Spacecraft Propellant Gauging via Thermal Interface Detection

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Solution Overview

Problem

Current methods for gauging the quantity of liquid propellant in spacecraft tanks are inaccurate and require complex calibration, especially in microgravity environments, and are not suitable for all tank configurations or propellant levels.

Innovation Solution

A method that utilizes high-thrust phases to create conditions similar to gravity, allowing for rapid temperature measurements of the tank wall to detect the liquid-gas interface, enabling accurate propellant volume determination without prior calibration, using a heating member and temperature sensors positioned on the tank's outer surface.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If thermal gauging methods are used in microgravity environment, then propellant quantity can be assessed, but the methods require complex calibration operations and multiple sensors for each tank geometry

Engineering Contradiction:

Improvepropellant quantity assessment accuracyVSAvoidcalibration operations and sensor configuration

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The invention changes the acceleration parameter from microgravity (near-zero) to high-thrust conditions (greater than 0.05 m/s²), which fundamentally alters the liquid behavior in the tank. During high-thrust phases, the liquid forms a planar interface perpendicular to the thrust axis, enabling simple thermal gauging without complex calibration. This parameter change transforms the measurement conditions to achieve both accuracy and simplicity.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If Dead Reckoning method is used to count propellant consumed, then propellant quantity can be determined, but the reliability decreases as liquid propellant quantity decreases

Engineering Contradiction:

Improvepropellant quantity assessment reliabilityVSAvoidremaining liquid propellant quantity

Core Design Contradiction:

ReliabilityVSQuantity of substance

Solution Approach 1:

The invention performs thermal gauging measurements during high-thrust phases before the mission concludes, when sufficient propellant remains to maintain the liquid interface. This preliminary action during specific flight phases provides reliable baseline measurements that can be used to assess remaining propellant with high reliability, even as the mission progresses and propellant depletes.

Inventive Principle:

Principle #10Preliminary action

3Measurement precision

If TPGT method is used to determine propellant volume, then mass can be deduced, but the method can only be applied when propellant quantity is low and requires binding calibration operations

Engineering Contradiction:

Improvepropellant mass determination accuracyVSAvoidapplicability to different propellant quantities

Core Design Contradiction:

Measurement precisionVSAdaptability or versatility

Solution Approach 1:

The invention changes the operational parameter from static microgravity conditions to dynamic high-thrust conditions, which fundamentally alters how the liquid distributes itself in the tank. During high-thrust phases, the liquid forms a predictable planar interface regardless of the total quantity, enabling the thermal gauging method to be applied across a wide range of propellant quantities without calibration, thus achieving both precision and versatility.

Inventive Principle:

Principle #35Parameter changes

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This method provides accurate and reliable propellant gauging, applicable to various tank configurations and propellant levels, improving mission duration estimation and compliance with de-orbit regulations by determining the exact moment of the liquid-gas interface during high acceleration.

Implementation Method 1

heating the wall of the tank using the heating member

Methodology Applied

Scientific EffectThermal conduction: Conduction (thermal)

Implementation Method 2

acquiring measurements of the temperature of the wall of the tank using the temperature sensor

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Data Source

PatentUS11307077B2Method for thermally gauging the tank of a spacecraft and a spacecraft equipped with means for implementing such a method

Publication Date: 2022.04.19 AIRBUS DEFENCE & SPACE SAS

AI summary

Disclosed is a method for gauging the liquid propellant tank of a spacecraft during a phase of high-thrust along an axis, the tank being thermally conductive and having a known geometry. The method includes steps of: attaching, on a wall of the tank, a heating member and at least one temperature sensor in proximity to the heating member and in a plane of interest perpendicular to the thrust axis; during the high-thrust phase, heating the wall of the tank and acquiring temperature measurements of the wall of the tank at rapid frequency; determining the instant I when the temperature measured by the sensor changes, such change indicating the presence of the liquid-gas interface in the tank in the plane of interest; and determining the volume of liquid propellant present in the tank at instant I.