The problem with all of these hyper velocity space vehicles, is the force they put on a human body. I read that a Chevy ZO-6 Corvette would have to maintain it's 0-60 maximum acceleration level FOR 13 MONTHS in order to achieve the speed of light, (186,000 miles a second). That's a long time to be pinned into your seat! Only to have to endure the same negative G load to slow back down.