Seminar : Modeling atmospheric drag for space trajectories

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Grant Barnett
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1 Seminar : Modeling atmospheric drag for space trajectories Thursday, April 10th 2014 (09:00 17:30) Institut Aéronautique et Spatial (IAS) 23 Avenue Edouard Belin, Toulouse, cedex 4, France *** The seminar will first give an overview of the current models and hypotheses (atmospheric models, solar activity prediction, wind models etc) that are used and implemented for mission design and operations. The second part will present the more recent works in the field of atmospheric drag modeling for the computation of space trajectories, including the development of the DTM2013 atmospheric model. Dans une première partie, ce séminaire présentera les différents modèles d atmosphère qui existent, comment ils sont utilisés aujourd hui en mécanique spatiale, et leur impact sur les résultats. Dans un deuxième temps, les dernières recherches qui ont eu lieu sur le frottement atmosphérique seront présentées. En particulier, un nouveau modèle de thermosphère (DTM2013) qui a était développé récemment sera détaillé. For registration / pour inscription :

2 PROGRAM : 09h00-09h15 Welcome & Coffee I Modeling of atmospheric drag on current projects 09h15-09h20 Introduction 09h20-09h40 for mission analysis (C. Le Fèvre CNES) Summary of the available models for prediction of solar activity fand their use The various models of solar activity prediction available for mission analysis are summarized. Both cases of short and long terms prediction are discussed, as they concern different needs of mission analysis. 09h40-10h00 impact on orbital position (C. Le Fèvre CNES) Characterization of the errors of NOAA predictions of the solar activity and their The prediction of solar activity provided by NOAA, up to 45 days in the future, is usually used during operations at CNES in order to predict orbit ephemerids and plan orbit control maneuvers. The objective of the study is to assess the accuracy of such a method. The historical database of NOAA solar actiivty prediction is analysed and compared with the actual solar activity which has been measured afterwards. The effect of errors on orbital trajectories of typical orbits is then estimated. 10h00-10h20 The use of MSIS00 model in mission analysis (A. Lamy CNES) When you want to use an atmospheric model like MSIS2000 in the most "standard" way and even if you look at the available documentation, many practical questions arise, related to solar or geomagnetic activity or to the model itself: how do you interpolate solar or geomagnetic data, what data to feed the model with when dates are fractional numbers, what is the exact meaning of "daily ap", how do you compute an average over a time period when data are missing, how should you use the model when only predicted data are available... The presentation will show the "standard" we have come up with at CNES for mission analysis purposes. Practical implementation examples using scilab will also be presented. 10h20-10h40 Delmas CNES) Atmospheric drag on LEO satellites: origin and station keeping strategies (D. 10h40-11h00 Coffee break

Both cases of short and long terms prediction are discussed, as they concern different needs of mission analysis. 09h40-10h00 impact on orbital position (C.

3 11h00-11h20 The model HWM93 and its impact on orbits (V. Morand CNES) The HWM93 model provides zonal and meridional wind components at high altitudes. A parametrical study is carried out to estimate the effect of wind speeds on orbital trajectories for orbits which are usually used for space missions. The impact of these winds on the drag force and the relevance of using this model for mission analysis are discussed. 11h20-11h40 (D. Joalland Airbus DS) The use of atmospheric models for mission analysis in Airbus Defense & Space 11h40-12h00 Fontdecaba Thales Alenia Space) The use of atmospheric models for mission analysis in (J. 12h00-13h30 Lunch break II Advances on drag modeling 13h30-14h30 Determination of solar forcing for satellite drag specification (T. Dudok de Wit University, France) Changes in the solar radiative output in the ultraviolet (UV) are one the main causes of the variability of the thermospheric density. For that reason, the solar spectrum in the UV is a key input to satellite drag models. However, since no long records of well-calibrated UV spectra exist, proxies are often used instead, such as the radio flux at 10.7 cm. Here, we'll address several issues: - to what degree can proxies faithfully reproduce the variability in the thermospheric density? - which proxies are the most suitable for satellite drag modelling? - what strategies are there for improving the description of the solar forcing? 14h30-15h30 Bruinsma CNES,GRGS, France) The thermosphere model DTM2013 and the near-real-time version DTM_nrt (S. The DTM thermosphere model was updated in the framework of the FP7 project ATMOP using in particular high-resolution accelerometer inferred densities from CHAMP, GRACE and GOCE. Also a different solar proxy is used, namely the 30 cm solar radio flux instead of the well-known 10.7 cm flux. A new version of DTM was developed that uses daily temperature observations (derived from densities) and a neural network model to correct for model bias and predict densities out from hr, which are significantly more accurate than using DTM with predicted solar and geomagnetic indices. This model is a prototype for a nearreal-time model that uses densities inferred from radar tracking of spacecraft or

The impact of these winds on the drag force and the relevance of using this model for mission analysis are discussed. 11h20-11h40 (D.

4 debris, as is done in the HASDM (high accuracy satellite drag model) model of the US Space Command. 15h30-16h00 Coffee break 16h00-17h00 Modelling of satellite aerodynamics - computational approaches and practical implementations (E. Doornbos University of Delft, Netherlands) The aerodynamic force on a satellite in low Earth orbit, consisting mainly of drag, depends on the state of the atmosphere, the geometry of the satellite, its orientation with respect to the flow, and on the mode of interaction of the atmospheric gas particles with the satellite outer surfaces. Using these inputs, the aerodynamic force can be computed using free molecular flow aerodynamic theory. In reality, not all of the input parameters will be available. The presentation will cover the simplifications that can be made and their implications for practical applications. 17h00-17h30 Discussion & Conclusion

Doornbos University of Delft, Netherlands) The aerodynamic force on a satellite in low Earth orbit, consisting mainly of drag, depends on the state of the atmosphere, the geometry of the satellite,

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