First, open the archive; then copy the files into your ../Diaspora/Data/
directory (i.e. it ends up looking like "[WhereYouInstalledTheGame]/Diaspora/Data/MaruenStation/mod.ini"
). Next, open the Diapora launcher and select the "Mods" tab. You should see at least two entries; one for Diaspora, and one for Maruen Station. Select the "Activate" button for Maruen Station, and everything is ready!
You can start the mission by selecting "Tech Data" from the main screen (bottom left option), then "Mission Simulator" from that screen (top left, second option). Maruen Station should be on the list of that screen, but if not then check that the lower left has "Single Missions" selected and not "Campaign Missions". Happy hunting!