Robert Zubrin, an aerospace engineer, popularized an exploration plan called Mars Direct in his 1996 book The Case for Mars. The book is organized coherently, with the earlier chapters focused on getting to Mars and the later ones discussing colonization and terraformation. It is largely a reaction against a 1989 NASA study, often called the "90-Day Study", which laid out a plan to get humans to the Red Planet. This plan involved sending a single, massive spaceship that would carry with it all necessary supplies, and would follow a trajectory through the highly irradiated neighborhood of Venus—all at a cost of around $450 billion.
Read more reviews on AmazonIn The Case for Mars, Zubrin compares the spacecraft architecture of the 90-Day Study to the enormous ships, backed by the British Admiralty, of Sir John Franklin's failed attempt to navigate the Northwest Passage in 1845. The essence of Mars Direct, on the other hand, is to explore Mars like the more successful Europeans explored the Arctic. These expeditions embraced the resources and ways of the local environment, for instance by using dog sleds for travel. A central feature of Mars Direct is to use the indigenous Martian atmosphere to produce breathing oxygen and rocket fuel.
Perhaps the biggest problem with Mars Direct is that it is not a very robust mission architecture. It relies on the near-perfect execution of many successive steps, with a single failure bringing the whole thing down. It's never a good sign when a broad mission strategy specifies the exact dates at which events are to take place. By now we should know that technical, political, and economic failures will inevitably interrupt our spacefaring plans. Mars Direct does not leave much room for these failures.
Robert Zubrin is a man of bold ideas and he doesn't shrink away from challenges. Though his writing style reflects that of an engineer, the vocabulary and concepts he presents are generally accessible. Zubrin is prejudiced in thinking that Mars is the only important target of exploration, but The Case for Mars is nonetheless a valiant attempt to outline a minimalist strategy for exploring the Red Planet.