Abstract: A liquid detector for thin-walled tanks Operating in a zero gravity environment (e.g., outer space). The liquid detector includes a small heater, such as a 1-watt patch heater, and two thermistors positioned on either side of the heater and diametrically opposed to each other. The heater and two thermistors are located on the outside of a propellant tank of, for example, a satellite. One of the thermistors is positioned directly over a region where a propellant management device retains liquid. The other thermistor is spaced apart from the region, while the heater is proximate to the region. In operation, the heater is activated for a short period of time and the change in temperature at each of the two thermistors is observed. The temperature of a thermistor located over a spot having liquid propellant in contact with the tank wall will increase less than the temperature of the thermistor located at a spot where no liquid propellant is present.