re: re:Magnitude in challenge
There is an order of magnitude in the difficulty between sending a crew to orbit Mars (and visit its moons) and actually landing on Mars.
To orbit Mars, you'd need one type of vehicle, to land on Mars , you'd need two different types. And different training, expertise, etc.
Now, if the same vehicle is meant for weightlessness for 6 months and 2 years or more on Mars surface, that makes it even more complicated!
The Shuttle too was meant to be a vehicle for all kinds of purposes.
Raoul