Yes and no.
It was planned to be a single novel at first, but grew into a trilogy. During writing research went on in parallel continuously.
When I started
writing it, I'd wanted it to be a big novel, a door-stopper, a thousand-page
So it indeed was intended, planned for, to be written as a single novel in one go. But KSR's writing style has the nature of an exploration process, making it an open ended process.
"And at a certain point, Ann and Sax take on these lives of their own... Working
hard on these books, I could get to a state where it was like taking down
telephone messages and being a medium about it.
In addition to that, knowledge about Mars evolved and KSR was in the middle of that.
During the seven years that Robinson was writing his Mars trilogy, he never
"It was a sort of a feedback loop [between researching and writing]," he says.
"I learned more, and between the publication of Red Mars and Green Mars, there
were some very important books that came out. McKay himself published a cover
article in Nature on the terraforming of Mars that really transformed that into
a scientifically respectable question.
But in the end, plan wise the broad outline WAS fixed:
For readers new to your Mars trilogy, can you explain the significance of the colours red, green and blue which form the titles of your books?
In a way I think it's nicely self-explanatory: Mars is red right now. If you talk about Mars being green then you immediately think that means life in the form of plants. In turn this must mean that something has been done to introduce these life-forms because right now it isn't possible. And then blue is both the colour of water and an oxygenated sky. So Mars being blue suggests that those responsible have gone as far as introducing oceans and an atmosphere. In the titles alone of the Mars trilogy I have given away the plot but I think that's actually kind of interesting.