To add a system open the 'system.dat' file with notpad and scroll all the way down. 

start a new entery.
the format is as follows

|123|45|67|Milky Way|

123. This is the number used to link planets and systems together. it is called the ID#.(explorer ends at 3510 so start at 3511)

45. This is the 'X' coord on the star map.

67. This is the 'Y' coord on the star map.

Milky Way. This is the system name.

For Example.
the explorer comes with the last system/planet ID# being 3510.
so to add a new system called Gotha, at the center of the galaxy you would type:
|3511|0|0|Gotha|
To add information about the system you would type it between Gotha and the next system E.G.:
|3511|0|0|Gotha|This is the information about Gotha|

there is always a '|' ('shift' + '\') between numbers and systems. Here is an example of 4 systems (Kuat, Dilonexa, Cyax, Coruscant) in a row. note that one has information.

|43|122|20|Kuat||772|43|-123|Dilonexa|A huge planetary system consisting of 40 planets. The inner 22 are intensely-irradiated by the system's primary star, a gigantic blue-white fireball. The outer 17 planets are too far away to receive any heat from the star, and are froxen wastes. The middle planet is perfectly situated to allow life to exist there.|753|-210|291|Cyax||49|-16|36|Coruscant| 
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To add a planet to a new system or to a pre-existing one, open the 'planet.dat' file with notpad and scroll all the way down. 

start a new entery.
use this format:
|1|2|3|456|7|Earth|

1. this is the planet number the explorer comes with numbers up to 845 taken so start at 846.
2. this is the 'X' coord within the system.
3. This is the 'Y' coord within the system.
456. This is the number used to link planets and systems together. it is called the ID#. It is the only number that the system and planet share. each planet in the same system MUST have the same number. (explorer ends at 3510 so start at 3511)
7. This is the type of planet. See below for list with corusponding numbers.
Earth. This is the Planet name.

City Planet ID = 0    (Like Couriscant)
Desert planet ID = 1  (Like Tatooine)
Forest Planet ID = 2   (Like Yavin 4)
Gas Planet ID = 3     (Like Bespin)
Ocean Planet ID = 4   (Like Mon Calimari)
Snow Planet ID = 5  (like Hoth)
Swamp Planet ID = 6  (Like Dagobah)
Temperate Planet ID = 7  (Like Naboo)

For Example.
the explorer comes with the last system/planet ID# being 3510.
so to add a new gas planet called flare to Gotha. you would type:
|846|0|0|3511|3|Flare|
To add information about the planet you would type it between Gotha and the next system E.G.:
|846|0|0|3511|3|Flare|This is the information about flare|

there is always a '|' ('shift' + '\') between numbers and planets. Here is an example of 4 planets (Duroon, Honoghr, Kir, Knolstee) in a row. note that one has information.

||53|3|1|841|6|Duroon||54|8|5|40|1|Honoghr|A planet with three moons and the homeworld of the Noghri. Honoghr is a devastated world; almost all of its plant and animal life hasbeen destroyed. From space it appears to be uniformly brown, broken only by the occasional blue lake and the green area known as the Clean Lands.|55|3|7|779|6|Kir||56|5|3|324|2|Knolstee|
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