© 2015 IEEE. While terahertz (THz) communication systems, operating from 100 GHz to 1 THz, have the potential to exploit wide swaths of unused spectrum for ultra-high bitrate communication, there are significant challenges. Particularly, the strong absorption of water vapor can result in very high atmospheric attenuation. We modeled a ground to geostationary satellite link and found that using large aperture THz stations, patterned after the 12.5 m Atacama Large Microwave Array dish and the 3.5 m Herschel Space Observatory optics, worst 10th percentile data rates in excess of one terabit per second in the THz bands are possible. The key is to site ground stations in dry regions. We locate these by coupling our link model, which selects optimum modulation and carrier bandwidth, with global, high-resolution satellite water vapor measurements. We present detailed maps showing modeled link performance over the surface of the Earth. Smaller apertures on aircraft and balloons are also able to exceed 1 terabit/second due to their location above nearly all water vapor. Compared to free-space optical links, evidence suggests THz systems are superior where fog, cloud cover and clear-air turbulence are of concern.