I first read proposals to use resources native to Mars to support a manned mission back in 1991 or 92. The idea is terrific because it would radically reduce the amount of mass you'd need to transport to Mars to support the return flight.

One way to look at Mars mission planning is to analyze the mass requirements in reverse order. You start with what is required to support the crew at the point of aerocapture or reentry into the Earth's atmosphere at the end of the mission and then work back through every stage of the mission to determine what is needed at the beginning. Here's how it works:

1. What mass is required to support the crew at the end of the mission? This will include heat shielding, structure, propellant, etc. necessary to keep the crew alive and to either enter Earth orbit or to reenter the atmosphere and land. It would include the basic vehicle mass.

2. What consumables are needed to support the mission from Mars to the Earth? These would include all propellant used for course corrections as well as the consumables used by the crew (discounting recycled materials).

3. What is needed to support the crew in Mars orbit before beginning the interplanetary trip back to the Earth?

4. What is needed to launch the crew from the Martian surface back to orbit? This is primarily propellant with perhaps some life support consumables included.

5. What is needed to support the crew while on the Martian surface? This will include all life support consumables, all exploration equipment, housing, etc. This determines the mass you need to land on the surface.

6. What is needed to land the mass determined in step 5 on the surface? This is mostly propellant.

7. What is needed to inject the spacecraft into Mars orbit? This will include the orbital section (if any) and the lander with all of its equipment needed in step 5. A direct atmospheric entry is an option that would greatly reduce the amount of propellant, but this also adds an element of risk (say, due to a possible windstorm on Mars like with the Viking missions) that might be undesireable.

8. What is needed to support the crew on the trip between Earth orbit and Mars orbit (primarily propellant for course corrections and life support consumables).

9. What is needed to inject the vehicle on a transMars trajectory? This will be the propellant needed to accelerate the mass determined up through step 8 to a velocity of about 25,000 MPH (or faster if you need to cut the travel time).

Using local resources greatly reduces the amount of material you have to land on Mars because you aren't having to carry the propellant you need to lift off from the surface. This reduction has a huge impact on all of the remaining steps. If you don't use local resources, then you're carrying a lot of dead mass for the entire mission. For every additional kilogram you have at the end of the mission, you'll need many additional kilograms of propellant at the start of the mission. Mass requirements tend to snowball rapidly with spacecraft. Being able to harness local resources while on Mars could well cut the mass required at the start of the mission (step 9) by a factor of 3-10, perhaps even more.

There really hasn't been a lot of discussion about this for the past year because the whole idea of a manned Mars mission is still the stuff of dreams instead of a real program. Until funding is allocated, that's all it'll ever be. The discovery of water ice on Mars would go a long way towards making the mission more affordable, but it still all comes down to money. Like the line from the movie "The Right Stuff", "No bucks, no Buck Rogers."