IRIDFLAR v2.21 by Rob Matson - March 4, 2002
--------------------------------------------

IRIDFLAR is a PC DOS-based program that produces a chronologically sorted
list of all Iridium satellite flares visible from an observer's location
over a user-defined time period meeting all the user's constraints.
Constraints include:

     1.  Minimum satellite elevation angle
     2.  Maximum flare angle (the angle off-specular, a.k.a. the
         mirror angle)
     3.  Minimum flare brightnesses (day/night)
     4.  Flare source (sun/moon)


System requirements
-------------------

IRIDFLAR 2.21 has been compiled so that it will run on any PC with at
least an 80386 processor.  A coprocessor is not required, but it is
highly recommended due to the large number of computations that are
performed.


Inputs/Configuration File
-------------------------

All of the necessary control parameters for IRIDFLAR are stored in an
ASCII text configuration (.CFG) file that looks much like a Microsoft
Windows .INI file.  When you first start up IRIDFLAR, it reads all these
input parameters from the configuration file of your choice, and then
displays a Main Menu showing the current values for all parameters.
(There are a number of submenus as well).  Menu items are selected by
using the function keys at the top of your keyboard (e.g. F1, F2, etc.),
or single alphanumeric keystrokes.  When you exit the program, IRIDFLAR
will give you the option of updating your configuration file with your
final parameter values.

The default configuration file is "IRIDFLAR.CFG".  If this file is not
present at run time, the program will set its own default values.  If
you wish to run with a configuration file of another name, type that
name following IRIDFLAR at run time:

C:\ IRIDFLAR myfile.cf1

In the above example, if "myfile.cf1" is not found, the program will
behave the same as if IRIDFLAR.CFG was not found.  Note that when a
configuration file is named on the command line, that file (whether
it exists or not) becomes the default *output* file for storing
configuration parameters.  (As of version 1.5, you have the option of
changing the configuration output filename as often as you like, and
you can also exit the program without updating the configuration
file).

To save a few keystrokes, if your configuration file has an extension
of .CFG, you don't have to explicitly type the extension.  For example,
"IRIDFLAR fred.cfg" and "IRIDFLAR fred" are equivalent.  For upward
compatibility, IRIDFLAR version 2.2 will recognize and translate
version 1.x and 2.x configuration files.

Dates/times can be UTC or local time, controlled by a toggle in the
Date/Time menu.  North latitudes and east longitudes are positive;
south latitudes and west longitudes are negative.  Altitude and range
values can be in either metric or English units, controlled by a
toggle (U) in the Main Menu.


ANSI.SYS Driver
---------------

The ANSI.SYS device driver must be named in your CONFIG.SYS file in
order to correctly display IRIDFLAR's menus:

               DEVICE = [path\] ansi.sys

                         -or-

               DEVICEHIGH [path\] ansi.sys

For Windows 95, this driver is most likely located in the directory
C:\win95\command (or C:\windows\command), so the line in CONFIG.SYS
would read:

               DEVICEHIGH C:\win95\command\ansi.sys

For Windows NT users, the configuration file is called CONFIG.NT.  It
is not located in the root directory, but rather in a subdirectory
with a name like C:\WINNT\SYSTEM32\CONFIG.NT.  ANSI.SYS is located in
this same directory, so the line to be added would be:

               DEVICEHIGH C:\WINNT\SYSTEM32\ansi.sys

You can make the necessary changes to CONFIG.SYS or CONFIG.NT using the
DOS EDIT program, or a word processing program such as Microsoft Word
or WordPerfect.  If you use a word processor, be sure to save the file
in ASCII format.  Once CONFIG has been modified, you will need to reboot
your system for the change to take effect.


Two-Line Element (TLE) File
---------------------------

The input TLE file can contain just Iridium satellite elements, or any
superset containing the Iridium satellites of interest.  The program
automatically searches for all Iridium satellites in your TLE file.
This file can also have a header in it (e.g. MOLCZAN.TLE); IRIDFLAR
will read past it.

Since new Iridium satellites are periodically launched, a method for
identifying and processing these new satellites was added in version 1.3.
This way, a new version of the program does not need to be released
for each addition to the Iridium constellation.  To flag any new Iridium
satellites in your TLE file, make sure the format of the name lines is
"Iridium XXX ...", where XXX can be any three characters.  These
characters will appear under the "Ird" column of the output.

As of version 1.62 an Iridium status flag will be output if it appears
in the TLE file.  The four recognized status flags are: "man", "tum",
"att" and "?" and may appear anywhere on the satellite name line
following the Iridium number.  For example:

Iridium 9 tum
1 24838U 97030C   02061.19373096  .00054051  00000-0  19516-2 0  8427
2 24838  86.4379 140.3253 0064287 336.3493  23.4820 15.26290759250192
Iridium 86 ?
1 25528U 98066B   02062.23847178 -.00000128  00000-0 -34733-4 0  7154
2 25528  86.5221 164.0550 0002382  54.3770 305.7603 14.54873203176500

Status flags are abbreviated to one character in IRIDFLAR output:

     blank = operational satellite
     M = maneuvering satellite
     T = tumbling/spinning satellite
     A = attitude not accurately maintained
     ? = not at operational altitude; attitude may not be reliable

As of version 1.62, IRIDFLAR does not make predictions for any of the
15 Iridium satellites known to have failed or decayed.  As of March 4,
2002, these are Iridiums 914, 9, 911, 920, 921, 27, 44, 24, 48, 69,
71, 73, 79, 85 and 2.  (Iridiums 27, 48, 79 & 85 have reentered).  For
all other satellites, IRIDFLAR will make predictions, and display a
status flag if one exists.


Iridium 920 (#24871)
--------------------

Thanks to the observing efforts of Richard Keen, Terry Pundiak, Ed
Cannon, Frank Reed, Don Gardner, Richard McKee, Craig Cholar, Ralph
McConahy, Walter Nissen, Rick Baldridge, Jari, Jim Nix and myself, I
have been able to intermittently establish and monitor the rotation
axis for Iridium 920 (formerly Iridium 20).  In mid-1998, there were
enough observations to establish the coning angles for four specular
surfaces.  However, since then the axis has changed drastically.  In
1999, I calculated a new axis that agreed well with a dozen observa-
tions, but it has since diverged.  For this reason I have disabled
flash predictions for Iridium 920 as of version 1.7 until a new stable
spin axis has been identified.


Ambiguous Iridium Names
-----------------------

At times, USSPACECOM has had different (i.e. incorrect) common names
for a number of the Iridium satellites.  For example, Iridiums 9 and
10 were reversed, as were 18 and 20, 24 and 46, and 35 and 37.   To
avoid confusion with other satellite programs, IRIDFLAR no longer
attaches its own common name translations to the 5-digit catalogue
numbers.  Instead, when there is a conflict IRIDFLAR will issue a
warning, but it will retain whatever Iridium number appears in the
TLE file.


Output
------

Output is to the screen and optionally to a disk file.  For each flare,
either one or three lines are generated depending on a user-set parameter.
In the 3-line mode, the first and third lines are the approximate times
that all constraints are first met and last met respectively.  The
second line in each triplet is the time of minimum flare angle and maximum
brightness.  In single-line mode, only the peak of each flare is output
to screen and disk.
 

Screen Output
-------------

There are 15 values on each screen output line.  From left to right,
these are:

 1. Iridium satellite number (or 3-character code -- see paragraph above)
 2. Iridium status flag (M, T, A, ?, or blank)
 3. Date in YYYY-MM-DD format (new 4-digit year in version 1.7).  Date is
    UTC or local depending on user input
 4. 24-hour time.  UTC or local, just as for date.
 5. Satellite azimuth in degrees, measured clockwise from north; east=90.
 6. Satellite elevation angle in degrees (a.k.a. altitude angle)
 7. Satellite range (in km or miles, depending on choice of units)
 8. Node (A=Ascending, D=Descending)
 9. Satellite illumination condition.  Lit=Sunlit, Pnb=Penumbra (sun
    has partially set as seen by satellite), or Lun=Moonlit but not
    sunlit.
10. Elevation of sun at observer's site (in degrees).  Negative when sun
    is below the horizon.
11. MMA (Main Mission Antenna) causing the flare.  Code: F=forward,
    L=left, R=right, or S=solar panel (NEW! in v2.2).
12. Flare angle (degrees).  This tells you how close the geometry is to
    satisfying a perfect specular reflection.  Any angle less than 0.25
    degrees leads to a direct reflection of some portion of the solar
    disk (or lunar disk, as of version 2.0).  However, flares can still
    be seen when the flare angle is greater than 0.25 due to diffraction,
    atmospheric turbulence, and antenna surface contamination and
    imperfections.  Flare brightness falls off quickly with increasing
    flare angle; as a rule of thumb, the flare angle needs to be less
    than 2 degrees for an MMA flare to reach 1st magnitude or brighter.
13. Visual magnitude.  This is a rough estimate of the flare visual
    magnitude based on the flare angle, the projected area of the
    antenna producing the reflection, and the satellite range.  For
    lunar flares, the magnitude estimate also takes the lunar phase
    into consideration.  In version 2.2, solar panel flare modeling
    was also added; the magnitude estimates for solar panel flares will
    not be as accurate due to looser tolerances on (and hence knowledge
    of) the solar panel pointing direction.
14. Flare latitude (degrees).  The geodetic latitude of the current
    point on the earth that has a flare angle of exactly zero.
15. Flare longitude (degrees; negative is west, positive is east).
    The instantaneous longitude of the center of the flare.

The flare latitude and longitude tell you where the maximum flare is
occurring at that time.  As of version 1.52, the flare lat/long for
the middle line of each triplet is replaced with the ground distance
and bearing to the point on the flare centerline closest to your
location.  This tells you how far you need to drive in order to see
the maximum flare.  (Bearing is always output as east or west,
although for locations at very high latitudes the actual bearing
will have a significant north or south component.)

While IRIDFLAR is calculating and displaying acceptable flares, you
can pause your display by hitting the space bar.  (Hit any key to
resume calculating).  The escape key can be used to terminate a
flare search in progress.


Verbose File Output
-------------------

If you elect to produce an output file (in addition to the screen
output), then columns will also appear for the satellite right
ascension and declination, solar azimuth angle, flare peak magnitude
and flare standard magnitude.


Peak Magnitude and Standard Magnitude
-------------------------------------

In the "verbose" file output, the flare magnitude is immediately
followed by the peak magnitude and standard magnitude.  The peak
magnitude is an estimate of what the flare magnitude would be if you
were located at the coordinates listed for the flare latitude and
longitude (14. and 15. in the screen output).  From this location,
the mirror angle is zero, and the MMA (or solar panels) reflect
the exact center of the sun (i.e. the brightest part of the sun).

The standard magnitude is only of use to modelers who are interested
in better defining the relationship between flare intensity and mirror
angle.  It does this by eliminating the two other variables that affect
flare brightness:  satellite range and MMA/solar-panel projected area.
The standard magnitude indicates what the flare visual magnitude would
have been if the satellite was at a range of 1000 km, and the MMA
causing the flare was perpendicular to the observer-satellite vector.
The standard magnitude can differ significantly from the regular
magnitude when the satellite is either low in the sky (i.e. at long
range), or at a poor phase angle (MMA viewed edge-on), or a combination
of both.


Abbreviated File Output
-----------------------

The "brief" format has fewer output values (RA, Dec, flare angle, peak
magnitude and standard magnitude are omitted), fewer digits of
precision, and more spacing between some columns for better readability.
This format is intended for the more casual observer and was changed
slightly in version 1.7 to make room for a 4-digit year.  An example
appears below:

       Local     Local    Iridium         Sun    Flare   Maximum Flare  Ird
Day    Date      Time   Azm El Rnge N I Azm Elv MMA Mag Latit.  Longit.  #  S
-----------------------------------------------------------------------------
Sat 2000- 1- 1 17:39:35 062 66  527 A L 249  -8  L   3  33.035 -117.845 70   
Sat 2000- 1- 1 17:39:48 050 63  540 A L 249  -8  L  -2     12.2 mi E    70   
Sat 2000- 1- 1 17:40:00 041 59  557 A L 249  -8  L   3  34.450 -117.936 70   


Satellite Orientation Errors
----------------------------

Paul Maley of NASA Johnson Space Center has reported that once each
Iridium satellite reaches its parking orbit, its orientation relative
to its velocity vector is maintained to within +/- 0.5 degrees in pitch,
+/- 0.4 degrees in roll and +/- 0.5 degrees in yaw.  If orientation
errors conspire in a worst-case fashion, the minimum flare angle
(a.k.a. mirror angle) for a particular pass can increase by as much
as 1.4 degrees (two times the rss of 0.5 and 0.5).  This could change
the brightness of a best-case pass by almost 7 visual magnitudes (chang-
ing flare angle from 0 to 1.4).  The effect is not as severe for larger
flare angles; for example, a change from 1.0 deg to 2.4 decreases the
theoretical brightness by only 2.3 visual magnitudes.

Since the satellite orientation errors cannot be known apriori, it is
not possible to reliably predict which flares will be absolute "show
stoppers."  Of course, orientation errors can work for or against you.
A predicted flare angle of 1.5 degrees could conceivably be improved
to 0.1 degrees, transforming a medium brightness flare into a -8
magnitude searchlight!


Anomalous Satellites
--------------------

As of March 4, 2002, 15 satellites out of 95 that have been launched
have either failed or decayed:  Iridiums 2, 9, 911, 914, 920, 921,
24, 27, 44, 48, 69, 71, 73, 79, and 85.  Since their orientations are
not maintained, and a stable orientation is necessary in order to
predict flares, I've removed these satellites from the prediction list.

Attempts have been made at establishing rotation axes for the tumbling
Iridiums so that their flashes can be predicted.  In 1998 and some of
1999, Iridium 920 (formerly Iridium 20) maintained a somewhat stable
spin axis which allowed flash predictions.  Alas, it has since diverged
and a new axis has not been identified.  Flash data has been analyzed
for Iridiums 911, 914, 24 and 27, and so far none has exhibited a
sufficiently stable spin axis.

Additional Iridium satellites have occasionally had orientation errors
exceeding the usual limits, causing erratic flare behavior.  For
example, Iridiums 5, 36 and 46 have gone through such phases.


Questions
---------

Questions or problems can be e-mailed to matsonr@saic.com.


Internal Modeling Details
-------------------------

Orbital propagator:  SGP4
Earth geoid:  WGS-84
Earth equatorial radius:  6378.137 km
RA/Dec equinox:  Equinox of date
Refraction at ground site:  Included
Refraction at satellite:  Included


Revision History
----------------

Version 2.21 (March 2002)
-------------------------

Internal Iridium names updated (added newly launched Iridium
satellites 90, 91, 94, 95 and 96, and removed decayed satellite
Iridium 27).

Fixed command-line parameter passing of configuration file so that
it doesn't delete the first character of the filename under
Windows 2000.


Version 2.2 (June 2001)
-----------------------

Added Iridium solar panel articulation model and code to predict
when solar panel flares are possible.  Preliminary observational
data used to calibrate solar panel flare brightness vs. off-axis
angle.  Toggle added to Main Menu to turn solar panel flare
modeling on or off.

Predictions no longer done for failed satellites Iridium 2 (#25527),
Iridium 9 (#24838), Iridium 69 (#25319) and Iridium 73 (#25344),
bringing the total to 15.


Version 2.1
-----------

Internal Iridium names updated (e.g. 911, 914, 920 and 921).

Verbose 1-line mode has been missing the 4th decimal place of the
latitude in the output file for some time.  Bug fixed.

To avoid confusion, the flare coordinates output are now always the
instantaneous ground coordinates of the flare center.  In prior
versions, the flare coordinates for the peak line were replaced with
the flare centerline coordinates closest to the observer.  The
difference is minor for bright flares at most latitudes, but for dim
flares at high latitudes, the difference is quite noticeable and the
program output is confusing.  The source of the confusion in these
cases is that the nearest point on the flare centerline is so far
away that the peak flare there occurs at a quite different time
than the peak at the observer's location.


Version 2.0
-----------

Lunar flare prediction added to IRIDFLAR.  A toggle has been added to
the Main Menu (S, for Source) to select either the sun or the moon
as the flare source.  For lunar flares, IRIDFLAR requires that the
sun also be blocked by the earth.  (Diffuse solar reflection by
Iridium is brighter than the brightest lunar specular reflection).
You will need binoculars or a telescope to see lunar flares.


Version 1.7
-----------

Numerical rounding produced flare azimuth angles of 360 whenever
the flare azimuth was greater than 359.5.  Program has been changed
to display 0 instead of 360.

Year expanded from two digits to four, principally to avoid date
sorting problems at century year transitions.

Per Jay Respler's suggestion, flare MMA and magnitude columns have
been swapped in the Brief File output to help avoid confusion between
solar elevation angle and visual magnitude.

Predictions no longer done for failed satellites Iridium 48 (#25107)
and Iridium 85 (#25529), bringing the total to 11.

Flash predictions for Iridium 20 disabled until a new spin axis can
be determined.


Version 1.65
------------

The switch to 3-character Iridium names (e.g. Iridium 11A) introduced
a chronological sorting bug in the output file for satellites with
status flags (e.g. Iridium 73 man, Iridium 2 ?).  Bug fixed.


Version 1.64
------------

In 3-line mode, replaced flare centerline coordinates on line 2 of
Brief file output with bearing information.  (Coordinates are also
replaced with bearing in 1-line mode).  Removed flare angle from
Brief file output.

Added a third column for the Iridium common name to accommodate
replacement satellites (e.g. Iridium 11A and 20A).

Added internal naming for launches of Iridiums 2, 3, 76, 77, 79-86,
11A and 20A.

All internal satellite names (used only for screen warnings) have
been changed to match the information provided by Motorola.  This
entailed swapping the names of Iridium 24/46 and 35/37, and correcting
Iridiums 50, 52, 53 and 54.

Only two specular surfaces now modeled for Iridium 20, identified as
'1' and '2' in the MMA column.

Predictions are no longer done for the failed satellites Iridium 14
(#24836), Iridium 44 (#25078), Iridium 71 (#25320) and Iridium 79
(#25470).

Start times can now be entered with colon delimiters or period
delimiters (e.g. 20:30 or 20.30).  Allowing periods is helpful
since the shift key isn't needed, and there is a period on the
numeric keypad.


Version 1.63
------------

Rotation axis improved for Iridium 20, and modeling added for one of
the solar panels.


Version 1.62
------------

Flash predictions now performed for the spinning satellite Iridium 20
(#24871).

To avoid confusion with other programs, Iridium numbers are no longer
changed internally.  For example, if a TLE file incorrectly has NORAD
#24871 listed as Iridium 18, the program will no longer switch it to
its correct name of Iridium 20.  Instead, a warning will be displayed
and the erroneous name maintained.

Added Iridium status flag to output based on Mike McCants' codes that
appear in IRIDIUM.TLE.  Flag codes are: M (maneuvering), T (tumbling),
A (attitude problem), and ? (non-operational altitude).

Predictions are no longer done for the failed satellites Iridium 11
(#24842) and Iridium 24 (#25105).

Added internal naming for Long March launch of 69 and 71, and May 17th
Delta 2 launch of Iridium 70 and 72-75.

For single-line mode, added a blank line between flares on different
days.

Additional bad element set detection added to trap outdated TLEs of
decayed satellites that contain "Iridium" in their name.

Added the site name to the header of the output file, and a dashed line
at the end of the file.


Version 1.61
------------

Fixed day-of-week and date bugs in brief file output (Tuesday was
corrupted, and dates were bad for single-line mode).


Version 1.6
-----------

Day of the week added to the brief file output.

Configuration files can now be loaded from within IRIDFLAR using the
"L" key in the Main Menu.  The number of lines per flare (1 or 3) is
now controlled with the "N" key instead of "L".

Toggle added to Main Menu to switch between metric and English units.
The parameters affected are the site altitude, satellite range and
maximum flare ground-point range.

Corrected internal naming of NORAD #25170 from Iridium 51 to 56.  Added
internal naming for recent launches of 51, 55, and 57-68.  Based on
new information from Motorola via Dr. T.S. Kelso, it appears that the
names Iridium 9 and 10 are swapped.  I have changed the internal hard-
coding so that Iridium 9 is #24838 and Iridium 10 is #24839.  Similarly,
the reported Iridium numbers corresponding to #'s 25169-25173 have
changed at least twice.  As of April 20 they are named Iridium 50, 56,
52, 53, and 54 respectively.

Predictions no longer done for Iridium 21 (#24873).

Some users have found ftp sites that provide Iridium two-line element
sets that have an extra linefeed following the end of each line
(<CR><LF><LF>).  Worse, this fact may be transparent to the user
unless he/she happens to open the file in a word processor.  Earlier
versions of IRIDFLAR would parse such files as being filled with
comments, and thus no predictions would be made.  Version 1.6 now
checks for the extra linefeed, and displays a warning if any are
found.

In 1.52, if a flare's brightest point was cutoff by either the minimum
elevation constraint or maximum mirror angle, then the program would
be missing a reference ground point from which to compute the bearing
to the maximum flare point.  This could lead to a fatal division by
zero error in some cases, or blank values for the bearing in others.
Additional program logic has been added to handle this case.

V1.52 failed to check for the existence of the TLE file unless its name
was changed.  This caused a fatal error when attempting to compute
flares (since the TLE file could not be opened.)  TLE file existence is
now verified before computing flares.


Version 1.52
------------

Configuration file format changed to be more consistent with Windows
.INI files and SkyMap configuration files.  Program now reads parameters
from [IRIDFLAR] section of configuration file, and ignores any other
sections that may be present.  This allows users to add comments at
the beginning of their configuration files, or combine configuration
sections used by multiple programs.

Automatic recognition and translation of version 1.51, 1.5 and 1.4
configuration files.  If configuration file is not found or not
recognized, IRIDFLAR will ask for your latitude, longitude and time
zone hour, set the start date and time to match your computer's
current date and time (truncated hour), and set reasonable default
values for all remaining parameters.

Added City file support (a la SkyMap), so you can enter your site
name rather than coordinates, assuming it's in SKYMAP.CTY (or
whatever City File name you use.)

Batch-run support added.  If the line "Batch=Yes" appears in your
configuration file, then IRIDFLAR will use the settings that appear
in that file, calculate once, and exit.  In essence, the results
are the same as if you had run IRIDFLAR with that configuration
file, typed the <F10> key to calculate, and then hit the <ESC> key
to exit.

Ground distance and bearing (east/west) to the flare peak added.

Predicted flare magnitude equation modified slightly to better match
observed flares.  Version 1.52 now predicts brighter flares than
earlier versions when the mirror angle is greater than 0.25 degrees.

Better filtering of non-Iridium satellites.  Calculations will NOT
be performed for Iridium 27, Iridium Sim1, Iridium Sim2, or any
satellite whose name starts with "Iridium" but later contains a
slash.  (This eliminates unwanted predictions for Iridium rocket
bodies).

Previously, the ground coordinates given for each flare peak represented
"instantaneous flare ground-zero."  However, this is not quite the same
as the point along the flare-line *closest* to the observer.  The latter
is the more useful, since it tells you the minimum distance you need to
move in order to see the maximum flare.  (For most latitudes, this point
will be nearly due east or due west of your location).  So version 1.52
now calculates this point.  (Note that when displaying three lines per
flare, the first and third lines are still the instantaneous ground
flare point.  Only the middle line is the *closest* flare point to the
observer.)

Maximum mirror angle limit extended from 15 degrees to 30 degrees.

Minor output heading change ("FlrAng" replaced with "Flare" above
"Angle").


Version 1.51 (beta release only)
--------------------------------

Automatic recognition and translation of version 1.4 configuration
files.

Flag added to Date/Time Menu which, when set, will automatically load
the current date as the start date at initial run time.


Version 1.5 (beta release only)
-------------------------------

Maximum sun elevation parameter replaced by a sun-elevation day/night
transition point.  For passes that occur when the sun is LOWER than
this elevation, the program will filter out flares dimmer than the
nighttime magnitude limit.  For passes occurring when the sun is
HIGHER than the transition angle, the daytime flare magnitude limit
will be used.  For example, if you set the angle to -7 degrees, your
daytime flare magnitude limit to -4 and your nighttime magnitude
limit to +2, the program will find all flares brighter than mag -4,
and any flares brighter than 2nd magnitude when the sun is more than
7 degrees below the horizon.

Sequential input of user parameters replaced with menu interface.

Separate visual magnitude filters for daytime and nighttime passes.

Program modified to allow for the possibility of more than one flare
on a given pass (e.g. separate flares from the forward and left MMAs).

Predictions no longer made for Iridium 27 (#24947).


Version 1.4
-----------

Minimum brightness visual magnitude filter added.

Federico Casazza discovered a bug which causes IRIDFLAR to get caught
in an endless loop if a satellite happens to enter the earth's umbra
shortly after a flare peak (and while still above the observer's
horizon).  This bug can also cause IRIDFLAR to miss flares under
other special circumstances.  Bug has been found and fixed.

Solar azimuth added to file output.

Peak magnitude added to screen output and verbose file output.

Standard magnitude removed from screen output; only appears now in
verbose file output.

Headers to output file have been expanded for easier understanding.

Minor bug fixed in the brief file output when "Does not intersect"
is supposed to appear.  Now replaced with "No intersection".

If seconds portion of time is less than 10, is padded with zero.

Magnitudes reported in brief-format output file now rounded to the
nearest integer magnitude (instead of truncated).

Formula for predicted magnitude versus mirror angle has been modified
slightly based on observed flare magnitudes.  Also, IRIDFLAR now
accurately models the radiance distribution of the solar disk (i.e.,
the center of the disk is brighter than the limb).  This causes
predicted flare magnitudes to continue to brighten as the flare
angle drops below 0.25 degrees.


Version 1.31
------------

Incorrect MMA identified in output.  Bug fixed.
Hard-coding of Iridium 42 name changed to Iridium 43.


Version 1.3
-----------

Method added for recognizing new Iridium satellites (see above).

Option added for (V)erbose or (B)rief output file format.

Option added for outputting 3 lines per flare or just the peaks.

Standard magnitude (1000-km range, square-on viewing) now calculated
to assist in refining the relationship between mirror angle and
visual magnitude.

Specific MMA causing each flare is now output under column "M".  The
codes are F-forward, L-left and R-right.  Directions are relative
to a "passenger" on the satellite facing in the direction of motion.

Special handling added for Iridium 11.

TLE file kept open only when running predictions (not while entering
parameters).  File-sharing of TLE file, configuration file and output
file now permitted (for multi-tasking environments).


Version 1.2
-----------

Added the maximum flare brightness location (latitude and longitude).

Eliminated screen output of right ascension and declination, and rounded
the satellite azimuth and elevation to the nearest degree to make room
for the flare latitude and longitude.  R.A. and declination are still
output to the file, though.

Eliminated handling of Iridium dummy satellites since these do not
have the highly reflective main mission antennae that the operational
Iridiums do.

Improved the flare search algorithm, greatly speeding up the program!


Version 1.1
-----------

Change MM-DD-YY output to YY-MM-DD.

Indicate in the longitude prompt that east longitudes are expected.
Have added "(- for W, + for E)".

Refraction now included when calculating sun and satellite horizon
coordinates.

Changed default configuration filename from IRIDDEF.DAT to IRIDFLAR.CFG.
Configuration filenames other than IRIDFLAR.CFG are allowed.

TLE filename is now included as one of the defaults, and it can be
changed between runs (just like all the other inputs).

Header added to output file with location coordinates, UTC offset, 
TLE filename, and configuration filename.

Non-integer timezones are now permitted (e.g. Australia).

Improved calculation of satellite lighting condition.  Now calculates
lighting the same way that SkyMap does -- 15 km or 20 km tangent height
extinction (depending on season), with 0.2 or 0.1 degrees of refraction
respectively.  (Version 1.0 incorrectly assumed that the sun was visible
from the satellite all the way down to the hard earth, where refraction
is about 1.2 degrees.  This was far too optimistic, leading to an
erroneous extension of sunlit times.)  Only two lighting conditions now
possible in IRIDFLAR output:  Lit or Pnb.

Start times can now be in any of the following formats:  HH:MM:SS,
HH:MM, or HH, where HH, MM and SS can be one or two digits.

Problem fixed with chronological sort intermixing output lines of two or
more satellites that happen to be flaring at approximately the same time.


Version 1.0
-----------

[Original release]
