I was drawn to this post because of where you are trying to retrieve data from and because I too have had problems with Net::Telnet scripts not working as expected... After much trial and error, I have arrived at a solution... not the best solution but it works. Most of your code is still there.

#!/usr/local/bin/perl
use strict;
use warnings;

#use Env qw(TERM);
#$ENV{TERM} = 'no-resize-vt100';  # doesn't work even if it is defined
+... at least on win2k with ActiveState Perl

use Net::Telnet;
my $connection = new Net::Telnet ( Host =>' ssd.jpl.nasa.gov',
                                Port => 6775,
                                Dump_Log   => './telnet.log',
                                Input_log  => './telnet.txt',
                                timeout => 10,
);
$connection->open();
$connection->print(''); # couldn't get the tty command to work either 
+but this forces it to continue
$connection->waitfor('/Press return to continue -->/'); # Is it waitin
+g for user input?
$connection->print('');    # what are you waiting for?  press return!
$connection->waitfor('/Horizons>\s+$/');
$connection->print('load vla-1');
$connection->waitfor('/Horizons>\s+$/');
$connection->print('page');
$connection->waitfor('/Horizons>\s+$/');
$connection->print('799');
$connection->waitfor('/.*Select.*: $/');
$connection->print('e');
$connection->waitfor('/.*Observe.*: $/');
$connection->print('o');
$connection->waitfor('/.*Coordinate.*: $/');
$connection->print('500@399');
$connection->waitfor('/.*Starting.*: $/');
$connection->print('1981-Mar-07 08:00');
$connection->waitfor('/.*Ending.*: $/');
$connection->print('1981-Mar-07 17:00');
$connection->waitfor('/.*interval.*: $/');
$connection->print('10m');
$connection->waitfor('/.*Accept.*: $/');
$connection->print('y');
$connection->waitfor('/.*Select.*: $/');
$connection->print('y');
$connection->print('q');
$connection->close;
exit 0;
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