I disagree with your reason of why it is a bad idea, and feel that it would be possible mentally. It's the science behind it that causes the problems. A couple of years in an enclosed space with nothing but a few board game with 5 other people can do wonders to you mind. Quick definition of quintessence: It's a dark energy/matter which fills up about 2/3 of the space. This dark matter is the cause of the exceleration of the Universe. This was discovered aboue 2 years ago. It's considered an "opposite" of gravity since it repulses or acts as a negative towards gravity. If we use this we can allow objects to gain speed in space with the use of gravity. it's something similar to this. Im not a professor on such a subject.