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With global mean sea level rising because of climate change, Copernicus Sentinel-6 is the radar altimetry reference mission to extend the legacy of sea-surface height measurements until at least 2030. The satellite carries a Poseidon-4 radar altimeter and a microwave radiometer. The analysis of the altimeter data relies on highly-accurate knowledge of the orbital position, in particular in the radial component, with errors below 1.5 cm. For this reason, Sentinel-6 carries several instruments, e.g. Laser Retroreflector Array, Doppler Orbitography and Radiopositioning Integrated By Satellite (DORIS) and also a GNSS receiver for generation of data, which allows to perform Precise Orbit Determination (POD) with the highest possible accuracy. Of particular interest for this paper is the GNSS receiver, because it is the first time that a high quality dual frequency Galileo/GPS receiver is flown on-board of a Sentinel satellite. ESA’s Navigation Support Office (NavSO), located at the European Space Operations Centre in Darmstadt, Germany is providing an independent Precise Orbit Determination solution for all Sentinel satellites. As part of this activity, the office has been operationally computing and delivering the POD products, including the Sentine-6 multi-GNSS-based precise orbits since its launch in November 2020. This presentation will describe the processing techniques adopted at the European Space Agency, with a particular focus on the POD aspects and the related processing of the Galileo and GPS observations. The latest results and their validation will be addressed in this context.

In early 2002 Queensland University of Technology (QUT) commenced to develop its own GPS receiver for space applications called SPARx (SPace Applications Receiver), such as sounding rockets and satellites in Low Earth Orbits. The QUT GPS receiver development is based on the Mitel GP2000 Chip set and is a modification of the Mitel Orion GPS receiver. The base for the software development is the Mitel GPS Architect development kit. In 2003 work was undertaken to extend the QUT GPS Receiver SPARx to have precise time synchronization capability. The software was improved to produce an accurate timing reference so that measurements and solutions time tagged to Co-ordinated Universal Time (UTC) may be obtained. In addition, work was undertaken so that the receiver has the ability to output a precise hardware time signal in the form of a pulse per second. This can be used as a time reference to synchronize the sub-systems onboard a satellite and provide precise timing for operations and measurements. This paper will discuss the implementation aspects of the pulse per second and synchronization issues, the high level concept and the results achieved. This work for time synchronization capability is also essential for the receiver’s use in 3-axis attitude determination based on GPS differential carrier phase measurements.

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.

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.

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.

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.

FedSat is the first satellite to be launched by Australia for 30 years. It is will be a scientific spacecraft with a number of experimental payloads. These payloads comprise of a single antenna GPS receiver, a 3-axis magnetometer, a Ka Band transponder and a re-configurable computing payload. It will be launched by Nasda on a H2A rocket as a piggyback payload with ADEOS-2. The GPS receiver is a NASA JPL designed "BlackJack" receiver, which was provided to the CRCSS by NASA. The high-level objectives, for the GPS receiver on the FedSat mission, are to provide an orbit determination capability and an attitude determination capability, whilst operating within strict power budget requirements. The current baseline is a total of 20 minutes of operation per 100 minute orbit. This paper presents the history of the attitude determination capability for FedSat, an outline of the antenna gain pattern tests performed for FedSat, a summary of results obtained to date, and recommendations for new approached to improve the performance of single antenna attitude determination systems.