Milky Way stars photobomb picturesque spiral galaxy in stunning Hubble photo

May 24, 2022
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300 million light years away. Space distance is always mind-blowing. We'd still never reach that galaxy alive if humans could travel 1 million light years in a calendar year. But there's plenty of areas of the Milky Way to explore. Someday. Maybe.
Actually, there is no technology we are aware of that would enable a human to travel to another star and return within their lifetime.
Travel would require acelleration to about .1c, coasting for about 40 years, decelleration to zero to explore the star system, acelleration to .1c for the return journey, coasting for another 40 years and decelleration to zero for landing on Earth. Each kilogram of payload thus needs four times the energy needed to reach .1c. At that speed, the kilogram has a kinetic energy of 4.5e14 joules. Four times that is 1.8e15 joules. A kilogram of matter contains but 9e16 joules of energy thus 2% of each kilogram of the spaceship would need to be converted to energy.

Fission only gives up .1% of its mass to energy, so a nuclear reactor based engine is out of the question.

Fusion of hydrogen to helium only gives up .3% of its energy so it is also ruled out.

Fusion all the way up to iron gives up but 1% so it is ruled out.

The only possible way is with antimatter but there is no way to make that much.
A fuel tank of anti matter would give 100% of its mass up to energy when combined with ordinary matter. However 75% of its energy is radiated in every direction by neutrinos, which cannot be directed backwards as propellant. Also, any source of heat needs to be converted to thrust and such a conversion cannot be more than 50% efficient by the laws of thermodynamics. Thus an antimatter engine could convert about 12.5% of its mass to propulsion. However, the making of antimatter is extrememly energy intensive. All of the atom smashers ever operated in the world to date have produced but a microgram of antimatter and tons of it would be required. This would require the amount of energy from sunlight falling on Earth over a 100 year period. Just not practical.

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