Spacecraft Thermal Control Handbook

Spacecraft thermal control systems (TCSs) ensure that a spacecraft remains within temperature limits that are appropriate to its orbit, power demand and operation. Equipment utilized includes radiators, Multi Layer Insulation blankets, two-phase devices such as heat pipes or capillary pumped loops as well as mechanical louvers and thermal switches.

These systems channel heat from spacecraft instruments, heaters, and solar absorption panels onto radiators for transfer outward to instruments through radiation loss.

Introduction

A thermal control system (TCS) in a spacecraft ensures the subsystems and components remain within their functional temperature limits to maintain proper functioning and survival. If temperatures surpass these parameters, permanent damage to electronics and batteries, mispointed sensors, freeze/rupture of propulsion lines or fatigue failure in wire bonds could result.

This book presents an introduction to space missions and their environment, followed by coverage of spacecraft thermal control processes such as heat transfer. Current technologies for thermal management as well as design and analysis techniques are reviewed throughout this work.

Passive thermal control hardware consists of heat pipes, thermal switches and heaters. Active systems employ actuators to direct heat away from instruments, solar absorption devices and radiators into other surfaces and over to other sources; any remaining heat loss occurs through radiation.

Part I: The Space Environment

Space environment refers to the conditions under which a spacecraft must operate while in orbit, including energy from solar, planet and albedo fluxes, heat generated internally by electronic equipment and thermal radiation emitted into deep space.

The final equilibrium state is determined by several factors such as spacecraft geometry, orbit and attitude stabilization. These conditions determine external thermal loads as well as maximum radiator sizes available to us.

Electromagnetic phenomena that impact spacecraft are particularly challenging; radiation, particles and ions interacting with molecules of the exosphere (the layer between Earth and interstellar space) may damage electronics as well as cause Single Event Upsets that disable it altogether.

Part II: Heat Transfer Processes

Spacecraft components must remain within certain temperatures in order to ensure their proper and reliable functioning over extended periods. Temperatures exceeding this threshold may damage electronics, misdirect sensors and cause fatigue failure of wire bonds – which all pose potential threats of malfunction and premature failure.

Temperature balance for spacecraft depends on an equilibrium between external solar, albedo, and planet heat fluxes and internal power dissipated and other device generated loads. Achieving such equilibrium requires conserving or rejecting thermal energy based on mission requirements and orbital environment conditions.

Thermal hardware typically included radiators, multilayer insulation blankets, two-phase devices (e.g. capillary pumped loops and heat pipes with fixed or variable conductance), mechanical louvers, thermal straps, radioisotope heater units, and thermal switches – with optimal selection dependent upon spacecraft geometry, thermal properties, stabilization type/location as well as equipment characteristics/power distribution.

Part III: Current Thermal Control Technologies

Spacecraft equipment and structural components require to remain within an optimal temperature range to function optimally, both physically and in terms of their effectiveness and reliability. Many electronic devices operate best at certain temperatures.

Thermal control techniques utilize passive systems that regulate temperatures without using power to actively move heat to and from components on spacecraft, such as insulation blankets, louvers, thermal switches and thermal straps.

Active systems used in SmallSat applications typically consist of heaters, refrigerators and fluid loops; in order to be as energy-efficient as possible given limited power, mass and volume available in spacecraft applications, these elements must often be miniaturized or otherwise modified so as to be more space efficient.

Part IV: Design and Analysis

Spacecraft thermal control systems aim to safeguard equipment against excessive heating by either shielding it from external solar and planetary infrared radiation, or dissipating heat generated internally through proper dispersion techniques. To do this, an initial thermal hardware configuration is generally established based on engineering experience.

Spacecraft thermal control hardware usually includes radiators, multilayer insulation blankets (where selecting the number and thermal finishes of layers and thermal finishes are one of many degrees of freedom for a thermal engineer), two-phase devices such as loop heat pipes or capillary pumped loops, mechanical louvers, compensation heaters, temperature sensors etc.

This revised and updated edition of the Satellite Thermal Control Handbook features an improved characterization of Earth orbit thermal conditions, new material on interplanetary spacecraft environments, more comprehensive information about each hardware element presented in the first edition, plus some cutting edge technologies such as heat switches.