The Southern African Large Telescope (SALT), currently being erected in Sutherland, South Africa, will be the largest single optical telescope in the southern hemisphere, and the 4th largest telescope in the world, when it is completed in late 2004. The SALT design is based on the Hobby-Eberly Telescope.
The prime focus payload design presented structural and layout challenges, since four instruments had to be accommodated in a restricted space envelope, combined with mass budget constraints. In addition, the secondary optics (spherical aberration corrector, atmospheric dispersion compensator), moving baffle/pupil mask and guidance system form part of the complete assembly.
To adhere to the mass budget and stiffness requirements the major structural components were manufactured from sandwich panels (foam core and carbon fiber skins). A volume that is actively cooled houses all electronics to prevent image degradation as a result of heat build-up. In addition to supporting closed loop guidance by means of four guidance probes (one per instrument bay) the payload also supports active focus control.
All components have been manufactured, good progress has been made on the integration and the aim is to have the payload functional in 2004.