New Prediction Software at Hx

Motivation

Solution

Results

Motivation

• We wanted to get a more software friendly system for our KHz system

• We needed better system for searching for lost satellites

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.• 1485 2 17.0216 284.1608 0.0300 0.0032 57071508.59-18000.55-0.0031 0.0025 …

• 1486 2 17.0516 284.1640 0.0300 0.0032 57053509.62-17997.87-0.0031 0.0025 …

• 1487 2 17.0816 284.1672 0.0300 0.0032 57035513.33-17995.19-0.0031 0.0025 …

• 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

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 8th 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.

1 30285.0000000000 30780.0000000000 30300.0000000000

4.375336089892557 -0.315196056410216 -0.001788076938903 0.000042357801743

0.000000145290622 -0.000000001750253 -0.000000000006689 0.000000000000036

1 30285.0000000000 30780.0000000000 30300.0000000000

7.723860586888546 0.022365268369107 -0.003156495704252 -0.000004068437809

0.000000218190605 0.000000000342339 -0.000000000006587 -0.000000000000021

1 30285.0000000000 30780.0000000000 30300.0000000000

8.165396657284129 0.141752580923960 -0.003339967617114 -0.000020409223048

0.000000223254579 0.000000001064295 -0.000000000005914 -0.000000000000039

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.

Results – typical Lageos scatter using old predictions

Typical Lageos residual scatter using new predictions

Larets residuals using old predictions

Larets residuals using new predictions

Topex residuals using old predictions

Topex residuals using new predictions

Short arc using different initial selections

• 9000 “lower” track only

• 9001 all data – old predictions

• 9002 all data – new predictions