Normally Unattended Facilities (NUF) are those where operations are either completely automated or operated remotely, with no personnel typically onsite. Currently, NUFs tend to be relatively simple facilities; the primary goal of this white paper is to explore how NUF operational principles can be applied to more complex facilities. This white paper examines the design principles governing NUF, including the reduction of site working hours and the removal of typical attended facilities equipment or systems such as living quarters, helidecks, and life support. The paper identifies the anticipated challenges such as remote operations, automation or elimination-by-design of routine maintenance, and equipment reliability that will need to be addressed to allow the implementation of long duration NUF concepts.