You will need to script a conditional that checks the numeric boolean that monitors the Star Map quest.
I would like to be more helpful, but I cannot recall the boolean in question. There may be a look-up sheet for you on that...
Essentially, you need a very simple conditional -
"If my PC has completed 2 Star Maps, 'X' NPC spawns into the landing area."
However, you will either need to copy this script and add it to every landing pad, since you have no clue where your PC is when this script returns TRUE, or edit each script to call this script as a separate function. The code is small, so that is up to you - I am not sure which would be more elegant.
It will be inserted into the area's "on enter" script, and should be a fairly simple cut & paste affair after you get your code working successfully.
I would write the code for you, but I am unsure of the boolean in question - and the script to spawn an NPC is in the tut's and is simple, so you can simply add that as the outcome of your conditional returning TRUE.
happy modding, and wish i could be more helpful. good news - what you are trying to do is possible and not horribly difficult