In this paper, results of the NRL LHP experimental studies, conducted by Naval Research Laboratory (NRL) and NASA Goddard Space Flight Center, will be presented. Emphasis in this test program is to examine the “turnkey” startup of the NRL LHP and its operational characteristics. Series of tests were performed, including startup tests, power cycling tests, low power tests, and high power tests. The NRL LHP has demonstrated very robust operations throughout the tests. In addition, hysteresis was found at low power operations. Importance of the two-phase dynamics in the evaporator core is realized, which has shown significant effects on loop operations.