The paper was presented at the 46th International Conference on Environmental Systems and discusses the estimated costs of a human mission to Mars. According to the document, the cost of the first human mission to Mars could be around “half a trillion dollars”. This estimate is consistent with most past estimates. Using mass-cost estimating factors based on the International Space Station (ISS) and other experiences, the cost of life support for the Mars mission could be two billion dollars or more. The cost to go to Mars is expected to be two or three times that of either Apollo, space shuttle, or ISS and could be as much as all three together.