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Published byReynaldo Setter Modified over 2 years ago

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New Prediction Software at Hx Motivation Solution Results

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Motivation We wanted to get a more software friendly system for our KHz system We needed better system for searching for lost satellites

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Current System Our current system produced a file with one record for each second containing Az, Azdot, El, Eldot, R,Rvel and Racc. The software then interpolated for given epochs … … … So for Lageos we need a file of 3600 records which we have to keep track of inside our KHz loop and read across a TCPIP link

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Solution Our first attempt at a solution was just to fit polynomial functions to Az, El and Range. This did not work very well at all. We then tried to fit a poly to x,y,z values. An 8 th order poly fitted very well to the low sats but not to Lageos and above. To get round this we did several poly fits to Higher sats.

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Being a small file it can quickly be read into system at the start of an observation. The downside to this method is that you have to convert from x,y,z to Az, El and range in real time. This in fact only takes a few microsecs. Point-ahead is obtained by getting Az El and range at any given epoch and at epoch + range. This also gives us an instantaneous value of Azdot and Eldot Comparisons showed agreement to a few seconds of arc and better than 2nsecs. For HEOs with more than one polynomial the data was also continuous from 1 poly to the next. We also include special polynomials for sun-avoidance.

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Results – typical Lageos scatter using old predictions

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Typical Lageos residual scatter using new predictions

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Larets residuals using old predictions

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Larets residuals using new predictions

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Topex residuals using old predictions

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Topex residuals using new predictions

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Short arc using different initial selections 9000 “lower” track only 9001 all data – old predictions 9002 all data – new predictions

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