The Mobile Remote Servicer Base System (MBS) is a base platform for the robotic arms. It was added to the station during STS-111 in June 2002. The platform rests atop the Mobile Transporter (installed on STS-110, designed by Northrop Grumman in Carpinteria, CA), which allows it to glide 108 metres down rails on the station's main truss. Canadarm2 can relocate by itself, but can't carry at the same time, Dextre can't relocate by itself. The MBS gives the two robotic arms the ability to travel to work sites all along the truss structure and to step off onto grapple fixtures along the way. When "Canadarm2" and "Dextre" are attached to the MBS, they have a combined mass of . Like "Canadarm2" it was built by MD Robotics and it has a minimum service life of 15 years.