The Impact of AXAF & XMM on Measurements of Omega_0 from Cluster   Abundances
  Two major X-ray satellites, AXAF & XMM, will be launched in 1998/1999. Both satellites have spectral and imaging capabilities, and are several times more sensitive than either ROSAT or ASCA. AXAF & XMM will yield significant scientific returns in many fields of astrophysics. We concentrate here on how AXAF & XMM will improve constraints on the density parameter, Omega_0, via measurements of the cluster abundance at high redshift. 
A. Kathy Romer