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JPL Horizons

Web interface

JPL HORIZON

Telnet example

Connect: 
telnet ssd.jpl.nasa.gov 6775
Choose Earth (399). 3: 3rd planet, 99: The planet itself: 
Horizons> 399
Enter E to select Ephemeris.
Enter to select Vectors.
Now: the coordinate center must be chosen. Using an id, one of 1500+ predefined sites can be selected. 500 is the geocenter. That's what I want here: 
Coordinate center [ <id>,coord,geo ] : ~500~
Press enter to confirm.
Reference plane: Choose e for eclip.
Starting TDB: for example 2017-01-01. Ending TDB: another date.
Output interval: 1d gives one record per day.
The returned coordinates (X, Y and Z) seem to be in kilometers.

Accessing cgi with a perl script

#!/usr/bin/perl
# 
# Access JOP's Horizons web interface.
#
# This script is an adapted version of a sample
# perl script written 2006-Mar-02 by Alain B. Chamberlin (JPL/Caltech).
# Unfortunately, I am unable to locate the script's url anymore.
#
# Use of this script is at your own risk.
#

use strict;
use LWP::UserAgent;

my @data = ( #_{
  "COMMAND    = 399"       ,
  "CENTER     = 500@0"     ,
  "MAKE_EPHEM = YES"       ,
  "TABLE_TYPE = VECTORS"   ,
  "START_TIME = 2017-01-01",
  "STOP_TIME  = 2017-01-10",
  "STEP_SIZE  = 1d"        ,
  "OUT_UNITS  = KM-S"      ,
  "VECT_TABLE = 2"         ,
  "REF_PLANE  = ECLIPTIC"  ,
  "REF_SYSTEM = J2000"     ,
  "VECT_CORR  = NONE"      ,
  "VEC_LABELS = NO"        ,
  "CSV_FORMAT = YES"       ,
  "OBJ_DATA   = YES"       ,
); #_}

for (@data) { #_{

# Remove any spaces surrouning '=' for compactness
  s/ *= */=/;

# Escape special URL characters
  s/ /%20/g;
  s/\&/%26/g;
  s/;/%3B/g;
  s/\?/%3F/g;

} #_}

# Create URL
my $url = 'https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&';
$url .= join('&', @data);

# print "URL: $url\n";

my $ua  = new LWP::UserAgent;
my $req = new HTTP::Request;

$req->method("GET");
$req->url($url);
my $res = $ua->request($req);
die "$url\n" . $res->status_line . "\n" if ( $res->is_error );

print $res->content;

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