Spacecraft have long used heat shields for protection during entry into planetary atmospheres. Future missions to the outer solar system will need more sophisticated materials than currently exist.
But the extreme heating conditions needed to study new shield materials are difficult to replicate experimentally on Earth.
During high-speed atmospheric entries of up to 100,000 miles per hour, such as those required in missions to the Solar System’s gas giants, the atmospheric gas surrounding the spacecraft turns into plasma (a mixture of ions and electrons) and spacecraft temperatures increase to more than 5,000°C.
To protect the scientific payload, the heat shield material burns in a controlled manner, which pulls the excess heat away from the core of the spacecraft.
Past heat shield testing approaches using lasers, plasma jets, and hypervelocity projectiles suffered 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 behaviour have sometimes over- or under-predicted ablation of the heat shield, with potentially disastrous results.
Scientists working at the DIII-D National Fusion Facility at General Atomics have demonstrated that the hot plasma created by a fusion reactor during operation offers a novel and potentially improved way of modelling heat-shield behaviour, especially for entries into Venus or the gas giants.
“Certain regions of the plasma in DIII-D closely approximate the conditions created when heat shields impact planetary atmospheres at extreme velocities,” said Dr Dmitri Orlov of the University of California San Diego, who led the multi-institutional team.
“Our intent with these experiments was to leverage both these conditions and DIII-D’s rich suite of diagnostic instruments to develop a more accurate model of heat shield behaviour.”
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 behaviour 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 researchers believe their results could help in the development of advanced heat shield materials necessary for planned missions to Venus and the Jovian moons.