Interstellar gas makes travel at near light speed impossible

New Scientists reports interstellar hydrogen atoms are a deadly problem for space travellers who posses the ability to travel at nearly the speed of light. For every cubic centimetre of interstellar space, there are fewer than two hydrogen atoms, on average, compared with 30 billion billion atoms of air here on Earth.

Yet, this minute amount of matter poses a great problem, according to William Edelstein of the Johns Hopkins University School of Medicine in Baltimore, Maryland, the hydrogen atoms would seem to reach a staggering 7 teraelectron volts at 99.999998 percent the speed of light. Hopkins estimates a crew of an interstellar spacecraft would get bombarded with a radiation dose of more than 10,000 sieverts within a second, which is several orders of magnitudes higher than the fatal dose of radiation for humans of 6 sieverts.

Worse is that the atoms' kinetic energy also increases. For a crew to make the 50,000-light-year journey to the centre of the Milky Way within 10 years, they would have to travel at 99.999998 per cent the speed of light. At these speeds, hydrogen atoms would seem to reach a staggering 7 teraelectron volts – the same energy that protons will eventually reach in the Large Hadron Collider when it runs at full throttle. "For the crew, it would be like standing in front of the LHC beam," says Edelstein.

The spacecraft's hull would provide little protection. Edelstein calculates that a 10-centimetre-thick layer of aluminium would absorb less than 1 per cent of the energy. Because hydrogen atoms have a proton for a nucleus, this leaves the crew exposed to dangerous ionising radiation that breaks chemical bonds and damages DNA. "Hydrogen atoms are unavoidable space mines," says Edelstein.