the foremost features of the new-fangled shuttle being , the massive internal fuel tanks , the inclusion of the internal atmosphere control system iacs for short which actually enables the crew to control the atmosphere and gravity inside the orbiter , the world-shattering attachment of the variable specific impulse magneto-plasma rockets vasimr which are electromagnetic orbiter thrusters that bridge the gap between high-thrust , low-specific impulse , and low-thrust , high-specific impulse propulsion systems and enable the warrior to travel at speeds of up to seventy-two-thousand miles per hour ; facilitating a trip to the moon in under ten hours and a return trip to mars in under forty days .