The severest hurdle which the planners of a manned mission to Mars will have to overcome, over and above the technological advances that have to be made, will be budgetary. Even with the construction of the space station and an sdv rocket, it is concluded that this mission could be achieved with only a three per cent annual increase in real terms in the NASA budget. The SDV-3R would be a highly capable rocket with a payload capacity to low Earth orbit of 82 tonnes and the authors of the report say that its existence is perhaps the most debatable premise in their estimates. The slight differences in cost, never more than a few per cent, are explained by the lower weights which are needed for aerobraked missions and for conjunction missions, in which the propulsive requirements are less. There are clearly two sets of people in the world as far as Mars missions are concerned.