Assuming that adequate water can be found on Mars (pretty likely) and that it is accessible, drilling would still be necessary.

In addition, I propose that the following things might prove to be heavier and bulkier than just carting the fuel all the way.

1. Pipelines (or trucks) to bring the water to the conversion site;

2. Tankage to hold the water and to permit settling of debris;

3. Filtering systems to purify it for electrolysis (otherwise the electrolytic cells will be fouled);

4. Much, much electric power to separate the water into hydrogen and oxygen -- this means either a good-sized nuclear reactor-turbogenerator setup (complete with cooling tower to dispose of waste heat) or a gigantic array of photovoltaic cells;

5. Insulated cryo-storage for hydrogen - or - combination of hydrogen with carbon dioxide from carbonates (with associated overhead) to produce more easily stored liquid fuels - the latter requiring catalytic reactors to re-form the carbon dioxide-hydrogen mixture;

and lots more.

Check out what is required to provide hydrogen for the Space Shuttle and you will see what I mean. Production of fuel from Mars' natural resources is a very large and ambitious task, with lots of things that could go wrong. I would consider the risk to be huge and the benefits to be small, if there are any at all, when all of the overhead is considered.

David F Mayer