this is a semi-known issue. I haven't seen any notes on it as of late in Bungie's 'known issues' article. I do recall it being in there at one point. As a workaround, you can have someone who has the Preservation mission unlocked launch you into it. I suggest you edit the tags in your post to include #bug and #bugreport for better visibility by the BNGHelp folks. The tags field is right above the yellow line below your post. It currently says #gameplay and #help on it.