Active Thermal Regulation System
Active Thermal Regulation System
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Yonder Dynamics @ UC San Diego • Oct 2025 - Feb 2026 | Mars Rover Life Detection System 2.0
Tag: Active Cooling SystemBackground and Motivation
Background and Motivation
During URC 2025 field testing, elevated desert temperature (35-40°C ambient temperature) caused degradation of Nile Red assay chemicals, leading to inconsistent optical readings.
To ensure repeatable in-field life detection experiments, the Science Module needs active thermal regulation that is capable of maintaining sub-ambient internal temperature under desert operating conditions.
The target objective here are:
Maintain a controlled sub-20°C internal environment
Stabilize temperature-sensitive chemical assays
Operate reliably in 35-40°C ambient desert temperature
This active thermal regulation system project is a part of Mars Rover Life Detection System 2.0
Cooling Architecture Trade Study
Cooling Architecture Trade Study
Passive Ice + Fan Cooling
Passive Ice + Fan Cooling
Pros:
Simple implementation
Low electrical demand
Limitations:
Potential logistical constraints (transport and melting)
No controllability
Mini Vapor-Compression Refrigration
Mini Vapor-Compression Refrigration
Pros:
High thermodynamics efficiency
Industry-standard refrigeration method
Limitations:
Bulky and heavy
Poor fit within rover mass constraint
Thermoelectric (Peltier) Cooling System
Thermoelectric (Peltier) Cooling System
Pros:
Compact size
Modular scalability
No logistical dependence
Limitations:
High electrical power consumption (12V, 4-5A per module)
Lower efficiency compared to vapor compression
Comparing the pros and limitations of each system, thermoelectric cooling system was selected due to compactness, modularity, and compatibility with rover power budget.
System Working Principle
System Working Principle
A Peltier (TEC) module creates a temperature difference(ΔT) when current is applied, producing a cold side and a hot side.
Critical requirement for this system:
The hot side must be actively cooled to maintain cold-side performance.
If insufficient heat rejection occurs, the system thermally saturates and cooling collapses.
Therefore, to maximize heat rejection efficiency, a water-cooled hot side architecture was selected over air cooling.
Major components used in this system:
Major components used in this system:
Peltier module (TEC), water block (hot side), heat sink + fan (cold side), DC water pump, 240mm radiator, tubing and fittings, PU foam, and water reservoir.
Heat flow path:
Heat flow path:
Heat generated inside the Science Module is conducted to heatsink, which is attached to the cold side of Peltier Module, which eventually leads to water block that is attached to the hot side of Peltier Module.
The circulating water, absorbs heat from the water block and transports it to the radiator.
The radiator dissipates heat to the environment.
Mechanical Integration
Mechanical Integration
Peltier Stack Assembly
Peltier Stack Assembly
This module is stacked in the following order (from top to bottom):
Water block → TEC (Peltier) → Aluminum plate → Heatsink → Fan
Thermal paste is applied at all interfaces, and clamping force was added to ensure effective heat transfer between each interface. Assembly is mounted to top enclosure for vertical heat extraction.
Insulation Strategy
Insulation Strategy
To reduce thermal leakage, 1-inch polyurethane (PU) foam insulation was applied to the enclosure and thermal bridging through mounting hardware was minimized. Additionally, a cold-side airflow shroud was integrated into the Peltier stack to enforce a controlled flow path and prevent short-circuit air recirculation.
Iterative Testing and Validation
Iterative Testing and Validation
Initial Testing (29 Jan 2026)
Initial Testing (29 Jan 2026)
Configuration
Configuration
No radiator fan.
Two TEC module, but one TEC failed during test.
Tested in room temperature
Observed
Observed
Temporary cooling effect
Thermal saturation after several minutes, water gets warm over times.
Cold-side detachment due to insufficient clamping.
Key Insight
Key Insight
Water gets warm due to insufficient heat rejection, and it is key to maintain cooling performance.
Heat rejection is a dominant constraint in thermoelectric cooling system.
Radiator Upgrade and Performance Breakthrough (7 Feb 2026)
Radiator Upgrade and Performance Breakthrough (7 Feb 2026)
Configuration
Configuration
Upgraded from 120mm to 240mm radiator
Single TEC module.
Improved airflow routing.
A cold-side airflow shroud was integrated into the Peltier stack
Observed
Observed
Minimum internal temperature observed: 6.5°C (43.7°F).
Hot side temperature: 21.2°C (70.1°F).
Steady-state reached after around 30 mintues.
Key Insight
Key Insight
This demonstrates a sub-ambient cooling capability of approximately 15°C below room temperature using single TEC module
The result validates the effectiveness of increased heat rejection area and airflow optimization.
Engineering Lessons Learned
Engineering Lessons Learned
In thermoelectric-based cooling system, heat rejection capacity is crucial to maintain its cooling performance. Radiator surface area significantly impacts steady-state temperature, improve heat rejection capacity. Besides that, airflow control inside enclosure is critical to mix internal air, ensuring air flows through the cold heat sink fins. This system requires proper clamping force to ensure TEC reliability.
Key achievement in the latest configuration:
Achieved sub-20°C cooling under ambient room temperature condition.
Reaches a minimum steady-state temperature of 6.5°C.
Moving Forward
Moving Forward
Future work will focus on iterative testing and optimization of thermoelectric cooling architecture, including multi-TEC scaling, radiator sizing studies and airflow refinement to improve steady-state performance. Besides that, I would like to conduct environmental validation testing to ensure reliable operation under high-ambient temperature.
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