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Space Exploration

Humans began the physical exploration of outer space in the 20th century with the advent of high-altitude balloon flights. This was followed by manned rocket flights and, later, manned Earth orbit, which Yuri Gagarin of the Soviet Union first achieved in 1961.

The economic costs of putting objects, including humans, into space are very high, limiting human spaceflight to low Earth orbit and the Moon. On the other hand, unmanned spacecraft have reached all known planets in the Solar System.

Outer space is a challenging environment for human exploration due to the dangers of vacuum and radiation. Microgravity hurts human physiology causing muscle atrophy and bone loss.

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