Researchers at Tokyo Metropolitan University have engineered a new system to test magnetohydrodynamic aerobraking for spacecraft reentering the atmosphere, utilizing a powerful electromagnet to generate intense magnetic fields while miniature vessels are hit with a shock wave traveling at over seven kilometers per second (4.3 miles per second). According to findings published in the Journal of Spacecraft and Rockets, the system is a crucial stepping stone toward tests with real vessels in the atmosphere.
The Limitations of Current Reentry Technologies
As vehicles plunge back into the atmosphere, they encounter shock waves moving at multiple kilometers per second that elevate temperatures on the craft’s exterior to thousands of degrees. To counter this intense heating, current technologies use heat-resistant tiles and sacrificial material that help dissipate heat and protect the craft. While reliable, this approach has serious limitations, increasing weight, surface wear, cost and repair times.
This is especially limiting as demand increases for reusable vessels.
How Magnetohydrodynamic Aerobraking Works
A promising technology for overcoming these challenges is magnetohydrodynamic aerobraking (MHD). By introducing a magnetic field into the weakly ionized plasma of the shock wave, the extremely hot shock layer expands and is forced outward away from the vehicle’s exterior. This mechanism simultaneously diminishes thermal transfer into the hull and enhances aerodynamic drag to help decelerate the vehicle.
Did You Know?
This dual action not only cuts down the amount of heat entering the craft, but it also boosts aerodynamic drag to decelerate the vehicle.
While previous work strongly supports this method, testing such systems is a major challenge. Traditional setups typically position a fixed permanent magnet within a compact testing scale model subjected to a shock wave, though this configuration restricts the ability to systematically evaluate diverse magnetic field geometries and intensities.
Pulse-Forming Networks and Hypersonic Testing
For the purpose of allowing researchers to examine a broader spectrum of magnetic fields, a group headed by Associate Professor Kohei Shimamura from Tokyo Metropolitan University developed an innovative apparatus featuring a robust electromagnet housed directly inside a scaled test article. The electromagnet consists of a tailored coil arrangement energized by a pulse-forming network (PFN), which delivers a massive surge of electric current to produce a high-intensity magnetic field for a brief duration.
During a trial, the scale model is exposed to a shock wave moving at more than seven kilometers per second (4.3 miles per second) for a duration lasting tens of microseconds inside a hypersonic expansion tube, which serves as a ground-based installation for evaluating aerospace vehicles under extreme conditions. The team engineered the apparatus to detect the arrival of the incoming shock wave and accurately coordinate the activation of the magnetic field with its timeframe, thereby achieving field intensities that far surpass the limits of standard neodymium magnets. Additionally, a high-speed camera was synchronized with the shock wave to capture the luminosity emitted by the heated shock layer, commonly referred to as the self-emission layer.
| Model Configuration | Generated Field Strength | Comparison to Standard Magnets |
|---|---|---|
| Model A Coils | 1.24 tesla | Significantly higher than standard neodymium |
| Model B Coils | 1.58 tesla | More than double conventional neodymium strength |
To evaluate the setup in practice, the researchers constructed two distinct models outfitted with customized coil layouts matching their respective geometries. Measurements verified the successful creation of 1.24 and 1.58 tesla magnetic fields, with the latter configuration yielding more than twice the intensity of traditional neodymium magnets. The self-emission layer was also observed to be more than 15% thicker with the field on.
Next Steps for Reusable Spaceflight
This achievement by the research group represents a crucial milestone leading up to upcoming practical reentry trials and the establishment of a foundational technology for any forthcoming space missions involving atmospheric reentry.
Pro Tip for Aerospace Enthusiasts
When tracking plasma aerodynamics research, look closely at how facilities handle short-duration pulse synchronization.
Frequently Asked Questions
What is magnetohydrodynamic aerobraking?
By introducing a magnetic field to the weakly ionized plasma surrounding the shock wave, the intensely hot shock layer can be widened and forced away from the vehicle body, which diminishes thermal influx while elevating aerodynamic drag.
Why are traditional heat shields problematic for reusable spacecraft?
Current technologies use heat-resistant tiles and sacrificial material that have serious limitations, increasing weight, surface wear, cost and repair times.
How did researchers test the new MHD system?
Within a hypersonic expansion tube, the test article is subjected to a shock wave traversing in excess of seven kilometers per second (4.3 miles per second) for several tens of microseconds, utilizing a high-power electromagnet driven by a pulse-forming network.
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