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Thermal Cycling

Scope and Description

This topic covers thermal cycling testing of electronics. Thermal cycling involves heating and cooling the environment at ambient pressure to expose the unit under test to specific temperature extremes and a specific rate of temperature change between those extremes. Performance of the system is monitored throughout the cycling process to verify complete functionality at temperature limits and basic function throughout the testing (i.e., during changes in temperature). This is accomplished by running full functional tests at the first and final hot/cold plateaus and by operating the unit in a more static but active configuration during the entirety of the test to excite and detect failures. The goal of thermal cycling is to verify the performance of the design on qualification units and to identify any workmanship or material defects in acceptance units. Smallsat projects often do not follow traditional thermal analysis and manufacturing processes and utilize COTS components. Thermal cycling can be a valuable tool to significantly improve smallsat reliability by screening for thermal design flaws and workmanship defects.

Resource in this topic area are primarily standards and white papers that outline traditional processes for thermal cycling and book chapters that provide nuanced guidance and background information. This background information can inform careful modification of traditional processes for smallsat projects.

Best Practices and Lessons Learned

  • It is important to recognize the logistical and technical complexity of thermal cycling and plan accordingly with sufficient budget and schedule. Determining appropriate requirements is relatively straightforward. However, setting up the facilities and procedures to support these requirements can be very challenging. Careful planning and qualification of the procedure is required to prevent damage to the unit under test (e.g., from moisture condensation or human error).
  • Thermal cycling is inherently dynamic - the humidity and temperature of the test chamber is changing and the electrical connections and operational states of the unit under test are typically switched repeatedly to check for hot/cold startup, nominal operation during transitions, and full functional testing. This means that if something goes wrong, the operator needs to be able to respond quickly to reduce the risk of damage to the unit under test. Make sure to include thorough monitoring of the unit under test and response plans to likely equipment failures or human errors in your test procedure.
  • During qualification runs of your test, carefully monitor the humidity in the test chamber and, if possible, use a window to visually inspect the unit under test for condensation and ice. Nitrogen or dry air supplies must be capable of sufficient flow-rates to support the intended rates of temperature change such that the the temperature of the coldest surface on unit under test is never below the dew-point inside the chamber.
  • Make sure to turn the unit under test off and back on at each hot and cold plateau to verify that the unit can start up under these conditions. Failure to support hot or cold startup could lead to a failure to recover from on-orbit faults (or to start up at all following deployment/separation).
  • The relative simplicity and size of smallsats creates an opportunity to only conduct thermal cycling at a higher-level of integration and significantly reduce cost. If you choose to take this approach to thermal cycling, consider whether to exclude certain subsystems or components whose thermal ratings will require less extreme hot/cold limits and therefore reduce the overall quality of the test (e.g., batteries). In addition, make sure to weigh cost savings against the elevated risk of failure when testing at higher-levels of integration.

Resources

White Paper
NASA

This page in the NASA Public Lessons Learned System recommends that thermal vacuum tests follow dynamics ... tests (e.g. vibration testing). It provides detailed guidance and motivation for this recommendation.

This conference paper presents detailed thermal analysis and thermal environmental test planning for ... a cubesat. It's a good case-study and example report for smallsat thermal analysts and thermal test engineers. Inputs, assumptions, methods, and results are all presented in detail.

Book
George Sebestyen et al.

This book chapter, titled "Thermal Design" covers thermal design, analysis, and testing for LEO satellites. ... This includes background on the physics of heat transfer, thermal control hardware, and processes for thermal design, analysis, and testing. Note that this chapter is only 13 pages, and does not go into significant detail on any of the included topics.

Book
David Gilmore

This chapter titled "Thermal Testing" is a comprehensive reference regarding thermal testing of space ... flight hardware. The tests covered are thermal cycling (ambient pressure), thermal vacuum, thermal balance, and burn-in. It includes a description of the elements and stages of the traditional approach, environments, margins, requirements, and required equipment/facilitates.

White Paper
US Department of Defense

This handbook provides in-depth guidance on testing of space vehicles. The testing covered includes structural ... loading, thermal vacuum, thermal cycling, thermal balance, pressure testing, burn-in, random vibration, acoustic, and pyroshock - among others. This is a dated but comprehensive source of space hardware test environments and processes.

Standard
ESA

This ECSS standard details specific standards for ground testing of space flight hardware. The testing ... covered includes mechanical, structural, thermal, electrical, and RF - among others.

White Paper
Aerospace Corporation

"This Standard establishes the environmental and structural ground testing requirements for launch vehicles, ... upper-stage vehicles, space vehicles, and their subsystems and units. In addition, a uniform set of definitions of related terms is established."

This document discusses the importance of early stress screening on flight hardware to identify latent ... defects to prevent schedule delays and program costs increasing. Pre-unit-level testing is thoroughly discussed and how it can be applied to the MIL-STD-1504E requirement for unit-level thermal testing.

White Paper
NASA

This site provides a high-level overview of thermal cycling and relevant graphs and equations used in ... thermal cycle modeling. There are multiple similar lessons offered such as thermal test levels & durations, heat sinks, thermographic mapping of PC boards, etc.

This site provides a high-level overivew, lessons learned, and recommendations related to thermal vacuum ... (T/V) testing. A NASA JPL study with a summary of analysis and test results is provided as an example when thermal/atmospheric (T/A) testing is performed instead of T/V testing.

White Paper
NASA

This site provides a high-level overview of thermal test levels & durations and provides lessons learned, ... graphs, and equations. Detailed analysis and results of thermal dwell testing on spacecraft like Voyager, Galileo, Viking, and Mariner are discussed in detail with recommendations for future spacecraft provided.

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