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JPL Horizons web site
http://forum.celestialmatters.org/viewtopic.php?f=18&t=577
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Author:  John Van Vliet [ Tue, 17-09-13, 7:41 GMT ]
Post subject:  JPL Horizons web site

The JPL Horizons web site and the web browser interface
http://ssd.jpl.nasa.gov/horizons.cgi

This site will take a little bit of time to learn , but not too long .

this is only going to be a tutorial for Mars's moon Phobos
the first moon needing this moving out from the SUN

everything can then be applied to all the other moons in the solar system
a shell script using telnet might be a good option
but that will TAKE A LOT OF WORK to auto create the ssc file using new times for updates
-- a lot of work and very OS dependent , the linux version would not run on windows , without using MinGW ---

typing and screenshots will be needed
-- a lot of Screenshots

one thing you will notice is that if you do not remove all cookies on browser shut down .The site will remember the last settings you used
-- This is rather HANDY --
So you might want to place an exception on this site , and NOT remove the cookies for this site on browser shut down .
-- there are NO tracker cookies and Ghostery shows NONE

Image

on the horizons site you see the word " [change] "
Ephemeris Type [change]
Target Body [change]
and so on

set the first one to
Code:
"Ephemeris Type [change] :     ELEMENTS

Image

now the "Target Body"
naming is VERY consistent
301 = The Moon
401 = Phobos
402 = Deimos
Saturn's Hyperion is = 607
all the major moons are listed in the de430.bsp
minor moons no
click "change"
and type in 401 in the box for " Lookup the specified body:"
or
use the built in search in the box below that
select ( for mars) "other satellites"
and from that list select 401

now for the center
Code:
Center [change] :     Mars Barycenter [500@4]

After you click "change" you might want to read the help section below it
Quote:
Use body-center codes preceded by "@". For example, enter "@0" to select the solar system barycenter, "@sun" to select the sun-centered (heliocentric), or enter "@499" for Mars body-center. For a list of possible sites enter "500@*".


Code:
Time Span [change] :     Start=1900-02-04, Stop=1900-02-05, Step=1 d

this is off the time in the ssc . I use a 1 day step
( this needs to be done for the BEFORE SPICE time to create the orbital elements , then for the AFTER SPICE time done twice )

Code:
Table Settings [change] :     output units=KM-D

the default EXCEPT for the KM per Day
Image

then click the "generate ephemeris "
and you will get this output

Quote:
*******************************************************************************
Ephemeris / WWW_USER Thu Sep 19 01:00:18 2013 Pasadena, USA / Horizons
*******************************************************************************
Target body name: Phobos (401) {source: MAR097}
Center body name: Mars Barycenter (4) {source: DE-0431LE-0431}
Center-site name: BODY CENTER
*******************************************************************************
Start time : A.D. 1900-Feb-04 00:00:00.0000 CT
Stop time : A.D. 1900-Feb-05 00:00:00.0000 CT
Step-size : 1440 minutes
*******************************************************************************
Center geodetic : 0.00000000,0.00000000,0.0000000 {E-lon(deg),Lat(deg),Alt(km)}
Center cylindric: 0.00000000,0.00000000,0.0000000 {E-lon(deg),Dxy(km),Dz(km)}
Center radii : (undefined)
System GM : 3.1971209196502756E+14 km^3/d^2
Output units : KM-D, deg, Julian day number (Tp)
Output format : 10
Reference frame : ICRF/J2000.0
Output type : GEOMETRIC osculating elements
Coordinate systm: Ecliptic and Mean Equinox of Reference Epoch
*******************************************************************************
JDCT
EC QR IN
OM W Tp
N MA TA
A AD PR
*******************************************************************************
$$SOE
2415054.500000000 = A.D. 1900-Feb-04 00:00:00.0000 (CT)
EC= 1.518802729398433E-02 QR= 9.235563379461844E+03 IN= 2.565060806629375E+01
OM= 8.267052630230310E+01 W = 3.043077757667075E+02 Tp= 2415054.452730800025
N = 1.128072607904199E+03 MA= 5.332308948173263E+01 TA= 5.473479431620792E+01
A = 9.377996648522498E+03 AD= 9.520429917583151E+03 PR= 3.191283942873409E-01
2415055.500000000 = A.D. 1900-Feb-05 00:00:00.0000 (CT)
EC= 1.491431152955771E-02 QR= 9.238591426592475E+03 IN= 2.564909586037001E+01
OM= 8.268823417901352E+01 W = 3.051019373087076E+02 Tp= 2415055.410145357717
N = 1.127988147833037E+03 MA= 1.013549716911301E+02 TA= 1.030242084146312E+02
A = 9.378464771869112E+03 AD= 9.518338117145749E+03 PR= 3.191522895799846E-01
$$EOE
*******************************************************************************
Coordinate system description:

Ecliptic and Mean Equinox of Reference Epoch

Reference epoch: J2000.0
xy-plane: plane of the Earth's orbit at the reference epoch
x-axis : out along ascending node of instantaneous plane of the Earth's
orbit and the Earth's mean equator at the reference epoch
z-axis : perpendicular to the xy-plane in the directional (+ or -) sense
of Earth's north pole at the reference epoch.

Symbol meaning [1 day=86400.0 s]:

JDCT Epoch Julian Date, Coordinate Time
EC Eccentricity, e
QR Periapsis distance, q (km)
IN Inclination w.r.t xy-plane, i (degrees)
OM Longitude of Ascending Node, OMEGA, (degrees)
W Argument of Perifocus, w (degrees)
Tp Time of periapsis (Julian day number)
N Mean motion, n (degrees/day)
MA Mean anomaly, M (degrees)
TA True anomaly, nu (degrees)
A Semi-major axis, a (km)
AD Apoapsis distance (km)
PR Sidereal orbit period (day)

Geometric states/elements have no aberration corrections applied.

Computations by ...
Solar System Dynamics Group, Horizons On-Line Ephemeris System
4800 Oak Grove Drive, Jet Propulsion Laboratory
Pasadena, CA 91109 USA
Information: http://ssd.jpl.nasa.gov/
Connect : telnet://ssd.jpl.nasa.gov:6775 (via browser)
telnet ssd.jpl.nasa.gov 6775 (via command-line)
Author : Jon.Giorgini@jpl.nasa.gov
*******************************************************************************


this is where the order in the Phobos ssc comes in
--- the Timline section
Code:
 
     Timeline
     [
     # Before
     {
       OrbitFrame { EclipticJ2000 { Center "Sol/Mars" }}
       BodyFrame  { EquatorJ2000  {Center "Sol/Mars"  }}
       Ending    "1900 02 04 00:00:41.184 " # add 1 month for drawing orbit
       
       EllipticalOrbit
       {
         Epoch        2415054.500000000              # 1900 02 04
         Eccentricity       1.518802400727606E-02    # well Ecc.
         AscendingNode      8.267052630230310E+01    # Deg.
         SemiMajorAxis      9.377996595568880E+03    # Km.
         ArgOfPericenter    3.043077586819960E+02    # Deg.
         MeanAnomaly        5.332310656837983E+01    # Deg.
         Inclination        2.565060806629375E+01    # Deg.
         Period             3.191283906993064E-01    # days
       }
 

if you read the legend in the horizons output and the data in the first section
Code:
---------
*******************************************************************************
$$SOE
2415054.500000000 = A.D. 1900-Feb-04 00:00:00.0000 (CT)
 EC= 1.518802729398433E-02        QR= 9.235563379461844E+03              IN= 2.565060806629375E+01
 OM= 8.267052630230310E+01        W = 3.043077757667075E+02              Tp=  2415054.452730800025
 N = 1.128072607904199E+03        MA= 5.332308948173263E+01              TA= 5.473479431620792E+01
 A = 9.377996648522498E+03        AD= 9.520429917583151E+03              PR= 3.191283942873409E-01
---------------------------------

it is rather easy to copy/past into the ssc
Code:
        Epoch    = 2415054.500000000
         Eccentricity       =  EC -- first column  1.518802729398433E-02
         AscendingNode      = OM  -- first column   8.267052630230310E+01
         SemiMajorAxis      = A   -- first column  -- and so on ---
         ArgOfPericenter    = W  -- second column  -- and so on ---
         MeanAnomaly        = MA  -- second column   -- and so on ---
         Inclination        = IN - Third column
         Period             = PR - Third column

Author:  John Van Vliet [ Sat, 05-10-13, 5:28 GMT ]
Post subject:  Re: JPL Horizons web site

--- For now "ssd(dot)jpl(dot)nasa(dot)gov" still works - this might change ????????

Well the http site can not do everything . There is a warning about, in yellow, that on the page

http://ssd.jpl.nasa.gov/?horizons

you DO need to use the telnet or email if you want to create a naif .bsp( well .xfr) kernel

In keeping with the two comets posted other places here and there

and one i picked out of the "EAR_A_5_DDR_STOOKE_SHAPE_MODELS_V1_0.zip"

--- 1682q1halley.tab ---

converting this text file to something useful
Code:
( Longitude , Latitude , radii in KM )
    0    0      3.000000
    0    5      3.000000
    0   10      3.050000
    0   15      3.091299
    0   20      3.316565
    0   25      3.621386
    0   30      3.870000

to a mesh that can be used is more an artform to get something more than the bare facts

-- "just the facts mam , just the facts " - Dragnet

this is a tiny 73 x 37 pixel image or a uv sphere with 73 segments and 37 rings
that is for a different post

this is Horizons and telnet
the Wikipedia page is a good quick overview of what Telnet is

( the www before it was the www in the "Gopher" days )

it is a TEXT ONLY !!! as in you have to type into a terminal

-- for MS Windows users ( cmd.exe , or the new "power shell" that win7 has)

I use Bash ( well Konsole - the kde default terminal )


--- for now this .gov site is still working ---
Code:
telnet ssd.jpl.nasa.gov 6775


if you have not used it before and if yyou use tellnet and ssh reading the instructions is a good idea
http://ssd.jpl.nasa.gov/?horizons#telnet

Image

you can also type in " ? " from the on screen instructions ( in terminal session window)

type in " HALLEY " and you get a list

( the first one for this one is an asteroid
" 2688 1982 HG1 Halley "


i am just going to use the last one "900033" for 1994

Image Image

from the selection list at the bottom i want a "SPK" file and using all default settings so type in " s"

it will ASK for your e-mail address - type it in
then type in " y" to confirm it

now i only want a text file transfer format spice kernel ( a .xfr format file )

so for
Code:
SPK text transfer format  [ YES, NO, ? ] : y

then the start and stop dates
-- i am using the full start and stop times

Code:
 SPK object START [ t >= 1900-Jan-01, ? ] : 1900-Jan-01

--- then the stop date ----

SPK object STOP  [ t <= 2101-Jan-01, ? ] : 2101-Jan-01

--- then for this ---

Add more objects to file  [ YES, NO, ? ] : n

--- and this is the output you get ---

Converting SPK to portable transfer format .... standby 
 After FTP transfer, convert file back to binary form.
 
 You have 30 minutes to retrieve the following by anonymous FTP:
   Machine name:  ssd.jpl.nasa.gov
   Directory   :  cd to "/pub/ssd/"
   File name   :  wld2684.15
   File type   :  ASCII (transfer format)
   Full path   :  ftp://ssd.jpl.nasa.gov/pub/ssd/wld2684.15
 
 Select ... [E]phemeris, [M]ail, [R]edisplay, ?, <cr>:



use ftp or a web browser for the address you get

modern terminals have the r-click menu option to "open the link in default web browser"
normally that is in Firefox

mouse over the address "ftp://ssd.jpl.nasa.gov/pub/ssd/wld2684.15" and it should be underlined
click on it ( in the terminal )
-- windows "cmd.exe" -- copy/paste" it onto firefox or IE
but you might have to type the full address into the web browser

save the text in the browser window ( all 6.4 meg of it ) as " Halley.xfr "


this is where one of the Cspice tools comes into needing to be used
the program " tobin "


Code:
tobin Halley.xfr Halley.bsp

now it is converted into the usable binary format that celestia uses

you might want to double check the kernel
Code:
brief -c Halley.bsp
 
BRIEF -- Version 3.0.0, January 14, 2008 -- Toolkit Version N0064
 
 
Summary for: Halley.bsp
 
Body: HALLEY (1000036) w.r.t. SUN (10)
      Start of Interval (ET)              End of Interval (ET)
      -----------------------------       -----------------------------
      1900 JAN 01 00:00:00.000            2101 JAN 01 00:00:00.000
 




and this kernel can be used in a spice ssc file
Code:


Replace "Halley:1P Halley" "Sol"

    {
       Class "comet"
       Mesh    "HalleyComet.2ppd.bin.cmod"  # my mesh that I added data to from 1682q1halley.tab
   
       Radius               7.6     
       Albedo               0.2   

       OrbitFrame { EclipticJ2000 { Center "Sol" }}

       Beginning  "1900 01 01 00:00:00.000"
       Ending    "2101 01 01 00:00:00.000"
       
       SpiceOrbit
       {
         Kernel "Halley.bsp"
         Target "1000036"
         Origin "10"   
         Period  76
         BoundingRadius 1e10
       }   
       
       PrecessingRotation              #  from svn data/comets.ssc
       {
        Period             170          # 7.1 day axial rotation period
        Inclination         66   
        PrecessionPeriod     0.010      # 3.7 day precession period
       }
    }


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