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NASA’s CREW HaT
In 2022, Elena D’Onghia and Paolo Desiati, scientists at the University of Wisconsin, submitted a magnetic shield project using a pumpkin-like configuration to NASA’s Innovative Advanced Concepts program and got funding. “Battiston’s conclusion was the same as always—active shields are way too heavy, but this is the best we can do at the moment,” said Desiati. “But in his report, he said that the future belonged to systems where magnetic fields are not confined in solenoids but are open into space. His team did provide some designs, but I have never seen dedicated technical studies. Our idea was to do such a technical study.”
CREW HaT stands for Cosmic Radiation Extended Warding Halbach Torus. It relies on eight magnetic racetrack coils made with ReBCO superconducting wires arranged to enhance the magnetic field outside the shielded habitat and suppress it inside. “It’s called the Halbach array. It’s used in maglev trains where you need the magnetic field only on the side facing the train, but don’t need it on the opposite side,” said Desiati.
Unlike the pumpkin design suggested by Battiston, CREW HaT is not self-supporting. Hoop stresses in the curved section of each individual coil reach 900 tons. They are contained by internal aluminum rib structures and Kevlar composites. Four coils facing the habitat with their flat side are expected to exert an outward force of about 85 tons. The remaining four coils exert an inward pressure on the structure, reaching 140 tons. These forces are counteracted by strong aluminum beams.
Overall, the CREW HaT team estimates its weight at a hair above 24 tons, and power requirements are a bit below 60 kW. “These are promising numbers. Passive shielding cuts roughly 20 percent of the particles hitting the spacecraft up to 500 MeV. CREW HaT adds another 50 percent on top of that. We are in the process of calculating everything precisely, but it is surprising that with such energies, we can achieve such shielding efficiency,” said D’Onghia.
60 kW, though, is the entire energy budget of the ISS, and it would need to go just into powering the shields. So, with nearly all the bets placed on next-gen superconducting magnets, NASA decided to try a different direction. In 2017, the Johnson Space Center and the Jet Propulsion Laboratory joined forces to launch their own active shielding project. And it turned out that electrostatic shields were way less dead than they appeared.
NASA’s active shield project
“When you look at literature on active shielding, the key takeaway is that such projects never make it out of what we call a paper study,” said Dr. Daniel Fry, a scientist working for the Space Radiation Analysis Group at NASA’s Johnson Space Center. So when he and Dr. Stojan Madzunkov, a scientist working at the JPL, started a new active shielding project, they opted for a more empirical approach.
“Stojan and I, we have always been experimentalists. We wanted to build small-scale shields, test them in a particle beam, learn how they function, and then scale them up to protect full-size spacecraft,” Fry said. This, in turn, pushed them toward electrostatic shields. “Simply because they are easy to do. You’re pretty much just flipping the power switch,” Fry added.
Electrostatics didn’t need advanced magnets, superconductors, or cryocooling systems. Instead, they relied on electrodes with positive and negative charges that created an electrostatic field that slows the incoming particles down and accelerates them away using the same force that makes your hair stand when you take off your sweater. On paper, they did the same thing as magnetic shields, but engineering-wise, they were entirely different.
“Take these solenoid designs. Your spaceship basically becomes an MRI tube. Like, how do you get out? And cryopumps are working all the time—clank, clank, clank—keeping liquid helium at 4 Kelvin,” said Madzunkow. And then there is quenching, which happens when part of a superconducting wire gets too hot and loses superconductivity. In a quench, all the energy accumulated in the coil is instantly released, which melts the wire and sends off a powerful electromagnetic pulse.
When a quench happened in the LHC’s superconducting magnets in 2008, its force was strong enough to squeeze and twist powerful steel hardware like it was made of paper. “You are surrounded by tons of liquid helium with a powerful magnet, and when it quenches, you are dead. That’s what they are talking about. Nobody would fly in that thing. It can kill you very, very badly,” Madzunkow said.
Electrostatic shields had been ignored because they required those 60 million volts that French and Levy talked about in their report. In 2008, NASA’s Kennedy Space Center and ASRC Aerospace Corporation proposed an electrostatic shield based on three huge Van de Graaff generators connected to an outer ring that looked like something taken straight from a Vulcan Combat Cruiser. It was undeniably cool, but it was completely infeasible. Fry and Madzunkow had to find something more realistic, so they turned to advanced modeling software and huge GPU clusters.
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