Welcome to the Low Earth Orbiter Pilot Project of the International GPS Service. This homepage contains the terms of reference, which summarize the objectives of the Pilot Project. Links in the text lead to background information or status reports on various aspects of the Pilot project. Further links at the top of the page can be used for quick navigation through the site.  Via regular updates* this website intends to reflect the actual status of the IGS LEO Pilot Project. At completion of the Pilot Project, the information and analysis results collected here will form the basis for a final report to the IGS Governing Board. * Last update:   21 March 2003

IGS LEO terms of reference

Goals
The objectives of the IGS LEO Pilot Project are to

• Reach adequate understanding of potential benefits of LEO flight receiver data for IGS product generation and in support of research
• Develop the means that are necessary to reach this understanding
• Identify the requirements for eventual operational use of flight receiver data in routine IGS product generation

• Tracking geometry
• Atmospheric perturbations on the signal
• Data flow from receiver to IGS analysis center
• Flight-receiver data processing

• The capacity to include LEO data in off-line generation of IGS products
• The availability of precise LEO orbits and clocks, either in the form of fixed input products or computed simultaneously with the GPS orbits and clocks.

LEO Pilot Project Structure
A small number of analysis centers can generate IGS products for classical GPS precise orbit determination purposes, while another group of analysis centers can produce LEO orbits at precision levels that are necessary for the Pilot Project analysis. An overlap must be created between the available GPS and LEO expertise to facilitate the Pilot Project analysis. It seems unlikely that LEO centers would generate IGS products in support of the LEO Pilot Project, so that the overlap must essentially come from implementation of LEO processing capabilities at typical GPS centers (i.e. some of the IGS ACs or centers with similar capabilities). Still, the LEO centers play an important role in supporting this development by exchange of knowledge and by providing precise reference orbits and clocks. The LEO Pilot Project therefore includes the following organizational entities:

• Associated Analysis Centers that can produce IGS products and aim to implement LEO data analysis capability.
• Associated Analysis Centers that do not generate the classical IGS products, but can contribute valuable expertise in LEO data processing.
• Associate Analysis Center Coordinator to coordinate the analysis efforts.

• Orbit comparison campaigns for new LEO satellites. All AACs can take part in these campaigns.
• LEO orbit combination solutions and comparisons with all contributions

An orbit comparison campaign takes place as soon as possible after the release of the LEO data for general use. This moment depends on the LEO mission. The main campaign will take two to three months, but incidental later updates can still be included.
 
• Specific flight receiver data analysis projects, aimed at investigating a particular property of orbiting receiver data in comparison to terrestrial data. Those AACs that can produce the IGS products can contribute to these projects.

Specific analysis projects can initially be based on external LEO orbits and clocks, so that the involved Analysis Centers do not have to be capable of doing the LEO POD themselves. Participating Analysis Centers that contribute IGS products for analysis purposes are requested, where appropriate, to gradually implement LEO POD capability, and if possible in the form of simultaneous solutions for LEO and GPS satellites. The latter will be necessary to compare simultaneous solutions against solutions based on external LEO orbits and clocks, so that realistic recommendations can be made on eventual operational use of LEO data. Analysis projects will last three to six months, and can take place throughout the duration of the Pilot Project.

• Demonstrations of the impact of LEO data on classical IGS products. Two kinds of demonstrations will be necessary to address the following questions in final project findings:
o Does LEO data bring benefits to the outputs of an individual AAC, and if so in what manner?
o Does LEO data enhance the IGS combination products in some way?
Demonstrations will be organized towards the end of the Pilot Project. They are expected to have durations of several months for their preparation and execution.