From Halopedia, the Halo wiki
The Tycho Observation Facility is a United Nations Space Command facility located at the lunar crater of the same name. Elements of ONI Section One are embedded in the facility, which were responsible for tracking new arrivals to the Earth Defense Coordination Zone during the Battle for Earth. Some of these personnel reported directly to Captain Veronica Dare. At some point prior to the interrogation with the Huragok Quick to Adjust on November 15, 2552, they noted that the ship that Avery Johnson and Miranda Keyes returned to Earth aboard was in fact a Covenant vessel.