World of Ham Radio 1997/WOHR97_AmSoft_(1997-02-01).iso/sat/sat_13/amsoft.iii

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                   Vector to Two-Line Elements
                       (VEC2TLE) Software


                           User Manual





                          Version 9421






                           16 May 1994







                       Kenneth J. Ernandes
                        16 Freshman Lane
                      Stony Brook, NY 11790
Kenneth J. Ernandes
16 Freshman Lane
Stony Brook, NY 11790







Vector to Two-Line Elements (VEC2TLE) Software User Manual







Copyright 1993-1994 by Kenneth J. Ernandes.  This publication may
be reproduced and distributed as long as the final product is a
complete, unaltered reproduction of the original document.  All
other rights are reserved.








IBM is a registered trademark of International Business Machines
Corporation.  Microsoft, Windows, and MS-DOS are registered
trademarks of Microsoft Corporation.
                        TABLE OF CONTENTS


1.0  INTRODUCTION  ..........................................   1
     1.1  Vector Types Supported ............................   1
     1.2  Keplerian Orbital Elements ........................   3
     1.3  Orbit Propagation Models ..........................   4


2.0  INSTALLATION ...........................................   6


3.0  USER INTERFACE DESCRIPTION .............................   8
     3.1  Menu Activation ...................................   8
     3.2  Menu Item Selection ...............................   9
     3.3  Dialog Boxes ......................................   9
     3.4  Windows ...........................................  12


4.0  OPERATING INSTRUCTIONS .................................  13
     4.1  Startup ...........................................  13
     4.2  File ..............................................  13
     4.3  Settings ..........................................  16
     4.4  Launch Date/Time ..................................  17
     4.5  Drag Multiplier ...................................  18
     4.6  Compute TLE .......................................  18
     4.7  Re-Epoch TLE at Asc Node ..........................  20
     4.8  Impulsive Delta-V .................................  20
     4.9  Compute Date ......................................  22
     4.10 Compute Day of Year ...............................  22
     4.10 Program Termination ...............................  22


5.0  REFERENCES .............................................  23


6.0  ACKNOWLEDGEMENTS .......................................  24


7.0  LICENSE STATEMENT ......................................  25
     7.1 Registration .......................................  25
     7.2 Distribution .......................................  25
     7.3 Limited Warranty ...................................  26
     7.4 Governing Law and General Provisions ...............  27



APPENDIX A  --  HOT KEY SUMMARY .............................  28
APPENDIX B  --  SEQUENTIAL DAY OF THE YEAR ..................  29
APPENDIX C  --  ACRONYMS AND ABBREVIATIONS ..................  31
APPENDIX D  --  VECTOR FILE FORMATS .........................  33
APPENDIX E  --  SOURCES OF STATE VECTORS ....................  36
APPENDIX F  --  SOURCES OF TLEs .............................  39
APPENDIX G  --  GENERAL INFORMATION .........................  42
APPENDIX H  --  ABOUT THE AUTHOR ............................  45
Page 1

1.0       INTRODUCTION

The Vector to Two-line Elements (VEC2TLE) software provides the
user with the capability to convert position/velocity/time state
vectors of a variety of formats to National Aeronautics and Space
Administration (NASA) Compatible Keplerian Two-Line Element (TLE)
sets.  These Keplerian elements contain orbit descriptions
compatible for propagation with the Simplified General
Perturbations (SGP) and SGP Version 4 (SGP4) orbit theories
developed for use by the North American Aerospace Defense Command
(NORAD) and United States Space Command (USSPACECOM).

TLEs have become an increasingly-popular source of orbital data.
This is due mainly to the fact that this format of data is
available for nearly all Earth-orbiting satellites.  As a result,
the popular satellite tracking software packages such as STSPLUS
and TRAKSAT use TLEs as their primary sources of input data along
with the SGP4 orbit propagator.

TLE data is available for most Earth-orbiting satellites from
several sources (see Appendix F).  VEC2TLE is not intended to
replace these as primary sources of TLE data.  Rather, its
primary purpose is for circumstances in which this data may not
be available in a timely fashion.  A prime example is the Space
Transportation System (STS) where position and velocity state
vectors may be the only orbital information available in near
real time.  In the past, users of the tracking software had
little choice but to wait (hours or days) until the TLE data was
available following thruster firings that changed the Shuttle's
orbit.  Often, the TLE data is out of date by the time it is
received due to subsequent thruster firings.  It is this
situation that resulted in the creation of VEC2TLE.  The TLEs
computed by VEC2TLE are fully compatible with SGP or SGP4 as true
and accurate renditions of the orbit specified by the input state
vectors.

Sections 1.1, 1.2, and 1.3 provide an overview of the technical
features of VEC2TLE.  Section 1.1 discusses the various vector
types that may be input to compute TLEs.  Section 1.2 is a brief
description of Keplerian orbital elements.  Section 1.3 is an
overview of the SGP and SGP4 propagation models.  It should be
noted, however, that VEC2TLE takes care of all of the intricate
details, requiring the user only to know the specific type of
input vector.  Thus, this information is just provided for the
benefit of the interested reader.

1.1       Vector Types Supported

VEC2TLE supports a variety of vector types in the creation of
TLEs.  The two basic vector types are Earth-Centered Inertial
(ECI) and Earth-Fixed Greenwich (EFG).  Both ECI and EFG
represent right-handed orthogonal cartesian reference frames with
the origin at the Earth's center of mass.
Page 2

1.1.1     Earth-Centered Inertial

The ECI coordinate frame is an inertial frame in the sense that
its orientation remains virtually fixed in space.  The primary
axis (X-axis) is in the equatorial plane and points in the
direction of the vernal equinox.  The Y-axis is also in the
equatorial plane, and points 90 degrees to the east of the vernal
equinox.  The Z-axis is perpendicular to the equatorial plane,
and points through the north pole.

The ECI coordinate frame, in truth, is not inertial.  The vernal
equinox is not a fixed direction in space due to precession
imparted on the Earth's rotational axis by the moon, sun, and
other planets in the solar system.  Precession is a long-term
effect.  The earth's equator/poles also do not maintain a fixed
obliquity to the ecliptic.  The moon and sun also impart a short-
term periodic wobble on the Earth's rotational axis called
nutation.  The result is a change in the orientation of the X-,
Y-, and Z-axes over time.  Reference 1 has a detailed discussion
of precession and nutation.

VEC2TLE provides two standard systems for specifying the
orientation of the ECI coordinate axes:  1) True Equator, True
Equinox of Date and 2) Mean Equator, Mean Equinox of 1950 (M50).
The former, as its name implies, orients the X-, Y-, and Z-axes
to the actual directions of the vernal equinox and polar axes at
the applicable time of the vector.  The latter orients the axes
to the respective directions of the equinox and pole at the
beginning of the Besselian Year 1950.

1.1.2     Earth-Fixed Greenwich (EFG)

The EFG coordinate frame rotates with the Earth.  The primary
axis (E-axis) is in the equatorial plane and is directed through
the Greenwich Prime Meridian (GPM).  The F-axis is also in the
equatorial plane and points 90 degrees to the east of the GPM.
The G-axis is perpendicular to the true equator, and points
through the north pole.  The EFG system is also known as the True
of Day Rotating (TDR).

The EFG coordinate frame is particularly useful for launch
planning in that the components of the position/velocity state
vectors remain fixed.  The applicable times for each state vector
are generally referenced as an offset from launch time.  Based on
the predicted or actual launch time, TLEs for all orbital
segments can be computed with VEC2TLE by entering the vectors and
adding the time offsets to the launch time.
Page 3

1.1.3     Vector Units

VEC2TLE can compute TLEs from state vectors in any one of the
following sets of units:

     - kilometers (km), kilometers per second (km/s)
     - nautical miles (nm), nautical miles per second (nm/s)
     - feet (ft), feet per second (ft/s)

1.2       Keplerian Orbital Elements

Keplerian orbital elements provide a geometric description of the
size, shape, orientation, and in-plane phasing of a satellite
orbit.  The following is a brief description of the Keplerian
elements.  For further details, see references 2 through 5.

The size and shape of an elliptical orbit are described by the
semimajor axis and eccentricity respectively.  These parameters
also specify the perigee (closest distance to Earth) and apogee
(farthest distance from Earth) of the orbit.

The semimajor axis is half the longest distance across the
orbital ellipse.  The size of the semimajor axis determines the
orbital period, which is the time it takes for the satellite to
make one complete revolution or orbit.  The period is sometimes
used instead of semimajor axis.  The mean motion, which is
essentially the reciprocal of the period, is also commonly used
in place of semimajor axis (as is the case with TLEs).

The eccentricity describes how much the orbit deviates from
circular.  A perfectly circular orbit has an eccentricity of
zero.  As the orbit becomes more elongated the eccentricity
increases.  Eccentricity must remain less than one for an orbit
to be elliptical.  A value greater than or equal to one describes
an escape trajectory (parabolic/hyperbolic).

The orientation of the orbital plane is described by the
inclination and the right ascension of the ascending node (RAAN).

The inclination describes the tilt of the orbital plane with
respect to the equatorial plane.  The inclination specifies the
northern most and southern most latitudes over which the
satellite will directly pass.  An inclination of zero degrees is
an equatorial orbit; an inclination of 90 degrees is a polar
orbit.  Inclinations greater than 90 degrees describe orbits
moving against the rotational direction of the Earth
(retrograde).
Page 4

The ascending node of an orbit is its south to north equatorial
crossing point.  In astronomical terms, right ascension is the
angle measured eastward from the vernal equinox to the point of
interest.  Thus the RAAN is the angle measured eastward from the
vernal equinox to the satellite's south to north equatorial
crossing point.

The final orientation angle is the argument of perigee.  This is
the angle measured from the ascending node to the perigee point,
in the direction of satellite motion.

The in-plane phasing is specified by the true anomaly.  This is
the angle measured from the perigee point to the position of the
satellite at the epoch time of the element set.  Since satellites
in elliptical orbits do not travel at a constant speed, true
anomaly has a counterpart called mean anomaly, which describes
the angle from perigee to the satellite were the satellite in a
circular orbit.  There is a standard mathematical conversion
between mean and true anomaly, based on the eccentricity of the
orbit.  Mean anomaly is often used in place of true anomaly (as
is the case with TLEs).

1.3       Orbit Propagation Models

This section provides a general discussion of the SGP and SGP4
orbit propagation models.  A detailed discussion of the
mathematics involved is beyond the scope of this manual.

Elements representing the physical Keplerian parameters are
referred to as "osculating" elements.  The data in TLE format
represent fictitious "mean" values for the various orbital
elements.  This was done to accommodate both speed and
convenience in the process of computing positions and velocities
of the satellites.  Thus the introduction of osculating elements
for propagation in SGP or SGP4 would result in erroneous
predictions.

The procedure to compute position and velocity state vectors for
any desired time using SGP or SGP4 is well understood and
detailed in reference 6.  The basic perturbations that cause a
satellite's path to deviate from an ideal Keplerian orbit result
from 1) the non-spherical mass distribution of the Earth and 2)
atmospheric drag.  SGP and SGP4 apply these perturbational
effects to orbits by the technique known as variation of
parameters, where the parameters being changed are the orbital
elements.  If these effects were ignored and the orbit were
propagated using 2-body (i.e., Keplerian) orbit theory, the error
in the predictions would be apparent within the span of 2-3
hours.
Page 5

1.3.1     Earth Gravitational Modeling

SGP uses a 3rd order geopotential model to describe the mass
distribution of the Earth.  This includes the equatorial bulge
(2nd order) and the greater amount of mass in the southern
hemisphere (3rd order) that describes the characteristic "pear"
shape of the Earth.  SGP4 uses a 4th order geopotential model
which includes an additional mass deviation that is smaller than
the second and third order deviations.

The geopotential deviations from an "ideal" spherical mass
distribution result in predictable changes to the orbit.  The
primary gravitational perturbational effects are on the orbital
plane and the orientation of the orbit's apogee-perigee (or
apsidal) line.  The primary effects are "secular" in nature as
they represent constant drift rates for the ascending node and
the apsidal line as a function of time.  The constant drift rates
are a function of the semimajor axis, eccentricity, and
inclination of the orbit.  The secondary effects are periodic in
nature and consist of both long- and short-term effects.  The
long term periodics are superposed on the secular effects.  The
short-term periodics, in turn, are superposed on the long-term
periodic effects.

1.3.2     Atmospheric Drag Modeling

Both SGP and SGP4 use static methods to model the effects of
atmospheric drag on satellite orbits.  SGP assumes a quadratic
variation of the mean motion as a function of time.  The
quadratic coefficients are one sixth the second derivative of
mean motion with respect to time (nddot/6) for time squared and
one half the derivative of mean motion with respect to time
(ndot/2) for time.  SGP4 models the density of the Earth's upper
atmosphere using the fourth power of the orbital altitude.  SGP4
applies drag effects to the orbit using a pseudo ballistic
coefficient (B*), normalized to the orbital altitude and current
atmospheric density profile.  For both SGP and SGP4, the drag
coefficients (n dot/2, nddot/6 or B*) are usually empirically-fit
(based on long-term behavior) in the orbit determination process.
Page 6

2.0       INSTALLATION

The VEC2TLE software is designed to operate on an International
Business Machines (IBM) compatible Personal Computer (PC) using
the Microsoft Disk Operating System (MS-DOS) version 3.2 or
higher.  The computer must be equipped with a video display
compatible with one of the following standard PC formats: CGA,
Hercules, EGA, MCGA, or VGA.  The VEC2TLE software automatically
detects the display adaptor format and displays at the highest
possible resolution.  A hard disk is recommended.

VEC2TLE works on IBM compatible PCs in the MS-DOS environment.  A
math coprocessor is recommended for 8088 and 80287-based systems.
The typical computation times for a 12 Mhz 80287-based system is
about 3 seconds with a coprocessor versus about 15 seconds
without a coprocessor.  A 40 Mhz 80387-based system without a
coprocessor computes a TLE in approximately the same time as a 12
Mhz 80287-based system with a coprocessor.  Using a 50 Mhz 80486-
based system, there is no perceptible computation delay.

The software must first be installed on either a floppy diskette
or the computer's fixed (i.e., hard) disk.  You may install
VEC2TLE automatically by placing the distribution diskette in a
floppy drive and setting that floppy as the default drive.
Automatic installation is accomplished by initiating the
INSTALL.BAT batch file by typing:

     INSTALL [drive:][path]

The default drive and path for INSTALL.BAT is C:\VEC2TLE.  (You
may specify an alternate destination drive and path as shown
above in the optional command line parameters.)

The installation procedure may also be accomplished manually.
Let us assume an installation from floppy disk A: to hard disk C:

Place the software floppy diskette into drive A:

Set drive C: as the default drive:

     C: [ENTER]

Create a directory for VEC2TLE:

     MD C:\VEC2TLE [ENTER]


Set the VEC2TLE directory as the default path:

     CD \VEC2TLE [ENTER]
Page 7

Copy all files to the default directory:

     COPY A:[path]*.* [ENTER]

Note that the manual installation procedure may be modified to
accommodate a different destination drive letter, a different
installation drive letter, or a different VEC2TLE directory name
as desired.  This is accomplished by making the appropriate
changes to the above procedure as follows:

     a) DESTINATION DRIVE - substitute the actual destination
           drive letter (followed by a colon) for C:
     b) INSTALLATION DRIVE - substitute the actual installation
           drive letter (followed by a colon) for A:
     c) PATH - substitute the actual directory names
           (i.e., paths) for \VEC2TLE (or the installation path)

If a mouse is to be used with the software, it must have its
driver installed prior to initiating the VEC2TLE software.  For
further information, consult the documentation provided with your
mouse.

When posted on a bulletin board system, VEC2TLE and its
associated files are compressed into a .ZIP format file.  The
files name is indicative of the version of VEC2TLE contained
within.  The file naming convention is "V2Lyyww.ZIP".  The V2L is
the prefix indicating that this is a compressed version of
VEC2TLE.  the yy digits indicate the year in which the current
version was created.  The ww digits indicate the week (1-54) in
which the current version was created.  This is consistent with
the version number indicated on the copyright notice display.
For example, the current version of VEC2TLE (9421) would be found
in a file named V2L9421.ZIP when posted on a Bulletin Board
Service (BBS).  This file naming convention provides a convenient
mechanism by which users can determine whether or not they have
the most current version of the software.

The files contained in the compressed (i.e., .ZIP) file are as
follows:

INSTALL.BAT         Installation Batch File
VEC2TLE.EXE         Executable program file
VEC2TLE.CFG         Program configuration file
VEC2TLE.DOC         Software user manual
VEC2TLE.ICO         Icon suitable for use with Microsoft Windows
REGISTER.FRM        Registration Form
STS-57.VIF          Sample State Vector from STS-57 in VEC2TLE-
                    readable format
VEC2TLE.NEW         Changes since the previous release
Page 8

3.0       USER INTERFACE DESCRIPTION

The user interface is designed to be both intuitive and
functionally efficient.

The intuitive characteristics of the interface include its use of
many de facto standards for PC graphic user interfaces (GUIs) as
well as liberal use of labels and comments.  Access to different
screens flow in a consistent and logical (e.g. top-down or
left-to-right) fashion.  The "look and feel" of the GUI is
intended to follow the standards and conventions for Microsoft
Windows applications.  The intent is to minimize the need for the
new user to refer to this user manual.

The author also recognizes that experienced users prefer to have
"short cuts" rather than be required to perform a tedious series
of actions for an operation.  Thus the functionally efficient
aspect of the user interface is that many operations can be
accessed by single action "hot keys."

Other features of this interface also include the ability to
access an operation by several different methods and the ability
to gracefully exit from any operation as necessary.

Much of the user interface may be driven with a
Microsoft-compatible mouse.  The left button of the mouse
activates the mouse cursor at its present position on the screen.


3.1       Menu Activation

Individual menus are identified by their title labels on the menu
bar at the top of the screen.  Each menu title label has a
highlighted activation character.  Menus may be activated by
either the mouse or the keyboard.  When a menu is activated, its
functional selections appear below the menu title in the work
screen area.

To activate a menu by the mouse, place the mouse cursor over the
menu title (on the top menu bar) and press the left mouse button.

To activate a menu by the keyboard, simultaneously press the
[ALT] key plus the highlighted character's key in the desired
menu title (e.g. press ALT-F to activate the "File" menu).
Page 9

3.2       Menu Item Selection

All menu items are identified by a descriptive label.
Additionally, some menu items also have a "hot key" (listed to
the right of the label).  The menu item labels have a highlighted
selection character.  One menu item is always highlighted in
reverse video as the default for selection whenever a menu is
active.  A menu item may be selected by any one of the following
methods:

Place the mouse cursor on the label of the menu item and press
the left mouse button.  OR:

Move the highlighting selection (i.e. reverse video) bar with the
"up" or "down" arrow keys to the desired menu item and press the
[ENTER] key.  OR:

Press the key corresponding to the menu item label's highlighted
selection character.  OR:

Press the "hot key" associated with that menu item.  (Note that
the corresponding menu need not be active to select a menu item
by the "hot key.")

3.3       Dialog Boxes

The dialog boxes (or data input screens) are designed to
facilitate data entry, provide a degree of error checking, and in
many cases prevent the entry of erroneous data.  All dialog boxes
consist of a rectangular window with a double line border and a
drop shadow.  On the top bar of the window is a short title
descriptive of the data to be input in the dialog box.


3.3.1     Data Items

Data items in any dialog box may be selected by either the
keyboard or the mouse.  The [TAB] key is the selection device to
be used for the keyboard.  Pressing the [TAB] key selects the
data items in sequential order.  Note that when the last item is
selected, pressing the [TAB] key will select the first data item
on the list.  When using the mouse, place the mouse cursor on the
desired data item and press the left mouse button.

3.3.1.1   Text Items

Text items may be entered or edited via the keyboard.  Text items
are identified by a rectangular input box.  Some text fields have
a label that is highlighted when the text box is selected.  When
working with non-blank text items, it is important to know
whether you are in the "entry" or the "edit" mode.
Page 10

The text item is in the "entry" mode if the data presently in the
input line is highlighted (i.e., in reverse video).  (The cursor
must also appear as a blinking underscore character.)  In this
mode, the old value of the text input line will be deleted and
replaced with the characters typed from the keyboard as soon as
the first character key is pressed.  The "entry" mode may be
activated by moving the cursor to the input line by the Tab key.
You may also enter this mode by placing the mouse cursor on the
input box and pressing the left mouse button twice in rapid
succession (i.e., double-clicking).

The text item is in the "edit" mode if the data in the input box
is not highlighted and/or the cursor appears as a blinking
rectangle.  In this mode, the data may be edited in a fashion
similar to that for most word processor software (i.e.,
backspace, delete, right arrow, left arrow, etc.).  This mode may
be entered by changing the shape of the mouse cursor with the
[INSERT] key, or by a single press of the left mouse button while
the cursor is on the input box.  It should be noted at this point
that the shape of the cursor indicates whether new text will be
inserted in front of the cursor or will overwrite the existing
text.  If the cursor is the blinking underscore, new text will be
inserted in front of the cursor; if the cursor is the blinking
rectangle, then new text will overwrite the existing text.  It
should further be noted that the size of all text fields is
limited and when the maximum size is reached, no further
characters may be inserted.

3.3.1.2   Buttons

Most dialog boxes have two buttons: OK and Cancel.  These buttons
control the manner in which processing is to be performed using
the data from the input screen.  When a dialog box is in a
sequence, it may have a Prev button which allows the user to
return to the previous dialog box.  These buttons may be accessed
by either the keyboard or the mouse.

3.3.1.2.1 OK Button  Activating the OK button instructs the
software to process the input screen data.  The OK button is
activated by either of the following methods:

Move the cursor (with the [TAB] key) to any item except the
Cancel button and the press the [ENTER] key.  OR:

Place the mouse cursor on the OK button and press the left mouse
button.

3.3.1.2.2 Cancel Button  Pressing the Cancel button instructs the
software to abandon the current operation.  This has the effect
of ignoring any data input.  The Cancel button is activated by
any one of the following methods:
Page 11

Move the cursor (with the [TAB] key) to the Cancel button and
press the [ENTER] key.  OR:

Press the keyboard [ESCAPE] key.  OR:

Place the mouse cursor on the Cancel button and press the left
mouse button.  OR:

Closing the input screen window (ALT-F3 on the keyboard or
selecting the button in the upper left corner of the window with
the mouse).

3.3.1.2.3 Prev Button  Pressing the Prev button instructs the
software to return to the previous dialog box in a sequence.  The
Prev button is activated by either of the following methods:

Move the cursor (with the [TAB] key) to the Prev button and press
the [ENTER] key.  OR:

Place the mouse cursor over the Prev button and press the left
mouse button.

3.3.1.3   Radio Buttons

Radio buttons are helpful data input items in that they promote
speed of data entry and do not allow the input of "illegal"
values.  A radio button is used to select one and only one item
from a set (cluster) of possible values.  A radio button always
has two or more items and one (and only one) of these items is
always selected.  Radio buttons are delimited by parenthesis ().

The selected item in a radio button cluster may be changed by the
up and down arrow keys or by placing the mouse cursor on the item
to be selected and pressing the left mouse button.  Note that
radio buttons generally have labels with highlighted characters.
In such cases, an item may also be selected by pressing the key
corresponding to the highlighted character.

3.3.2     Other Features

The dialog boxes are constructed to appear at the center of the
work screen area. Should the dialog box be blocking needed data
in another open window, it is possible to move the input window
out of the way with the mouse.  This is accomplished by placing
the mouse cursor on the top bar then holding the left mouse
button down while moving the window by mouse action.

It is not possible to have two dialog boxes open simultaneously.
Page 12

3.4       Windows

Windows provide a means of visual information input and output
for VEC2TLE.  The dialog boxes and error messages fall into the
general category of windows.  As such, the information generally
applies to these windows, but more importantly applies to the
data output windows displaying the computed TLEs.

All windows can be moved around the desk top by activating the
cursor on the top bar and dragging the window.  In the upper left
corner of the window is a "close" button that will destroy the
window.  The currently-active window may also be closed by an
Alt-F3 hot key action as well as by selecting the Close item from
the Window menu.

The TLE output windows stack on top of each other in the desk
top.  A new window assumes its position in the desk top stack
with its order being immediately after the currently-active
window.  The user may move through the stack of windows in the
desk top to view previously-computed data.  This is accomplished
by the Pg Up (previous window) or Pg Dn (next window) hot key
actions or by selecting the corresponding entries under the
Window menu.

An output window may also be shrunk down to a only a small
fraction of the desk top size by dragging the lower right corner
with the mouse.  However, this action is not generally
recommended since the window will obtain the data from the last
TLE computation when the window is restored to fit the full size
of the desk top.  Restoring and/or centering the active window to
the full desk top may be accomplished by the activating the mouse
cursor on the arrow in the upper right corner of the window, by
the Alt-Z hot key action, or selecting the Zoom option from the
Window menu.
Page 13

4.0       OPERATING INSTRUCTIONS

This section provides the operating instructions for the VEC2TLE
software including any applicable background information.  It
should be noted that detailed explanation of each input option is
not provided as it would be redundant.  Rather, the operator
should have a functional understanding of the user interface
before attempting any serious operation of the software.

4.1       Startup

The software is initialized by setting the Disk Operating System
(DOS) default drive and directory (i.e., path) to that where
software resides.  For the purposes of these instructions, it is
assumed that the software resides on hard drive C: in directory
\VEC2TLE.  (If this assumption is incorrect, the information
below needs to be modified accordingly.)

Change to the default drive:

     C: [ENTER]

Change the directory to the program-resident directory:

     CD \VEC2TLE [ENTER]

Start the program:

     VEC2TLE [ENTER]

Note that VEC2TLE may also be initiated from the Microsoft
Windows operating environment.

4.2       File

This section provides a description of the functions listed in
the menu under the File heading.  As the name implies, these
functions are concerned with actions associated with input and
output files.  Files are selected using a list selector in a
dialog box.  The desired path and file name may be entered
directly or a "wildcard" may be entered altering the names
appearing in the scrollable list box.  Alternatively, the desired
file may be selected as a pick from the list box.  A short
history of wildcard entries are accessible from the down arrow to
the right of the wildcard entry area.

4.2.1     Vector Input File

The Vector Input File function allows the user to identify a text
file from which state vectors may be read for conversion to TLEs.
The default wildcard is *.VIF for the list box when selecting a
Page 14

vector input file.  If entering the path and file name directly,
the identified file must exist.  If the file does not exist, you
must respond to a dialog box with the following message:

     Error  Could not open file: [filename]

The identified file must contain a header line with a code
specifying the format and attributes of the state vectors.  The
code must apply to all state vectors in the file.  The code must
be a contiguous block of from one (1) to four (4) digits, must be
in the first 80 characters of the first non-blank line of the
file, and must be the first digit(s) appearing on that line
following an equal (i.e., '=') sign.  (Note that the first non-
blank line must be in the first ten [10] lines of the file.)  If
the code is less than four digits, leading zeros are implied.
The meaning of each digit is as follows:

     Ten Thousands  Vector Time Reference
     0              Coordinated Universal Time (UTC)
     1              Mission Elapsed Time (MET)

     Thousands      Inertial Reference Frame
     0              True Equator and Equinox of Date
     1              Mean Equator and Equinox of 1950

     Hundreds       Vector Type
     0              ECI
     1              EFG

     Tens           Vector Units
     0              km, km/s
     1              ft, ft/s
     2              nm, nm/s

     Ones           Vector Format
     4              Single line per datum
     5              Space delimited, two line
     6              Comma delimited, one line
     7              Single line per datum

If the code read in the file header is not within the bounds
listed above, VEC2TLE will present you with a dialog box with the
following message:

     Error  Unknown vector format in file: [filename]

An explanation of the vector file formats appears in Appendix D.
Appendix D also includes examples of the file headers as well as
each of the three basic formats.  There is no default vector
input file.
Page 15

4.2.2     TLE Input File

The TLE Input File function allows the user to identify a text
file from which TLE may be read for delta-V application.  The
default wildcard is *.TLE for the list box when selecting a
vector input file.  If entering the path and file name directly,
the identified file must exist.  If the file does not exist, you
must respond to a dialog box with the following message:

     Error  Could not open file: [filename]


4.2.3     TLE Output File

The TLE Output File allows the user to specify the file to which
TLEs are to be written.  The default wildcard is *.TLE for the
list box when selecting a TLE output file.  If the specified
output file name is entered directly and the output file does not
exist, it will be created; if the file does exist, any TLEs
written will be appended to the existing file.  If the file does
not exist and cannot be created, VEC2TLE will present you with a
dialog box with the following message:

     Error  Could not open file: [filename]

When a TLE output file is selected, its path and name are saved
to the configuration file (VEC2TLE.CFG).  This path and name are
used to identify the default output TLE file, which is opened at
program startup.  If no configuration file exists, or the default
configuration file is used, OUTPUT.TLE is the default TLE output
file.

4.2.4     Launch Date/Time File

The launch date/time file provides VEC2TLE with a satellite-by-
satellite reference of launch dates and times.  Reference to this
file is required if vectors are to use a Mission Elapsed Time
(MET) epoch reference (also called Ground Elapsed Time [GET]) or
if VEC2TLE is commanded to estimate the revoultion number of an
input state vector.

Once selected, the launch date/time file path and name are
automatically saved in the configuration file (VEC2TLE.CFG).

The launch date/time file is text-based and is structurally
identical to the STSORBIT PLUS launch time/date file
(STSPLUS.LTD).  Users of STSORBIT PLUS are encouraged to use the
STSPLUS.LTD file as the launch time reference.
Page 16

4.2.5     Output TLEs

The Output TLEs menu item is a toggle control that allows the
user to enable/disable the writing of the computed TLEs to the
output file.  This setting may be changed any number of times
during the program execution.  The default setting is to enable
output to the [default] output TLE file.


4.3       Settings

The selections made under the Settings heading apply to the
manual entry of position and velocity state vectors.  These
settings are format descriptors for the state vectors and their
associated times.

4.3.1     Defaults

The defaults are the settings saved in the program configuration
file (VEC2TLE.CFG).  If this file is not found at program
startup, a standard configuration file will be created.  Any
changes made under this menu item will be saved to the
configuration file once the OK button is activated or ENTER is
selected.  All configuration items are controlled by radio
buttons.  The following is a list of the configuration items:

INERTIAL REFERENCE  This setting applies only to ECI vector types
and selects the applicable inertial reference frame.  The choices
are:
     -- True equator, true equinox of date
     -- Mean equator, mean equinox of 1950

TYPE  Two cartesian vector types are supported:
     -- Earth-Centered Inertial (ECI)
     -- Earth-Fixed Greenwich (EFG) / True of Day Rotating (TDR)

VECTOR UNITS  Three sets of vector dimensional units are
supported:
     -- km, km/s
     -- nm, nm/s
     -- ft, ft/s

TIME FORMAT  Two UTC date and time formats are supported:
     -- YYYYDDDHHMMSS.SSS  (Year, Day, Hour, Min, Sec, Decimal
                           Sec)
     -- YYYYDDD.DDDDDDDDD  (Year, Day, Decimal Day)

Additionally, two MET date and time formats are also supported:
     -- DDDDDDDHHMMSS.SSS  (Day, Hour Min, Sec, Decimal Sec)
     -- DDDDDDD.DDDDDDDDD  (Day, Decimal Day)
Page 17

Note that VEC2TLE allows for implicit two-digit years to be
entered from 1950 to 2018 (inclusively).  If the first two digits
of the year are 00-18, the years 2000-2018 are assumed; if the
first two digits are from 50-99, the years 1950-1999 are assumed.

EPOCH CONTROL  The epoch time of the computed TLE may be one of
two times:
     -- The time of the State Vector
     -- The time of the Ascending Node (south to north equatorial
        crossing) prior to the State Vector epoch

Note that setting epoch of the TLE to the time of the State
Vector is slightly more accurate and is thus the preferred method
when there is a choice.

VECTOR TIME REFERENCE  The epoch time of input vectors may be
referenced by two possibilities:
     -- Coordinated Universal Time (UTC)
     -- Mission Elapsed Time (MET)

4.3.2     Inertial Reference

This menu item allows the user to override the default setting
for inertial reference without changing the value in the
configuration file.

4.3.3     Vector Units

This menu item allows the user to override the default setting
for vector units without changing the value in the configuration
file.

4.3.4     Epoch Control

This menu item allows the user to override the default setting
for the TLE epoch control without changing the value in the
configuration file.

4.3.5     Vector Time Reference

This menu item allows the user to override the default setting
for the vector time reference without changing the vaile in the
configuration file.

4.4       Launch Date/Time

This menu item allows the user to set (or change) the launch
date/time for any satellite in the launch date/time reference
file.  The launch date/time is stored for each satellite in units
of Julian Days and fractions of days.  This is the time elapsed
(in days) since 0.5 Jan 4713 B.C.
Page 18

4.5       Drag Multiplier

This function allows the user to manually set the drag multiplier
for any satellite in the drag reference file (VEC2TLE.DRG).  The
drag multiplier is used by the drag model to compensate for
differences between the actual and the model's "standard"
spacecraft ballistic coefficient and the actual and the model's
"standard" atmospheric density profile.

The drag multiplier is maintained/updated automatically by
VEC2TLE whenever the ndot/2 and/or Bstar drag parameters are
entered in with a state vector to compute Keplerian elements.
The current multiplier is updated by exponential smoothing with
what the multiplier should have been in order for the drag model
to compute the exact drag paratemer(s) which was/were entered.
The reason for the exponential smoothing is so that future drag
estimations will be based on the history of measured drag values.
This also allows empirical measurements by different methods to
all be assimilated into the drag multiplier.

One method to empirically estimate the ndot/2 drag parameter is
by measuring the change in the mean motion between two sets of
Keplerian elements as follows:

     ndot/2 = 0.5 * ( n(2) - n(1) ) / dt

     where:
     -- n(1) is the mean motion (rev/day) of one Keplerian TLE
     -- n(2) is the mean motion (rev/day) of the other
     Keplerian TLE
     -- dt is the time difference (days) between the epoch times
     (Te) of the two TLEs (i.e, dt = Te(2) - Te(1) ).

In order for the drag estimation method above to work properly,
the two TLEs should have a reasonable time separation (preferably
24 hours or more) and there should be no orbit-changing maneuvers
occurring between the two TLEs.

4.6       Compute TLE

The Compute TLE menu is where VEC2TLE performs its computational
function.  The vectors may be input manually or read from vector
input files.  For both cases, a reasonability check is run to
ensure that the input state vector represents a closed trajectory
(circular, elliptical), that the apogee of the orbit is above the
surface of the Earth, and the epoch time of the vector is not
zero.  If any if these conditions is violated, an error message
is displayed and the user is given the option to edit the state
vector or cancel the operation.
Page 19

It should be noted, for all TLE computation methods in this
section, that if either the ndot/2 or the Bstar drag parameter is
zero and the orbit theory is SGP4, the zero drag parameter will
be automatically computed from the non-zero drag parameter and
elements from the resulting TLE.

4.6.1     Input State Vector

The Input State Vector menu item allows the manual input of
position and velocity state vectors and associated data in order
to compute TLEs.  The following is a summary of the fields in the
input dialog box:

Satellite Name or ID          - 12 characters (max) free-form
Catalog Number                - 5 digit integer USSPACECOM ID
                                number
International Designator      - International Astronomical Union
                                (IAU) designator*
Position Vector Components    - 16 Character floating point or
                                scientific notation
Velocity Vector Components    - 16 Character floating point or
                                scientific notation
Vector Type                   - Radio Button
Time Format                   - Radio Button
Orbit Theory                  - Radio Button
ndot/2                        - 10 Character floating point or
                                scientific notation
nddot/6                       - 10 Character floating point or
                                scientific notation
Bstar                         - 10 Character floating point or
                                scientific notation
Element Set #                 - 3 digit integer
Rev #                         - 4 digit integer revolution number

Numeric fields are truncated when the first digit in the input
character string is not a legal part of an integer or floating
point number as applicable.  All characters after the first
illegal character are ignored.  Blank fields or those beginning
with an illegal character are interpreted as zero.

*The IAU designator has three components: year, sequential launch
of the year, and the sequential piece designator for that launch.
The year is invariably a two-digit number; the sequential launch
is invariably a three-digit number.  The piece designator is one
to three characters in length, with legal characters being A-Z,
excluding the letters "I" and "O".  The IAU designator is
generally right-justified with a space between the three
components if the sequential piece designator is a single letter.
Page 20

The latest data manually entered in the vector input dialog box
under the Input State Vector function is automatically saved in a
test file called OUTPUT.VIF.  This file is in the labeled data,
one item per line vector file format (see appendix D for
details).  This feature saves the user unnecessary typing if an
error in the inputs is detected after the program has been
exited.  This feature also provides a convenient method by which
state vector data may be easily shared with other VEC2TLE users.

4.6.2     Read Vector File

The Read Vector File menu reads the next sequential vector from
the input vector file and otherwise processes the data with the
same procedure for Input State Vector menu item.  If no vector
file has been selected, the following error message will be
displayed:

     Error  You must first identify a vector input file!

If the end of file (EOF) is reached when attempting to read the
state vector, the following error message be displayed:

     Error  End of File reached for: [filename]

See appendix D for vector file formats and examples.

4.7       Re-Epoch TLE at Asc Node

VEC2tle has the ability to move the epoch time on an existing TLE
to the time of the ascending node prior to the TLE's current
epoch time.  It should be noted that this feature is slightly
less accurate than deosculating a state vector directly at the
ascending node.  Thus, if the TLE must be epoched at the
ascending node and if the choice of inputs is an osculating state
vector or a TLE, the state vector is the data of choice.

The source for the TLE is the TLE input file if it has been
specified.  VEC2TLE reads the TLEs from this file in a sequential
fashion.  If the user wishes to skip to a TLE later in the file,
the 'Cancel' button should be activated until the desired TLE is
loaded.  If the user wishes to use a TLE earlier in the file, the
file should be re-opened under the TLE Input File option.  If
either no TLE input file has been designated or the TLE file has
been read past the last TLE, VEC2TLE allows the user to manually
input the TLE data.

4.8       Impulsive Delta-V

VEC2TLE has the ability to impart an impulsive or quasi-impulsive
delta-V to a TLE, computing the appropriate changes to the TLE.
This feature approximates the post-burn state vector and thus is
somewhat less accurate that a direct state vector deosculation.
Page 21

The source for the TLE is the TLE input file if it has been
specified.  VEC2TLE reads the TLEs from this file in a sequential
fashion.  If the user wishes to skip to a TLE later in the file,
the 'Cancel' button should be activated until the desired TLE is
loaded.  If the user wishes to use a TLE earlier in the file, the
file should be re-opened under the TLE Input File option.  If
either no TLE input file has been designated or the TLE file has
been read past the last TLE, VEC2TLE allows the user to manually
input the TLE data.

VEC2TLE performs some error detection and/or correction on the
TLE.  VEC2TLE cannot correct for: negative or zero mean motion,
eccentricity of one or more, or date/time errors in the TLE.

It should be noted that the element number and the revolution
number will be automatically incremented by VEC2TLE while it is
computing the post-burn TLE.

The delta-V burn data is entered in a dialog box following the
TLE input dialog.  This data must be entered manually.  The user
may return from this dialog box to the TLE dialog box by the Prev
button.

VEC2TLE will perform an impulsive (i.e., instantaneous) delta-V
at the burn ignition time if the burn duration, initial mass, and
final mass are all zero.  Otherwise, a quasi-impulsive burn is
assumed.  The difference between an impulsive and quasi-impulsive
delta-V is the effective time of the delta-V application.  The
quasi-impulsive delta-V assumes an impulsive burn at the time one
half the total burn delta-V is achieved.

If the delta-V is null (i.e., the three components are zero),
VEC2TLE will compute a new TLE representative of the orbit at the
effective time of the delta-V application.  This feature is
useful when the epoch on an element set needs to be moved to a
different time.

When a quasi-impulsive delta-V is requested, the mass/weight
units of the spacecraft and thruster propellant flow rate are at
the discretion of the user; the only restriction is that they
must be common units.  The total mass of the spacecraft must be
greater than the consumed propellant mass (i.e., initial mass
must be greater than the product of the burn duration and the
propellant consumption rate).

VEC2TLE cannot correct for the following in the delta-V data:
date/time errors, propellant consumption exceeding spacecraft
mass, or delta-V placing the spacecraft in an escape trajectory.
Page 22

4.9       Compute Date

This menu item is a date computation utility which is an on-line
complement to Appendix B of this User Manual.  This function
computes the month and day corresponding to a date input in
year/day-of-year format.  (The year/day-of-year format is
standard for space operations.)  An abbreviation for the day of
the week (Sun, Mon, Tue, etc.) is also provided.

4.10      Compute Day of Year

This menu item is a day-of year computation utility which is an
on-line complement to Appendix B of this User Manual.  This
function computes the sequential day-of year (1-366)
corresponding to a date input in MM-DD-YY format.  (The year/day-
of-year format is standard for space operations.)  An
abbreviation for the day of the week (Sun, Mon, Tue, etc.) is
also provided.

4.11      Program Termination

The program may be exited by either menu selection or by "hot
key."

To terminate the program by menu selection, activate the "Exit"
menu item in the "File" menu.

To exit the program by "hot key," depress ALT-X.
Page 23

5.0       REFERENCES

1.        Spherical Astronomy, Robin M. Green, Cambridge
          University Press, 1985.

2.        Fundamentals of Astrodynamics, Roger R. Bate et al,
          Dover Publications, Inc., 1971.

3.        Orbital Mechanics, Vladimir A. Chobotov, American
          Institute of Aeronautics and Astronautics, 1991.

4.        Orbital Motion, Third Edition, A.E. Roy, Adam Hilger,
          1988.

5.        Methods of Orbit Determination, Pedro Ramon Escobal,
          Robert E. Krieger Publishing Company, 1976.

6.        PROJECT SPACE TRACK, Models for Propagation of NORAD
          Element Sets, Felix R. Hoots and Ronald L. Roehrich,
          Spacetrack Report No. 3, ADC/DO6, December 1980.

7.        Computertalk Space Object Catalog, Joel Runes, 1992.

8.        Vector to Two-Line Elements (VEC2TLE) Orbit Computation
          Software, K. Ernandes, The AMSAT Journal, Volume 17,
          No. 2, pp. 26-29, March/April 1994.
Page 24

6.0       ACKNOWLEDGEMENTS

The author would like to express his appreciation to Dave Ransom
(Sysop RPV Astronomy BBS and author of STSPLUS) and Joel Runes
(Journalist and Computer Consultant) for their encouragement and
enthusiasm.  Without their timely and constructive comments,
VEC2TLE would be a less useful program.

Both Dave and Joel also provided valuable testing and validation
support during the STS-55, STS-56, and STS-57 missions as well as
key contributions to this User Manual.
Page 25

7.0       LICENSE STATEMENT

This software is protected by copyright law of the United States
of America.  This software is licensed as "Shareware".  This
software may be evaluated for a period of up to thirty (30) days.
If you wish to continue using this software after the initial 30
day trial period you must register.  You may not modify,
decompile, disassemble, or reverse-engineer the software, and you
may not remove or obscure the copyright notices.   Each
registered copy of this software may be used on only one computer
or one computer network at a time.

7.1       Registration

Registration of this software is accomplished by completing the
registration form (REGISTER.FRM) and remitting the $10.00 (U.S.)
registration fee as applicable in this section.  The registration
fee is applicable and required for all professional and
commercial users.  For the purposes of this section, a
professional or commercial user is defined as an individual or
organization who uses the data generated by the software in the
conduct, support, or pursuit of their profession or business.

Distribution of VEC2TLE by an Electronic BBS or by other
commercial shareware distribution methods is not considered
professional or commercial use of this software.  Distribution of
VEC2TLE-generated data (i.e., TLEs) are considered professional
or commercial use of this software.  Registration of a previous
release of VEC2TLE for professional use does not constitute
registration of any future releases.

The registration fee is not required (but would be appreciated)
for those using the software in support of a hobby.  For the
purposes of this section, a hobby is considered to be an activity
or pursuit for entertainment or relaxation purposes which is not
supporting professional or commercial activities.

Users who remit the $10.00 registration fee shall be licensed to
use the software for professional and/or commercial purposes.
Those licensed to use the software for professional and/or
commercial purposes shall receive a distribution diskette.  Users
who remit $20.00 shall receive a license to use the software for
professional and/or commercial purposes as well as a printed
version of the user manual found in the VEC2TLE.DOC file
(included with all distributions of the software).

7.2       Distribution

This software may be posted on Electronic Bulletin Board Services
(BBS) or otherwise distributed to individuals interested in its
capabilities.  This distribution is for the purpose of providing
Page 26

those individuals with the opportunity to evaluate its
capabilities under the above shareware restrictions.  When this
software is distributed, all original distribution files must be
included.  The following is a complete list of the original
distribution files:

INSTALL.BAT         Installation Batch File
VEC2TLE.EXE         Executable program file
VEC2TLE.CFG         Program configuration file
VEC2TLE.DOC         Software user manual
VEC2TLE.ICO         Icon suitable for use with Microsoft Windows
REGISTER.FRM        Registration Form
STS-57.VIF          Example State Vector from STS-57 in VEC2TLE-
                    readable format
VEC2TLE.NEW         Changes since the previous release

Except as stated in this section, you may not otherwise
distribute, lend, transfer, rent, lease, sub-license, or time-
share the software, diskettes, or documentation.

7.3       Limited Warranty

The publisher (Kenneth J. Ernandes) warrants the physical
diskette(s) and documentation provided to registered users (as
applicable) to be free of defects in materials and workmanship
for a period of ninety days (90) from the registration date.  If
the publisher is notified of defective materials or workmanship
during the warranty period, and such notification is determined
to be valid by the publisher, the publisher shall replace the
defective diskette(s) or documentation.

The entire and exclusive liability and remedy for breach of this
Limited Warranty shall be limited to replacement of defective
diskette(s) or documentation and shall not include or extend to
any claim for or right to recover any other damages, including
but not limited to, loss of profit, data, or use of the software,
or special, incidental, or consequential damages or other similar
claims, even if the publisher has been specifically advised of
the possibility such damages.  In no event will the publisher's
liability for any damages to you or any other party ever exceed
the registration fee paid for the license to use the software,
regardless of any form of the claim.

KENNETH J. ERNANDES SPECIFICALLY DISCLAIMS ALL OTHER WARRANTIES,
EXPRESSED OR IMPLIED, INCLUDING BUT NOT LIMITED TO, ANY IMPLIED
WARRANTY OF MERCHANTABILITY OR SUITABILITY FOR A PARTICULAR
PURPOSE.  Specifically, the publisher makes no representation or
warranty that the software is suitable for any particular purpose
and any implied warranty that the software is suitable for any
particular purpose and any implied warranty of merchantability is
Page 27

limited to the ninety-day duration of the Limited Warranty
covering the physical diskette(s) and documentation only (and not
the software) and is otherwise expressly and specifically
disclaimed.

This limited warranty gives you specific legal rights; you may
have others that vary from state to state.  Some states do not
allow the exclusion of incidental damages or consequential
damages, or the limitation on how long an implied warranty lasts,
so some of the above restrictions may not apply to you.

7.4       Governing Law and General Provisions

This license statement shall be construed, interpreted, and
governed by the laws of the State of New York.  If any provision
of this statement is found void, invalid, or unenforceable, it
will not affect the validity of the balance of this statement,
which shall remain valid and enforceable according to its terms.
If any remedy provided is determined to have failed of its
essential purpose, all limitations of liability and exclusion of
damages set forth in the Limited Warranty shall remain in full
force and effect.  The terms of this statement may only be
modified in writing signed by you and an authorized officer of
the publisher.  All rights not specifically granted in this
statement are reserved by Kenneth J. Ernandes.
Page 28

APPENDIX A -- HOT KEY SUMMARY


Menu Selection:

F10                           Menu Bar Selection
Alt-space                     =
Alt-F                         File
Alt-S                         Settings
Alt-C                         Compute TLE
Alt-W                         Window


Menu Item Selection:

=
About...                      N/A

File
Vector Input File             Alt-V
TLE Input File                Alt-E
TLE Output File               Alt-T
Launch Date/Time File         Alt-L
Output TLEs                   Alt-O
Exit                          Alt-X

Settings
Defaults                      F2
Inertial Reference            F3
Vector Units                  F4
Epoch Control                 F5
Vector Time Ref.              F6
Launch Date/Time              F7
Drag Multiplier               F8

Compute TLE
Input State Vector            Alt-I
Read Vector File              Alt-R
Re-Epoch TLE at Asc Node      ALT-N
Impulsive Delta-V             Alt-D
Compute Date                  Alt-A
Compute Day of Year           Alt-Y

Window
Close                         Alt-F3
Next                          PgDn
Previous                      PgUp
Zoom                          Alt-Z
Page 29

APPENDIX B -- SEQUENTIAL DAY OF THE YEAR

The tables in this appendix represent the sequential day of the
year corresponding to any date for both conventional years and
leap years.  The year and sequential day of the year is the most
common date format used for orbital applications.  The following
tables provide a look-up reference for conversion.

Table B.1  Day of the Year Calendar -- Non-Leap Years

Day  Jan  Feb  Mar  Apr  May  Jun  Jul  Aug  Sep  Oct  Nov  Dec
 1   001  032  060  091  121  152  182  213  244  274  305  335
 2   002  033  061  092  122  153  183  214  245  275  306  336
 3   003  034  062  093  123  154  184  215  246  276  307  337
 4   004  035  063  094  124  155  185  216  247  277  308  338
 5   005  036  064  095  125  156  186  217  248  278  309  339
 6   006  037  065  096  126  157  187  218  249  279  310  340
 7   007  038  066  097  127  158  188  219  250  280  311  341
 8   008  039  067  098  128  159  189  220  251  281  312  342
 9   009  040  068  099  129  160  190  221  252  282  313  343
10   010  041  069  100  130  161  191  222  253  283  314  344
11   011  042  070  101  131  162  192  223  254  284  315  345
12   012  043  071  102  132  163  193  224  255  285  316  346
13   013  044  072  103  133  164  194  225  256  286  317  347
14   014  045  073  104  134  165  195  226  257  287  318  348
15   015  046  074  105  135  166  196  227  258  288  319  349
16   016  047  075  106  136  167  197  228  259  289  320  350
17   017  048  076  107  137  168  198  229  260  290  321  351
18   018  049  077  108  138  169  199  230  261  291  322  352
19   019  050  078  109  139  170  200  231  262  292  323  353
20   020  051  079  110  140  171  201  232  263  293  324  354
21   021  052  080  111  141  172  202  233  264  294  325  355
22   022  053  081  112  142  173  203  234  265  295  326  356
23   023  054  082  113  143  174  204  235  266  296  327  357
24   024  055  083  114  144  175  205  236  267  297  328  358
25   025  056  084  115  145  176  206  237  268  298  329  359
26   026  057  085  116  146  177  207  238  269  299  330  360
27   027  058  086  117  147  178  208  239  270  300  331  361
28   028  059  087  118  148  179  209  240  271  301  332  362
29   029       088  119  149  180  210  241  272  302  333  363
30   030       089  120  150  181  211  242  273  303  334  364
31   031       090       151       212  243       304       365
Page 30

Table B.2  Day of the Year Calendar -- Leap Years

Day  Jan  Feb  Mar  Apr  May  Jun  Jul  Aug  Sep  Oct  Nov  Dec
 1   001  032  061  092  122  153  183  214  245  275  306  336
 2   002  033  062  093  123  154  184  215  246  276  307  337
 3   003  034  063  094  124  155  185  216  247  277  308  338
 4   004  035  064  095  125  156  186  217  248  278  309  339
 5   005  036  065  096  126  157  187  218  249  279  310  340
 6   006  037  064  097  127  158  188  219  250  280  311  341
 7   007  038  067  098  128  159  189  220  251  281  312  342
 8   008  039  068  099  129  160  190  221  252  282  313  343
 9   009  040  069  100  130  161  191  222  253  283  314  344
10   010  041  070  101  131  162  192  223  254  284  315  345
11   011  042  071  102  132  163  193  224  255  285  316  346
12   012  043  072  103  133  164  194  225  256  286  317  347
13   013  044  073  104  134  165  195  226  257  287  318  348
14   014  045  074  105  135  166  196  227  258  288  319  349
15   015  046  075  106  136  167  197  228  259  289  320  350
16   016  047  076  107  137  168  198  229  260  290  321  351
17   017  048  077  108  138  169  199  230  261  291  322  352
18   018  049  078  109  139  170  200  231  262  292  323  353
19   019  050  079  110  140  171  201  232  263  293  324  354
20   020  051  080  111  141  172  202  233  264  294  325  355
21   021  052  081  112  142  173  203  234  265  295  326  356
22   022  053  082  113  143  174  204  235  266  296  327  357
23   023  054  083  114  144  175  205  236  267  297  328  358
24   024  055  084  115  145  176  206  237  268  298  329  359
25   025  056  085  116  146  177  207  238  269  299  330  360
26   026  057  086  117  147  178  208  239  270  300  331  361
27   027  058  087  118  148  179  209  240  271  301  332  362
28   028  059  088  119  149  180  210  241  272  302  333  363
29   029  060  089  120  150  181  211  242  273  303  334  364
30   030       090  121  151  182  212  243  274  304  335  365
31   031       091       152       213  244       305       366
Page 31

APPENDIX C  -- ACRONYMS AND ABBREVIATIONS

ASCII          American Standard Code for Information Interchange
AFIT           Air Force Institute of Technology

BBS            Bulletin Board System

CGA            Color Graphics Adapter
CIM            CompuServe Information Manager

ECI            Earth-Centered Inertial
EFG            Earth-Fixed Greenwich (see also TDR)
EGA            Enhanced Graphics Adapter
EOF            End Of File

ft             feet
ft/s           feet per second

GET            Ground Elapsed Time (see also MET)
GSFC           Goddard Space Flight Center
GPM            Greenwich Prime Meridian
GPS            Global Positioning System
GUI            Graphic User Interface

IAU            International Astronomical Union
IBM            International Business Machines

km             kilometers
km/s           kilometers per second

M50            Mean Equator, Mean Equinox of 1950
MET            Mission Elapsed Time
MS-DOS         Microsoft Disk Operating System

NASA           National Aeronautics and Space Administration
nm             nautical miles
nm/s           nautical miles per second
NORAD          North American Aerospace Defense Command
NPOE           Numerical Prediction of Orbital Events

OIG            Orbital Information Group

PC             Personal Computer

RAAN           Right Ascension of the Ascending Node
RAID           Reports and Information Dissemination
RBBS           Remote Bulletin Board System
RPV BBS        Rancho Palos Verdes Astronomy BBS

SGP            Simplified General Perturbations
SGP4           Simplified General Perturbations Version 4
STS            Space Transportation System
STSPLUS        STS Orbit Plus
Page 32

TDR            True of Day Rotating (see also EFG)
TLE            Two-Line Elements

USSPACECOM     United States Space Command
UTC            Coordinated Universal Time

VEC2TLE        Vector to Two-Line Elements
VGA            Video Graphics Array
Page 33

APPENDIX D -- VECTOR FILE FORMATS

This section outlines the vector file formats accepted by
VEC2TLE.  It should be noted that these formats are modifications
to formats output by Dave Ransom's STSPLUS software.  The
modifications were coordinated with Dave and were made such that
they were generalized without impacting VEC2TLE's ability to read
an STSPLUS state vector.

The vectors read in by VEC2TLE are in standard PC text format or
American Standard Code for Information Interchange (ASCII).  The
specifications for these files is not overly rigid since VEC2TLE
is intended to be reasonably flexible in terms of ability to read
vector files.

D.1       Header Line

The header line defines the parameter definitions of the vector.
This is the input vector file's counterpart to the configuration
parameters.  The header line must be the first non-blank line in
the vector file and must occur within the first 10 lines of the
file.  The header line may have a maximum of 80 characters, but
will be terminated when the first character with ASCII code
outside the range 21-127 is detected.  (This range covers most
keyboard characters exclusive of the carriage return and line
feed.)  VEC2TLE searches for the first digit (0-9) in the header
line following the equal (i.e., '=') sign.  Once a digit is
detected, up to the next three characters are read until a non-
digit character is read.  VEC2TLE forms up to a 4-digit integer
that specifies the parameters applicable to all vectors that
follow in the file.  The first contiguous integer string (up to 4
digits) specifies the file format.  Note that leading zeros are
implied and need not be included.

The significance of each digit is listed below:

TEN THOUSANDS DIGIT - VECTOR TIME REFERENCE
0         Coordinated Universal Time (UTC)
1         Mission Elapsed Time (MET)

THOUSANDS DIGIT     - INERTIAL REFERENCE
0         True equator, true equinox of date or ECI
1         Mean equator, mean equinox of 1950

HUNDREDS DIGIT      - VECTOR TYPE
0         Earth-Centered Inertial (ECI/XYZ)
1         Earth-Fixed Greenwich (EFG)

TENS DIGIT          - VECTOR UNITS
0         km, km/s
1         ft, ft/s
2         nm, nm/s
Page 34

ONES DIGIT          - DATA MODE FORMAT
4         Labeled data, one item per line
5         Two-line space delimited data
6         Single-line comma delimited data
7         Labeled data, one item per line

Note that a '4' or a '7' for the data mode format indicates the
same vector file format.  This was done to accommodate vector
data output from STSPLUS.  (Data mode '4' in STSPLUS is identical
to data mode '7' except that state vectors are only written to
the output file immediately after the satellite has crossed the
ascending node.)

D.2       Vector Formats

This section specifies the three vector formats that VEC2TLE is
capable of correctly reading.  Each format has an example,
provided courtesy of Dave Ransom, using True equator/equinox ECI
vectors in units of ft and ft/s.  All vector formats have a
date/time format with a two-digit year and decimal day.

D.2.1     Two-Line Space Delimited

The two line space delimited format has the following data on the
first line: satellite catalog number, vector date/time format,
and the three components of the position vector.  The second line
has the three components of the velocity vector.  Each line may
be up to 80 characters long.

The example below has two state vectors in it.  Note that some of
the spaces have been removed in the interest of easily fitting
the data within the margins.

STSORBIT PLUS Data Output to STSPLUS.LOG, Data = 15
20580 93110.045081 13656864.66720 17514322.54968 -5452252.42794
      -16168.27686974290  15789.75251859515  10248.33566657315
20580 93110.045139 13575822.39276 17593013.13238 -5400930.14914
      -16248.48336702945  15686.35334359047  10280.38786725583

D.2.2     Single-Line Comma Delimited

The single-line comma delimited format has data in the following
order: epoch flag (single digit -- ignored), units flag (single
digit -- ignored), date/time, the three components of the
position vector, and the three components of the velocity vector.
Each vector line may be up to 130 characters long.

The example below has two state vectors in it.  Note that the
vectors have been placed on multiple lines in the interest of
easily fitting the data within the margins.
Page 35

STSORBIT PLUS Data Output to STSPLUS.LOG, Data = 16
0,1,20580,93110.0482060185,8771281.06140276,20969911.6226162,
   -2491608.1429704,-19762.0576284838,9623.02409449012,
   11524.6952898439
0,1,20580,93110.0482638889,8672341.7437806,21017717.5456987,
   -2433947.77946384,-19813.4647395816,9499.28476766938,
   11539.2506632381

D.2.3     Labeled Data, One Item Per Line

The labeled data, one item per line format has data in the
following order: satellite name or ID, satellite catalog number
and IAU designator, date/time, descriptive date time (ignored),
the components of the position vector, the components of the
velocity vector, ndot/2, nddot/6, and Bstar.  Each line may be up
to 80 characters long, but characters with ASCII codes outside
the range 21-127 are ignored.  VEC2TLE will also ignore any data
in columns 1-24 on the satellite name or ID line and will also
ignore data in columns 1-17 on the remaining lines.  The IAU
designator must be in column 32, following the satellite catalog
number.

The example below has one state vector in it.

Vector format = 1017
Satellite Name:         STS-57
Catalog Number:         22684  93 37  A
Epoch Date/Time:        93180.63736111111
                        06/29/1993  15:17:47.000 UTC
ECI X:                     8024498.723185 ft
M50 Y:                   -19652913.243254 ft
    Z:                     6620097.066346 ft
    Xdot:                     20418.75391 ft/s
    Ydot:                     11591.42188 ft/s
    Zdot:                      9232.20312 ft/s
ndot/2 (drag):              0.00002834000 rev/day^2
nddt/6:                       0.00000E+00 rev/day^3
Bstar:                        5.17270E-05 1/Earth Radii
Elset #:                               71
Rev @ Epoch:              126.10967365930
Page 36

APPENDIX E -- SOURCES OF STATE VECTORS

This section provides sources of state vector information.

E.1       The NASA OIG RAID-RBBS

Beginning with STS-61, NASA OIG RAID-RBBS [phone] [and
InterNet] has been posting state vectors in real-time for the
Space Shuttle.  These vectors are posted hourly between the hours
of 08:00 and 17:00 Eastern Time while the Shuttle is on orbit.
The vectors are in the ECI True Equator, True Equinox coordinate
system in units of km, km/s.

At the time fo this writing, these vectors are not formatted for
direct read by VEC2TLE.  However, the Sysop has indicated that an
intention of formatting these vectors in labeled data, one item
per line format described in section D.2.3.  The NASA OIG RAID
RBBS Sysop has also indicated that vectors may be posted
automatically and around the clock for all NASA-controlled Earth-
orbiting spacecraft.  See section F.1 for the NASA OIG RAID RBBS
address and further details for gaining access to this system.

E.1       NASA Spacelink

State vectors for current Space Shuttle missions may be obtained
from NASA Spacelink (see Appendix F.5 for log-on details).  There
is usually one vector posted each evening (approximately 17:00
Central Time) during an active Shuttle mission.  These may be
found under the following menu sequence: Current NASA
News::Current Shuttle Flight::Keplerian Orbital Elements/State
Vectors.  These vectors are in the ECI Mean of 1950 (M50)
coordinate system in units of ft, ft/s.  While these are usually
accompanied with TLEs, the state vector is usually more current
than the TLE.  At times planned maneuver data is posted as well,
which is useable in the Impulsive Burn function.

E.2       RPV BBS

Dave Ransom's RPV BBS  (see Appendix F.3 for details) is a source
of pre-launch nominal EFG vectors for Space Shuttle missions.
Due to the nature of EFG vectors, the nominal orbits of an entire
mission may be computed using VEC2TLE once the Shuttle liftoff
time is known.  This is accomplished by adding the vector offset
time to the launch time and using the EFG position and velocity
components as listed.  While this data are the predicted state
vectors, it can be very helpful when real-time information is not
available.
Page 37

E.3       NASA Television

NASA Television is a real-time source for Space Shuttle maneuver
burn data (the state vectors are not particularly legible).  NASA
Television is available by direct downlink from Spacenet 2
(located 69 degrees West), Transponder 5H (channel 9, horizontal
polarization) and on some cable TV systems.  (For what it's
worth, a group in Houston got their local cable TV company to
provide NASA Television by providing a petition with 300 names on
it.)  The audio portion of NASA Television is rebroadcast by many
HAM radio clubs through repeaters on VHF and UHF frequencies.
For a listing of known repeater locations and frequencies, see
file STSAUDIO.ZIP on the RPV BBS.

The burn data is useful in that it supplies the changes to the
Shuttle's velocity vector at the burn time.  If you supply
VEC2TLE with the Shuttle's most current TLE and burn data, you
can estimate the post-maneuver TLE using the Impulsive Delta-V
function.

E.4       CompuServe

The author periodically posts state vectors related to a Space
Shuttle mission in the CompuServe Astronomy, Space, and HamNet
Forums.  These vectors are part of general informational forum
messages (with the VEC2TLE-readable portion encapsulated between
dotted lines.  This portion of the message may be copied to a
text file (with a .VIF extension recommended) for use by VEC2TLE.
The CompuServe Information Manager (CIM) software has a copy-and-
paste feature and text file support that are well-suited to
accomplish this task.

E.5       Other Orbit Propagators

VEC2TLE may be used to convert the elements of other orbit
propagators to TLEs.  This assumes that you have that orbit
propagator available to you in order to compute positions and
velocities.  Those velocities, in turn, may be input to VEC2TLE
in order to compute TLEs representative of the other propagator's
orbital elements.

A good program to obtain is David Eagle's Numerical Prediction of
Orbital Events (NPOE).  This software propagates orbits by
numerical integration in a fashion similar to that done by NASA.
Output state vectors from NPOE may be used by VEC2TLE to compute
Keplerian TLEs.  To get further information on NPOE, send a SASE
to:
Page 38

          Science Software
          P.O. Box 2188
          Reston, VA 22090
          USA

          Attn: David Eagle
Page 39

APPENDIX F -- SOURCES OF TLEs

[This section was provided courtesy of Joel Runes.]

One of the most frequently asked questions is "Where can I obtain
TLEs?"  There are several different sources for TLEs which are
outlined in this section.

F.1       The NASA OIG RAID-RBBS

This source is the primary method to obtain TLEs on over 6,000
unclassified objects.  More than eight years in development, this
bulletin board system became operational in September, 1991, and
has revolutionized near real-time random access dissemination of
TLEs.  For a long time NASA discharged its responsibilities to
disseminate orbital elements to non-military users by mailing
Prediction Bulletins with TLEs, node crossing times and
longitudes, and information on other latitude crossings relative
to the node crossings.  This was a direct descendant of the
satellite observer network infrastructure of the late 1950's and
early 1960's.  The Prediction Bulletin system was quite limited.
Users were allowed to select a maximum of 20 satellites from a
list of only a thousand or so objects available at all.  The
predictions are in hardcopy form, received after postal delays,
and had to be hand-transcribed into computer systems to be of
much use.  The RBBS is a bulletin board system which replaced the
old Prediction Bulletins, saved innumerable forests from
destruction, saved the government money and provides useful
information to users WHILE it is still useful.  The RBBS is
maintained by a Goddard Space Flight Center (GSFC) contractor.

In order to use the RBBS, you MUST submit a WRITTEN request to
the address below.  No big song and dance is required in the
request (nor paid attention to).  Just state that you would like
to use the OIG's RAID-RBBS to download TLEs.  Mail the request to
the address below and they will mail you a copy of the User's
Guide and you User ID and initial password.  Why can't you
register online as you can with almost any other bulletin board?
Because NASA is part of the government and they say you can't.
The address:

                NASA Goddard Space Flight Center
                Project Operations Branch, Code 513
                Greenbelt, MD 20771  (USA)

                ATTN: OIG RAID-RBBS Access Request

When logged on to the RBBS there are two basic methods to obtain
TLEs.  For popular objects, such as manned spacecraft, ham sats,
weather satellites, communications satellites, Global Positioning
Page 40

System (GPS) satellites, visible satellites and recently launched
satellites, the RBBS has downloadable files with the most recent
TLEs.  For other satellites, rocket bodies and debris objects,
the RBBS has a random access database of TLEs which you may
query.  The database is keyed to the objects NORAD number.  A
cross-reference facility is available to correlate NORAD numbers
and Int's Designations.

F.2       Celestial BBS

While impatiently awaiting NASA's step forward into the era of
personal computers, Major T.S. Kelso, a professor at the Air
Force Institute of Technology (AFIT) in Ohio founded the
Celestial BBS.  It has been a source for TLEs since 1986 or so.
Originally the TLEs on his bulletin board were transcribed from
Prediction Bulletins.  Capitalizing on his Air Force contacts, he
has been able to distribute TLEs obtained from Space Command
since 1990.  The TLEs available on Celestial BBS cover hundreds
of satellites frequently of interest to the user community.  The
TLEs are maintained in downloaded files.  The bulletin board also
contains many programs to track satellites and maintain TLEs and
is a messaging facility for many satellite users and observers.
You CAN become a user of Celestial BBS by registering online,
the phone number is [phone].  The bulletin board is a free
access bulletin board but contributions are accepted and
deserved.  Even though the government has finally gotten around
to distributing TLEs in electronic form through the RBBS, Maj.
Kelso's bulletin board continues to provide an invaluable service
to satellite users and observers.

F.3       Dave Ransom's RPV BBS

While there is a number of bulletin boards which redistribute
TLEs from Celestial BBS and the RAID-RBBS, special mention should
be made of Dave Ransom's RPV BBS in Rancho Palos Verdes, CA.  The
phone numbers are [phone] for the main BBS and (310) 544-
8977 for the Hotline BBS.  In addition to compilations of TLEs
redistributed from the RBBS, Celestial BBS and the Canadian Space
Society BBS, the RPV BBS contains up-to-date versions of
satellite tracking software and utilities (including VEC2TLE) and
catalogs of orbiting objects.  It also contains much high quality
astronomical software,  Dave Ransom is the author of the STSORBIT
and STSPLUS satellite tracking programs.  STSPLUS is particularly
well-suited for use in conjunction with VEC2TLE.  In addition,
the RPV BBS is a premiere source for CURRENT TLEs during Space
Shuttle missions.  Shuttle TLEs are frequently available on the
RPV BBS hours sooner than they are available from any other
source due to Dave Ransom's persistence and resourcefulness.
Page 41

F.4       CompuServe's Astronomy Forum

For members of CompuServe, files containing TLEs are maintained
in ASTROFORUM Lib 3.  Messages relating to satellite viewing are
in Message Section 3 of the ASTROFORUM.  Access to CompuServe is
usually obtained on the first try as opposed to frequent busy
signals for Celestial BBS and RPV BBS.

F.5       NASA SpaceLink

NASA SpaceLink BBS is maintained by the Marshall Space Flight
Center in Huntsville, Alabama.  It can be accessed at (205) 895-
0028.  The BBS is primarily oriented to educators and contains
many files related to various spaceflight activities and
spaceflight-related educational opportunities.  It operates 24
hours/day and users may register online.  SpaceLink posts TLEs
for Shuttle missions and some other satellites.  It is also a
source for state vectors and press kits for NASA missions in
electronic form.
Page 42

APPENDIX G -- GENERAL INFORMATION

This section is used for information pertaining to general topics
related to VEC2TLE.

G.1       Suggested Uses for VEC2TLE

[This section was provided courtesy of Joel Runes.]

While the normal use of VEC2TLE is to generate TLEs from State
Vectors as outlined throughout this document, there are a number
of applications of VEC2TLE which may not be immediately obvious.
This section discusses some of those potential applications, but
this discussion should be considered representative rather than
exhaustive.  Uses of the program are constrained by the
imagination of the user more than by the limitations of the
software.

One use of VEC2TLE is to explore the effect of an orbit adjust
maneuver on the orbit of a spacecraft.  If the user has TLEs for
the object from before the orbit adjust maneuver, an alongtrack,
crosstrack, and radial delta-velocity may be applied to change
the TLE parameters or STSPLUS may be used to generate a state
vector at the time of the maneuver.  Given the latter case,
adjusting the values of Xdot, Ydot, and Zdot to reflect the
velocity adjustments associated with the maneuver, VEC2TLE can be
used to generate post-burn TLEs.  To compare the pre-burn
trajectory with the post-burn trajectory, simply use the pre-burn
and post-burn TLEs in a prediction program such as STSPLUS.  This
application has been successfully demonstrated during Shuttle
missions STS-56 and STS-55.  The result was useful post-burn TLEs
prior to availability of post-burn TLEs from Space Command.

Another use of VEC2TLE is to explore the effect on a satellite's
orbit due to minor dispersions in velocity and position during
the launch phase.  When a spacecraft such as the Space Shuttle is
launched, the desired post-launch state vector is used by the
spacecraft's and/or launch vehicle's guidance software.  But the
orbit achieved may vary from the planned orbit.  What effect does
that variation have on the orbit?  VEC2TLE is a valuable tool for
the exploration of this question.  Suppose that the desired post-
launch state vector is known (or assumed), and that the position
and time of the state vector are held constant.  Suppose further
that the achieved velocity in each axis varies by ± 0.2 ft/sec.
VEC2TLE can generate a number of TLEs, first for the nominal
trajectory, then for trajectories where the velocity components
are adjusted up and down by the 0.2 ft/sec dispersion assumption.
The resulting TLEs may be used with prediction programs such
STSPLUS to show the effect of the injection errors on the orbit
achieved and the satellite position at any time thereafter.
Page 43

Another use of VEC2TLE is to explore the required velocity change
to put a satellite into an orbit different from its initial
orbit.  There a large number of situations that can be examined
with the aid of VEC2TLE along these lines, but let's consider a
very simple situation.  A spacecraft is in an orbit with a very
low eccentricity -- approximately a circular orbit.  We desire to
raise the orbit's apogee by 500 km.  First we construct TLEs that
exhibit the low eccentricity and initial altitude.  The process
of constructing the initial TLEs may be simplified by using the
tables from Part 0 of the Computertalk Space Object Catalog
(reference 7 -- may be found on CompuServe Astronomy Forum and
many of the BBSs listed in Appendix F, files NC00.ZIP -
NC13.ZIP).  The next step is to generate a state vector for the
time when the apogee raising maneuver is to be performed (this
can be accomplished using STSPLUS).  In VEC2TLE, apply the
posigrade burn by incrementing the magnitudes of Xdot, Ydot, and
Zdot by the same percentage and maintaining the same sign for
each of the velocity components.  (An excellent first guess would
be to compute the two-body elliptical velocity using the standard
formula, which may be found in references 3-5.)  VEC2TLE can now
create a new set of TLEs which will have a perigee of the
original orbital altitude and an apogee which is greater
according to the percentage increase of the velocity components
applied.  Using either the Computertalk Space Object Catalog or
displays from a prediction program, you can determine whether the
apogee was raised by more or less than the desired 500 km.
Return to the original state vector and adjust the percentage
change to Xdot, Ydot, and Zdot until the desired 500 km apogee
increase is obtained.  To calculate the total change of velocity
which raised the apogee by 500 km, take the square root of the
sum of the squares of the changes to Xdot, Ydot, and Zdot.

While the previous example was relatively simple, the same basic
method of iteratively creating and examining the resultant TLEs
can be used to explore strategies for accomplishing the
rendezvous between orbiting objects.  Taking into account the
dispersions in the orbit determination process and the
effectiveness of orbit adjust maneuvers, the user can calculate
the required velocity change to accomplish a rendezvous sequence.
The ways in which VEC2TLE, in conjunction with satellite tracking
programs such as STSPLUS, may be used for the teaching of orbital
mechanics and astrodynamics in the high school, undergraduate, or
graduate school environments are limited only by the imagination
of the educators.  Educators who utilize VEC2TLE for such
instructional purposes are encouraged to contact the author so
that those educational strategies may be detailed in future
versions of this documentation.
Page 44

G.2       Planned Upgrades for VEC2TLE

This section provides information regarding planned upgrades to
VEC2TLE.  Registered users are always encouraged to suggest items
to be added to this list.  The following upgrades are planned for
the next (or some subsequent) release of VEC2TLE:

-- The ability to estimate the TLE drag parameters (ndot/2,
   nddot/6, and Bstar) based on spacecraft ballistic coefficient
   and solar activity.
-- The ability to read and write Keplerian elements in Amateur
   Radio Satellite (AMSAT) format if there is sufficient
   interest.
Page 45

APPENDIX H -- ABOUT THE AUTHOR

Ken Ernandes is an aerospace consultant specializing in
astrodynamics analysis, system simulation, and software
development.  He has a BS in Physics/Mathematics from Manhattan
College in New York City (1980) and a ME in Space Systems
Engineering/Engineering Management from the University of
Colorado at Boulder (1990).

Ken started in the space program after joining NORAD in October
1981, working as a crew Orbital Analyst in Cheyenne Mountain.
The job entailed detecting, tracking, identifying, and computing
orbits for all man-made Earth-orbiting satellites as well as
real-time analysis of foreign space events, support of manned and
unmanned space missions, direction of the worldwide tracking
network, precision orbital decay predictions, management of on-
line computer activities, and operational command briefings.

Ken was selected to be an Orbital Analyst Instructor in November
1981.  His job responsibilities included developing and
conducting initial and follow-on training for all crew-certified
Orbital Analysts as well as space indoctrination training for
senior and flag rank officers.  His greatest achievement as an
instructor was the development of the Orbital Analyst Positional
Handbook.  A derivative of this training manual and reference is
still in operational use today.

After leaving active service in the Air Force, Ken joined Martin
Marietta Aerospace, Denver, CO in July 1984.  During his tenure
at Martin Marietta, Ken was responsible for astrodynamics and
mission analysis as well as system and mission simulation for
design-phase spacecraft.

Ken joined Science Applications International Corporation in
October 1985.  At SAIC he was the lead orbital engineer in the
development of test scenarios; exercising Cheyenne Mountain's
computers under wartime conditions.  This led him to being the
lead test designer for integration testing of the Space Defense
Operations Center (SPADOC) computer upgrade.  Ken left SAIC in
April 1992 in order to become an independent consultant.

Ken may be contacted at the following addresses:

Ken Ernandes
16 Freshman Lane
Stony Brook, NY 11790-2712

CompuServe:    70511,3107
Internet:      [e-mail]  or  [e-mail]
Packet Radio:  N2WWD@N2BQF.#NLI.NY.USA.NOAM