Magnets in space

By Mazzin Ajamia

From the moon, the Earth looks like a tiny marble in space. Alone and defenseless — or is it? Source: Bill Anders

Our Sun gives much (light and energy), but it also takes: solar radiation eradicated Mars’ early atmosphere and oceans.

Why that didn’t happen to Earth? Well, the way the Earth protects us from the sun’s radiation is pretty mag-neato.

Like many other planets in our solar system, but unlike Mars, Earth has a magnetosphere. It’s a magnetic field that protects the Earth’s surface — and those of us who thrive on it — from harmful solar flares and radiation.

What creates the Earth’s magnetic field? This is a complicated question, but it boils down to the fact that our mostly-iron core is extremely hot — it’s a nuclear reactor. That extreme heat means our core is molten. It’s liquid, and it’s constantly churning as the hotter liquid rises and the cooler liquid sinks. The motion of that molten metal core is what generates our magnetic field.

The Aurora Borealis from space. When a particularly strong solar wind interacts with the Earth’s magnetosphere, it creates a beautiful light show. Source: NASA JPL

That’s right. The Earth is one big magnet. (I explain how magnets are made on P4’s podcast last week.)

“But, Mazzin,” you say, “Phase Four builds space propulsion systems. Why are you so obsessed with magnets?”

I previously worked on attitude and control simulations for cubesats at PolySat — that is, I helped ExoCube 2 figure out which way it was oriented. I learned that if your satellite has a magnetic field, that field will interact with the Earth’s magnetic field. It’ll try to line itself up with the Earth’s field, which applies a torque on your satellite that needs to be taken into account in attitude determination.

Understanding magnets and the Earth’s magnetic field is crucial to attitude determination and control. This week, I follow up with a sequel: dipoles in space. Dipoles are measure of how large your magnetic field is. The smaller the satellite and the weaker its attitude control, the smaller its dipole moment needs to be.

Magnets are also crucial to Phase Four’s electric propulsion system. We use passive, permanent magnets as a key part of our thruster. Because our Maxwell propulsion system is designed for small satellites, we’ve engineered a system that relies on passive magnets to generate thrust — while simultaneously achieving a net zero dipole configuration.

Wouldn’t you be obsessed with magnets, too?