Spacecraft heat shields!

It has been recognized both by NASA (2018 Strategic Plan) and the National Academy of Sciences (2019 Search for Life report) that the future of space exploration will require challenging missions to nearby planets and moons. Such missions will involve high-speed aircraft atmospheric entries, which become increasingly technical in thick atmospheres, such as the atmospheres of gas giants, due to the resulting extreme heating of the spacecraft. This motivates the desire to develop and test the next generation of heat shields that can protect spacecrafts during such ambitious entries. To address this problem of high significance to the U.S. goals in space exploration, we collaborate with Dr. Dmitri Orlov and Dr. Igor Bykov from University of California San Diego in a project where we study what happens to aircraft heat shield materials when exposed to extreme conditions.

We aim to reproduce the processes occurring during spacecraft atmospheric entries by exposing material targets to the plasma environment of the DIII-D National Fusion Facility in San Diego and the IPG6-B inductive plasma generator in the CASPER lab (figure on the left). DIII-D experiments can reproduce the high heat environments encountered in some of the most ambitious missions ever attempted, such as the Galileo probe, which entered Jupiter’s atmosphere with a speed of almost 50 km/s. Instead of accelerating test materials to such extreme speeds, we recognized that the DIII-D tokamak plasma itself rotates with comparable speed, which means that any object launched radially from the wall of the tokamak incurs motion relative to the plasma which is comparable to the entry speed of Galileo.

More is different. Anomalous is normal. That’s why Turbulence.

Fig. 1. a) Non-interacting particles move randomly (normal diffusion.) b) Correlated particles can make huge jumps in space (anomalous diffusion.)

In a famous 1972 publication, Philip Anderson argued that the behavior of complex systems cannot be reduced to the interactions of elementary entities. Instead, at each level of complexity entirely new properties emerge due to the many-body correlations involved. Simply put, more is different. While non-interacting particles move in a random fashion, called normal diffusion, correlated particles move in a less random way, called anomalous diffusion. Anomalous diffusion is so common in the natural world that scientists often conclude: anomalous is normal. The marriage between increasing complexity and anomalous transport often results in turbulent dynamics of the many-body system. Dusty plasmas are ideal media for the investigation of these phenomena.
In this project we study turbulence in a dusty plasma by computing the spectrum of energies available to the dust particles as a function of random disorder and properties of nonlocal interactions mediated by the plasma. We argue that at critical scales within the system, anomalous dust diffusion, guided by nonlocal interactions, leads to enhancement of energy transport and increased probability for turbulent dynamics. These theoretical predictions are compared against results from many-body simulations and dusty plasma experiments conducted on board the International Space Station.

This research is funded by NSF-1903450, NSF- 1707215, NASA- 1571701, DE-SC0021284

All authors acknowledge the joint ESA / Roscosmos “Experiment Plasmakristall-4” onboard the International Space Station.

Check out a video talk on this subject: