  Among the recent advances and innovations in satellite communications,
Non-Geostationary Orbit (NGSO) satellite constellations are gaining popularity
as a viable option for providing widespread broadband internet access and
backhauling services. However, a more complex ground segment with multiple
ground stations is necessary due to these satellites' high speeds and low
altitudes. The complete dimensioning of the ground segment, including gateway
optimal placement and the number of ground access points, remains a relevant
open challenge. In this article, we provide an overview of the key factors that
shall be considered for NGSO gateway station geographical planning.
Subsequently, we propose a ground segment dimensioning approach that combines
several criteria, such as rain attenuation, elevation angle, visibility,
geographical constraints, and user traffic demands. The operational concept is
first discussed, followed by a methodology that combines all these constraints
into a single map-grid to select the best position for each gateway.
Furthermore, a case study is presented, which demonstrates the performance of
the proposed methodology, for one example constellation. Finally, we highlight
relevant open challenges and key research directions in this area.
