The maximum viewing opportunity will be available in the last few days of October. 3I/ATLAS will reach its nearest point to the Sun on October 29-30, during which time it will no longer be visible from Earth. However, this would be the time when three spacecraft will be positioned to observe the alien comet.
Hera spacecraft flying to Dimorphos will enter the tail of 3I/ATLAS
European Space Agency's Hera spacecraft is set to encounter 3I/ATLAS between October 25 and November 1. It is travelling to the Didymos binary asteroid system, where it will study the crater made by the DART mission on Dimorphos. The mission altered its orbit in 2022, and Hera will measure the efficiency of the head-on collision.