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NAPEOS (NAvigation Package for Earth Orbiting Satellites) is a portable navigation software for Earth Orbiting satellite missions. It provides orbit determination and prediction, manoeuvre optimization and global parameter estimation capabilities and is able to process a wide variety of observation data: angles, range, range-rate, altimetry, satellite-to-satellite links and GNSS data. The most widely used techniques at the Navigation Support Office are: GNSS (GPS, GLONASS and GIOVE), SLR and DORIS.

In the late 1990s, due to the growing number of on-going projects involving Earth satellite missions (ERS-1/2, Envisat …), with generically similar requirements on orbit determination, prediction and control, ESOC identified the need for a software package to cover all the upcoming missions. Therefore NAPEOS was thought to be a general-purpose software package to provide support for all phases of an Earth Orbiting Mission in terms of mission preparation and operational support for orbit determination, prediction and control. It has since become ESOC’s state-of-the art tool for high-precision orbit determination and proven to be capable of centimetre-accuracy orbit restitution.

The Navigation Support Office is currently using NAPEOS for all its operational systems with results comparable to other state-of the-art software packages for orbit determination and geodesy and with an extremely good performance in terms of computing speed. In particular, it is used as processing engine of the GRAS GSN system for EUMETSAT. It is also used for the generation of ESOC’s contributions as analysis centre to the International GNSS Service (IGS), the International DORIS Service (IDS) and the International Laser Ranging Service (ILRS). Moreover, it is widely used for dozens of analyses and projects involving GNSS, DORIS and SLR measurements due to its high flexibility.

Its performances have been validated against other software packages and are maintained through the use of several test cases, each one of them covering different features of the software (e.g., orbit estimation or propagation of LEO or MEO satellites). All of these test cases provide excellent results with respect to the state-of-art for this kind of processing.

NAPEOS is operated through an X-Windows graphical user interface and was initially developed for SUN client/server architecture running the Solaris operating system. However, over time it has been very successfully ported to several other architectures and UNIX-like operating systems (SUSE/Ubuntu Linux, Mac OS, Cygwin on Windows) and currently it is most commonly used under Linux for performance reasons. In order to achieve its objectives the NAPEOS software:
  • Implements all the knowledge on orbit determination and parameter estimation acquired up to now at ESOC in Earth Orbiting Missions (ERS-1, ERS-2, ENVISAT, GPS, GLONASS, GIOVE, Lageos, GOCE…)
  • Integrates a set of tools to provide operational support in terms of orbit determination and prediction satisfying a wide range of requirements and to compute very accurate orbits derived from different tracking system inputs separately or in combination (Satellite Laser Ranging, DORIS, GNSS and many others). It also provides the capability of simulating satellite tracking data in order to support the preparation of a new mission
  • Retrieves tracking data from external nodes, processes it, generates products derived from the orbit determination and prediction and transmits them to external nodes. All steps are executed automatically via a sequence of tasks defined by the user
  • Supports the user to define the input and output data to configure and validate a system for the different components in a friendly and structured way through a Graphical User Interface based on X-Windows
  • Allows potential software extensions to support other missions of interest to ESA without major redesign of the system. This is a very important requirement that has driven the architectural design of the system, because in order to attain it, both modularity and flexibility of the system have been encouraged
The processing option of GNSS pseudo-range and phase measurements was implemented in NAPEOS in 2002. It is able to handle GNSS measurements types either coming from ground-based receivers or from satellites carrying GNSS receivers, to use standard formats, to process GNSS pseudo-range and phase data, or single or double-differenced data from both single-frequency and geodetic class dual-frequency GNSS receivers. Continuous improvements of the GNSS processing part (computation load efficiency and versatility improvement, functionality extension for clock estimation/prediction, new solar radiation pressure models, standardisation of product formats, ambiguity fixing, normal equation stacking for coping with the ever-increasing number of stations and satellites) have taken place over the last few years. Enhancement and maintenance of the software have been performed either directly by ESOC or by industry through off-site contracts. In the field of GNSS processing, NAPEOS is very well suited for:
  • GNSS precise global estimation (station coordinates, earth rotation parameters, orbits and clocks of satellites and stations, ambiguities, troposphere). It can combine GPS, GLONASS and GIOVE (in the future GALILEO) data even for very large station networks (> 150 stations) very efficiently
  • Station precise point positioning, both static and kinematic, using as input precise information about satellite clocks and orbits
  • Low Earth orbit satellites precise orbit estimation