There are a number of technical challenges associated with LISA. For instance, great care has to be taken to hold the satellites in position and not to disturb the free floating test masses inside. To this end, special propulsion units have been developed (see image), which can be regulated with extremely high precision and which can exert minute forces on the space-craft, as small as the weight of a piece of paper.
These and other technological advances made for the LISA mission will be put to the test in 2008: The SMART-2 mission involves a satellite developed especially for this purpose. The starting date for the LISA mission itself is set for 2013.