By interplanetary space, we are talking about an environment in which space radiation is much more intense than it is in LEO, because above Earth orbit is the geomagnetosphere, the Van Allen belts, which trap charged particle radiation coming from deep space.

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Our star can sometimes despatch big bursts of shortwave and longwave radiation, superfast particles and colossal volumes of charged gas (plasma) in our direction.

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The Radiation Belt Storm Probes will map out the density of charged particles across the belts, which are divided into two: an inner belt, and an outer.

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The radiation belt, which contains "two concentric rings of charged particles trapped by Earth's magnetic fields" doesn't affect current astronauts going to and from space because they are moving too fast to be hit by the radiation.

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The radiation the researchers used in their testing is composed of highly charged iron particles, which are relatively common in space.

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In 1966 Kenneth Greisen, Vadim Kuzmin and Georgiy Zatsepin showed that high-energy charged particles (cosmic rays are mostly atomic nuclei, and thus positively charged) should be slowed by collisions with the photons of the cosmic microwave background (radiation left over from the Big Bang that permeates all space).

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