If we can't build a magnetic bubble for a spacecraft, how about a magnetic tunnel?

If it is impractical to provide an artificial magnetosphere on the ship which would travel to Mars (due to cosmic ray cascades in the material of the ship), what about generating the magnetic fields externally and projecting them into space at a series of waypoints? Or would the distance involved (225 million miles) be too great?
Our planet's magnetic field changes shape constantly due to strong winds from the sun. Image credit:  NASA's Scientific Visualization Studio

Our planet's magnetic field changes shape constantly due to strong winds from the sun. Image credit: NASA's Scientific Visualization Studio

A little while ago we covered some of the main radiation based difficulties of sending people to Mars, and while the solar wind is generally not so troublesome, cosmic rays, which we are shielded from here on Earth, are both more dangerous and much harder to redirect or stop.

Generally we want the outer walls of our spacecraft to be pretty durable, both for airtightness, protection against space junk, and to help protect against the solar wind, which can be stopped by a pretty reasonable amount of shielding. However, as you build up your shield, cosmic rays will start to play a nastier role. While you certainly don’t want a cosmic ray to be able to pass straight through your spacecraft and hit your astronaut unhindered (they’re very energetic particles, the sort that bodies deal very badly with), when a cosmic ray hits a dense object like a wall, it doesn’t just bounce back the way it came from.

Standard spacecraft shielding, integrated into hull design, is strong protection from most solar radiation, but defeats this purpose with high-energy cosmic rays it simply splits into deadly showers of secondary particles. Image credit: NASA

Standard spacecraft shielding, integrated into hull design, is strong protection from most solar radiation, but defeats this purpose with high-energy cosmic rays it simply splits into deadly showers of secondary particles. Image credit: NASA

It creates a radiation cascade instead; what was one particle is now two, four, sixteen, and beyond, very rapidly, as the particle interacts with the dense material of the spacecraft wall. Sixteen slightly lower energy particles is mathematically worse than one high energy one, and a serious point of concern once we get out of the Earth’s magnetic shielding. So a very reasonable response is to ask if we can bring along our own magnetic shielding, to prevent the high energy cosmic rays from hitting the wall of the spacecraft in the first place. Theoretically, this should reduce the amount of radiation inside the spacecraft cabin, since it would reduce the number of cosmic rays that can make it all the way to the spacecraft shield. The main reason this is impractical right now is simply a logistical one - we don’t have a good way to build a generator for a sufficiently strong magnetic field which is also lightweight enough not to be hard to launch.

Setting up waystations would be an interesting way of approaching the same challenge. If there were a fixed orbital path between the Earth and Mars, and we could build a magnetic tube between the two planets, you could do away with the need to have an onboard magnetic bubble. Because you’re not trying to launch them on the spacecraft, you wouldn’t need to worry about the weight as much, but the magnetic field you’d have to generate would need to be much larger, to guarantee that the spacecraft (within errors) would definitely travel safely through the buffered region. The distances involved here are vast, and so setting up a series of waypoints would almost definitely be unfavorable, at least from an energy consumption perspective. There’s also the question of fueling those waypoints. Are they solar powered? Fission powered? What happens if their solar panels break down or they run out of energy? They’d also have to be able to correct their own orbits in order to be in the right places for the protection of the traversing spacecraft, and at this point we’re looking at a giant electromagnet with rockets, which is a great sounding device to have, but practically speaking, it’s a more powerful version of what we’d like to have on the spacecraft in the first place, and if we can get by with one device instead of several hundred, one is probably better.


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Does The Earth's Magnetic Field Go Past The ISS?

Does the Earth’s magnetosphere encompass the ISS and does it offer the same protection as it does our atmosphere and planet?
A profile view of the magnetic field and density data. Image Credit: NASA's Scientific Visualization Studio, the Space Weather Research Center (SWRC), the Community-Coordinated Modeling Center (CCMC) and the Space Weather Modeling Framework (SWMF).

A profile view of the magnetic field and density data. Image Credit: NASA's Scientific Visualization Studio, the Space Weather Research Center (SWRC), the Community-Coordinated Modeling Center (CCMC) and the Space Weather Modeling Framework (SWMF).

Originally posted on Forbes!

The International Space Station, or ISS, orbits our planet once every 90 minutes at the lofty height of 400 kilometers (about 248 miles) above the surface of our planet. This altitude puts it pretty well above the vast majority of the atmosphere, but it doesn’t place it outside the reaches of the magnetic field which surrounds our Earth.

The International Space Station, in orbit around Earth. Image credit: Science@NASA and NASA’s Goddard Space Flight Center, International Space Station image courtesy of NASA

The International Space Station, in orbit around Earth. Image credit: Science@NASA and NASA’s Goddard Space Flight Center, International Space Station image courtesy of NASA

The magnetic field of our planet — otherwise known as the magnetosphere — extends out to about 65,000 kilometers (40,000 mi) above the surface of the planet. However, that “about” part is pretty critical — the magnetosphere isn’t a fixed boundary, which always remains at exactly 40,000 miles from the surface. This surface is a little more flexible, and if you’ve ever held two opposing magnet ends against each other, you’ve felt this exact flexibility. The resistance between two magnets isn’t a wall, where suddenly you can’t move them any closer to each other. The pressure there is a little more like pressing on a slightly under-inflated balloon.

In the case of the Earth’s magnetic field, the pressure on our magnetic field comes from the Sun. The Sun is constantly battering everything surrounding it with a solar wind, made up of charged particles. If you’re a planet without a protective magnetic field, this solar wind will slam into your atmosphere, and can destroy it over time. This is roughly what we believe happened to Mars’ atmosphere. The Earth has a very fortunate protective shield, but this constant pressure on the Sun’s side of our planet means that this magnetic protection is pressed back, closer to the planet. That 40,000 mile number I gave is this: the typical, Sun-compressed, Sun-facing side of our magnetosphere. The nighttime side of our planet, facing away from the Sun, has a long magnetic tail drifting out beyond it, extending several times farther out than the Sun-side.

A profile view of the magnetic field and density data during a solar outburst. Image Credit: NASA’s Scientific Visualization Studio, the Space Weather Research Center (SWRC), the Community-Coordinated Modeling Center (CCMC) and the Space Weather Modeling Framework (SWMF).

A profile view of the magnetic field and density data during a solar outburst. Image Credit: NASA’s Scientific Visualization Studio, the Space Weather Research Center (SWRC), the Community-Coordinated Modeling Center (CCMC) and the Space Weather Modeling Framework (SWMF).

If the Sun has a particularly strong outburst – a coronal mass ejection or any kind of solar flare — the pressure on our magnetic field gets much stronger, but nothing the Sun typically does will press the magnetic field down close enough to the Earth’s atmosphere so that the ISS would exit the magnetic field. Some of our highest orbiting satellites do exit the magnetic field of the Earth, as of course all craft going to other planets must also do. However, these satellites and spacecraft must be constructed to protect their inner workings from the charged particles in the solar wind. Satellites are effectively very elaborate electronics, and electronics do not like being exposed to charged particles. It shorts their circuits.

All this really means that the ISS is in a much safer region of space than it could be – not that it’s totally safe. Our magnetic field is not a perfect blocker of high energy particles, and so things like gamma rays, cosmic rays, and other damaging radiation can still appear in higher quantities than they would if the astronauts were still safely on  the ground. Our atmosphere is pretty good at blocking a lot of these high energy particles, so on the ground you’d never get exposed to them. But the ISS is above the atmosphere, and doesn’t have this extra layer of shielding, so there are radiation monitors on the space station to keep track of how much of a radiation dose they’re getting. If a solar flare is on its way, the astronauts usually have a few days’ warning, and can take shelter in more strongly shielded section of the ISS if they need to. (Not all solar storm are aimed in their direction, and not all storms are strong enough to require this precaution.)

So yes, the ISS is firmly embedded in the Earth’s magnetosphere, making it — for a space based outpost — a relatively safe haven for our astronauts.

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