On-Orbit Temperature Sensor Calibration Using Phase Change Materials
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Solution Overview
Problem
Current methods for calibrating infrared instruments in-flight are inadequate as they rely on temperature sensors that drift over time, leading to inaccuracies in climate measurements, and existing calibration techniques do not provide absolute calibration.
Innovation Solution
A temperature calibration system using phase-change materials (PCMs) is employed, where a cell containing PCM is heated or cooled to induce a phase change, allowing temperature sensors to record the stable phase-change temperatures for calibration, enabling accurate recalibration and correction of sensor deviations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If temperature sensors are used for calibration in infrared instruments, then calibration can be performed, but the sensors drift over time causing measurement inaccuracies
Solution Approach 1:
The patent uses phase-change materials (PCMs) that undergo phase transitions at precisely known temperatures. During the phase change, the material maintains a constant temperature despite heat input, providing a stable reference point for calibration. This resolves the drift problem by replacing unstable sensor readings with the physically defined phase transition temperature, which does not change over time.
Solution Approach 2:
The phase-change material serves its own calibration function without requiring external temperature sensors. The material's inherent physical property (phase transition temperature) provides the reference, and the system self-calibrates by detecting the temperature at which the phase change occurs, eliminating reliance on drift-prone sensors.
2Measurement precision
If on-board blackbodies are used as reference points for calibration, then calibration can be performed, but the system is subject to temperature sensor drift
Solution Approach 1:
The phase-change material acts as an intermediary between the blackbody reference and the temperature sensors. Instead of directly measuring the blackbody temperature with drift-prone sensors, the system uses the PCM's phase transition as an intermediate reference point that occurs at a known temperature, providing a more stable calibration reference.
Solution Approach 2:
The patent introduces phase transitions as a new reference mechanism that is independent of the blackbody's temperature control system and its associated sensors. The phase change temperature is determined by the material's physical properties rather than sensor measurements, providing a more reliable reference.
3Measurement precision
If temperature sensors are re-calibrated yearly as recommended, then accuracy can be maintained, but this requires frequent interruptions and does not provide long-term stability for seven to ten year missions
Solution Approach 1:
The phase-change materials are pre-selected and pre-characterized to have specific, known phase transition temperatures. This preliminary preparation allows the system to perform self-calibration at any point during the mission without requiring external intervention or frequent re-calibration events, supporting long-term mission durability.
Solution Approach 2:
The system performs its own calibration using the phase-change materials, eliminating the need for external calibration events. The PCM-based reference provides ongoing stability throughout the mission lifetime, removing the requirement for yearly re-calibration interruptions.
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 a reliable, long-term, in-flight calibration system that ensures consistent and absolute calibration of temperature sensors, maintaining measurement accuracy over extended periods.
Implementation Method 1
a method and apparatus are disclosed in one embodiment of the present invention as including a temperature calibration system based on the melting or solidification of one or more phase-change materials (PCMs)
Implementation Method 2
a heat transfer device (e.g., heater, thermoelectric cooler (TEC)) located between the cell and the radiant portion of the blackbody may be used to heat or cool the phase-change material to effect the phase change
Implementation Method 3
One or more temperature sensors (e.g., thermistors, platinum resistance thermometers (PRTs)) to be calibrated may record the temperature change with time and identify the temperature plateau corresponding to the phase change
Data Source
AI summary
A method for on-orbit calibration of the temperature sensors of a simulated blackbody is disclosed. The method may include selecting a simulated blackbody traveling in a micro-gravity environment and comprising a sensor, a container positioned proximate the senor and containing a material, and a heat transfer device positioned proximate the at least one container. The heat transfer device may transition the material through a phase change. The temperature sensor may monitor the temperature of the material during the phase change. A correction may be calculated to correct any disparity between the temperature reported by the temperature sensor during the phase change and the known plateau temperature corresponding to that phase change. The correction may be applied to subsequent temperature readings obtained using the temperature sensor.