Mount and Coudé Lab Thermal Control 25 August 2003 ATST CoDR Dr. Nathan Dalrymple Air Force Research Laboratory Space Vehicles Directorate

Coudé Lab Thermal Control Coudé lab will be held at a constant, uniform temperature –Instruments always immersed in same environment –“Shirt-sleeve” environment for investigators in lab Subjective, but probably in the range 15 < T coudé < 25 ˚C Telescope assembly will track ambient temperature –Varies by ~15 ˚C over day, ~20 ˚C over year Over much of the year, there will be a large volume of warm air beneath much cooler air—unstable situation

Coudé Lab Thermal Control warm cool Need some kind of “window” system Hole in deck

“Window” Requirements 1.Allow no more than error budget of seeing a.Diffraction limited: 10 nm rms wavefront b.Seeing limited: 0.03 arcsec, 50% enc. energy c.Coronal: 0.03 arcsec, 50% enc. energy 2.Pass entire wavelength range of telescope visible  thermal IR a.Truly simultaneous visible/IR observations require air “window” b.Visible and near-IR observations could use fused silica or similar window

Coudé Lab Thermal Control

Coudé Window Concept Ventilation reduces “chimney effect” Air knives act to contain separate air volumes Several possible windows: 1.Open (no window) 2.Fused silica 3.IR window

Mount Thermal Control Mount is shaded by enclosure Wind passes over mount Mount temperature will lag ambient (thermal inertia) Provision for drawing air through structural members to assist thermal equilibration

Higher wind = shorter time constant Lumped Capacity Mount Model