Inflatable aerodynamic decelerators could offer radically new material opportunities for aerospace
Off the back of the Pheonix 1 launch, IDTechEx’s Mika Takahashi sits down with Jake Holmes to discuss how inflatable aerodynamic decelerators could offer radically new material opportunities for space flight
Space travel has remained a fascination to humankind, with Neil Armstrong’s infamous ‘one small step for a man, one giant leap for mankind’ etched into the minds of an entire species. Previously, economic restrictions limited space travel to just a select few, but with the latest technological developments, prices may allow more of us to embark on the final frontier.
The successful inaugural flight of Atmos Space Cargo’s Pheonix 1 re-entry capsule has much wider implications for space travel, thanks to its novel inflatable heat shield that allows it to re-enter the Earth’s atmosphere for recovery. Mika Takahashi from IDTechEx was able to explain the technologies involved and what this means for the sector.
HEAT SHIELDS
“The reason you need a heat shield is because spacecraft travel very fast, and the heat shield is the way they slow themselves down,” Takahashi says. “Spacecraft travel quickly, either orbiting Earth or travelling from another planet. As they return to Earth, instead of aerodynamically entering the atmosphere, the goal is to slow down.”
“Spacecraft enter with a blunt body and use the drag of the atmosphere to slow themselves down, and in a sense that’s an energy conversion from energy as velocity to energy as heat” he adds. “This generates significant amounts of heat, we call this aerothermic heating.”
Historically, two varying methods have been used to deal with this intense heat: ablative heat shields and tile-based systems.
Ablative heat shields are designed to wick away heat as they evaporate. The material burns itself up in the process of re-entering the atmosphere and its descent to Earth, protecting the spacecraft behind the shields from the intense temperatures. These are single-use and were most famously used on the Apollo space missions.
Tile-based systems are low-density silicon installation tiles that absorb heat but are not conductive through their surface and reject the heat out. This means the material is not consumed in the process of slowing down the spacecraft.
This is where the heat shield design of the Phoenix 1 is unique and changes established practices in the industry.
Takahashi says: “Pheonix 1 takes a different approach. The way thermodynamics works, if you have a larger surface area of your heat shield, you’re going to have less intense heating. Typically, the surface area of your heat shield is limited by the rocket payload cone.
“What Phoenix has done is have a small, stowed heat shield but upon re-entry, the heat shield is inflated, giving a much larger surface area and then the heating will be less intense, therefore there’s less restrictions about what sort of materials we can use.”
This is a fairly new technology; NASA previously tested a similar project named Lofted in a low-orbit flight test demonstrator in 2022. For this project, NASA took a large nitrogen gas tank up to inflate the shield in space. However, this takes up both weight and space on the spacecraft, and also requires extra tubing and decompression valves.
“What Phoenix has reportedly done, and there’s not a huge amount of technical data they’ve released about this, but it’s using the hot gas in the upper atmosphere to inflate the heat shield,” Takahashi explains. “So rather than taking compressed gas with them and then reregulating that and inflating the heat shield, instead they have some sort of inlet valve which they open upon re-entry and hot gases from the upper atmosphere inflate that heat shield. Again, there is very little technical and concrete data about that, but if they were able to achieve that, it’s quite a unique development.”
UN-BURNING MATERIALS
Atmos Space Cargo has yet to unveil what specific materials it is using in their initial Pheonix 1 capsule, but NASA has been transparent about its use of materials, and it’s likely to be similar to what the former is using, according to Takahashi.
The Thermal Protective System (TPS) is twofold. It needs to be able to be compacted and stowed away, but also needs to protect against temperatures of 1400°C, and not conduct that heat through to the spacecraft.
Takahashi says: “Typically, you’d see an outer layer of ceramic fibre, the purpose being to structurally and mechanically withstand the high temperatures. That’s going to be the outermost layer. Beneath that, you have an insulator, with one of the upcoming materials in this field being an aerogel. An aerogel is a very low-density and low-conductivity material. The role of the aerogel insulator is to protect the delicate parts underneath from the hot ceramic fibre.”
For the inflatable structure, a braided fabric yarn is used, as it has very strong fibres and features a gas-proof laminate, allowing the structure to inflate and preventing hot gases from the atmospheric heating from getting inside. NASA filled this section with nitrogen, whilst Atmos Space Cargo claims to have filled it with hot gases from the upper atmosphere. Another layer of braided fabric is underneath this, creating a concentric ring design for NASA’s deployment of the technology.
The materials need to fill three functions to be suitable for use in TPS applications: high temperature resistance, low thermal conductivity and being flexible and stable under inflation.
WIDER IMPACT
Atmos Space Cargo has announced that for its second rendition of the Pheonix project it will be adding re-entry direction control, meaning operators can control where the capsule lands. This allows for landing near to the launch site, speeding up recovery of the capsule and the time taken to prepare for a new launch. SpaceX has found this niche with landing components of its spacecraft for later reuse, allowing its Falcon Nine system to launch at a far higher regularity.
This elevates the current issue of landing in the ocean. Salt water is corrosive to heat shields and capsules and can cause them considerable damage, leading to costly and time-consuming repairs. Further to this, there are the associated costs with moving capsules from where they happen to land, such as the Indian ocean, to the launch site.
By not having to rebuild capsules and instead being able to reuse previously used models, launches could be increased from one to two a year up to five or six times this number of launches. This is a dramatic increase in operations, as capsules can take between six to eight months to produce, whereas reusing capsules allows them to be used on a four-week cycle.
Industry can also take advantage of the cheapening of space travel. Manufacturers of high-value goods are looking at micro-gravity manufacturing at these altitudes. We do not have the capacity for high volumes yet, therefore production is limited to very high-value products. Companies such as American enterprise VADA are currently developing products in the field.
By developing more cost-effective methods of re-entering the atmosphere, through re-usability, the space sector can open the door for more regular trips to the stars. This can be utilised by explorers, researchers, and industry, all having their own unique reasons for why they want to explore space’s untapped potential
