The Marathon Internal Engineering Documents are a set of documentation about the UESC Marathon. Below is an excerpt.
== Section 1-c appendix H == Subject: Doors<br/> By: Estasia Orestes, Dominick I. Plackar, and Ursa Simbalzi<br/> Date:<2402.03.23.16.42><br/> There are five basic door designs to be used on the Marathon: 1. Outer Bulkhead Doors<br/> 2. Airlock Doors<br/> 3. Inner Bulkhead Doors<br/> 4. Tertiary or Inner Sealed Non-Vacuum Safe Doors<br/> 5. Quaternary or Inner Powered Automatic Opening Doors Direct control of all doors except the Tertiary and Quaternary doors will be given to Durandal with indirect control of all other doors going to Durandal. The difference between direct and indirect control primarily has to do with the manner of opening the doors. Durandal will only open a directly controlled door when he is specifically asked to do so. Indirectly controlled doors are automatically controlled by Durandal to open when needed. However, due to the expense involved with adding thermal and visual spectrum sensors to the Tertiary and Quaternary door groups, these doors will be minimally used. The expected savings of not using this extra sensory input is estimated to be fifty-seven percent of the base cost of the basic inner bulkhead door. The types of doors are all basically the same with some slight variations. The doors in classes 1 and 3 are the same doors classified separately to distinguish between the level of safety checking required to assure acceptable leakage. The airlock doors are specifically modified to work with manual and remote activation switches. Airlocks are all to be marked with a specific airlock symbol and to be outfitted with an air recharge system. The tertiary and quaternary doors are designed exactly as the bulkhead doors, but are checked coarsely for air leakage. This article as well as articles 530-f and 532-g on windows and elevators respectively will be placed for public access in the Marathon Internal Engineering Documents section 1-c appendix H.