IRS Orbit Determination Accuracy Improvement

  • PDF / 1,536,851 Bytes
  • 12 Pages / 496.063 x 722.835 pts Page_size
  • 34 Downloads / 209 Views

DOWNLOAD

REPORT


IRS Orbit Determination Accuracy Improvement' N. ~ Vlghnesanr', Anatta Sonney', and B. Subramanian" Abstract Orbit determination results are obtained for all IRS satellites by ISRO operational orbit determination software developed at ISRO Satellite Centre, Bangalore, using a batch leastsquares estimator to process S-band range and range rate measurements. The orbit solutions are obtained through estimation of ballistic coefficient in addition to orbital parameters. A noteworthy improvement in orbit determination accuracy is noticed through this method. The position and velocity errors are in the range of 50 m to 80 m and 5 cm/s to 8 cm/s respectively.

Introduction This paper assesses the IRS orbit determination accuracy of the S-band based orbit solutions. In the near future, ISRO plans to launch very low Earth orbiting satellites during very high solar activity periods. These are mainly dominated by atmospheric drag, which is the largest uncertainty in determining orbits of low altitude satellites. For precise orbit computation, it is mandatory to compute the acceleration due to aerodynamic drag more precisely along with other perturbing forces. The acceleration due to atmospheric drag is a function of drag coefficient, atmospheric density and spacecraft velocity relative to the atmosphere. The drag coefficient is difficult to evaluate as it depends upon the satellite shape, the nature of its surfaces and the projected area normal to the velocity vector. These three factors change with time. A rigorous study was already made on IRS orbit determination accuracy assessment based on operational estimated orbital parameters of IRS-Ie, IRS-ID, and IRS-P3 missions over long periods (6-12 months), in which the ballistic coefficient was not estimated and IRS-P4 was not studied [1]. The realized IRS orbit determination position accuracy and velocity accuracy were about 150 m and 10 cm/s respectively. In this paper orbit determination (OD) is carried out with estimation 'Presented as paper IAF-01.6.06 at the 52nd International Astronautical Congress, Toulouse, France, October 1-5, 2001. 2Engineer, Orbit Dynamics and Determination Section, Flight Dynamics Division, ISRO Satellite Centre, Bangalore, India. 3Engineer, Orbit Dynamics and Determination Section, Flight Dynamics Division, ISRO Satellite Centre, Bangalore, India.

355

356

Vighnesam, Sonney, and Subramanian

of the ballistic coefficient along with state parameters to obtain an appropriate value for the true drag acting on the satellite, as the OD process will absorb the density errors due to uncertainty in solar flux values and model errors, in the adjusted ballistic coefficient [2]. Drag coefficient estimation is presented in [3], [4], and [5]. In [3] and [4] the ballistic coefficient is estimated through IRS operational orbit determination software using range and Doppler measurements. The feasibility of orbit determination process using the MSIS-90 atmospheric density model along with estimation of the ballistic coefficient was demonstrated in [3] using IRS-

Data Loading...