Thermal protection systems (TPS) are designed to protect spacecraft from the enormous aerodynamic heating generated during the entry into an atmosphere. The hottest parts of the Space Shuttle during re-entry reached 1,650°C, while the Galileo probe that entered Jupiter's atmosphere reached 16,000°C. Protecting the spacecraft during this intense thermal heating is the sole purpose of a TPS - and since the earliest days of space travel, innovations and advancements in TPS have been crucial to enabling space missions. The space industry is rapidly evolving, with commercial operators beginning to take on roles in the emerging 'Space Economy' and seeking to reduce launch costs. Governmental agencies remain at the forefront of material science and development as mission goals become more ambitious, from landing greater payloads on Mars to exploring the outer planets. This report contextualizes the TPS requirements of different re-entry profiles and breaks down the core categories of TPS.

A new geometry for Starship seeks to solve the problems of the Shuttle-era TPS

For the 'lower' heating rates (1,650°C is still beyond the melting point of stainless steel) encountered on returning from a low-Earth-orbit (LEO) - high-temperature insulative silicon tiles are an often-used approach. Because the overall heat flux is lower, utilizing reusable TPS is possible and desirable as it lowers the cost to orbit and enables a higher launch cadence. The NASA Space Shuttle program was intended to provide a low-cost, rapidly reusable spacecraft that could ferry crew and cargo from the surface to a LEO. However, the Shuttle's TPS was plagued by high construction costs, lengthy maintenance requirements, and damaged tiles were the cause of the Columbia disaster.

 

The promise of rapidly reusable silicon-tile based insulation remains appealing, and SpaceX has opted for this TPS for its Starship upper-stage. However, several key design differences of Starship could potentially negate some of the cost and performance problems of the Starship. The report breaks down how tile shape, spacecraft geometry, and choice of substructure material could all contribute to greater TPS performance. The report also outlines the developments of the key subcategories of reusable TPS, from advanced carbon-carbon and other hot structures to developments in high emissivity coatings and TUFROC, offering performance data and material composition throughout.

 

Inflatable TPS - an emerging option at the forefront of development

One of the fundamental constraints of any launched spacecraft is the 'rocket-fairing', that is, the width of the rocket nose at launch. However, the physics of atmospheric entry favors the largest heat shield diameter possible. A novel and emerging technique is to use an inflatable or mechanically expandable TPS that is stowed on launch but expands before re-entry. This is seen as a viable way to enable greater payload missions, with some commercial operators also pursuing this avenue for LEO cargo return. This approach comes with a host of technical challenges, but great advancements are being made, and in 2022, NASA completed the first successful LEO re-entry with its LOFTID (Low Earth Orbit Flight Test of an Inflatable Decelerator). The report unpacks the key material opportunities in these TPS, such as aerogel insulators, high-temperature ceramic fabrics, and the need for solid-gas generators. Potential applications for this development are also examined, including high-value booster engine return, high-altitude landings, and higher payload delivery.

An ablative TPS is the ultimate form of protection, used when a spacecraft's reentry speed means all other options would simply not stand up to the heat. Ablation can aptly be described asenergy management through material consumption, and the ablator itself disintegrates in a controlled manner during re-entry, transferring away heat and protecting the substructure beneath. Ablators have been used from lunar returns (AVCOAT honeycomb on Apollo) to entry into Jupiter (Carbon Phenolic). This report breaks down the material families of ablators, highlighting their material construction, installation, and performance envelopes. Historical context is provided, such as the atrophy of Carbon Phenolic capabilities due to the cessation of aerospace-grade Rayon production, and where 3D-woven fabrics may fit in as a replacement. Commercially developed variants, such as SpaceX's PICA-X (Phenolic impregnated carbon ablator-X) are covered, as well as assessing the potential semi-reusability of ablators well within their performance envelope.

Industry overview and market analysis

As part of its research, IDTechEx has examined several existing and upcoming space cargo/crew vehicles with a variety of TPS selections. Factors such as launch cadence, dimensions, and material selection provide a detailed assessment of the state of the industry. This extensive market analysis also forms the foundation of IDTechEx's market forecasts for TPS systems up to 2035, split by material demand (in m2) and USD.

Key Aspects

A review and context of the space industry

The emerging presence of commercial space operators for a variety of purposes (launch operators, commercial LEO cargo transfer)

Implications of commercialization on material design for thermal protection systems

Development timeline of cargo and crewed spacecraft

 

Atmospheric Entry

Overview of reentry physics and atmospheric heating (split by convective and radiative heat.

Blunt body concept and the need for thermal protection systems.

Material selection and design for TPS, and performance envelopes for a variety of categories.

 

Tile-based TPS

Density, emissivity, conductivity and temperature limits for tile-based TPS.

Historical overview of tile-based systems, from the Shuttle-era to Starship.

Development pathway of component categories, from high-insulation tiles, coatings, ceramic blankets, and hot structures

Silica based tiles, Reinforced-carbon-carbon, TUFROC, Starship tiles

Material density and temperature limit benchmarking

 

Expandable Aerodynamic Decelerators

How increasing the diameter beyond the launch fairing affects ballistic coefficient and peak heating.

Overview of NASA's HIAD and LOFTID test programs, including construction techniques and materials used.

How expandable aerodynamic decelerators could unlock commercial booster reusability.

Mechanically deployable aerodynamic decelerators

Key commercial players with test-flights planned.

 

Ablative TPS

Overview of the need of ablators in the most challenging reentry environments.

Summary of ablative and pyrolysis heat transfer mechanisms

Summary of ablator families and development timeline

Honeycomb ablators (e.g. AVCOAT)

PICA heat shields, and its potential reusability.

Carbon Phenolic heat shields

Emerging 3D Woven thermal protection systems, such as NASA's HEEET

 

Forecasts

Granular 10-year market forecasts for TPS, split by category and operators (governmental vs commercial).