide information about the QUT GPS receiver design characteristics with respect to software and hardware. The testing environment will be presented, which includes a GPS signal simulator and in-house custom designed software. Further, this paper will provide an outlook for future plans in order to implement additional features aiming for attitude determination based on GPS measurements.

The problem of dynamic orbit determination is that a batch estimator assumes use of sophisticated force and observation models, where tens of parameters are estimated to compensate the orbit and observation errors. In this paper, the short-arc batch estimation techniques are studied in order to achieve decimeter orbit accuracy over a few orbit periods. The technical basis and estimation strategies for the batch estimation will be outlined first. The results from a 24-hour data set collected from SAC-C mission have demonstrated that submetre 3D RMS orbit accuracy can be achieved with a 24h SAC-C data arc. With a data arc of 2-resolutions the batch estimation can achieve a 3D RMS orbit determination accuracy of 1.5m consistently with GPS carrier phase smoothed pseudoranges and broadcast GPS ephemerides. However, the results have also demonstrated the potential that further improvement towards data quality control could lead to 3D RMS orbit accuracy of 50cm with precise IGS GPS orbits and clocks. In general, the proposed orbit estimation strategies could lead to decemetre-level ground-based and onboard autonomous precise LEO orbit determination.

The Australian Federation Satellite, FedSat, was successfully launched into a 780-km low-earth orbit on 14 December 2002. Since then, the onboard Blackjack GPS receiver has operated on a duty cycle basis, providing effective data sets at an average of 10 to 15 minutes per orbit with its only aft-looking antenna, which views a field of two-third of the hemisphere. This paper presents the technical description of the FedSat Orbit Determination and Tracking (FODT) software, which is used to perform FedSat orbit filtering and prediction on daily basis. We present results from GPS flight data sets of two periods: the very first 24 hour data collected on Day 364/02 and the very first data sets of 5 consecutive days in March 2003. The analysis is focused on the evaluation of the FedSat flight GPS data quality and the accuracy of orbit propagation solutions currently achievable with the FODT software. The results from the two data periods have shown that the FODT derived FedSat orbits from code measurements can be propagated forward 72 and 96 hours with the maximal orbit errors of 120m and 240m respectively, which will satisfy the precise pointing requirement for Ka-Band tracking. In general, these preliminary FedSat orbit determination results are considered encouraging and promising, given consideration of rather harsh FedSat observational environment.

ABSTRACT

The European initiative for the provision of Radionavigation Satellite Services (RNSS) – GALILEO - will comprise all segments for an independent and fully operational infrastructure under civil control. Some of the signal transmissions will share carrier frequencies and some of the available spectrum with the USGPS system. Signals on common centre frequencies have been designed for functional inter- operability, making GPS and GALILEO two systems of the next generation infrastructure for Global Navigation Satellite Services. The GALILEO system architecture comprises a space segment, the associated ground segment for performance monitoring and satellite control and, last but not least, the User segment. This paper provides a general overview of the GALILEO architecture. The individual segments of the GALILEO architecture and their internal interaction are described. Finally, external interfaces to other systems for the provisioning of time as well as the boundaries of the GALILEO system are explained.

On 14th December 2002, the Australian small satellite FedSat was launched with a Japanese HII-A rocket into an 800 km sun-synchronous orbit with an inclination of 98.6 degrees. One of the payloads is a dual frequency GPS BlackJack receiver from NASA Jet Propulsion Laboratory (JPL). This receiver provides a Position, Velocity and Time (PVT) solution and also raw measurements (code and carrier), which will be used in different ways for Precise Orbit Determination (POD), Orbit Determination (OD) based on GPS position solutions, 2-axis Attitude Determination (AD) and atmospheric experiments.

The applications of GPS in space, such as orbit and attitude determination, offer several advantages, e.g. complete navigation information on board, low weight, volume and power consumption. GPS used for attitude determination in space has many important advantages like the fast and reliable initial acquisition, the resistance against high spin rates and the fact, that at least two satellites for deterministic attitude determination are visible for most of the duration of the mission. GPS could also be used as a safe mode sensor. Therefore GPS based attitude determination seems very promising. Due to the achievable accuracy, depending on the baseline length and the signal noise figure, a GPS attitude sensor cannot be used for missions were high accurate attitude measurements are needed and the baseline lengths are restricted. A particular field of interest is the broad and evolving area of earth observation missions and their corresponding requirements for a high position and attitude accuracy related to image processing. For these missions, a star sensor will be the adequate attitude sensor. Star sensors are highly accurate and well established algorithms are available. The disadvantages using star sensors are e.g. restricted field of view, operation only at low angular rates, sensor performance degradation and sensitive to problems related to star pattern recognition. Taking all these individual advantages and disadvantages into account, the combination of a GPS attitude sensor and a star sensor seems extremely promising, because such a sensor combination can be applied to a broad area of missions and their requirements of a high accurate attitude. The GPS attitude sensor aids the star sensor within the star pattern recognition process, resulting in improvement of accuracy and robustness with respect to the attitude solution. This can even be achieved in scenarios with high angular rates. Due to the fact that the star sensors used in this research did not support the input of reference attitude data for aiding, a software simulation approach was set up. GPS based attitude measurements are fed into the star sensor software model in order to increase the area of applicability.

The applications of GPS in space, such as orbit and attitude determination, offer several advantages, e.g. complete navigation information on board, low weight, volume and power consumption.

For future board autonomous navigation tasks, GPS offers the possibility to perform these tasks on board the user satellite with a single sensor, including the advantages of low weight and power consumption, small volume, complete navigation information on board and reduced ground operation costs. With the development of the algorithms for orbit and attitude determination and the receiver hardware, a great potential with significant influence on future missions and applications has arisen.Attitude determination using GPS carrier phase measurements relies on the interferometric principle. Hereby an ambiguity appears, corresponding to an integer number of carrier phase cycles of the received GPS signal. The resolution of this integer ambiguity is an important initialization process for attitude determination and serves as a starting point for further algorithms to calculate the attitude solution.This paper presents a new method for solving the cycle ambiguities, called the STAR-algorithm (Spherical Trigonometry Ambiguity Resolution). The STAR-algorithm relies purely on spherical trigonometry. Results of simulations and ground experiments have shown that it works very successful and robust.

The paper describes a simple and effective concept for aiding the signal acquisition of a GPS receiver in sounding rocket applications. A segmented, low-order polynomial representation of the nominal flight path is employed to provide the receiver with approximate position and velocity values of the host vehicle. These are used for an open-loop Doppler and visibility prediction, which in turn assists the channel allocation and code search. The proposed concept has been implemented in the 12-channel GPS Orion receiver, which employs Mitel's GP 2000 chipset and supports firmware modifications via the Architect developer kit. Using hardware-in-the-loop simulations in a GPS signal simulator testbed, the modified receiver's robustness against temporary signal losses has been demonstrated.

This paper presents results from theoretical investigations and experiments concerning the development of GPS an- tennas concepts in the context of the application of GPS on sounding rockets. The results are based on research activi- ties, which has been undertaken at the German Aerospace Center (DLR), the National Institute of Space Research of Brazil (INPE) and the Aerospace Technical Center of Bra- zil (CTA/IAE). The objective of the research activities from INPE and CTA/IAE were to obtain detailed perform- ance characteristics and design aspects for various possible antennas concepts directly linked to applications on Brazil- ian sounding rockets. The Germans DLR antenna experi- ment were performed in order to test a simple and low cost antenna concept, which was proposed by the Brazilian partners for a German GPS flight experiment on-board a Brazilian sounding rocket. This flight experiment was planned for the end of the year 2000 with the objective to track the trajectory of the sounding rocket based on GPS. Originally it was also planned to conduct this experiment on the Brazilian sounding rocket SV-40, but now the launcher is a VS30/Orion and the launch in spring 2001. The results of the DLR antennas experiment are based on the SV-40 as the launcher. A simple and low cost GPS an- tennas concept, based on only two off the shelf GPS an- tennas will be presented. Results for this GPS antennas concept and the related performance characteristics like satellite visibility will be discussed in detail. Further on, the observed problems will also be covered by the discus- sion.