The space trip to Mars seems likely impossible by some problems proposed by the writer, whereas the professor mentions corresponding solutions to them to verify the feasibility.
First, the writer points out that the room of space vehicle is so limited that we cannot put enough resources for astronauts. However, the professor refutes this idea by saying that there is a new method which could help us overcome this difficulty. By growing plants in water, which only need a little space, oxygen could be supplied by the breath of those plants and besides, they could release water vapor that we can collect it as water source.
Second, the writer suggests that astronuauts will meet zero-gravity environment at that time, which could exert negative effects on their muscles and bones. Nevertheless, the professor disagrees with it by evidence that a lot of well-trained men have already paid amounts of effort to overwhelm this disadvantage. They could do regular exercise and absorb vitamin, such as calcite, which would slow down those bad changes.
Third, the writer believes that astronauts could face dangerous radiation from Sun in that area. But the professor argues that the radiation occasionly active and we could also construct small shelter that would not add too much weight in vehicle for astronauts. They could stay in it until the radiation pass.