The James Web Space telescope will replace the aging Hubble in 2012. One instrument onboard will be the Near Infrared Spectroscope which will require a reconfigurable slit mask to control light incident upon it. One design for this device is called the Mechanically Actuated Reconfigurable Slit mask (MARS). The MARS uses several electromagnetic clamps to move shutters though the focal plane. The goal of this thesis is to develop a system to characterise these clamps at cryogenic temperatures. FEA simulations predicted clamp performance and aided in the development of a test apparatus. An apparatus which utilises the Lorentz force to force the clamp jaws open was developed, built and tested. The device was built inside a cryostat which operated at 30 K. It was found that the test apparatus performed as intended. The clamps themselves proved to be problematic. Small perturbations or misalignments caused significant inconsistencies in experimental results.