Why does the Deep Space Network need three antenna sites?
If we only had one antenna site, as the Earth rotated, any spacecraft we were communicating with could only be in ‘line of sight’ with that one location for a maximum of 10 – 12 hours a day. The rest of the time the one site would be turned away from the spacecraft because the Earth rotated. By having three sites, as the Earth rotates, the first antenna site ‘hands off’ the tracking to the next site, thereby maintaining constant communications. So California hands off to Canberra, and Canberra to Madrid, then back to California.
