The broad X-ray iron line seen in the spectra of many AGN is thought to originate from the inner regions of the putative black hole accretion disk, and hence provides a rare probe of that central region. In principle, future high throughput X-ray spectrometers should be able to examine the temporal response of this fluorescent line to flares in the X-ray continuum source (which energizes this emission line) - i.e. iron line reverberation mapping will be possible. It has been previously found that there are robust reverberation signatures of the black hole spin, mass and the X-ray flare location above the accretion disk. Here, we simulate observations of a bright Seyfert nucleus with the proposed NASA mission Constellation-X and demonstrate the feasibility of detecting these reverberation signatures with this mission. Hence, starting with XMM in 1999, and maturing with Constellation-X in c2010, iron line reverberation will open a new window on the innermost regions of AGN.

7 pages, 7 figures (some compressed postscript). Accepted for publication in ApJ