Abstract: The Sun/Moon simulator facility is used in earth sensor lab for interface checking, mapping checks and other purpose used in geostationary satellites. This has been mounted in the earth lab in Laboratory for Electro Optics Systems (LEOS), ISRO. The overall design has been carried out in rational design. First we select suitable material for designing lead screw which fulfils the design requirements. A suitable AC motor along with a gear is selected, and bevel gear is used to convert rotary motion into a reciprocating motion of the simulator. To locate the simulator to desired location a horizontal beam has been designed with standard diameter which meets the design requirements & this simulator should travel freely.