Spaceflight Inc. has unveiled its Sherpa in-space tug vehicle to inject hosted payloads into different orbits. 
   The Sherpa 400 is optimized for low Earth orbit (LEO) missions. The company will build two versions of Sherpa – a smaller version that will be capable of accelerating a payload to 400m/s change in velocity and a larger version that will be capable of delivering a payload at 2,200m/s.
   The system will be used on SpaceX’s Falcon 9 rocket. A sun-synchronous test flight is planned for early 2014, with a first operational mission for late 2014. "In a lot of cases, as a secondary payload, you’re restricted by where the primary payload goes. That’s often descent inclinations but a different altitude," Spaceflight Inc. CEO Jason Andrews said in a statement.