Colonization of the asteroid belt

Asteroids are not large enough to produce significant gravity, making it difficult to land a spacecraft.[1] Humans have yet to land a spacecraft on an asteroid in the asteroid belt, but uncrewed spacecraft have temporarily landed on a few asteroids, the first of which in 2001 was 433 Eros, a NEA from the Amor group, more recently 162173 Ryugu, another NEA of the Apollo group.[18] This was part of the Hayabusa2 mission that was conducted by the Japanese Space Agency.[19] The landing used four solar ionic thrusters and four reaction wheels for orientation control and orbit control of the spacecraft to land on Ryugu.[19] These technologies may be applied to complete a successful similar landing in the asteroid belt.

The asteroids of the inner Solar System and Jupiter: The belt is located between the orbits of Jupiter and Mars.

Sun   Jupiter trojans   Orbits of planets

Asteroid belt   Hilda asteroids (Hildas)   Near-Earth objects (selection)

Since Mars is much closer to the Asteroid belt than Earth is, it would take less Delta-v to get to the Asteroid belt and return minerals to Mars. One hypothesis is that the origin of the Moons of Mars (Phobos and Deimos) are actually Asteroid captures from the Asteroid belt.[20] Using the moon Phobos to launch spacecraft is energetically favorable and a useful location from which to dispatch missions to main belt asteroids.[21] Mining the asteroid belt from Mars and its moons could help in the Colonization of Mars.[22][23][24]

A space elevator based on Phobos could reduce the cost of transport. See Colonization_of_Mars#Transportation

• 
  Space elevator Phobos
• 
  Earth vs Mars vs Moon gravity at elevation

Lack of gravity has many adverse effects on human biology. Transitioning gravity fields has the potential to impact spatial orientation, coordination, balance, locomotion, and induce motion sickness.[25] Asteroids, without artificial gravity, have relatively little gravity in comparison to earth.[26] Without gravity working on the human body, bones lose minerals, and bone density decreases by 1% monthly. In comparison, the rate of bone loss for the elderly is between 1-1.5% yearly.[25] The excretion of calcium from bones in space also places those in low gravity at a higher risk of kidney stones.[25] Additionally, a lack of gravity causes fluids in the body to shift towards the head, possibly causing pressure in the head and vision problems.[25]

Overall physical fitness tends to decrease as well, and proper nutrition becomes much more important. Without gravity, muscles are engaged less and overall movement is easier.[25] Without intentional training, muscle mass, cardiovascular conditioning and endurance will decrease.[25]

Artificial gravity offers a solution to the adverse effects of zero gravity on the human body. One proposition to implement artificial gravity on asteroids, investigated in a study conducted by researchers at the University of Vienna, involves hollowing out and rotating a celestial body. Colonists would then live within the asteroid, and the centrifugal force would simulate Earth's gravity. The researchers found that while it may be unclear as to whether asteroids would be strong enough maintain the necessary spin rate, they could not rule out such a project if the dimensions and composition of the asteroid were within acceptable levels.[27]

Currently, there are no practical large-scale applications of artificial gravity for spaceflight or colonization efforts due to issues with size and cost.[28] However, a variety of research labs and organizations have performed a number of tests utilizing human centrifuges to study the effects of prolonged sustained or intermittent artificial gravity on the body in an attempt to determine feasibility for future missions such as long-term spaceflight and space colonization.[29] A research team at the University of Colorado Boulder found that they were able to make all participants in their study feel comfortable at approximately 17 revolutions per minute in a human centrifuge, without the motion sickness that tends to plague most trials of small-scale applications of artificial gravity.[30] This offers an alternative method which may be more feasible considering the significantly reduced cost in comparison to larger structures.

Most asteroids are located in the asteroid belt, between Mars and Jupiter. This is a cold region, with temperatures ranging from -73 degrees Celsius to -103 degrees.[31] Human life will require a consistent energy source for warmth.

In space, cosmic rays and solar flares create a lethal radiation environment.[32] Cosmic radiation has the potential to increase risk of heart disease, cancer, central nervous system disorder, and acute radiation syndrome.[33] On Earth, we are protected by a magnetic field and our atmosphere, but asteroids lack this defense.[1]

One possibility for defense against this radiation is living inside of an asteroid. It is estimated that humans would be sufficiently protected from radiation by burrowing 100 meters deep inside of an asteroid.[32][1] However, the composition of asteroids creates an issue for this solution. Many asteroids are loosely organized rubble piles with very little structural integrity.[1]

Space travel has a huge impact on human psychology, including changes to brain structure, neural interconnectivity, and behavior.[33]

Cosmic radiation has the ability to impact the brain, and has been studied extensively on rats and mice.[33][34] These studies show the animals suffer from decreases in spatial memory, neural interconnectivity, and memory.[33][34] Additionally, the animals had an increase in anxiety and fear.[33]

The isolation of space and difficulty sleeping in the environment also contribute to psychological impacts. The difficulty of speaking with those on Earth can contribute to loneliness, anxiety, and depression.[34] A Russian study simulated the psychological impacts of extended space travel. Six healthy males from various countries but with similar educational backgrounds to astronauts lived inside an enclosed module for 520 days in 2010–11.[34] The members of the survey reported symptoms of moderate depression, abnormal sleep cycles, insomnia, and physical exhaustion.[34]

In addition, NASA reports that missions on the global scale have ended or been halted due to mental issues.[35] Some of these issues include shared mental delusions, depression, and becoming distressed from failed experiments.[35]

However, in many astronauts, space travel can actually have a positive mental impact. Many astronauts report an increase of appreciation for the planet, purpose, and spirituality.[36] This mainly results from the view of Earth from space.