The configuration and thermal analyses of NASA’s Next Generation Space Telescope (NGST) Yardstick concept utilizing a novel sunshield approach for passive cooling is described. The NGST mission concept of a large aperture optical telescope passively cooled to less than 40 K and instrument detectors passively cooled to below 30 K is unique from any other mission flown to date. Achieving such a low operational temperature requires reducing by a factor of several thousand the internal heat dissipation and environmental heating of the telescope. The techniques for achieving these requirements, i.e. orbit selection, configuration, etc., along with the supporting thermal analyses are described.