The SSRMS is the Space Station Remote Manipulator System, now officialy named
Canadarm 2*. It is similar to, but bigger than, the
space shuttle's
robotic arm. Used primarily to build
Space Station Alpha, move large loads and help dock the shuttle, it is 17.6 m long in full extension and has 7 motorized
joints. The
SPDM - Special Purpose Dextrous Manipulator (the so-called Canada Hand) - can be attached to one end to perform delicate operations with its two smaller arms. The other end can be mounted on a moving base that slides along rails. The official
acronym for the the moving base is
MBS, which stands for
Mobile Base System, of course. Together with the SSRMS and SPDM, it constitutes the
MSS (Mobile Servicing System). The SSRMS can also
move in an
inchworm fashion across the
ISS thanks to its two identical
grapple end points (the Latching End Effectors). This enables it to move from
mounting point to mounting point, each of them providing
control and
power.
*Isn't this kind of unimaginative or at least uninspired considering other potential names, such as the lovely Canipulator...