Future X-ray timing missions

Thanks to the Rossi X-ray Timing Explorer (RXTE), it is now widely recogniz ed that fast X-ray timing can be used to probe strong gravity fields around collapsed objects and constrain the equation of state of dense matter in n eutron stars. We first discuss some of the outstanding issues which could b e solved with an X-ray timing mission building on the great successes of RX TE and providing an order of magnitude better sensitivity. Then we briefly describe the 'Experiment for X-ray timing and Relativistic Astrophysics' (E XTRA) recently proposed to the European Space Agency as a follow-up to RXTE and the related US mission 'Relativistic Astrophysics Explorer* (RAE),