Terahertz (THz) communication is considered as a promising technology for the Earth-space application due to its high potential of supporting large data capacity. However, THz wave suffers extreme attenuation from absorption of water vapor (WV) molecules in the propagation path. In this work, we present a theoretical model and analyze the capacities of both inter-satellite and geostationary satellite-to-Earth station (GEO-ES) optoelectronic links operating in the 100-500 GHz band within low- and mid-latitude regions. In our work, THz frequency windows in the 140, 220, 340, and 410 GHz bands with relatively low atmospheric loss are selectively used, targeting a data capacity of 10 Gbps per gigahertz. Our analysis indicates that, in the low-latitude regions, due to high water vapor density (WVD), transmitting and receiving antennas with extremely high gains are required. On the contrary, the mid-latitude regions require less power due to comparatively lower WVD. Moreover, due to seasonal variation in the mid-latitude regions, the requirement of link power budget is tens of decibels less in winter as compared to summer. The results suggest that the establishment of GEO-ES THz links in low- and mid-latitude regions is more realistic in the sub-THz bands, such as 140 and 220 GHz, while the potential of using higher carrier frequencies above 300 GHz for inter-satellite THz links, due to the absence of WV-induced absorption, is supported. (C) 2019 Optical Society America