Psychological Stress and Health Issues

In the initial video it was mentioned that the psychological stress of being in a confined space for long duration presents some challenges, but the physical health issues seem to be of more concern. As Wired points out, "Outside the safe cocoon of Earth’s atmosphere and magnetic field, subatomic particles zip around at close to the speed of light. This is space radiation, and it’s deadly. Aside from cancer, it can also cause cataracts and possibly Alzheimer’s."

Cosmic Radiation

One of the most challenging problems of space travel is the cosmic radiation (gamma rays, solar energetic particles and galactic cosmic rays) penetration through the hull of the space craft. The space craft would have to have very thick walls of some kind of non penetrable material, i.e., concrete cement, water, etc., to protect humans safely when traveling through space. On a long voyage, for example to Mars (a round-trip to Mars will last at least 2 years), the humans would be cooked before they arrive without some counter measures to prevent the health risks associated with cosmic radiation which includes "damage to all parts of the body including the central nervous system, skin, gastrointestinal tract, skeletal system, and the blood forming organs." Actually, there is no real data on such long term trips since humans have only gone to the moon and back rather quickly and is a comparatively short distance. NASA has dubbed this 'The Radiation Challenge.'

"Currently, the main operational countermeasure against the adverse affects of radiation is simply limiting astronaut exposure, which means limiting the amount of time astronauts are allowed to be in space." The Radiation Challenge

Since the above countermeasure can't be implemented on a trip to Mars, what has NASA proposed as countermeasures for such a voyage? NASA proposes "better shielding and mitigation strategies."

Shielding

So far all the proposals for better shielding for a trip to Mars are problematic since the material that is able to protect humans has to be so thick that it is too expensive and heavy to produce and impracticable.

Mitigation

NASA states that mitigation includes 'dietary countermeasures.'

"Dietary countermeasures are drugs, that when ingested by an astronaut, may have the potential to reduce effects of ionizing radiation." So far such dietary and drug countermeasures are wanting.

Traveling Through the Van Allen Belts

It can be quite dangerous traveling through the Van Allen Belts. The Apollo missions all traveled through them so if you wonder how this is possible, Jillian Scudder, PhD, explains in a Forbes article, Why Aren't The Van Allen Belts A Barrier To Spaceflight? So while traveling through the Van Allen Belts can be accomplished since the Apollo missions proved that, after leaving these belts the cosmic galactic radiation still has to be dealt with.

Safely Traveling Through Space

While NASA or any space agency hasn't resolved the problem of safely transporting humans from the earth to Mars and back, nevertheless, NASA is optimistic. Note this statement, “Some people think that radiation will keep NASA from sending people to Mars, but that’s not the current situation,” said, Pat Troutman, NASA Human Exploration Strategic Analysis Lead. “When we add the various mitigation techniques up, we are optimistic it will lead to a successful Mars mission with a healthy crew that will live a very long and productive life after they return to Earth.” Space Radiation Won’t Stop NASA’s Human Exploration, Oct. 12, 2017, NASA

"At the 2017 International Astronautical Congress in Adelaide, Australia, Musk announced his plans to build large spaceships to reach Mars." SpaceX, Wikipedia

If humans ever do take the challenge of traveling to Mars and back, these first travelers into space beyond the Van Allen Belts will be the first humans to experience what is considered one of the biggest challenges, exposure to cosmic galactic radiation. Without a doubt, there would be volunteers to take such a voyage, but so far, the problems associated with space travel will probably be highly detrimental to human health and safety resulting in serious health risks and/or death.

Physics of Space Travel to Another Star Other Than The Sun

On the subject of traveling to another star other than the Sun, Michel Mayor, an astrophysicist who was a co-recipient of the Nobel Prize in physics in 2019 for discovering the first planet orbiting a sun-like star outside of our solar system is reported to say on this subject, "in this case, the required physics to reach the stars, if it exists, is not known to us and it would require a fundamental change in our understanding of the relationship between mass, acceleration and energy." ^[1]

One article explains how long it would take to get to the nearest star system based upon the rate of using 'ionic propulsion' which current technology has "managed to reach a velocity of 56,000 km/hr (35,000 miles/hr)" it would "take over 81,000 years to traverse the 4.24 light years between Earth and Proxima Centauri."

End Notes

^[1] Humans Will Never Live on Another Planet, Nobel Laureate Says. Here's Why., Tasemin Saplakoglu, Live Science

^[2] NASA Is About to Launch the Fastest Spacecraft in History. Target: The Sun!, by Meghan Bartels, Space.com