The most compelling nature of X-ray astronomy is its richness and scale. Almost every observable object in the sky either naturally emits X-ray radiation or can be probed by X-ray absorption. Current X-ray observatories such as Chandra and XMM-Newton have considerably advanced our understanding of many of these systems by using dispersed X-ray spectrometers and imaging CCD cameras. However, it is the combination of these two techniques, a true broad-band, high spectral resolution, imaging spectrometer, that will drive the next revolution in X-ray astronomy. This is where Low Temperature Detectors can play a key role but also where the science will continuously challenge the technology. In this Chapter we will explore the constraints that both the science goals and the space environment place on the implementation of LTDs, and the solutions implemented in current missions such as the XQC and the XRS on Astro-E2. In addition we will see how the NeXT, Constellation-X, and XEUS missions will drive LTD instruments to a much larger scale. Finally, we will address scaling rules in current LTD detectors and where the LTD community needs to proceed to address both the science goals and expectations of the astrophysics community.