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PREDICT 2.2.x Release
======================
The major revisions in PREDICT 2.2.x include the use of
SGP4/SDP4 orbital models for improved tracking accuracy,
a re-written Single Satellite Tracking Mode to provide
more useful real-time satellite communications data,
and several new command-line options.

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 prior to version 2.2.x.  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 the time of closest approach.

The adoption of SGP4/SDP4 orbital models in PREDICT 2.2.x should
result in improved tracking and orbital prediction accuracy.
In benchmark testing, the SGP4 model has demonstrated an accuracy
of 0.1 degrees in both azimuth and elevation bearings using TLE
elements sets that are several days old.

PREDICT 2.2.x invokes the SGP4 model for near earth satellites having
orbital periods less than 225 minutes.  For deep space satellites
having orbital periods greater than 225 minutes, the SDP4 model
is used.


New Single Satellite Tracking Mode
==================================
The Single Satellite Tracking Mode has been completely revised
in PREDICT 2.2.x.  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.x is run, a transponder database file
(predict.db) is read by the program.  At present, the database
provides for many new features, some of which have not been
completely implemented by PREDICT in this early release of the
2.2.x series.  The most glaring omission is the 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 this
version of PREDICT, 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 selects 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
display screen is abbreviated accordingly.

Future versions of PREDICT will likely include a database editor
as well as possible modifications to the format of the database.


Other changes
=============
PREDICT contains code to control several different antenna rotator control
systems via the serial port.  HOWEVER, DOS lacks serial port drivers, so
these features probably will not work at the present time.

Despite the major revisions to the tracking code, all other program
functions, with the exception of the Single Satellite Tracking Mode,
should behave as they did in earlier versions.


--
John, KD2BD
November 2, 2002