NARRATOR：

Now listen to part of a lecture on the topic you just read about.

FEMALE PROFESSOR：

A trip to Mars will definitely be challenging, but scientists have proposed solutions to the problems the reading selection discusses.

First of all, food, water, and oxygen. Well, astronauts can use hydroponics.

Hydroponics is a technique for growing plants with their roots in water rather than in soil.

It requires relatively little space.

Using hydroponics, the astronauts should be able to cultivate food crops in the spacecraft.

In addition, the hydroponically grown plants will recycle wastewater and release it as clean water vapor, which can be collected as drinking water.

And of course, all plants absorb carbon dioxide and release oxygen, so thanks to hydroponics, the astronauts will also have fresh air to breathe.

Second, the effects of zero gravity.

Over the last few decades, we have launched several space stations orbiting the Earth, and a number of astronauts have spent many months on them in a zero-gravity environment.

These astronauts have learned to use several techniques to safely manage the effects of zero gravity.

For example, regular exercise prevents the decrease in muscle mass.

Likewise, taking vitamins and minerals like calcium slows down the decrease in the astronauts’ bone density.

Third, solar radiation. Astronauts traveling to Mars will be exposed to some solar radiation, but this radiation will not be at dangerous levels all the time.

The Sun only releases dangerous amounts of radiation occasionally, during periods when it's particularly active.

In order to avoid this threat, the spacecraft could be equipped with special instruments that monitor solar radiation, and with a small shelter that is shielded against radiation but doesn't add much weight to the ship.

Most of the time, the astronauts would go about their normal business in unshielded areas of the spacecraft.

But when their instruments detect increased radiation, they could stay in the small shielded area until the danger has passed.