Came across this information on the ED forums from “Grimes.” I thought it most helpful for people trying to populate the Stennis with static objects and such for immersion during play. Might be useful here for the mission makers among us. Quote below is from “Grimes” of the ED Testers Team.
Spawning on the carrier has some pretty basic rules for ramp starts. It will spawn you based on where objects are at on the carrier and when you spawn. Spawning at mission start: 4 spawns on the “street” section. After the mission has started you cannot spawn there. Spawning at any time: Elevator 2, 3, and 4 each have two spawn points next to each other. It will always spawn on elevator 2 first, then 3/4 (I forget).
Some caveats, spawning may be different with the Tomcat due to its size. Forrestal class will probably have a different setup due to its elevator configuration. Plus ED might add/change spawns in the future, but this is how it currently works (2.5.4)