Challenger-A Upper Sensor Platform
The access panel to the jeffries tube to the external upper sensor platform is located right beside the turbo lift.
This jeffries tube leads directly up to another access hatch that also doubles as a airlock. On the other side of this access hatch is a small flat shaped room. It is impossible for most people to stand upright in this area as it is only 4' tall.
The primary systems for both short range and long range sensors are all located here. So are the primary communications systems.