Consolidated Prediction Format (CPF)
Prior to June 2008, the satellite laser ranging stations used the standard 'Tuned IRV' prediction format. This format consists of daily satellite state vector (x,y,and z positions and velocities at a given time plus other parameters) tuned to specific field integrator software and gravity field to provide maximum accuracy over the integration period. Lunar laser ranging stations have used multi-year ephemeris with lunar and planetary ephemeris software packages.
These procedures have worked well through the years, but new requirements make it necessary to update our prediction techniques. Remote receivers and transponders are now on the horizon for the moon, planets and extraterrestrial missions. Some of these will be launched with in the near future. Our current prediction format cannot accommodate this need. In addition, with the Galileo complex on the horizon and the possibility of more GPS satellites with retroreflectors, we must improve both day and nightime ranging to high satellites, which means improving our prediction capability. We must be looking toward range gate windows in the 1 - 10 nsec regimes.
The ILRS Predictions Formats Study Group has created a Consolidated Prediction Format (CPF) for laser ranging that will accurately predict positions and ranges for a much wider variety of laser ranging targets than had been previously possible. Rather than using the 'Tuned IRV's' with an integrator, the new predictions will provide daily tables of x,y, and z positions for each target that can be interpolated for very accurate predictions. There are four versions of the formats for (1) Earth-orbiting retroreflector satellites, (2) Lunar reflectors, (3) Asynchronous transponders, and Synchronous Transponders. The format also provides additional information on items such as 'leap seconds' that have historically caused operational confusion. Aside from the expanded format capability, the new prediction system should greatly improve tracking on low satellites because the full modeling potential of the orbit computation at the prediction center will be passed on to the stations. Drag files and special maneuver files will no longer be necessary.
At the ILRS Governing Board Meeting in Eastbourne in October, this new CPF Format was adopted for implementation into the ILRS network.
An explanation of the format can be found in the CPF Prediction Format document and appendices that include:
- Appendix A. Prediction Format
- Appendix B. Sample Prediction Configurations
- Appendix C. How to Create Condolidated Prediction Format Files: A Cookbook
- Appendix D. Consolidated Prediction Format User's Guide
- Appendix E. Maximum Prediction Grid Spacings
It may be helpful to review Appendices C and D prior to reading the material in Appendix A and B.
Sample software code will be available to accommodate all targets. Stations may choose to implement the most relevant sections first and add the others later as required. Using the sample code will save considerable time and avoid confusion. A page of errata is also available.
To avoid confusion, we plan to use a separate exploder for these predictions so that stations can subscribe to it only when they are ready to implement the CPF format.
For reference, CPF files can be found at:
The ILRS adopted this new format as of June 30, 2006 and discontinue the 'Tuned IRV' format thereafter. Stations were asked to implement the new format prior to that time; predictions centers were asked to implement the new format by February 1, 2006.