Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999aas...19411601t&link_type=abstract
American Astronomical Society Meeting 194, #116.01
Astronomy and Astrophysics
Astronomy
Scientific paper
We present results of our recent study of the issue of relativistic stellar aberration requirements for SIM in Earth-trailing orbit. In particular, we estimated the astrometric errors introduced by imperfect metrology, errors in baseline length estimations, and those due to the relativistic orbital motion. We have shown that motion of the spacecraft in the direction perpendicular to a tile of interest provides the most stringent requirement on the accuracy of knowledge of the barycentric velocity of the spacecraft: $sigma (2_alpha =) frac {sigma (2_{delta_ {c_0}}}{b^2 cos ^2(alpha )/(2)}+) (4 sigma (2_b)/(b^2) tan ^2(alpha )/(2)) +(4 sigma (2_v)/(c^2)) sin (2(alpha )/(2)) + frac {4 sigma_ {delta_ {c_0}}sigma_b }{b(2}) rho (c_0,b) (sin frac {alpha )/(2)}{cos (2(alpha )/(2)},) where \alpha, \sigma_\alpha is the angular separation between the stars of interest and corresponding error; b, \sigma_b is the interferometer's baseline length and corresponding error; c_0, \sigma_{\deltac_0} is the calibration term and corresponding error; v, \sigma_v is the velocity's magnitude and corresponding error; \rho(c_0,b) is a possible correlation between the calibration term and baseline estimations, |\rho(c_0,b)|\le 1. The maximicrons error in knowledge of the velocity's magnitude was obtained \sigma_v =3.9$ mm/s. It is expected that the unmodelled non-gravitational accelerations are a potential source of systematic errors. We estimated the magnitudes of non-gravitational forces acting on the spacecraft. In particular, we consider five sources of non-gravitational accelerations: (i) solar radiation and (ii) solar wind pressure, (iii) emitted radio power, (iv) anisotropic thermal radiation of the spacecraft, and (v) attitude motions. We evaluated these perturbing forces and show that their contribution, besides the solar radiation pressure, to the measurement error is negligible. There are few proposals that may minimize the impact of the solar radiation pressure and, therefore, improve the overall navigation accuracy: 1). on-board processing of data, as oppose to increasing the use of DSN time; 2). the use of a precisely positioned solar shade for maintaining constant solar pressure loading; and 3). velocity determination using integrated and time averaged accelerometers.
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