Spacecraft are subject to some of the hottest temperatures with their generation of kinetic energy during taking off and landing, and as a result of their high speeds. IDTechEx's report, "Heat Shields & Thermal Protection Systems for Spacecraft 2025-2035: Technologies and Market Outlook", covers the different thermal management techniques that can be employed to effectively manage these temperatures safely.
Commercial and governmental expeditions and launch types
The need for thermal protection systems for spacecraft is currently a hot topic a result of recent growth within the space tech industry. This activity is seeing an increase in frequent commercially operated flights, moving away from less frequent governmental expeditions.
Commercial expeditions focusing on low-Earth orbit returns are increasing, while governmental missions continue to push the frontiers with Martian sample return missions and landings on far-flung bodies such as Titan.
IDTechEx lists sub orbital, orbital, and beyond earth orbit as different launch types, each with different heat shield requirements. Sub orbital generates less speed and therefore less heat as a result of not needing to reach escape velocity, while beyond earth orbit may require heat shields for the purpose of entering the atmosphere of another planet.
Passive, active, and ablative TPS for spacecraft
The materials and design of specific thermal protection systems are determined by factors including peak heat load, total heat load, and stagnation pressure. IDTechEx's report categorizes thermal protection systems into passive, active, and ablative.
In a passive system, the material used is required to not allow conductive heat to transfer to the main body and needs to have high emissivity. Tile-based insulators such as silica fiber-based are typically used and coated with high emissivity substance. In active systems, which are still largely in development, liquid methane stored in fuel tanks around a spacecraft could be used for active cooling to reject the heat. While both of these are intended to be reusable systems, ablative systems see materials ablated into gas which absorbs energy and are the only option for both planetary entry and far distance re-entry into Earth.
Aerobraking and retrograde rockets for moon landings
Aerobraking is a method which uses drag generated by blunt-body impact on the upper atmosphere in order to reduce speed and is described in the report as being the only practical way to lower speeds to ensure re-entry is safe. During this process, kinetic energy is transformed into heat energy at extremely high temperatures, requiring thermal protection systems. Ablative TPS, reusable TPS, and expandable TPS are the three categories of aerobraking, explored in depth in IDTechEx's report.
During moon landings where there is no atmosphere, the retrograde rocket technique is used, though is otherwise not a first-choice option as a result of the need to carry extra fuel and firing the rockets in the opposite direction to travel. It also is not currently viable as a means of re-entry, except in situations where aerobraking is not possible, such as when there is no atmosphere in which to do so.
Developing new thermal protection systems for spacecraft is high-cost and takes long periods of time and is largely done by governmental organizations such as ESA and NASA, which are two of the main government agencies responsible for R&D in the space sector. IDTechEx also reports that testing facilities are also limited, while certification can be tricky to obtain, providing further hurdles to fast developments within this sector. There are also limited aerospace-grade material suppliers, with many specialty materials not yet widely available for commercial use but instead reserved for government and national defense applications.
For more information, visit IDTechEx's report, "Heat Shields & Thermal Protection Systems for Spacecraft 2025-2035: Technologies and Market Outlook" and the wider portfolio of Thermal Management Research Reports.
