Living Planet   

 

The GOCE End-To-End System Simulator

Dr Giuseppe Catastini(1), Dr Davide Andreis(2) , Dr S. Cesare(1) , Dr S. De Sanctis(1) , Dr M. Dumontel(1) , Dr Rune Floberghagen(3) , Dr Daniel Lamarre(3) , Dr M. Parisch(1) , Dr M. Saponara(1) , and Dr G. Sechi(1)

(1) Alenia Spazio SpA, Strada Antica di Collegno, 253, 10146 Torino, Italy
(2) Politecnico di Torino, Corso Duca degli Abruzzi, 24, 10129 Torino, Italy
(3) ESA-ESTEC, Keplerlaan 1, 2200 AG Noordwijk, Netherlands

Abstract

The idea of an end-to-end simulator was conceived in the early stages of the GOCE programme, as an essential tool for assessing the satellite system performance, that cannot be tested in its globality on the ground. The simulator in its present form is under development at Alenia Spazio for ESA since the beginning of Phase B and is being used for checking the consistency of the spacecraft and of the payload specifications with the overall system requirements, supporting trade-off, sensitivity and worst-case analyses, and preparing and testing the on-ground and in-flight calibration concepts. The software simulates the GOCE flight along an orbit resulting from the application of Earth's gravity field, non-conservative environmental disturbances (atmospheric drag, coupling with Earth's magnetic field, etc.) and control forces/torques. The drag free control forces as well as the attitude control torques are generated by the current design of the dedicated algorithms.

Realistic sensor models (Star Tracker, GPS receiver and gravity gradiometer) feed the control algorithms and the commanded forces are applied through realistic thruster and magnetic torquer models. The output of this stage of the simulator is a time series of Level-0 data, namely the gradiometer raw voltages, star tracker quaternions and spacecraft ancillary data. The next stage of the simulator transforms Level-0 data into Level-1b (gravity gradient tensor) data, by implementing the following steps:

- transformation of raw voltages of each pair of accelerometers, including phase and gain correction, into common and differential accelerations

- calibration of the common and differential accelerations

- application of the post-facto algorithm to estimate the GOCE angular velocity and attitude

- computation of the Level-1b gravity gradient tensor from calibrated accelerations and estimated angular velocity in the gradiometer reference frame;

- computation of the spectral density of the error of the tensor diagonal components (measured gravity gradient minus input gravity gradient) in order to evaluate the scientific performance, i.e. the error of gravity gradient and the spectral density of the tensor trace within the measurement bandwidth

- processing of GPS observation for orbit reconstruction within the required 10m accuracy and for gradiometer measurement geolocation.

The current version of the end-to-end simulator includes the outcome of the redesign activity started in July 2003, which yielded to the identification of a new set of actuators (ITA and MTR) and to a major redesign of the DFAC control law. The current simulation scenarios are mainly focusing on the gradiometer payload (in flight calibration manoeuvre, scientific telemetry-like output, basic gradiometer transition) and the simulator is undergoing detailed testing based on a time span of 30 days of simulated flight. The paper will describe the simulator's current status and will illustrate its capabilities for supporting the assessment of the quality of the scientific products resulting from the current spacecraft and payload design.

 

Workshop poster

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry

GOCE04