  The Advanced Laser Interferometer Antenna (ALIA) and the Big Bang Observer
(BBO) have been proposed as follow on missions to the Laser Interferometer
Space Antenna (LISA). Here we study the capabilities of these observatories,
and how they relate to the science goals of the missions. We find that the
Advanced Laser Interferometer Antenna in Stereo (ALIAS), our proposed extension
to the ALIA mission, will go considerably further toward meeting ALIA's main
scientific goal of studying intermediate mass black holes. We also compare the
capabilities of LISA to a related extension of the LISA mission, the Laser
Interferometer Space Antenna in Stereo (LISAS). Additionally, we find that the
initial deployment phase of the BBO would be sufficient to address the BBO's
key scientific goal of detecting the Gravitational Wave Background, while still
providing detailed information about foreground sources.
