The correct answer is option 2: microgravity.

During space flight, astronauts experience microgravity, where the gravitational force is significantly lower than on Earth. This microgravity environment has various effects on the human body, including the loss of calcium through urine.

Calcium is an essential mineral for the human body, necessary for maintaining strong bones and teeth, as well as for other vital functions. In microgravity, the lack of gravitational force on the skeletal system causes a decrease in the mechanical stress placed on the bones. This leads to decreased bone density and increased calcium loss.

Option 1: Hypergravity is not the correct answer, as hypergravity refers to higher-than-normal gravity, which is not present during space flight.

Option 3: The intake of dehydrated food tablets may have other effects on the body, but it is not the direct cause of calcium loss through urine during space flight.

Option 4: Low temperature in space (cosmos) is also not the cause of calcium loss through urine.

In summary, the loss of calcium through urine during space flight is primarily due to the microgravity environment experienced by astronauts.