Ham Radio 2000/Ham Radio 2000.iso/ham2000/misc/v2l9435/quickv.doc

Text File | 1994-08-24 | 20KB | 399 lines

                      VEC2TLE User Instructions

These are step-by-step user instructions for the VEC2TLE software.
These instructions are designed primarily for the beginning user.  The
instructions are listed by the different tasks performed by VEC2TLE and
are sorted in the following order, based on what is believed to be
high to low incidence of usage.  The following tasks are covered in
these instructions:

A.   AUTOMATIC READ OF STATE VECTORS
B.   KEYBOARD ENTRY OF STATE VECTORS
C.   IMPULSIVE DELTA-VELOCITY MANEUVERS
D.   RE-EPOCH TLE AT THE ASCENDING NODE
E.   IF YOU HAVE TROUBLE



A.   AUTOMATIC READ OF STATE VECTORS

Automatic read of formatted state vectors is one of the more popular
uses for VEC2TLE.  The vector format was designed to provide the
software with all the information necessary to produce a complete
Keplerian Two-Line Element (TLE) set.  This formatted vector is often
embedded in a message that provides general information.  An example of
a vector message from the STS-65 Shuttle mission is appended to these
instructions.


A-1  Isolate the Formatted State Vector

If the state vector is embedded in a general message, you must first
isolate the formatted state vector from the posted message.  The
formatted vector is found between (but not including) the dotted lines
in the message.  The vector may be isolated using a text editor or
commercial on-line service software such as CompuServe Information
Manager (DOSCIM or WINCIM).  The formatted vector should be saved as a
text file with a ".VIF" extension in the same directory in which VEC2TLE
is located -- this makes the file readily found for read-in by VEC2TLE.

Since it is not possible to provide specific instructions for every
text editor or on-line software package, the following instructions are
an example of how to accomplish this task using the CompuServe Information
Manager (CIM):

(a)  Drag the mouse cursor down to highlight only the formatted vector
information (i.e., the information between but not including the dotted
lines).

(b)  Copy the vector data to the CIM paste buffer -- under the "Edit" menu
select "Copy".

(c)  Create a new text file -- under the "File" menu select "New".  Now
paste the contents of the text buffer (the vector data you copied) into
the new file -- under the "Edit" menu select "Paste".

(d)  This new file should IDEALLY be saved in the same directory as VEC2TLE
with a ".VIF" file extension -- under the "File" menu select "Save As"
and follow the CIM instructions.  An example of a properly formatted ".VIF"
file is included with VEC2TLE (file name is STS-57.VIF).


A-2  Initiate VEC2TLE

(a)  This may be accomplished directly in DOS or launched from Windows if
the program has been installed there.

(b)  Press the "Enter" key or activate the "OK" button with the mouse to
clear the Copyright screen.

(c)  Select the name of the vector file (VIF) you just created -- under the
"Compute TLE" menu select "Read Vector File."  (The Compute TLE menu may be
activated by the mouse or by ALT-C from the keyboard.)  If your file is in
the same directory as VEC2TLE and has a VIF extension, it should appear in
the file list.  You may select your file with the mouse or use the "Tab"
and Up/Down "Arrow" keys to get to your file.  Once your file is selected,
hit the "Enter" key or press the "Open" button with the mouse.  NOTE:  If
your file is in a different directory, you may choose directory names from
the file list or move up one level in the structure by selecting the ".."
(double period) designator.

(d)  Once step (c) is accomplished, VEC2TLE should automatically read
in the formatted state vector.  The state vector and its ancillary
information and data will then be displayed in the State Vector Input
dialog box.

(e)  The vector information is likely to be meaningless to all but the most
sophisticated users.  (Details on this information are in the VEC2TLE User
Manual.)  If you are like most, just accept the data "as is" by hitting the
"Enter" key or selecting the "OK" button with the mouse.  VEC2TLE will then
compute the Two-Line Elements for you.

(f)  The Two-Line Elements are saved to an output file (default  or
previously specified by the user).  OUTPUT.TLE is the name of the default
two-line element output file.  The name of the TLE output file is maintained
in the VEC2TLE configuration file.  It may be changed at any time by the user
-- under the "File" menu select "TLE Ouptut File".  These elements may be
read directly by STSORBIT PLUS or other popular satellite tracking programs.

(g)  NOTE: VEC2TLE is designed to be capable of reading multiple state
vectors [sequentially] from the same VIF file.  This may be accomplished by
repeating steps (c) through (f) for as many vectors as desired or until
the End-Of-File (EOF) is reached.  Since VEC2TLE assumes the VIF file
to be the same, subsequent runs of step (c) will automatically omit the
construction of the VIF file selection dialog box.  (A different VIF
file may be selected by an override -- under the "File" menu select
"Vector Input File.")


APPENDIX A --  Sample STS-65 Vector Message from CompuServe HamNet Forum


               S H U T T L E   V E C T O R   D A T A

Below is the rev 145 Earth-Fixed Greenwich (EFG) state vector for STS-65.
This vector data comes from Goddard Space Flight Center (GFSC) and is
provided courtesy of the DOD C-Band Radar Network.

The data between the dotted lines may be read directly by VEC2TLE to
estimate the Keplerian Elements for STS-65 in NASA Two-Line (TLE) format.
(See Amateur Satellites Library [5] - File VC2TLE.ZIP to get a copy of
VEC2TLE.)

..........................................................................
Vector format = 117
Satellite Name:         STS-65
Catalog Number:         23173  94039A
Epoch Date/Time:        94198.75242859954
                        07/17/1994  18:03:29.831 UTC
EFG E:                         6583064.32 ft
    F:                       -20708921.30 ft
    G:                        -2817195.34 ft
    Edot:                      19454.7232 ft/s
    Fdot:                       7750.2930 ft/s
    Gdot:                     -11646.2425 ft/s
ndot/2 (drag):              0.00076617609 rev/day^2
nddt/6:                       2.46215E-08 rev/day^3
Bstar:                        2.29789E-04 1/Earth Radii
Elset #:                               25
Rev @ Epoch:              145.54322716647
..........................................................................

Drag values are estimated using a 2.7 drag multiplier.

To create a file for use by VEC2TLE, simply use the 'copy and paste' and
the 'save as' features in CIM to write the data to a new (text) file.  I
recommend that the file you save the data have a .VIF extension (default
for VEC2TLE vector input files).



B.   KEYBOARD ENTRY OF STATE VECTORS

Keyboard entry of state vectors is required to compute Keplerian TLEs
from unformatted state vectors.  Unformatted state vectors have been
available for the Space Shuttle from several NASA sources (see Appendix
E of the VEC2TLE User Manual).  Such state vectors are available in a
variety of coordinate systems and units of measure.  Therefore, when
manually entering state vectors, you must provide VEC2TLE with the
appropriate information about the vector.


B-1  Set Vector Parameters

The vector parameters that need to be set in VEC2TLE to specify
information about the state vector are: Inertial Reference, Vector
Units, Epoch Control, and Vector Time Reference.  Details on these
parameters may be found in the VEC2TLE User Manual.  These paremeters
may be set as the defaults in the VEC2TLE.CFG file or temporarily (for
the current run of VEC2TLE).  These parameters are specified under the
"Settings" menu.  (The Settings menu may be activated by the mouse or by
ALT-S from the keyboard.)

All of the vector parameters are set by "radio buttons."  This provides
the user with a discrete list of legal values from which to choose,
ensuring that only a legal value can be selected.  Once the value(s)
is/are set in the dialog box, the selection(s) can be submitted to
VEC2TLE by hitting the "Enter" key or selecting the "OK" button with the
mouse.

(a)  To set these parameters as defaults in the VEC2TLE.CFG file,
select "Defaults" from the Settings menu or "F2."  Otherwise, follow
steps (b) through (e) below.

(b)  The Inertial Reference may be selected from the Settings menu or
"F3."  The inertial reference applies ONLY to inertially-referenced
state vectors (i.e., this setting need not be made for Earth-Fixed
Greenwich [EFG] / True of Day Rotating [TDR] state vectors).  VEC2TLE
supports True Equator and Equinox of Date and Mean of 1950 (M50)
inertial state vectors.

(c)  The Vector Units may be selected from the Settings menu or "F4."
All vectors MUST have their proper units identified to VEC2TLE.
VEC2TLE supports vector units of km,km/s; nm,nm/s; and ft,ft/s.

(d)  The Epoch Control may be selected from the Settings menu or "F5."
Epoch control is somewhat optional, but setting the epoch of the
Keplerian elements to the time of the state vector is recommended.


B-2  Manually Enter the Vector

(a)  This process begins by the user having VEC2TLE construct the State
Vector Input dialog box -- under the "Compute TLE" menu select "Input
State Vector."  (The Compute TLE menu may be activated by the mouse or
by ALT-C from the keyboard.)

(b)  The user should then enter the appropriate data in each entry
position.  The user may elect to have VEC2TLE estimate the following
parameters by entering a "-1" in the respective entry position: Ndot/2
(drag), Nddot/6 (drag), Bstar (drag), and Rev #.

(c)  Some parameters do not have an effect on the Keplerian elements
and/or their computation of the orbital positions and velocities.  The
"Satellite Name or ID" is free-form and may be considered arbitrary.
The five (5) digit "Catalog Number" will be reflected in the Keplerian
elements; leading zeros need not be entered.  The "International
Designator," if not known or assigned, may be left blank.  The "Element
Set #" is more or less arbitrary, but traditionally follows a numerical
sequence.

(d)  The author has the following recommendation for selection of Orbit
Theory: SGP4 is generally recommended for satellites in a Low-Earth Orbit
(Mean Motion greater than 6.4 rev/day); SGP is recommended when Mean
Motion is less than or equal to 6.4 rev/day.  The Mean Motion is the next-
to-last independent number on Line 2 of the TLE (i.e., the line beginning
with "2 ").  If the computed TLE's Mean Motion is inconsistent with the
recommended Orbit Theory, the State Vector Input dialog box may be
reconstructed (i.e., redo steps [a] through [e] ) with the appropriate
change made to the Orbit Theory.  All other parameters in the State Vector
Input dialog box should remain the same.



C.   IMPULSIVE DELTA-VELOCITY MANEUVERS

VEC2TLE provides a rather unique capability to estimate the orbit of
the Space Shuttle (or other spacecraft) following an impulsive
maneuver.  This capability provides the ability to immediately compute
the post-maneuver orbit, provided that both a good pre-maneuver TLE and
the burn parameters are available.  This capability was added to
VEC2TLE because of the availability of Space Shuttle "Burn PAD" data on
the Mission Control audio of NASA TV.  Estimated Keplerian TLEs using
this feature have proven to be quite accurate and have held up very well
until the availability of a post-burn state vector.


C-1  Select the Pre-Maneuver Keplerian TLE

(a)  Select the name of the Two-line Element file (TLE) that contains
the pre-maneuver Keplerian TLE -- under the "Compute TLE" menu select
"Impulsive Delta-V."  (The Compute TLE menu may be activated by the
mouse or by ALT-C from the keyboard.)  If your file is in the same
directory as VEC2TLE and has a TLE extension, it should appear in the
file list.  You may select your file with the mouse or use the "Tab" and
Up/Down "Arrow" keys to get to your file.  Once your file is selected,
hit the "Enter" key or press the "Open" button with the mouse.  NOTE: If
your file is in a different directory, you may choose directory names
from the file list or move up one level in the structure by selecting the
".." (double period) designator.

(b)  Ideally, the pre-maneuver TLE should be the first (or only) set of
Keplerian elements in the selected TLE file.  When step (a) is
accomplished, the Two-Line Element Data dialog box is constructed
containing the parameters in the TLE.  If the first TLE is the correct
set of Keplerian elements, hit the "Enter" key or press the "OK" button
with the mouse.  Otherwise, hit the "Esc" key or press the "Cancel"
button with the mouse.

(c)  If the desired set of Keplerian elements is NOT the first set in
the file, steps (a) and (b) may be repeated as many times as necessary
until either the correct TLE is found or the the End Of File (EOF) is
reached.  NOTE that in subsequent runs of step (a), the selected TLE file
is presumed to be the same.  Therefore, the file selection dialog box
will not reappear.  (A different TLE file may be selected by an override
-- under the "File" menu select "TLE Input File.")


C-2  Specify the Maneuver Burn Parameters

(a)  Once step C-1(c) is accomplished, VEC2TLE will automatically
construct the Impulsive Delta-V Data dialog box.  The user should then
enter the appropriate burn data in each entry position.  Blanks are
interpreted as zeros for both required and optional burn parameters.

(b)  The required burn data parameters are: Ignition Time, Alongtrack
Delta-V, Crosstrack Delta-V, and Radial Delta-V.  The optional burn
data parameters are: Burn Duration, Initial Mass, and Mass Flow Rate.
Assuming zeros for the optional burn parameters (i.e., instantaneous
delta-V at ignition with insignificant mass loss) generally provides a
reasonable estimate for the post-maneuver orbit.  For best results,
enter accurate values for the optional burn parameters.

(c)  The mass units used for Initial Mass and Mass Flow Rate are
unimportant as long as they are consistent.  Therefore mass units
representing equivalent Earth weight (such as pounds) are also valid.



D.   RE-EPOCH TLE AT THE ASCENDING NODE

VEC2TLE has the ability to change the epoch time (i.e., reference time)
of the Keplerian elements to the the ascending node just prior to an
arbitrary epoch time.  In the past, all Keplerian Two-Line Element sets
had the ascending node as the epoch time.  The main purpose was to
simplify orbital revolution computations.  The implementation of the re-
epoch feature in VEC2TLE is to accommodate the software that requires
Keplerian elements to have epoch time at the ascending node.

NOTE: the Keplerian elements re-epoched at the ascending node are
somewhat less accurate than those with epoch at the time of the state
vector; the degree of difference is directly dependent on the accuracy
of the TLE's applicable drag terms.


(a)  Select the name of the Two-line Element file (TLE) that contains
the desired Keplerian TLE -- under the "Compute TLE" menu select "Re-
Epoch TLE at Asc Node."  (The Compute TLE menu may be activated by the
mouse or by ALT-C from the keyboard.)  If your file is in the same
directory as VEC2TLE and has a TLE extension, it should appear in the
file list.  You may select your file with the mouse or use the "Tab" and
Up/Down "Arrow" keys to get to your file.  Once your file is selected,
hit the "Enter" key or press the "Open" button with the mouse.  NOTE: If
your file is in a different directory, you may choose directory names
from the file list or move up one level in the structure by selecting the
".." (double period) designator.

(b)  Ideally, the desired TLE should be the first (or only) set of
Keplerian elements in the selected TLE file.  When step (a) is
accomplished, the Two-Line Element Data dialog box is constructed
containing the parameters in the TLE.  If the first TLE is the correct
set of Keplerian elements, hit the "Enter" key or press the "OK" button
with the mouse.  Otherwise, hit the "Esc" key or press the "Cancel"
button with the mouse.

(c)  If the desired set of Keplerian elements is NOT the first set in
the file, steps (a) and (b) may be repeated as many times as necessary
until either the correct TLE is found or the the End Of File (EOF) is
reached.  NOTE that in subsequent runs of step (a), the selected TLE
file is presumed to be the same.  Therefore, the file selection dialog
box will not reappear.  (A different TLE file may be selected by an
override -- under the "File" menu select "TLE Input File.")

(d)  Once the desired set of Keplerian elements are selected, VEC2TLE
will compute the corresponding Keplerian elements with epoch time at
the prior ascending node.  The Two-Line Elements are saved to an output
file (default  or previously specified by the user).  OUTPUT.TLE is the
name of the default two-line element output file.  The name of the TLE
output file is maintained in the VEC2TLE configuration file.  It may be
changed at any time by the user -- under the "File" menu select "TLE
Ouptut File".  These elements may be read directly by STSORBIT PLUS or
other popular satellite tracking programs.



E.   IF YOU HAVE TROUBLE

VEC2TLE was designed with the intent of having as trouble-free operation
as possible.  Because of the complexity of both VEC2TLE and the large
variety of computer hardware and software configurations, there will
inevitably be situations where things just don't work as expected.
Because of the large number of potential problems, it's not practical
to cover all solutions in these user instructions.  This section should
however, evolve and provide a list of solutions to some of the more
common problems.

Users who experience problems not covered in the list should provide
specific details of the circumstances and the computer's hardware and
software configuartions (CONFIG.SYS, AUTOEXEC.BAT, TSR's) to the author.
Instructions on how to contact the author may be found in Appendix H of
the VEC2TLE User Manual.


PROBLEM                            RECOMMENDATION / ACTION
----------------------------------------------------------------------
Program experiences an abnormal    Use a much smaller drag term or
termination while computing a      drag multiplier (as applicable);
TLE in which a rev estimate was    this occurs mainly with high
requested.                         altitude orbits in which drag is
                                   significantly non-linear. Alter-
                                   natively, specify the rev value.

Systems hangs and/or program       Delete the VEC2TLE configuration
experiences an abnormal term-      file (VEC2TLE.CFG).  This problem
ination while computing a          has been known to occur when the
Keplerian TLE.                     configuration file is corrupted.

Computed TLE has an extraneous     Delete the extraneous line feed
line feed following the Inter-     at the end of the International
national Designator when doing a   Designator in the Vector Input
formatted vector read.             dialog box or from the TLE.  The
                                   extraneous line file has been
                                   known to be added by some text
                                   editors.

Parameters such a Units or Time    Set the correct reference parameters
Standard (UTC or MET) are incon-   -- under "Settings" menu.  (See pro-
sistent with parameters to be      cedures B-1 for further details.)
manually entered (in procedures    These paramters must be properly set
A through D).                      when manually entering data.