Liquid detector for thin-walled tanks operating in zero gravity

A liquid detector for detecting a liquid propellant in a thin-walled tank operating in zero gravity, said tank including a propellant management device which selectively positions the liquid propellant in said tank in such a way that, so long as liquid propellant exits outside of said propellant management device, the liquid propellant will locate itself in a region under said propellant management device due to surface tension forces which predominate in zero gravity, said liquid detector comprising:

• a heatinq means disposed on an outer surface of said thin-walled tank and proximate to said region;
• means for periodically activating said heating means for a preset period of time;
• a first temperature sensing means positioned on the outer surface of said thin-walled tank and directly opposite to said region, said first temperature sensing means being located on one side of said heating means;
• and
• a second temperature sensing means positioned on the outer surface of said thin-walled tank and at a location spaced apart from said region, said second temperature sensing means being located on a side of said heating means opposite to said first temperature sensing means;
• whereby when said heating means is selectively activated for said preset period of time, so long as liquid propellant is present at the wall of said thin-walled tank in said region, a temperature sensed by said first temperature sensing means will rise at a slower rate than that of a temperature sensed by said second temperature sensing means when no liquid propellant is present at the wall of said thin-walled tank proximate to said second temperature sensing means;
• and
• when liquid propellant is no longer present at the wall of said thin-walled tank in said region, the temperature sensed by both said first and second temperature sensing means will rise at substantially the same rate, and a quantity of said liquid propellant remaining in said tank is then known within the limits of a capacity of said propellant management device.

A liquid detector for detecting a liquid in a thin-walled tank operating in a zero gravity environment, said thin-walled tank including an internal zero gravity liquid management device which selectively positions the liquid in said thin-walled tank at a specific region along a wall of said thin-walled tank and under said internal zero gravity liquid management device due to surface tension forces which predominate in said zero gravity environment, said liquid detector comprising:

• a heating means disposed on an outer surface of said thin-walled tank and proximate to said region;
• means for periodically activating said heating means for a preset period of time;
• and
• a temperature sensing means positioned on the outer surface of said thin-walled tank and directly opposite to said region;
• whereby when said heating means is activated for said preset period of time, a change in temperature at said temperature sensing means is sensed and compared with known rates of temperature change for detecting conditions where liquid is present at said region or is absent from said region, and a quantity of the liquid remaining in the tank is then known within the limits of a capacity of said internal zero gravity liquid management device.