I don't know the math offhand, but the return trip from Mars would take far less fuel than the initial trip. The atmosphere is almost non-existent and Mars' gravity is about 2/5 of Earth's. Similar to our experience on the moon, it took a Saturn V to get to the moon, but the Lunar Lander + CSM were enough to get back to earth from there.

Solar panels and water gets you all the fuel you ever need. One of the things that is interesting is finding asteroids with water and parking a solar panel on them to quietly sit and make hydrogen so that you have loads of refueling stations zipping around the inner solar system.

You've got it all wrong. If there's gold on Mars, there's a financial incentive to send a million people to Mars to create a market for it!

An example I always found quite fun: if you knew how to turn lead into gold in LEO, for free, it still wouldn't be a profitable venture.

Gold costs ~$38,000/kg [1], lead costs ~$4/kg, and launching 1 kg to LEO costs ~$4,000 [2]. It would be an extremely profitable venture.

[1] http://goldprice.org/gold-price-per-kilo.html

[2] http://space.stackexchange.com/questions/1989/what-is-the-cu...

Fair enough. I probably read the claim back when gold was ~$9k/kilo and there was no SpaceX.