Spacecraft heat shields tested using fusion reactors

Scientists have shown it is possible to test the heat shields of spacecrafts using fusion reactors – a development that will provide the right kind of temperatures to test out new and advanced materials that can be utilized to develop spacecrafts that can easily withstand the extreme heat conditions during re-entry into Earth’s atmosphere.

Further, future missions to the outer solar system will also require new and advanced materials that could withstand harsh conditions of space including extreme heat of solar flairs and other deep space conditions.

The extreme heating conditions needed to study new shield materials are, however, very difficult to achieve experimentally on Earth. Scientists working at the DIII-D National Fusion Facility at General Atomics (GA) recently developed an innovative approach that uses the conditions inside a fusion reactor for testing heat shield materials.

When spacecrafts re-enter Earth’s atmosphere, they have to withstand extreme heat conditions at superfast speeds. The atmospheric gas surrounding the spacecraft turns into plasma (a mixture of ions and electrons) and spacecraft temperatures increase to more than 10,000 F. To protect the scientific payload, the heat shield material burns (or ablates) in a controlled manner, which pulls the excess heat away from the core of the spacecraft.

Previously used heat shield testing methods have been using lasers, plasma jets, and hypervelocity projectiles. However, they suffer from the problem that no single method could simulate the exact heating conditions present during a high-speed atmospheric entry. Consequently, past models of heat shield behavior have sometimes over- or under-predicted ablation of the heat shield, with potentially disastrous results. The experiments at DIII-D demonstrated that the hot plasma created by a fusion reactor during operation offers a novel and potentially improved way of modeling heat shield behavior, especially for entries into Venus or the gas giants.

Most experiments conducted at DIII-D are intended to explore the physics basis for fusion energy. An existing system at DIII-D, known as the Divertor Materials Evaluation System (DiMES), is designed to test materials for future reactors. DiMES can expose test samples to various plasma conditions as well as launch pellets of test material through the plasma.

Because DIII-D is one of the most flexible and highly instrumented fusion reactors in the world, the team was able to gather a range of valuable data on the behavior of the samples. By using scaling techniques, they extrapolated the results to larger projectiles and longer exposures, which allowed for comparison with experimental data from previous space flight missions and other on-ground testing facilities. The results offer considerable promise to develop the advanced heat shield materials necessary for planned missions to Venus and the Jovian moons.

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