Method for thermally gauging the tank of a spacecraft and a spacecraft equipped with means for implementing such a method

A method for gauging the liquid propellant tank of a spacecraft, said propellant tank comprising a thermally-conductive wall, having a known geometry and containing a volume of liquid propellant, and said spacecraft being equipped with means of propulsion capable of exerting, according to a given thrust axis, a high thrust allowing said spacecraft to achieve an acceleration of greater than or equal to 0.05 m/s2,

• said method comprising steps of:
• during a phase of high-thrust along said thrust axis exerted by said means of propulsion supplied with liquid propellant from said propellant tank, remotely controlling said spacecraft in which are attached, on an outer surface of said wall of the tank, a heating member and at least two temperature sensors, each of which is in a known position in proximity to said heating member and arranged on the outer surface of the wall of the propellant tank in a position for measuring the temperature of said wall, in a plane perpendicular to said thrust axis, referred to as plane of interest, in which the liquid-gas interface in said tank is likely to be located at some time during a phase of high-thrust exerted by said means of propulsion along said thrust axis, said temperature sensors being aligned along a so-called measurement axis, the heating member having a height, measured along said measurement axis, that is greater than the height occupied by said temperature sensors along said measurement axis, and a height of the heating member protruding beyond an end temperature sensor being greater than a distance between adjacent temperature sensors arranged along said measurement axis, further comprising the steps of:
• heating the wall of the tank using the heating member;
• and acquiring measurements of a temperature of the wall of the tank using a first of said temperature sensors, at an acquisition rate of one measurement every 30 seconds or less;
• determining a moment I at which the temperature measured by said temperature sensor changes, which corresponds to a moment at which a break of slope occurs on a digital curve representing the temperature recorded by said temperature sensor as a function of time, such a change indicating a presence, in the plane of interest associated with said first temperature sensor, of the liquid-gas interface in the tank;
• and determining, from a geometrical data of the tank and the known position of the first temperature sensor on the wall of the tank, the volume of liquid propellant present in said tank at the moment I.