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  • Onboard State vector accuracy improvement by segmentation of orbit for Mars Orbiter Mission

    Paper number

    IAC-13,C1,5,4,x18899

    Author

    Ms. Tintu Chacko, ISRO Satellite Centre (ISAC), India

    Coauthor

    Mrs. Bannihatti Parameshwarappa Dakshayani, ISRO Satellite Centre (ISAC), India

    Coauthor

    Dr. Narayanasetti Venkata Vighnesam, Indian Space Research Organization (ISRO), India

    Coauthor

    Mr. N.S. Gopinath, ISRO Satellite Centre (ISAC), India

    Coauthor

    Mr. M.Nageswara Rao, Indian Space Research Organization (ISRO), India

    Year

    2013

    Abstract
    Indian Space Research Organization is planning a mission to Mars in the near future with its launch vehicle  in October 2013. The objective of the mission is to demonstrate  the technology of reaching Mars,  exploration of Mars surface  and  its atmosphere.  Being the first Indian mission to Mars, the likely orbit for a less thermally complex spacecraft forgoing aerobraking for orbit insertion could be a highly eccentric orbit with apoareion height of 80000km and periareion height of 500km. Payloads are mounted along yaw axis of the spacecraft and  high gain antenna, mounted on roll axis of the spacecraft is used for communication with the ground. This necessitates pointing roll axis  towards Earth and yaw axis towards Mars for imaging. The computation of reference attitude of the spacecraft required for controlling the orientation of spacecraft needs orbit information onboard with a better  accuracy near periareion region than near apoareion region.  Two different approaches for onboard state vector generation is thought off, one based on  Chebyshev polynomial and the other with numerical integration (NI) of equation of motion with limited dynamical model. In Chebyshev’s approach, the state vector obtained from full force model is fitted with  Chebyshev polynomial series and  coefficients are uplinked. Using these uplinked coefficients, orbit is generated onboard by evaluating the Chebyshev polynomial series. High eccentricity of the orbit leads to unacceptable curve fitting error  in state vector  due to large variation of the orbit around periareion. An attempt is made to improve the accuracy  by splitting  orbit into two segments with a smaller segment around periareion and larger one around apoareion.  Curve fitting  accuracy realized with this is of 200mt around periareion and 12km around apoareion region over an orbit. In NI approach, state vector generation onboard is by integrating the equations of motion using numerical integration method with zonal and tesseral harmonics of order 4 by 4 using a Predictor-corrector and Runge-Kutta-Gill Integrator using uplinked initial state vector. Even in this approach, prediction error over an orbit is very high due to which   reinitializing the input to  NI  onboard with  one for periareion segment and the other for apoareion segment is done which  improved the position accuracy  from 80 km to 4 km around periareion and 35km around apoareion.  The study indicates segmentation of highly eccentric orbit is a must for better position accuracy onboard for either of polynomial  or by numerical integration approach.
    Abstract document

    IAC-13,C1,5,4,x18899.brief.pdf

    Manuscript document

    IAC-13,C1,5,4,x18899.pdf (🔒 authorized access only).

    To get the manuscript, please contact IAF Secretariat.