Results of the simulation of the startup from a frozen state of a molybdenum heat pipe with lithium working fluid are presented and discussed. The 1.8-m-long heat pipe was tested in the horizontal position and had a liquid annular space between the porous wick and the wall. The 30-cm-long evaporator section was inductively heated and the 147-cm-long condenser was cooled by thermal radiation to the quartz tube enclosing the heat pipe and to the ambient. The space between the quartz tube and the heat pipe was evacuated in order to minimize heat losses by convection and conduction. Model results on the progression of the thaw front, liquid pooling at the end of the condenser, and the wall temperature along the heat pipe were found to be in good agreement with experimental measurements. Results showed that, as the heat pipe reached quasi-steady state operation at an evaporator wall temperature of 1550 K, the wall temperature near the end of the condenser dropped precipitously by 450 K, because of the formation of a 8.3-cm-long liquid plug and the end heat losses in the condenser.