IGS LEO operational requirements

For the time being, there will be nothing more on thsi page than some basic considerations on operational implications of LEO data. This is because the IGS LEO Pilot Project analysis is still in a very early stage, and no clear operational requirements can be defined yet. Even if the main recommendation of the Pilot Project would be not to proceed with operational use of LEO data in IGS processing, this page will accumulate findings from the Pilot Project that lead to such a conclusion. The nature of any conclusion coming from the Pilot project is that of a recommendation to the IGS Governing Board, who will take a decision on eventual operational use of LEO data on the basis of these recommendations, and any additional information that may be relevant at that time.

Operational use of LEO data
With 'operational use' is meant the routine processing of LEO data together with the land-based GPS tracking data by at least some of the IGS Analysis Centers. This typically requires some form of automation of the data flows and processing system to ensure product availability during out-of-office hours.

LEO data flow
In terms of LEO data processing, the input data flow will consist of GPS tracking data, provided by the LEO mission centre, and perhaps of additional products like precise reference orbits if these are not computed within the IGS routine processing. The possible data products are TBD, but for now the assumption is that the LEO data will be used in the context of normal IGS processing, without generating any new LEO-based products. If the usefulness of any particular LEO product can be demonstrated, such a new product may become part of the IGS product family after acceptance of such a proposal by the IGS Governing Board.

LEO mission centres
The LEO mission centers are the operators of the various LEO satellites. In the case of existing land-based IGS tracking stations, the entire set of IGS stations consists of sub-networks that are operated by a large number of independent organisations. The data from these IGS stations is collected and distributed through the IGS regional and global data centres. In the case of orbiting receivers, the GPS tracking data will typically be collected by the satellite operator during a telemetry and control pass over a master station. The actual collection and distribution of the LEO data is a matter of future concern, and will have to be defined in agreement with the LEO satellite operator. Some requirements with respect to data contents and latency will of course be necessary to ensure stable IGS operations, in a way not unlike the requirements that IGS sets for land-based tracking stations.
 
 
 

On the basis of experience with other new implementations of algorithms or data products, the IGS AC Coordinator has assessed that new processing features will only have a relevant impact on the final combination products if at least three of the six Analysis Centres would implement this new feature. In addition to this empirical requirement, the Pilot Project should consolidate certain minimum operational standards for the ACs that implement LEO data in their processing flow.
 
 
 

IGS LEO requirements 2.xx

Requirements and recommendations with respect to the LEO constellation

On the basis of Pilot Project findings, requirements should arise on the minimum LEO constellation that is of use to IGS routine processing. Some requirements coul relate to the LEO orbit itself, in particular related to orbit height, orbital inclination, mission duration and availability of alternative (non-GPS) tracking systems on board the LEO. None of these issues has so far been addressed in sufficient detail to formulate a practical requirement for operational use of LEO data.
 
 
 

IGS LEO requirements 3.xx

Requirements and recommendations with respect to the LEO orbit precision

With respect to the precision of the LEO antenna location, the Pilot Project should produce clear requirements in analogy to the requirements for land-based IGS stations. Other than just stating a positioning precision level - which is hard to verify in any case - it seems more useful to formulate the requirement in a sense that a error level of the LEO orbit should not occur for more than X percent of the time period covered by the LEO data.
 
 

IGS LEO requirements 4.xx

Requirements and recommendations with respect to the LEO data infrastructure

The infrastructure that is necessary to transfer the GPS flight receiver data from the LEO satellite to the IGS Analysis Centres will differ substantially from that of the land-based IGS stations. Requirements will have to be consolidated in terms of data quantity, quality and latency. these requirements may depend on the number of LEO satellites that are available simultaneously, as well as on their different orbital characteristics.
 

Further categories of requirements and recommendations may arise during the course of the IGS LEO Pilot Project.