  This paper develops a general observing strategy for missions performing
all-sky surveys, where a single spacecraft maps the celestial sphere subject to
realistic constraints. The strategy is flexible such that targeted observations
and variable coverage requirements can be achieved. This paper focuses on
missions operating in Low Earth Orbit, where the thermal and stray-light
constraints due to the Sun, Earth, and Moon result in interacting and dynamic
constraints. The approach is applicable to broader mission classes, such as
those that operate in different orbits or that survey the Earth. First, the
instrument and spacecraft configuration is optimized to enable visibility of
the targeted observations throughout the year. Second, a constraint-based
high-level strategy is presented for scheduling throughout the year subject to
a simplified subset of the constraints. Third, a heuristic-based scheduling
algorithm is developed to assign the all-sky observations over short planning
horizons. The constraint-based approach guarantees solution feasibility. The
approach is applied to the proposed SPHEREx mission, which includes coverage of
the North and South Celestial Poles, Galactic plane, and a uniform coverage
all-sky survey, and the ability to achieve science requirements demonstrated
and visualized. Visualizations demonstrate the how the all-sky survey achieves
its objectives.
