This paper presents an overview of the thermal analysis and results of the Hubble Space Telescope (HST) Servicing Mission 3A (SM3A). The shuttle mission took place from December 19-27, 1999, with the servicing mission taking place December 21-25, 1999. During the mission, several components were replaced during three planned Extra Vehicular Activities (EVAs). Also, a New Outer Blanket Layer (NOBL) was installed on several bays to repair the damage to the Multi-layer Insulation (MLI) that was seen during Servicing Mission 2.The timeline analysis predicts temperatures for all HST installed hardware in order to determine if they will remain within their temperature limits for the duration of Servicing Mission 3A. The maximum electrical power required by the HST while attached to the Orbiter is predicted and compared to the documented maximum. The analysis is done using two models, the Forward Section of the HST including all equipment bays and Solar Arrays, and the Aft Shroud of the HST including all axial and radial instruments. The divisions of HST can be seen in Figure 1. Fourteen different HST and shuttle attitudes or orientations were analyzed and integrated into the thermal math models, as well as over one hundred instrument and electronics configuration changes incorporated as outlined in the mission timeline. The two models use the same orientations and mission timeline but the analysis is conducted separately using different thermal computer codes. The results of the preflight analysis have been documented for use during the mission, and will be compared to the mission actual temperatures.