A PC-based computer program called ITAS is presented for spacecraft thermal analysis. The code supports full Monte Carlo ray tracing and/or conventional algorithms for view factors, shadow factors, orbital incident/absorbed fluxes, radiation interchange factors, and steady-state and/or transient temperature computations for stationary or spinning spacecraft. The geometry generator is based on primitives: polygon, box, hole-in-a-plate, cylinder, cone, disc, sphere, generic surface of revolution, generic parallelopiped, and elbow. The integrated thermal analyzer allows power and temperature profiles, thermostats, temperature-dependent thermal conductivity, user-defined nodes and conductances. Automatic 2D and/or box/plate conductance generation, single-phase fluid-flow modeling, sub-models, beta angle variation with time, spacecraft foot-print on the earth, integrated libraries for optical and physical properties and interfaces with SINDA, TRASYS, and NASTRAN.