12,165 research outputs found
LATOR Covariance Analysis
We present results from a covariance study for the proposed Laser Astrometric
Test of Relativity (LATOR) mission. This mission would send two
laser-transmitter spacecraft behind the Sun and measure the relative
gravitational light bending of their signals using a hundred-meter-baseline
optical interferometer to be constructed on the International Space Station. We
assume that each spacecraft is equipped with a drag-free system and assume
approximately one year of data. We conclude that the observations allow a
simultaneous determination of the orbit parameters of the spacecraft and of the
Parametrized Post-Newtonian (PPN) parameter with an uncertainty of
. We also find a determination of the
solar quadrupole moment, , as well as the first measurement of the
second-order post-PPN parameter to an accuracy of about .Comment: 9 pages, 3 figures. first revision: minor changes to results. Second
revision: additional discussion of orbit modelling and LATOR drag-free system
requirement feasibility. Added references to tables I and V (which list PPN
parameter uncertainties), removed word from sentence in Section III. 3rd
revision: removed 2 incorrect text fragments (referring to impact parameter
as distance of closest approach) and reference to upcoming publication of
ref. 2, removed spurious gamma from eq. 1 - Last error is still in cqg
published versio
GRAVSAT/GEOPAUSE covariance analysis including geopotential aliasing
A conventional covariance analysis for the GRAVSAT/GEOPAUSE mission is described in which the uncertainties of approximately 200 parameters, including the geopotential coefficients to degree and order 12, are estimated over three different tracking intervals. The estimated orbital uncertainties for both GRAVSAT and GEOPAUSE reach levels more accurate than presently available. The adjusted measurement bias errors approach the mission goal. Survey errors in the low centimeter range are achieved after ten days of tracking. The ability of the mission to obtain accuracies of geopotential terms to (12, 12) one to two orders of magnitude superior to present accuracy levels is clearly shown. A unique feature of this report is that the aliasing structure of this (12, 12) field is examined. It is shown that uncertainties for unadjusted terms to (12, 12) still exert a degrading effect upon the adjusted error of an arbitrarily selected term of lower degree and order. Finally, the distribution of the aliasing from the unestimated uncertainty of a particular high degree and order geopotential term upon the errors of all remaining adjusted terms is listed in detail
Long and short arc altitude determination for GEOS-C
The accuracy with which the GEOS-C altitude may be estimated over long (7 day) and short (40 minute) orbital arcs is investigated. Over the long are excellent agreement was attained between a simulation of the orbit determination process and a covariance analysis. Both approaches yielded RMS altitude errors of about 1.5 meters over the Caribbean calibration area and approximately 7.5 meters overall. The geopotential was identified as the largest error source. For the short arc, the covariance analysis revealed that the propagated altitude error is linearly dependent upon station survey component errors which are also the largest source of altitude errors. An Appendix contains the mathematics of covariance analysis as applied to orbit determination
Space shuttle navigation analysis. Volume 2: Baseline system navigation
Studies related to the baseline navigation system for the orbiter are presented. The baseline navigation system studies include a covariance analysis of the Inertial Measurement Unit calibration and alignment procedures, postflight IMU error recovery for the approach and landing phases, on-orbit calibration of IMU instrument biases, and a covariance analysis of entry and prelaunch navigation system performance
Covariance analysis of the airborne laser ranging system
The requirements and limitations of employing an airborne laser ranging system for detecting crustal shifts of the Earth within centimeters over a region of approximately 200 by 400 km are presented. The system consists of an aircraft which flies over a grid of ground deployed retroreflectors, making six passes over the grid at two different altitudes. The retroreflector baseline errors are assumed to result from measurement noise, a priori errors on the aircraft and retroreflector positions, tropospheric refraction, and sensor biases
Generalized Linear Covariance Analysis
We review and extend in two directions the results of prior work on generalized covariance analysis methods. This prior work allowed for partitioning of the state space into "solve-for" and "consider" parameters, allowed for differences between the formal values and the true values of the measurement noise, process noise, and a priori solve-for and consider covariances, and explicitly partitioned the errors into subspaces containing only the influence of the measurement noise, process noise, and a priori solve-for and consider covariances. In this work, we explicitly add sensitivity analysis to this prior work, and relax an implicit assumption that the batch estimator s anchor time occurs prior to the definitive span. We also apply the method to an integrated orbit and attitude problem, in which gyro and accelerometer errors, though not estimated, influence the orbit determination performance. We illustrate our results using two graphical presentations, which we call the "variance sandpile" and the "sensitivity mosaic," and we compare the linear covariance results to confidence intervals associated with ensemble statistics from a Monte Carlo analysis
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