Like all his books, Red Planet shows Robert A. Heinlein's focus on realistic technology for space travel and living. An engineer by training, Heinlein prided himself on using feasible and scientifically accurate technology in his books. In Red Planet, technology is used for making life on Mars possible; the thin atmosphere and low gravity are barriers to human life, so advances in habitation and protection technology would allow humans to live on Mars with fewer health problems.
The walls were separated by a food of dead air space, which provided insulation... the colonials maintained about two-thirds Earth-normal pressure indoors for comfort and the pressure on Mars is never as much as half of that. A visitor from Earth, not conditioned to the planet, will die without a respirator.
(Heinlein, Red Planet, Google Books)
It has been proven that the Martian atmosphere is not breathable by any human standards, and in the book, there are plans made to terraform Mars and make it Earth-like. This shows how technology is important both for Heinlein, who understood how humans needed to protect themselves against the elements, and for humankind as a race. Since humans are only evolved to live in a certain temperature, air quality, and gravity, technology will be the most important factor in colonizing the Solar System. Without methods of constraining the environment to fit human needs, there is no possibility of expanding off Earth.