Computer Science – Performance
Scientific paper
Jan 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002iaf..confe.497t&link_type=abstract
IAF abstracts, 34th COSPAR Scientific Assembly, The Second World Space Congress, held 10-19 October, 2002 in Houston, TX, USA.,
Computer Science
Performance
Scientific paper
The knowledge of the structural mass fraction (or the mass ratio) of a given stage, which affects the performance of a rocket, is essential for the analysis of new or upgraded launchers or stages, whose need is increased by the quick evolution of the space programs and by the necessity of their adaptation to the market needs. The availability of this highly scattered variable, ranging between 0.05 and 0.15, is of primary importance at the early steps of the preliminary design studies. At the start of the staging and performance studies, the lack of frozen weight data (to be obtained later on from propulsion, trajectory and sizing studies) leads to rely on rough estimates, generally derived from printed sources and adapted. When needed, a consolidation can be acquired trough a specific analysis activity involving several techniques and implying additional effort and time. The present empirical approach allows thus to get approximated values (i.e. not necessarily accurate or consistent), inducing some result inaccuracy as well as, consequently, difficulties of performance ranking for a multiple option analysis, and an increase of the processing duration. This forms a classical harsh fact of the preliminary design system studies, insufficiently discussed to date. It appears therefore highly desirable to have, for all the evaluation activities, a reliable, fast and easy-to-use weight or mass fraction prediction method. Additionally, the latter should allow for a pre selection of the alternative preliminary configurations, making possible a global system approach. For that purpose, an attempt at modeling has been undertaken, whose objective was the determination of a parametric formulation of the mass fraction, to be expressed from a limited number of parameters available at the early steps of the project. It is based on the innovative use of a statistical method applicable to a variable as a function of several independent parameters. A specific polynomial generator, validated on several technical and econometrical cases, has been used for this purpose. A database of several conventional stages, operated with either solid or liquid propellants, has been made up, in conjunction with an evolutionary set of geometrical, physical and functional parameters likely to contribute to the description of the mass fraction and presumably known at the early steps of the preliminary design. After several iterations aiming at selecting the most influential parameters, polynomial expressions of the mass fraction have been made up, associated to a confidence level. The outcome highlights the real possibility of a parametric formulation of the mass fraction for conventional stages on the basis of a limited number of descriptive parameters and with a high degree of accuracy, lower than 10%. The formulas have been later on tested on existing or preliminary stages not included in the initial database, for validation purposes. Their mass faction is assessed with a comparable accuracy. The polynomial generation method in use allows also for a search of the influence of each parameter. The devised method, suitable for the preliminary design phase, represents, compared to the classical empirical approach, a significant way of improvement of the mass fraction prediction. It enables a rapid dissemination of more accurate and consistent weight data estimates to support system studies. It makes also possible the upstream processing of the preliminary design tasks through a global system approach. This method, currently in the experimental phase, is already in use as a complementary means at the technical underdirectorate of CNES-DLA. * IRIS :Instrument de Recherche des Indices Structuraux
Balu A.
Taponier V.
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