Introduction

To ensure successful vehicle and payload operation, space programs subject hardware to extensive ground testing. Thermal tests demonstrate the performance and operation of units, subsystems, payloads, and entire space vehicles in thermal environments that are, at minimum, realistic simulations of flight conditions. At the unit level, these tests include thermal cycling and thermal vacuum tests. At the space vehicle level, they include thermal cycling, thermal vacuum, and thermal balance tests. This chapter provides the objectives of each thermal test and describes the test parameters and procedures used to meet those objectives.

Over the past decades, a series of documents has specified and described military requirements for spacecraft thermal testing. The first, MIL-STD-1540A, was written in 1974 for Department of Defense space programs to standardize test requirements and establish a uniform set of definitions, environmental criteria, and test methods for military space vehicles, subsystems, and units. It introduced a common language defining test categories, levels, and sequences.

Published in 1982, MIL-STD-1540B was an update to MIL-STD-1540A and was oriented toward low-risk, long-life space vehicles. This document expanded testing provisions in that it disallowed flying qualification hardware, introduced the protoflight concept, reduced testing requirements for one-time or low-volume programs, separated the roles of workmanship verification and design demonstration, emphasized performance testing, and increased the role of thermal cycling. Three years later, MIL-HDBK-340 was published as an application guideline for MIL-STD-1540, providing much-needed explanations, guidance, and rationale to the users of MIL-STD-1540B.

MIL-STD-1540C,...