Development of an inflatable heat shield in Europe
On June 5th of this year, the kickoff for a new project within the European Horizon-Europe program, ICARUS, took place in Madrid. ICARUS, which stands for Inflatable Concept Aeroshell for the Recovery of a re-Usable launcher Stage, focuses on developing an inflatable heat shield that can safely return larger payloads through the atmosphere, allowing for soft landings. Although the acronym suggests the project is focused on launch systems, it is actually a general technology demonstration with wide-ranging applications. For example, ICARUS could be used to return payloads from space stations and space-based manufacturing facilities, or to enable landings on Mars or other planets.
Until now, the diameter of heat shields has been limited by the size of the rocket’s nose cone. Due to this relatively small diameter, re-entry capsules pass through the upper layers of the atmosphere without losing much speed, leading to most of the deceleration happening in the lower layers. This causes significant heating and deceleration, placing heavy stress on the returning capsule and its contents. By increasing the heat shield’s surface area, much more deceleration occurs in the higher layers of the atmosphere, spreading out both deceleration and heating over a longer period. This significantly reduces thermal and mechanical stresses. An inflatable heat shield can be launched in a compact form and then inflated just before re-entry. With its larger diameter, it substantially reduces these stresses, and because of the reduced thermal load, flexible thermal protection is sufficient to protect the structure.
The idea of an inflatable heat shield is not new and has been around for quite some time. Since the 1990s, the concept has been studied in Europe, including projects like IRDT (Inflatable Reentry and Descent Technology), which was conducted in collaboration with Russia. However, the United States has made more significant progress in this area. After several projects such as IRVE (Inflatable Re-entry Vehicle Experiment) and LSDS (Low-Density Supersonic Decelerator), the LOFTID (Low-Earth Orbit Flight Test of an Inflatable Decelerator) was launched in November 2022, successfully returning from Earth’s orbit using an inflatable heat shield. Several earlier projects related to inflatable heat shields are described in the sidebars.
IRDT
In the late 1990s, a collaboration began between DASA (Deutsche Aerospace AG, later part of EADS in 2000, now Airbus since 2014), ESA, and Russia’s Lavochkin to test an inflatable heat shield developed by the Russians: the Inflatable Reentry and Descent Technology (IRDT). On February 8, 2000, the IRDT was launched aboard a Soyuz rocket. Although the inflation process was only partially successful, with the structure only partially inflating, it survived re-entry from Earth’s orbit and was recovered. A second flight, using a Volna rocket, failed when the nose cone detached prematurely, damaging the structure. A third attempt on October 6, 2005, was partially successful, but the spacecraft was never recovered. It is believed the structure failed near the point of maximum deceleration, which altered its aerodynamics and caused the flight path to deviate significantly, making it impossible to locate.
IRVE
NASA’s Inflatable Re-entry Vehicle Experiment (IRVE) involved several sounding rocket tests using inflatable heat shields. Four IRVE flights were conducted (IRVE-1 through IRVE-4), all using Black Brant sounding rockets. The first test in 2004 involved launching a heat shield packed into a 38 cm diameter rocket, which then inflated to a diameter of three meters. After reaching an altitude of over 200 km, the heat shield safely returned to Earth.
LDSD
To specifically test inflatable heat shields for Mars landings, NASA carried out the Low-Density Supersonic Decelerator (LDSD) tests. In two flights, in 2014 and 2015, an inflatable heat shield, along with a balloon and a STAR 48B solid rocket motor, was taken to an altitude of 56 km and reached a speed of Mach 4.3, simulating conditions similar to those expected during a Mars landing. The 4.7-meter diameter heat shield successfully inflated during both tests, but in both cases, the experimental parachute designed to ensure a soft landing failed.
LOFTID
The Low-Earth Orbit Flight Test of an Inflatable Decelerator (LOFTID) was a U.S. project testing re-entry into Earth’s atmosphere from orbit using an inflatable structure. The flight took place on November 10, 2022. LOFTID was launched as a piggy-back payload on an Atlas rocket and, after 2 hours and 11 minutes, successfully re-entered and landed in the Pacific Ocean. The vehicle was later retrieved by a ship.
Since 2019, the EFESTO consortium in Europe has been laying the groundwork for ICARUS through the EFESTO 1 and 2 projects. While EFESTO focused primarily on research, design, and analysis, ICARUS shifts the focus to hardware, with a European inflatable heat shield scheduled for a test flight on a sounding rocket in 2028. This is a much larger project, with a budget of 10 million euros, compared to the 5 million euros combined for EFESTO 1 and 2.
EFESTO 1 and 2
Since 2019, a European team, including INDRA-DEIMOS (Spain), ARESCOSMO (Italy), DLR (Germany), ONERA (France), Aviospace (Italy), and Politecnico di Torino (Italy), has been developing inflatable heat shields as part of the European EFESTO project. EFESTO, which stands for European Flexible Heat Shields advanced TPS design and test for future in-Orbit demonstrations, aimed to build foundational knowledge in this field. The project focused on system design, analysis, and partial hardware construction.
In 2022, the EFESTO 2 project followed, advancing toward hardware development. By this time, the team included INDRA-DEIMOS (Spain), DLR (Germany), CIRA (Italy), ONERA (France), PANGAIA (Italy), and Politecnico di Torino (Italy). After EFESTO 2, the team was ready to make the leap to flight hardware, leading to the establishment of EFESTO 3. The team further expanded to include additional hardware-focused partners such as Atmos Space Cargo and HDES. A test flight of an inflatable structure using a sounding rocket was planned, and during the proposal phase, the name ICARUS was chosen instead of EFESTO 3. The proposal was submitted in April 2023 and approved by the EU in August 2023.
The flight profile for ICARUS is shown in Figure and consists of the following key components: the rocket will launch from the DLR base near Kiruna, Sweden, using a Red Kite sounding rocket. Once the rocket motor burns out, the ICARUS payload will detach and follow a ballistic trajectory toward its apogee, reaching well beyond the atmosphere. As the inflatable structure descends past 100 km, a cooling gas generator will activate, inflating the heat shield. The shield will stabilize itself in a nose-first orientation due to its shape, facilitating re-entry into the atmosphere. Deceleration will begin in the upper layers of the atmosphere, and as ICARUS descends, it will experience maximum dynamic load and heating. At subsonic speeds, ICARUS may either deploy a parachute for a soft landing or perform a semi-hard landing. Throughout the flight, a wide range of measurements will be taken and transmitted to a ground station, as well as stored in an onboard memory module designed to withstand a hard landing.
After landing, ICARUS will be retrieved for inspection, and the heat shield will undergo analysis. The internal data storage will also be accessed to assess flight data.
The ICARUS consortium, depicted in Figure, comprises eleven prominent organizations and is led by INDRA-Deimos, a European company with headquarters in Madrid and operations in five countries. Key participants include:
- DLR (Germany) – responsible for the rocket and test flight execution
- CIRA (Italy) – providing thermal protection
- ONERA (France) – designing the heat shield shape and analyzing pre- and post-flight data
- Pangaia Grado Zero (Italy) – developing innovative sensor networks
- Politecnico di Torino (Italy) – overseeing public dissemination of results
- Atmos Space Cargo (Germany) – building the inflatable structure.
Two Dutch companies are also involved:
- Demcon (Delft) – providing fiber-optic sensor technology to collect data from the test flight. Their sensor system will allow simultaneous measurements at multiple points on the structure..
- HDES Service & Engineering BV (Noordwijk) – responsible for the inflation system using innovative cooling gas generator technology. This system, which expands on previous designs, represents a significant step forward for HDES as it will be their first time building the entire system between the cooling gas generator and the inflatable structure.
The project will unfold over several phases:
- Phase 1 (9 months): Defining the mission and system design, with technology development as needed.
- Phase 2 (2 years): Building and ground-testing the final design.
- Phase 3: Construction of the flight hardware and the test launch, scheduled for 2028. After the launch, the data will be analyzed to evaluate the accuracy of the models.
When folded, the ICARUS heat shield will have a diameter of 40 to 50 cm, but when inflated, it will expand to three meters. Future versions of the technology could support inflatable heat shields with diameters of up to 10 meters. The spacecraft, including the heat shield, will weigh between 250 and 350 kg.
Inflatable heat shields, due to their compactness, can easily be carried on satellites or rocket stages, allowing for the reuse of upper rocket stages and significantly reducing launch costs. This technology also enables satellites to return to Earth affordably for examination or component recycling, avoiding ocean splashdowns.
Moreover, inflatable heat shields are of great interest for planetary missions, especially those targeting planets with thin atmospheres like Mars. The larger diameter provided by an inflated shield allows for effective deceleration in a thin atmosphere, which is crucial for landing heavier payloads on the Martian surface.
ICARUS aims to position Europe as a key player in inflatable heat shield technology, securing independence alongside the United States and other countries. The project is being closely followed by the EU, ESA, and the European space industry due to its potential impact on the commercial space sector. This project is funded by the Horizon Europe research and innovation program of the European Union, under Grant Agreement No. 101134997.
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