Major update published on 5 August 2014
One of the key features of Living Reviews is that its articles are kept up-to-date by their authors. A major update is considered a new publication. As such it is again subject to peer review and is issued with a new publication number.
Major revision, updated and expanded. The number of references increased from 35 to 65. This revised version includes new and major theoretical and experimental results that have appeared in the literature since the original review got released. The new Section 5.3 covers recent work performed by S.V.D. and collaborators on the mathematical foundations of second-generation TDI. Section 5.4 instead addresses the derivation of the TDI space corresponding to a laser interferometer architecture with only two arms. This covers both the LISA mission in the eventuality of failure of one of its arms, or other mission concepts in which by design only two arms are envisioned. Finally, in Section 7 some practical and experimental aspects related to the performance specifications of the different subsystems used for implementing TDI have been included.