Obtaining other values from NASA 2-Line Element

Hi, We are trying to use the NASA two line elements as the source for
satellite nodes in Network Simulator (an open source network
simulation program) to generate simulation scenarios. Is there a
straight forward algorithm we can use to convert the NASA 2-Line
elements to get all of the values we need (altitude and semi-major
axis are not separately called out, and it would also be useful to fix
the start of the orbit at a specific point in time)? Below is the
excerpt from the NS-2 manual as well as what I believe I can get from
the 2-Line element. Thanks Ray

Value Source

altitude Can this be computed from
2-Line?
semi-major axis Can this be computed from
2-Line?
eccentricity 2-Line!
right ascension of ascending node 2-Line!
inclination 2-Line
time of perigee passage Argument-of-Perigee (is this
what I want?)?

For now it seems we need altitude and the semi-major axis, but as
these satellite orbits are continuously changing (at least for the
polar orbits) it would seem we want to tie them to a simulation where
we know what time we start and tie network events to them to see how
the orbits affect them (e.g. if we use a LEO bird it may not be in
view, but 5 minutes into the simulation come on line to affect the
available bandwidth).


From the ns-2 manual at http://www.isi.edu/nsnam/ns/doc/node200.html

# Position/Sat/Geo A geostationary satellite is specified by its
longitude above the equator. As simulation time evolves, the
geostationary satellite moves through the coordinate system with the
same orbital period as that of the Earth's rotation. The longitude
ranges from degrees. As we describe further below, two flavors of
geostationary nodes exist: ``geo'' (for processing satellites) and
``geo-repeater'' (for bent-pipe satellites). The node generator can be
used to create a geostationary satellite with an attached position
object as follows:

$ns node-config -satNodeType geo (or ``geo-repeater'') \bs
(other node config commands go here...)
set n1 [$ns node]
$n1 set-position $lon; # in decimal degrees

# Position/Sat/Polar A polar orbiting satellite has a purely circular
orbit along a fixed plane in the coordinate system; the Earth rotates
underneath this orbital plane, so there is both an east-west and a
north-south component to the track of a polar satellite's footprint on
the Earth's surface. Strictly speaking, the polar position object can
be used to model the movement of any circular orbit in a fixed plane;
we use the term ``polar'' here because we later use such satellites to
model polar-orbiting constellations.

Satellite orbits are usually specified by six parameters: altitude,
semi-major axis, eccentricity, right ascension of ascending node,
inclination, and time of perigee passage. The polar orbiting
satellites in have purely circular orbits, so we simplify the
specification of the orbits to include only three parameters:
altitude, inclination, and longitude, with a fourth parameter alpha
specifying initial position of the satellite in the orbit, as
described below. Altitude is specified in kilometers above the Earth's
surface, and inclination can range from degrees, with corresponding to
pure polar orbits and angles greater than degrees corresponding to
``retrograde'' orbits. The ascending node refers to the point where
the footprint of the satellite orbital track crosses the equator
moving from south to north. In this simulation model, the parameter
longitude of ascending node specifies the earth-centric longitude at
which the satellite's nadir point crosses the equator moving south to
north.17.3 Longitude of ascending node can range from degrees. The
fourth parameter, alpha, specifies the initial position of the
satellite along this orbit, starting from the ascending node. For
example, an alpha of degrees indicates that the satellite is initially
above the equator moving from north to south. Alpha can range from
degrees. Finally, a fifth parameter, plane, is specified when creating
polar satellite nodes- all satellites in the same plane are given the
same plane index. The node generator used to create a polar satellite
with an attached position object as follows:

$ns node-config -satNodeType polar \bs
(other node config commands go here...)
set n1 [$ns node]
$n1 set-position $alt $inc $lon $alpha $plane

Hi, We are trying to use the NASA two line elements as the source for
satellite nodes in Network Simulator (an open source network
simulation program) to generate simulation scenarios. Is there a
straight forward algorithm we can use to convert the NASA 2-Line
elements to get all of the values we need (altitude and semi-major
axis are not separately called out, and it would also be useful to fix
the start of the orbit at a specific point in time)? Below is the
excerpt from the NS-2 manual as well as what I believe I can get from
the 2-Line element. Thanks Ray

Go here for an explination of the 2 line format.

http://amsat.org/amsat/keps/formats.html

Hi, We are trying to use the NASA two line elements as the source for
satellite nodes in Network Simulator (an open source network
simulation program) to generate simulation scenarios. Is there a
straight forward algorithm we can use to convert the NASA 2-Line
elements to get all of the values we need (altitude and semi-major
axis are not separately called out, and it would also be useful to fix
the start of the orbit at a specific point in time)? Below is the
excerpt from the NS-2 manual as well as what I believe I can get from
the 2-Line element. Thanks Ray

Go here for an explination of the 2 line format.

http://amsat.org/amsat/keps/formats.html

In article ,
(Ray Williams) writes:
Hi, We are trying to use the NASA two line elements as the source for
satellite nodes in Network Simulator (an open source network
simulation program) to generate simulation scenarios. Is there a
straight forward algorithm we can use to convert the NASA 2-Line
elements to get all of the values we need (altitude and semi-major
axis are not separately called out, and it would also be useful to fix
the start of the orbit at a specific point in time)? Below is the
excerpt from the NS-2 manual as well as what I believe I can get from
the 2-Line element. Thanks Ray


Google for SGP and SDP. Those are the algorithms used with 2-line
elements to compute satellite position in an inertial reference
frame at any time. One is for low earth orbits and the other for higher
orbits - I can't remember which is which.

J

In article ,
(Ray Williams) writes:
Hi, We are trying to use the NASA two line elements as the source for
satellite nodes in Network Simulator (an open source network
simulation program) to generate simulation scenarios. Is there a
straight forward algorithm we can use to convert the NASA 2-Line
elements to get all of the values we need (altitude and semi-major
axis are not separately called out, and it would also be useful to fix
the start of the orbit at a specific point in time)? Below is the
excerpt from the NS-2 manual as well as what I believe I can get from
the 2-Line element. Thanks Ray


Google for SGP and SDP. Those are the algorithms used with 2-line
elements to compute satellite position in an inertial reference
frame at any time. One is for low earth orbits and the other for higher
orbits - I can't remember which is which.

J

(Ray Williams) wrote:

Hi, We are trying to use the NASA two line elements as the source for
satellite nodes in Network Simulator (an open source network
simulation program) to generate simulation scenarios. Is there a
straight forward algorithm we can use to convert the NASA 2-Line
elements to get all of the values we need (altitude and semi-major
axis are not separately called out, and it would also be useful to fix
the start of the orbit at a specific point in time)?

format http://www.mindspring.com/~n2wwd/htm...le_format.html
model http://celestrak.com/NORAD/documentation/spacetrk.pdf
library http://www.brodo.de/english/pub/sgp/

The answer to your question is in one or more of those; only you know
how much accuracy you require.

(Ray Williams) wrote:

Hi, We are trying to use the NASA two line elements as the source for
satellite nodes in Network Simulator (an open source network
simulation program) to generate simulation scenarios. Is there a
straight forward algorithm we can use to convert the NASA 2-Line
elements to get all of the values we need (altitude and semi-major
axis are not separately called out, and it would also be useful to fix
the start of the orbit at a specific point in time)?

format http://www.mindspring.com/~n2wwd/htm...le_format.html
model http://celestrak.com/NORAD/documentation/spacetrk.pdf
library http://www.brodo.de/english/pub/sgp/

The answer to your question is in one or more of those; only you know
how much accuracy you require.

"Ralph Mowery" wrote in message ...

Go here for an explination of the 2 line format.

http://amsat.org/amsat/keps/formats.html

Have already looked up the TLE, but after looking around some we found
at http://iss-transit.sourceforge.net/c...ions.java.html the
routine which converts out of the TLE to get us altitude and
semi-major axis. And being java guys we are happy as all we have to
do is a slight mod to that code and we are in business. Ray

"Ralph Mowery" wrote in message ...

Go here for an explination of the 2 line format.

http://amsat.org/amsat/keps/formats.html

Have already looked up the TLE, but after looking around some we found
at http://iss-transit.sourceforge.net/c...ions.java.html the
routine which converts out of the TLE to get us altitude and
semi-major axis. And being java guys we are happy as all we have to
do is a slight mod to that code and we are in business. Ray