PREDICT 2.2.0 Release ===================== The major revisions in PREDICT 2.2.0 include the use of SGP4/SDP4 orbital models for improved tracking accuracy, as well as a re-written Single Satellite Tracking Mode to provide more useful real-time satellite communications data. New Orbital Models ================== The simplified orbital model used in previous versions of PREDICT provided very accurate and dependable results for the majority of users, but was not quite good enough for more demanding applications at NASA. In July 2002, a test was performed on the accuracy of the orbital model used in PREDICT. The test was performed by a software engineer working at Edwards Airforce Base in California, and involved comparing data provided by PREDICT's Calc() and PreCalc() functions to that of a radar system used to track the International Space Station. Ranging data from the radar was taken every 50 milliseconds for the duration of the pass. The error in azimuth was found to be almost zero at AOS, and increased to 0.3 degrees over the duration of the pass. The elevation was about 0.2 degrees lower than that measured by radar for the entire pass. The calculated range was approximately 7000 meters low at AOS, and approximately 7000 meters high at LOS with a crossover at TCA. New Single Satellite Tracking Mode ================================== The Single Satellite Tracking Mode has been completely revised in PREDICT version 2.2.0. PREDICT now supports a database of satellite transponder data so that the program can provide path loss and Doppler-corrected uplink and downlink frequency information in real-time. For satellites containing linear transponders, uplink and downlink frequencies may be adjusted by pressing the '<' and '>' keys to tune down across the transponder in 1 kHz steps, or the ',' and '.' keys (unshifted '<' and '>') to tune in 100 Hz steps. Switching between transponders may be accomplished by pressing the SPACE bar. Eclipse depth, an angle representing how deep a satellite is in solar eclipse, is also provided. Eclipse depth is positive when the spacecraft is in eclipse, and negative when it is in sunlight. Spacecraft antenna squint angle is provided if ALAT/ALON (spacecraft attitude coordinates) parameters are included in the transponder database file. Transponder Database ==================== When PREDICT version 2.2.0 is initially run, a default transponder database file (predict.db) is copied into the user's $HOME/.predict directory. At present, the database provides for many new features, som of which have not been completely implemented by PREDICT in this early release of the 2.2.x run. The most glaring omission is lack of a facility to edit or modify the database file. For the time being, it may be edited by hand if care is excercised. The format for the database file is as follows. Using NOAA-17 as an example: NOAA-17 Name of satellite 27453 Object number (must match predict.tle) No alat/alon ALAT/ALON spacecraft attitude information APT Downlink Description of transmitter/transponder 0.0, 0.0 Uplink passband limits in MHz (0.0 = no uplink) 137.620, 137.620 Corresponding downlink passband limits (single downlink) No weekly schedule Days of the week this transponder is active No orbital schedule Orbital phase when this transponder is active HRPT Downlink Description of second transmitter/transponder 0.0, 0.0 Uplink passband limits (low end limit, high end) 1707.0, 1707.0 Corresponding downlink passband limits (single downlink) No weekly schedule Days of the week this transponder is active No orbital schedule Orbital phase when this transponder is active end End of data for this satellite OSCAR-29 contains linear (inverting) as well as digital (Pacsat) transponders: OSCAR-29 24278 No alat/alon Mode JA Transponder 145.900, 146.000 435.900, 435.800 No weekly schedule No orbital schedule Mode JD Channel A 145.850, 145.850 435.910, 435.910 No weekly schedule No orbital schedule Mode JD Channel B 145.870, 145.870 435.910, 435.910 No weekly schedule No orbital schedule Mode JD Channel C 145.910, 145.910 435.910, 435.910 No weekly schedule No orbital schedule end Weekly and orbital schedules have not yet been implemented in PREDICT 2.2.0, so for the time being, entries for these parameters should begin with the word "No". ALAT/ALON should be entered as 30.0, 0.0 for alat=30.0 and alon=0.0. See $HOME/.predict/predict.db for further examples. Entries in predict.db need not be in the same order as they appear in predict.tle. Satellite names need not match either, but the object numbers in predict.db must be correct. predict.db may contain more satellite entries than those appearing in predict.tle (normally 24). PREDICT reads the entire database file, and reads only the information that applies to the satellites in the predict.tle file in use at the time. If no transponder data is available, or if a satellite contains no communication transponders, the Single Satellite tracking mode screen is modified accordingly. Future revisions of PREDICT will likely include a database editor as well as possible modifications to the format of the database. Other changes ============= PREDICT now installs into a directory whose name includes the revision number (ie: predict-2.2.0). Despite the major revisions to the tracking code, all other program functions, with the exception of the Single Satellite Tracking Mode, should act as they did in earlier versions. -- John, KD2BD October 12, 2002