The writer and the speaker have a debate on sending astronauts. The writer puts forward three obstacles, which are opposed by the following lecture.
First, the writer claims that the landing is not safe. From 1996 to 1999, four spacecratfs crashed because of computer errors. While the speaker views this issue from an opposite angle, according to him/her, computer program accuracy has been improved. Besides, astronauts could adjust conditions to avoid unexpected events. No spacecratfs have crashed since 1999.
Secondly, the passage states that It is hard for spacecraft to carry fuels. Spacecraft needs to carry large amounts of fuels for its way to Mars as well as back then. However, the speaker casts doubt on this opinion by saying that when the there is no need to take a lot of fuels. Hydrogen and Oxygen in ice on Mars can make fuels. Therefore, spacecraft only need to take fuel that supports it to Mars.
Last, the writer argues that the trade between the without protection, astronauts would suffer radiation. By contrast, in accordance with the speaker, this claim does not hold water. Magnetic field can be created to guarantee safety. It is as same as the earth magnetic field.