It has been observed that at the 0g level (ISS), the risk of living in weightlessness is unacceptable in the long term due to SANS syndrome (Spaceflight Associated Neuro-ocular Syndrome). Does this mean we should give up the idea of physically going to Mars, where gravity is not zero but weak? To answer this question, we need to study precisely (1) the effects of a 0.38g gravity and (2) build two rotating space stations.