Aerobraking and Ablation - Thermal Management for Spacecrafts

The commercial space industry has taken off in recent years with a surge in launches and exponential growth, creating a need for increased thermal protection systems. IDTechEx's report, "Heat Shields & Thermal Protection Systems for Spacecraft 2025-2035: Technologies and Market Outlook", covers approaches to managing the heat produced upon re-entry, the materials necessary, and timelines for growth.

 

Thermal protection systems (TPS) for spacecrafts are extremely necessary due to the significant kinetic energy that accompanies extremely high speeds. In order to land safely, this energy has to be dissipated, with the two options explored by IDTechEx for decelerating a spacecraft including burning retrograde rockets, or aerobraking.

 

 

Carrying extra fuel and firing retrograde rockets will increase total costs and decrease payload capacity, though is the method adopted when there is no alternative. Realistically, landing on the moon with no atmosphere would be the only scenario in which retrograde rockets would be feasibly used.

 

Aerobraking is another approach to landing safely; a process which uses the drag created by the blunt-body impact on the upper atmosphere in order to slow down, converting the kinetic energy into heat energy. This is where thermal protection systems are necessary.

 

There are three key metrics for thermal protection systems that will determine the materials and design. These are peak heat, total heat, and stagnation pressure. The peak heat load is the highest single transfer of heat energy that occurs during re-entry, and is largely impacted by atmospheric conditions, spacecraft geometry, and the flight path.

 

The total heat load takes into consideration the heat curve created from the beginning of the spacecraft's re-entry until the end. The total heat therefore determines how much thermal protection is required to protect the spacecraft from overheating during the process. The final metric, stagnation pressure, is described as what would be generated as a result of all the kinetic energy of atmospheric gases around the spacecraft was converted into pressure instantaneously.

 

 

Aerobraking can be divided into three methods, each with different thermal protection systems, including expandable, ablative, and reusable. Expandable TPS is an emerging technology and refers to either mechanically expanded or gas inflated systems that work to increase the surface area of a space craft to reduce the peak and total heat loads. Ablative TPS are the only flight-proven option beyond a certain heat flux, with many missions requiring ablators including far solar system return, Gas Giant entry, Mars landing, Ice Giant entry, lunar return, Venus entry, and Martian sample return.

 

Reusable TPS came about as a result of NASA's Shuttle orbiter, which intended to create the opportunity for economically viable missions. Reusable TPS can consist of low density, low conductivity silica tiles that provide thermal insulation, and can have special coatings to increase emissivity. The leading edges and nose of the spacecraft generate much more heat, meaning heavier carbon composites are required instead. However, due to the repair necessary between missions, IDTechEx reports that rapid reusability was not achievable with the Shuttle's TPS. The Space X Starship, however, learnt from this, and was fitted with a cylindrical stacked formation instead.

 

The material requirements for reusable TPS include high thermal emissivity, high maximum temperature, low thermal conductivity, and low density. These qualities are necessary to ensure nothing melts, heat is not transferred from the outside in, and that the launch weight is not too great. According to IDTechEx, the ideal TPS will have all of these, alongside being easy to assemble and being a low cost.

 

IDTechEx outlines more key requirements for spacecraft thermal protection systems, along with the many potential materials and their renowned qualities. For more information, visit "Heat Shields & Thermal Protection Systems for Spacecraft 2025-2035: Technologies and Market Outlook" and the wider portfolio of Thermal Management Research Reports and Subscriptions.