Why, when you've already spent a thousand hours there?
 

Context) TIME 10 Questions

A veteran of six shuttle flights, Story Musgrave, 75, talks about the end -and the future- of space travel

(Question No.1 -No6, omitted)
(Question No.7)
What will you miss most if you never go to space again?
I'm planning to go to space again. I'll go as a tourist with the tourist companies.

(Question No.8)
Why, when you've already spent a thousand hours there?
I have a 5-year-old child now, and we're working on another one. Would you say, "Why do that?" Little Story is the light of my life. Would you say, "You got a 50-year-old---why do you need a 5-year-old?" Same thing.

(question No.9)
What's the strangest thing you ever did in zero gravity?
I'm the only one I know that sleeps floating. It's delicious. You don't know where you are, and after a while, because our limbs aren't touching anything, you lose sense that you even have them.
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Hi.
I can understand No.7 and No.9 clearly, yet I can't understand question No. 8 and its answer at all.

What is the question?
Why "why" and "when" exists at the same time?

"We're working on another one" means"I and my wife are planning to have another child and doing s*x", right?

"Little Story is the light of my life" means what?

Thank you.

Question 8 is asking "Why do you plan to go again? You have already been there 1000 hours, isn`t that enough?" The "Why?" is a response to his answer for #7.

The answer is explaining his feelings using the feelings he has about his children as an example.
He has a 5 year old, and wants another child. (It doesn`t have to mean that he is trying to make the baby - it could be talk of adoption or surrogacy, etc. Working on it just mostly means that they do want another, and are trying to get another child in some way.) He asks if someone would ask "Why would you want to have another child? You already have one!" He also already has a 50 year old child.
He is comparing his feelings about his desire to have children as being similar to his desire to go to space again.

His son must be named "Story" - because his own name is "Story" too, "Little Story" is a nickname for his son. Light of my life is saying that something is extremely important to his happiness.

I explained in English, but if it is unclear I will be happy to do so in Japanese.

Thank you, Nyororin, for your explanation.
It is crystal clear now. :)