Friday, May 21, 2010
Friday, May 21, 2010
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IDSat 1.0 Copyright (C) 1987-2007 by Ted Molczan. All rights reserved.
You may use IDSat.exe free of charge. The source code is not available.
You may share IDSat.exe with others, as long as you distribute it in the original IDsat.zip distribution file, without any alterations.
If you have questions, problems or comments, you may reach me at molczan@hotmail.com
1. Introduction
---------------
IDSat assists in the identification of observed satellites, by computing and tabulating close appulses of known satellites relative to the observed time and position. It is conceptually similar to Mike McCants' Findsat program, but provides additional information, and includes various convenience features.
In addition to reporting appulse time and position difference, IDSat provides the direction of travel, angular velocity and estimated prediction accuracy. Subject to the availability of data, it can also provide the predicted visual magnitude and radar cross-section area (RCS).
IDSat automatically detects and decodes observations input in the IOD and U.K. formats, including Russell Eberst's variant of the latter. It also reads Findsat's *.ctl input files.
The program obtains size and magnitude data from a file derived from my database. Mike McCants' quicksat.mag may be used as an alternative.
IDSat is an MS-DOS program, developed and tested within DOS windows running under Windows 95 and Windows XP Professional.
2. Program Installation
-----------------------
The IDSat,zip distribution archive file, contains the following files, which should be copied to a single directory of your choice.
IDSat.exe - the executable program
IDSat.ini - initialization file used to customize the program's operation
Cospar.txt - text file containing co-ordinates of a number of observing sites which have been issued Cospar identification numbers
Objects.txt - satellite name, size and magnitude data extracted from my database
IDinput.txt - default observation data file. As distributed, it contains the observation used in the demo described in Section 2.
readme.txt - the file you are reading now
IMPORTANT!
You must provide a file of 2-line orbital elements, named in accordance with MS-DOS conventions, and then edit line 2 of IDSat.ini to show the name of the file. For additional information on orbital elements, including sources, please see Section 3.3.
3. Running IDSat
----------------
3.1 General Operation
---------------------
As distributed, IDSat begins execution by issuing the following prompts:
Observation file : IDinput.txt
NORAD 2-line elements source file : <name of file that you entered at line 2 of IDSat.ini>
Maximum time difference (sec) = 120
Maximum angular separation (deg) = 3
To accept the default values, hit the enter key.
The following information and prompt appears when the search has concluded:
x objects met the search criteria.
Do you wish to perform another search?
You may view the search results by opening file IDout.txt using a text editor.
To perform another search type y and hit enter; to exit, simply hit enter.
NOTE:
- you do not have to exit the program to view the output file.
- IDSat always over-writes IDout.txt, so if you wish to save your search results, rename the file before you perform another search.
You can greatly alter the above behaviour by editing the default settings found in the text file IDSat.ini:
- if you prefer to be prompted for a different observation file, edit line 1
- if you prefer to be prompted for a different orbital elements file, edit line 2
- if you prefer to be prompted for a different maximum time difference, edit line 3
- if you prefer to be prompted for a different maximum angular separation, edit line 4
- if you always use the same default values, you may not wish to see the above prompts, in which case, edit line 5
- if you wish to switch between objects.txt and Quicksat.mag for satellite data, edit line 6
- if you wish to reduce search time by about 20 percent, you may wish to disable the checking of elements for non-numeric characters, Edit line 7
- you can alter or disable the prompt that occurs at the conclusion of a search by editing line 8. The string "resume" tells IDSat to ask whether or not you wish to perform another search; "exit" tells IDSat whether or not you wish to exit; "none" tells IDSat to exit after each search, without either prompt
3.2 Observation Data Files
--------------------------
Observations are input to IDSat by means of text files.
As distributed, IDSat's default file name for observations is IDinput.txt. Users may specify an alternative file name at run-time, in response to a prompt.
To change the default file name, simply use text editor to change the name that appears on line 1 of file IDSat.ini.
IDSat processes one observation per session, and expects to find the observation on the first line of the observation data file.
The next two sections discuss the observation formats read by IDSat.
3.2.1 IOD and U.K. Format
-------------------------
IDSat automatically detects and decodes observations in the IOD and U.K. formats, including Russell Eberst's variant of the latter. Only the R.A. and Dec formats are supported; altitude/azimuth observations may be entered via the Findsat format *.ctl file, as described in Section 3.2.3.
A description of the IOD format, and software for reporting observations in IOD format is available here:
http://users2.ev1.net/~mmccants/programs/
Download the file obsentry.zip
PLEASE NOTE: in order to process observations in the IOD, U.K. or Eberst formats, IDSat requires that the observer's Cospar number, latitude, longitude and height above sea level, appear in the file Cospar.txt. Please see Section 6 for more information.
3.2.2 Russell Eberst's Format
-----------------------------
Russell Eberst's variant of the U.K. format requires three lines per observation, for example:
2420 0103 0.211 1204
03
9900000 044841.96 065347+685118 7.2 7.2 0 S
The first line appears at the start of each one of Russell's reports, and specifies the year and month of the observations, as well as other information that seldom changes.
The second line is the day of the month of the observation.
The third line contains the details of the observation.
3.2.3 Findsat's *.ctl Format
----------------------------
IDSat processes files ending with the extension .ctl as Findsat input files. This feature will be of interest to those who:
- make R.A. and Dec observations, but do not use the IOD, U.K. or Eberst reporting formats
- make altitude/azimuth observations
- are familiar with Findsat and prefer its input data format
Findsat observation input files consist of four lines. Here is a sample for Russell Eberst's location:
55.9486 3.1386 141. Eberst
01 01 14 18 50 39.03 19 30.25 58.47861 1950 comments
120 3
<name of 2-line elements file>
Descriptions of each line follow:
Line One
--------
55.9486 degrees north latitude (enter south latitudes as negative values)
3.1386 degrees west longitude (enter east longitudes as negative values)
141. feet above sea level
"Eberst" is an optional descriptive text.
Note: IDSat can read an alternate format of line one, in which the latitude, longitude and height are replaced by the observer's COSPAR number. IDSat accepts this variant of the Findsat format only via files named with the extension "unk". Also, IDSat requires that the observer's Cospar number, latitude, longitude and height above sea level, appear in the file Cospar.txt. Please see Section 6 for more information.
Line Two
--------
01 01 14 is the date of the observation, 2001 Jan 14
18 50 39.03 is the time of the observation, 18:50:39.03 UTC
19 30.25 is the right-ascension of the observation, in hh dd.dd format
58.47861 is the declination of the observation, in decimal degrees. Enter southern declinations as negative numbers.
1950 is the epoch of the observation
"comments" is an optional comment text
Note: observers who prefer to use altitude and azimuth instead of R.A. and Dec should use the following alternate format:
01 01 14 18 50 39.03 AA 67 106 comments
The time and date fields are the same, but the R.A. and Dec are replaced by the letters "AA", which indicate that the position is altitude and azimuth, followed by those two values.
Line Three
----------
120 seconds maximum time difference between observation and appulse by satellites found by IDSat
3 degrees maximum position difference between observation and appulse by satellites found by IDSat
Line Four
---------
Line four states the name of the file containing the orbital elements of the satellites which IDSat will attempt to match to the observation.
3.3 Orbital elements files
--------------------------
To maximize the probability of identifying observed satellites, it is necessary to provide IDSat with as complete a collection of orbital elements as possible, with epochs as close to the date of the observation as possible.
IDSat processes only NORAD "2-line" elements. Space-Track.org is the primary distributor of U.S. Department of Defense (DoD) 2-line orbital elements and related data, replacing NASA Goddard Space Flight Center's Orbital Information Group (OIG), which permanently ceased operations on 2005 Mar 31.
Elements files need not contain only elements. IDSat will skip over blank lines or lines containing other text. It does so by looking for the distinctive format of the 2-line elements.
IMPORTANT!
Your 2-line orbital elements file must be named in accordance with MS-DOS conventions, and you should edit line 2 of IDSat.ini to show the path and name of the file, e.g. tle.txt, or c:\tledata\070521.tle, etc
3.4 Output File
---------------
IDsat writes its results to a file named IDout.txt. Here is a sample of the output format:
start of sample
9900000267501062021554796 010 12162595 +02380 2 5
Observation: 2001 06 20 21 55 47.96 16 25.95 +02 38.0 2000
Site 2675 co-ordinates: 52.1358 N 2.3264 W 70 m
NORAD 2-line elements source file: <name of file you provided>
Maximum time difference = 120 s
Maximum angular separation = 3 deg
tdiff Sep Mv RCS Range Trk FE Vang Age Unc
Name Desig NORAD s deg pred m^2 km deg hour deg/s days s
-------------- -------- ----- -------- ----- ------ ---- ----- --- ---- ----- ---- -------
Cosmos 586 r 73065B 6829 104.41 2.30 5.2 v 7.18 1430 170 11.7 0.22 1 0.0
Cosmos 1808 86100A 17239 -49.93 1.36 6.5 d 3.84 1461 170 11.9 0.21 0 0.0
Cosmos 2227 r 92093B 22285 -0.18 0.02 3.3 v 17.8 1232 27 4.5 0.29 -0 0.0
99057MG 99057MG 26759 52.03 0.02 9.3 r .005 1072 348 6.1 0.30 7 1.2
NOTE: tdiff < 0 means observation was earlier than prediction.
end of sample
The first several lines echo the input data and settings.
The results are tabulated under 13 column headings, which are described in the following sections:
3.4.1 Name - if IDSat can not find a name in its data base, it uses the International Designation
3.4.2 Desig - International Designation
3.4.3 NORAD - satellite catalogue number issued by U.S. Space Command, aka NORAD number
3.4.4 tdiff - the difference between the observed time and the predicted time of the appulse of the observed position by the listed satellite. Negative values denote early observations.
3.4.5 Sep - appulse distance of listed satellite relative to observed position
3.4.6 mv - predicted magnitude. IDSat predicts the magnitude using standard magnitudes derived using any of three methods. In order of preference, they are:
visual - std magnitude determined from visual observations, denoted by "v" after the magnitude
dimensions - std mag estimated from the satellite's dimensions, denoted by "d" after the magnitude
radar cross-section - std mag estimated from the satellite's radar cross-section (RCS), denoted by "r" after the magnitude
If no standard magnitude data is available to IDSat, it reports predicted magnitude as ????
If the object is in the umbra of Earth's shadow, then "shadow" appears in place of magnitude. I decided to list objects that were in shadow for two reasons. First, the boundary of the shadow can not be determined with great precision, so an object computed to be in shadow, may still be in the penumbra. Second, self-illuminated objects cannot be ruled out. A number of observers have reported observing the space shuttle deep in shadow, illuminated by the flood-lights in its cargo bay. In 1996, an observer reported seeing a satellite in shadow, which turned out to be glowing as it passed through its very low perigee.
3.4.7 RCS - radar cross-section area
3.4.8 Range - distance between observer and listed satellite, km
3.4.9 Trk - satellite's track relative to Earth, i.e. direction of travel, expressed as degrees azimuth, measured clock-wise from North
3.4.10 FE - field-entry angle. Indicates the point at which the listed satellite would have entered the observer's field of view using non-inverting optics, such as binoculars. Expressed as the hours on the face of a clock. For example, FE = 3 means that the satellite moved from right to left; FE = 12 means the satellite moved from top to bottom.
3.4.11 Vang - listed satellite's angular velocity at the point of appulse
3.4.12 Age - age of the listed satellite's orbital elements, in days
3.4.13 Unc - prediction time uncertainty, assuming 10 percent uncertainty in the rate of decay. Expressed in seconds. The time uncertainty varies in direct proportion to the uncertainty of the rate of decay.
The 2-line elements of each object in the table are listed immediately below the table.
3.5 Rejection of Bad Elements
Rejected elements are listed in the output file, immediately following the elements of the objects that met the search criteria.
As distributed, IDSat checks each orbital element to ensure that it has the correct structure, and has not been corrupted with non-numeric characters. If an element is found to have been corrupted, then the entire element set is rejected. This check can be disabled by editing line 7 of the IDSat.ini file. The only advantage do doing so, is an approximately 20 percent reduction in execution time.
To protect against crashes and promote accurate results, IDSat's implementation of the SGP4/SDP4 orbit propagators reject elements that propagate to unrealistic values of eccentricity and semi-major axis.
Eccentricity must remain greater than or equal to zero and less than one. Semi-major axis must remain greater than or equal to the Earth's radius and not exceed 20 Earth radii.
Despite my best efforts, there likely are element sets that can bring down IDSat. To help cope with this eventuality, IDSat lists each NORAD number it has processed to a text file named progress.txt.
If all goes well, you will never see this file, because it is erased upon the completion of each search run. However, if IDSat crashes during a search, the file will remain on disk. So, if there is reason to suspect a bad element set, you can determine which element set was being processed at the time of the crash, by opening file progress.txt and noting the NORAD number on the final line.
4. Satellite Data Files
-----------------------
Three of the files distributed with IDSat contain data that assists in the identification process.
As distributed, the file objects.txt is used by default to provide the name, dimensions, radar cross-section area, and standard magnitude. Objects.txt is extracted from data that I have compiled over the past 15 years from various sources.
User's who prefer Mike McCants' similar file, Quicksat.mag, can instruct IDSat to use it instead of objects.txt by editing line 6 of the IDSat.ini file.
It should be noted that IDSat uses standard magnitudes based on 1000 km and a phase angle of 90 deg. The standard magnitudes in Quicksat.mag are based on 1000 km and zero phase angle (i.e. full illumination), IDSat adjusts for the different phases angles by adding 1.243 to Quicksat.mag standard magnitudes.
If IDSat does not find a record for a satellite in the specified file, then it looks for it in two other places.
For example, certain orbital element files include the name of each satellite on a third line. Others add dimensions, standard magnitude and RCS value to the name line:
ISS 20.0 10.0 0.0 -2.0 d 103
IDSat automatically detects and uses this data if it does not appear in the standard files.
Finally, if IDSat does not find standard magnitude, dimensions or RCS values in any of the aforementioned sources, then it looks for a file of RCS values, named "rcs". RCS values are less reliable for estimating visual magnitude than standard magnitudes derived from observations or satellite dimensions, but they are better than nothing.
File "rcs" must be a standard MS-DOS text file. Each line contains data for a single satellite, except for the final line, which should contain only "99999". The satellite data must be formatted as follows:
sssss rrrr nn
5 0.12 35
where sssss = catalogue number
rrrr = RCS values (a decimal point may appear at any position within this field
nn = number of RCS values evaluated to obtain the listed value. This field may be left blank.
Although objects.txt (or Quicksat.mag) and file "rcs" provide important information, IDSat will operate even if each one is missing. IDSat does not report the absence of any of these three files, so it is up to users to ensure that they are in the same directory as IDSat.exe.
5. COSPAR Site Co-ordinates
---------------------------
In order to process observations in the IOD, U.K. or Eberst formats, IDSat requires that the observer's Cospar number, latitude, longitude and height above sea level, appear in the file Cospar.txt. The .unk variant of Findsat's .ctl file also requires this file.
Additional sites may be added by editing Cospar.txt using a text editor.
Here is a sample entry:
2701 43.68764 79.39243 230
Interpretation:
2701 = COSPAR number
43.68764 deg north latitude (enter south latitudes as negative values)
79.39243 deg west longitude (enter east longitudes as negative values)
230 metres above sea level
PLEASE NOTE: IDSat expects to find the above values in specific fields:
COSPAR : columns 1 to 4
latitude : columns 6 to 14
longitude : columns 16 to 25
hasl : columns 27 to 33
PLEASE NOTE: If you plan to share or publish your observations, you should obtain a permanent COSPAR number for your observing site(s). I will be pleased to put you in touch with the person who assigns COSPAR numbers.
Download
You may use IDSat.exe free of charge. The source code is not available.
You may share IDSat.exe with others, as long as you distribute it in the original IDsat.zip distribution file, without any alterations.
If you have questions, problems or comments, you may reach me at molczan@hotmail.com
1. Introduction
---------------
IDSat assists in the identification of observed satellites, by computing and tabulating close appulses of known satellites relative to the observed time and position. It is conceptually similar to Mike McCants' Findsat program, but provides additional information, and includes various convenience features.
In addition to reporting appulse time and position difference, IDSat provides the direction of travel, angular velocity and estimated prediction accuracy. Subject to the availability of data, it can also provide the predicted visual magnitude and radar cross-section area (RCS).
IDSat automatically detects and decodes observations input in the IOD and U.K. formats, including Russell Eberst's variant of the latter. It also reads Findsat's *.ctl input files.
The program obtains size and magnitude data from a file derived from my database. Mike McCants' quicksat.mag may be used as an alternative.
IDSat is an MS-DOS program, developed and tested within DOS windows running under Windows 95 and Windows XP Professional.
2. Program Installation
-----------------------
The IDSat,zip distribution archive file, contains the following files, which should be copied to a single directory of your choice.
IDSat.exe - the executable program
IDSat.ini - initialization file used to customize the program's operation
Cospar.txt - text file containing co-ordinates of a number of observing sites which have been issued Cospar identification numbers
Objects.txt - satellite name, size and magnitude data extracted from my database
IDinput.txt - default observation data file. As distributed, it contains the observation used in the demo described in Section 2.
readme.txt - the file you are reading now
IMPORTANT!
You must provide a file of 2-line orbital elements, named in accordance with MS-DOS conventions, and then edit line 2 of IDSat.ini to show the name of the file. For additional information on orbital elements, including sources, please see Section 3.3.
3. Running IDSat
----------------
3.1 General Operation
---------------------
As distributed, IDSat begins execution by issuing the following prompts:
Observation file : IDinput.txt
NORAD 2-line elements source file : <name of file that you entered at line 2 of IDSat.ini>
Maximum time difference (sec) = 120
Maximum angular separation (deg) = 3
To accept the default values, hit the enter key.
The following information and prompt appears when the search has concluded:
x objects met the search criteria.
Do you wish to perform another search?
You may view the search results by opening file IDout.txt using a text editor.
To perform another search type y and hit enter; to exit, simply hit enter.
NOTE:
- you do not have to exit the program to view the output file.
- IDSat always over-writes IDout.txt, so if you wish to save your search results, rename the file before you perform another search.
You can greatly alter the above behaviour by editing the default settings found in the text file IDSat.ini:
- if you prefer to be prompted for a different observation file, edit line 1
- if you prefer to be prompted for a different orbital elements file, edit line 2
- if you prefer to be prompted for a different maximum time difference, edit line 3
- if you prefer to be prompted for a different maximum angular separation, edit line 4
- if you always use the same default values, you may not wish to see the above prompts, in which case, edit line 5
- if you wish to switch between objects.txt and Quicksat.mag for satellite data, edit line 6
- if you wish to reduce search time by about 20 percent, you may wish to disable the checking of elements for non-numeric characters, Edit line 7
- you can alter or disable the prompt that occurs at the conclusion of a search by editing line 8. The string "resume" tells IDSat to ask whether or not you wish to perform another search; "exit" tells IDSat whether or not you wish to exit; "none" tells IDSat to exit after each search, without either prompt
3.2 Observation Data Files
--------------------------
Observations are input to IDSat by means of text files.
As distributed, IDSat's default file name for observations is IDinput.txt. Users may specify an alternative file name at run-time, in response to a prompt.
To change the default file name, simply use text editor to change the name that appears on line 1 of file IDSat.ini.
IDSat processes one observation per session, and expects to find the observation on the first line of the observation data file.
The next two sections discuss the observation formats read by IDSat.
3.2.1 IOD and U.K. Format
-------------------------
IDSat automatically detects and decodes observations in the IOD and U.K. formats, including Russell Eberst's variant of the latter. Only the R.A. and Dec formats are supported; altitude/azimuth observations may be entered via the Findsat format *.ctl file, as described in Section 3.2.3.
A description of the IOD format, and software for reporting observations in IOD format is available here:
http://users2.ev1.net/~mmccants/programs/
Download the file obsentry.zip
PLEASE NOTE: in order to process observations in the IOD, U.K. or Eberst formats, IDSat requires that the observer's Cospar number, latitude, longitude and height above sea level, appear in the file Cospar.txt. Please see Section 6 for more information.
3.2.2 Russell Eberst's Format
-----------------------------
Russell Eberst's variant of the U.K. format requires three lines per observation, for example:
2420 0103 0.211 1204
03
9900000 044841.96 065347+685118 7.2 7.2 0 S
The first line appears at the start of each one of Russell's reports, and specifies the year and month of the observations, as well as other information that seldom changes.
The second line is the day of the month of the observation.
The third line contains the details of the observation.
3.2.3 Findsat's *.ctl Format
----------------------------
IDSat processes files ending with the extension .ctl as Findsat input files. This feature will be of interest to those who:
- make R.A. and Dec observations, but do not use the IOD, U.K. or Eberst reporting formats
- make altitude/azimuth observations
- are familiar with Findsat and prefer its input data format
Findsat observation input files consist of four lines. Here is a sample for Russell Eberst's location:
55.9486 3.1386 141. Eberst
01 01 14 18 50 39.03 19 30.25 58.47861 1950 comments
120 3
<name of 2-line elements file>
Descriptions of each line follow:
Line One
--------
55.9486 degrees north latitude (enter south latitudes as negative values)
3.1386 degrees west longitude (enter east longitudes as negative values)
141. feet above sea level
"Eberst" is an optional descriptive text.
Note: IDSat can read an alternate format of line one, in which the latitude, longitude and height are replaced by the observer's COSPAR number. IDSat accepts this variant of the Findsat format only via files named with the extension "unk". Also, IDSat requires that the observer's Cospar number, latitude, longitude and height above sea level, appear in the file Cospar.txt. Please see Section 6 for more information.
Line Two
--------
01 01 14 is the date of the observation, 2001 Jan 14
18 50 39.03 is the time of the observation, 18:50:39.03 UTC
19 30.25 is the right-ascension of the observation, in hh dd.dd format
58.47861 is the declination of the observation, in decimal degrees. Enter southern declinations as negative numbers.
1950 is the epoch of the observation
"comments" is an optional comment text
Note: observers who prefer to use altitude and azimuth instead of R.A. and Dec should use the following alternate format:
01 01 14 18 50 39.03 AA 67 106 comments
The time and date fields are the same, but the R.A. and Dec are replaced by the letters "AA", which indicate that the position is altitude and azimuth, followed by those two values.
Line Three
----------
120 seconds maximum time difference between observation and appulse by satellites found by IDSat
3 degrees maximum position difference between observation and appulse by satellites found by IDSat
Line Four
---------
Line four states the name of the file containing the orbital elements of the satellites which IDSat will attempt to match to the observation.
3.3 Orbital elements files
--------------------------
To maximize the probability of identifying observed satellites, it is necessary to provide IDSat with as complete a collection of orbital elements as possible, with epochs as close to the date of the observation as possible.
IDSat processes only NORAD "2-line" elements. Space-Track.org is the primary distributor of U.S. Department of Defense (DoD) 2-line orbital elements and related data, replacing NASA Goddard Space Flight Center's Orbital Information Group (OIG), which permanently ceased operations on 2005 Mar 31.
Elements files need not contain only elements. IDSat will skip over blank lines or lines containing other text. It does so by looking for the distinctive format of the 2-line elements.
IMPORTANT!
Your 2-line orbital elements file must be named in accordance with MS-DOS conventions, and you should edit line 2 of IDSat.ini to show the path and name of the file, e.g. tle.txt, or c:\tledata\070521.tle, etc
3.4 Output File
---------------
IDsat writes its results to a file named IDout.txt. Here is a sample of the output format:
start of sample
9900000267501062021554796 010 12162595 +02380 2 5
Observation: 2001 06 20 21 55 47.96 16 25.95 +02 38.0 2000
Site 2675 co-ordinates: 52.1358 N 2.3264 W 70 m
NORAD 2-line elements source file: <name of file you provided>
Maximum time difference = 120 s
Maximum angular separation = 3 deg
tdiff Sep Mv RCS Range Trk FE Vang Age Unc
Name Desig NORAD s deg pred m^2 km deg hour deg/s days s
-------------- -------- ----- -------- ----- ------ ---- ----- --- ---- ----- ---- -------
Cosmos 586 r 73065B 6829 104.41 2.30 5.2 v 7.18 1430 170 11.7 0.22 1 0.0
Cosmos 1808 86100A 17239 -49.93 1.36 6.5 d 3.84 1461 170 11.9 0.21 0 0.0
Cosmos 2227 r 92093B 22285 -0.18 0.02 3.3 v 17.8 1232 27 4.5 0.29 -0 0.0
99057MG 99057MG 26759 52.03 0.02 9.3 r .005 1072 348 6.1 0.30 7 1.2
NOTE: tdiff < 0 means observation was earlier than prediction.
end of sample
The first several lines echo the input data and settings.
The results are tabulated under 13 column headings, which are described in the following sections:
3.4.1 Name - if IDSat can not find a name in its data base, it uses the International Designation
3.4.2 Desig - International Designation
3.4.3 NORAD - satellite catalogue number issued by U.S. Space Command, aka NORAD number
3.4.4 tdiff - the difference between the observed time and the predicted time of the appulse of the observed position by the listed satellite. Negative values denote early observations.
3.4.5 Sep - appulse distance of listed satellite relative to observed position
3.4.6 mv - predicted magnitude. IDSat predicts the magnitude using standard magnitudes derived using any of three methods. In order of preference, they are:
visual - std magnitude determined from visual observations, denoted by "v" after the magnitude
dimensions - std mag estimated from the satellite's dimensions, denoted by "d" after the magnitude
radar cross-section - std mag estimated from the satellite's radar cross-section (RCS), denoted by "r" after the magnitude
If no standard magnitude data is available to IDSat, it reports predicted magnitude as ????
If the object is in the umbra of Earth's shadow, then "shadow" appears in place of magnitude. I decided to list objects that were in shadow for two reasons. First, the boundary of the shadow can not be determined with great precision, so an object computed to be in shadow, may still be in the penumbra. Second, self-illuminated objects cannot be ruled out. A number of observers have reported observing the space shuttle deep in shadow, illuminated by the flood-lights in its cargo bay. In 1996, an observer reported seeing a satellite in shadow, which turned out to be glowing as it passed through its very low perigee.
3.4.7 RCS - radar cross-section area
3.4.8 Range - distance between observer and listed satellite, km
3.4.9 Trk - satellite's track relative to Earth, i.e. direction of travel, expressed as degrees azimuth, measured clock-wise from North
3.4.10 FE - field-entry angle. Indicates the point at which the listed satellite would have entered the observer's field of view using non-inverting optics, such as binoculars. Expressed as the hours on the face of a clock. For example, FE = 3 means that the satellite moved from right to left; FE = 12 means the satellite moved from top to bottom.
3.4.11 Vang - listed satellite's angular velocity at the point of appulse
3.4.12 Age - age of the listed satellite's orbital elements, in days
3.4.13 Unc - prediction time uncertainty, assuming 10 percent uncertainty in the rate of decay. Expressed in seconds. The time uncertainty varies in direct proportion to the uncertainty of the rate of decay.
The 2-line elements of each object in the table are listed immediately below the table.
3.5 Rejection of Bad Elements
Rejected elements are listed in the output file, immediately following the elements of the objects that met the search criteria.
As distributed, IDSat checks each orbital element to ensure that it has the correct structure, and has not been corrupted with non-numeric characters. If an element is found to have been corrupted, then the entire element set is rejected. This check can be disabled by editing line 7 of the IDSat.ini file. The only advantage do doing so, is an approximately 20 percent reduction in execution time.
To protect against crashes and promote accurate results, IDSat's implementation of the SGP4/SDP4 orbit propagators reject elements that propagate to unrealistic values of eccentricity and semi-major axis.
Eccentricity must remain greater than or equal to zero and less than one. Semi-major axis must remain greater than or equal to the Earth's radius and not exceed 20 Earth radii.
Despite my best efforts, there likely are element sets that can bring down IDSat. To help cope with this eventuality, IDSat lists each NORAD number it has processed to a text file named progress.txt.
If all goes well, you will never see this file, because it is erased upon the completion of each search run. However, if IDSat crashes during a search, the file will remain on disk. So, if there is reason to suspect a bad element set, you can determine which element set was being processed at the time of the crash, by opening file progress.txt and noting the NORAD number on the final line.
4. Satellite Data Files
-----------------------
Three of the files distributed with IDSat contain data that assists in the identification process.
As distributed, the file objects.txt is used by default to provide the name, dimensions, radar cross-section area, and standard magnitude. Objects.txt is extracted from data that I have compiled over the past 15 years from various sources.
User's who prefer Mike McCants' similar file, Quicksat.mag, can instruct IDSat to use it instead of objects.txt by editing line 6 of the IDSat.ini file.
It should be noted that IDSat uses standard magnitudes based on 1000 km and a phase angle of 90 deg. The standard magnitudes in Quicksat.mag are based on 1000 km and zero phase angle (i.e. full illumination), IDSat adjusts for the different phases angles by adding 1.243 to Quicksat.mag standard magnitudes.
If IDSat does not find a record for a satellite in the specified file, then it looks for it in two other places.
For example, certain orbital element files include the name of each satellite on a third line. Others add dimensions, standard magnitude and RCS value to the name line:
ISS 20.0 10.0 0.0 -2.0 d 103
IDSat automatically detects and uses this data if it does not appear in the standard files.
Finally, if IDSat does not find standard magnitude, dimensions or RCS values in any of the aforementioned sources, then it looks for a file of RCS values, named "rcs". RCS values are less reliable for estimating visual magnitude than standard magnitudes derived from observations or satellite dimensions, but they are better than nothing.
File "rcs" must be a standard MS-DOS text file. Each line contains data for a single satellite, except for the final line, which should contain only "99999". The satellite data must be formatted as follows:
sssss rrrr nn
5 0.12 35
where sssss = catalogue number
rrrr = RCS values (a decimal point may appear at any position within this field
nn = number of RCS values evaluated to obtain the listed value. This field may be left blank.
Although objects.txt (or Quicksat.mag) and file "rcs" provide important information, IDSat will operate even if each one is missing. IDSat does not report the absence of any of these three files, so it is up to users to ensure that they are in the same directory as IDSat.exe.
5. COSPAR Site Co-ordinates
---------------------------
In order to process observations in the IOD, U.K. or Eberst formats, IDSat requires that the observer's Cospar number, latitude, longitude and height above sea level, appear in the file Cospar.txt. The .unk variant of Findsat's .ctl file also requires this file.
Additional sites may be added by editing Cospar.txt using a text editor.
Here is a sample entry:
2701 43.68764 79.39243 230
Interpretation:
2701 = COSPAR number
43.68764 deg north latitude (enter south latitudes as negative values)
79.39243 deg west longitude (enter east longitudes as negative values)
230 metres above sea level
PLEASE NOTE: IDSat expects to find the above values in specific fields:
COSPAR : columns 1 to 4
latitude : columns 6 to 14
longitude : columns 16 to 25
hasl : columns 27 to 33
PLEASE NOTE: If you plan to share or publish your observations, you should obtain a permanent COSPAR number for your observing site(s). I will be pleased to put you in touch with the person who assigns COSPAR numbers.
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