Spacecraft arriving back on planetary home turf can face one of the trickiest challenges of a space mission: re-entering the planet's atmosphere. When the vehicle arrives at hypersonic speeds, the leading edge of a re-entry spacecraft can create a region of compressed, superheated air that can ionize into what is essentially a plasma.

Researchers in Japan and Europe are working on an innovative approach called magnetohydrodynamic (MHD) aerobraking and magnetic shielding that is an alternative to standard heat shields for spacecraft.

Instead of a standard approach, that actively shields the spacecraft from the plasma, these researchers have an idea to use a powerful magnetic field to influence the behavior of the plasma.

Let's take a closer look at the concept, how it could be applied and compare it to current technology.

How Does the Magnetic Shield Work?

When a spacecraft is coming back at hypersonic speeds, a shockwave forms at its leading edge.

This means the air right ahead of the vehicle is being compressed and heated. Hot enough, that it starts to ionize and form a plasma that conducts electricity. By surrounding a spacecraft with a powerful magnetic field (perhaps generated by high temperature superconducting coils), the researchers theorize that they could interact with the plasma to generate a cushioning effect.

The electrically conducting plasma would interact with the magnetic field to produce a Lorentz force that would push some of the superhot material away from the spacecraft, shielding some of its superheated surface from the plasma.

Can It Replace Traditional Heat Shields?

One of the neatest concepts about this technology is that it has the potential to dramatically reduce the amount of thermal protection that a spacecraft needs.

The traditional approach for spacecraft re-entry, is to use an ablative shield that can stand the test of time.

These materials can be incredibly dense and heavy, and can add significantly to the overall mass of a spacecraft and may even have to be replaced after a single mission.

A more modern approach is an active cooling system, where the heat is transferred away from the airframe, and sometimes (as in the case of SpaceX Falcon 9), can burn through the exhaust plume on the way back to the landing site.

The potential benefit of a shield that could reduce the amount of heat being transferred to a spacecraft could drastically reduce the size and weight of heat protection systems, and possibly enable more spacecraft to be reused during their missions.

The MEESST project in Europe has tested this technology in a wind tunnel, where they have demonstrated the ability to reduce the heat flux on a test vehicle by 40% in a "lunar return" scenario, and up to 80% for a "high energy return".

We need to interpret these findings with a grain of salt, keep in mind that these are experimental results in a wind tunnel.

Although the technology is decades behind our current thermal protection systems, the potential seems very enticing.

What About the Communications Blackout?

There is another interesting phenomenon that occurs during re-entry.

As the plasma forms around the spacecraft, it can prevent radio signals from getting through - sometimes referred to as a communications blackout.

Can a magnetic shield help with that as well?

The paper by the MEESST team shows that magnetic shielding can reduce the effects of radio blackout, but the overall improvement was not as dramatic as the thermal protection benefits. The paper notes that further work is needed, including improvements to position the antennas in the most advantageous position to minimize signal loss, and to further increase the strength of the magnetic field and optimize the flow conditions.

Could It Help Missions Returning From the Moon or Mars?

One of the most compelling applications for this technology could be on spacecraft returning from a deep space mission.

A spacecraft returning from the Moon or Mars would have to slow down significantly before it could return to Earth.

This means that it would have to endure the extreme heating of re-entry at hypersonic speeds.

A magnetic shielding technology could buy enough margin to protect a spacecraft that is returning from a mission beyond low Earth orbit.

The MEESST team has been working on scaling the technology for actual space flight applications, including the potential for a future low Earth orbit re-entry test.

Still an Experimental Technology

Although the technology seems very exciting, it is still a ways off from becoming a full replacement for current thermal protection technology.

The experimental work by the MEESST team is a good start, but researchers still need to incorporate this technology in actual spacecraft, and test out its performance in a real atmosphere.

Future work could include additional tests in a wind tunnel before transitioning to a flight test to see how the technology performs in the wild.

If the technology can be made to work in practice, it has the potential to reduce the size and weight of thermal protection technology on spacecraft, and possibly enable a new class of vehicles that can be reused for multiple missions.

The researchers are attempting to tackle the problem of plasma formation and extreme heating at re-entry by taking a completely different approach to the problem.

Instead of building a stronger shield to stand off the plasma, these researchers are instead trying to control the plasma.

Watch a Related MEESST Presentation

MEESST coordinator Andrea Lani has also presented the magnetic shielding technology and its potential applications on spacecraft re-entry.

References

European Commission CORDIS - MEESST Project:

Gizmodo - Scientists test a new magnetic approach to protecting spacecraft during re-entry:

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