<font color="yellow">"... how the Soyuz capsules are considered space-worthy for six-months at a time..."</font><br /><br />I haven't studied the Soyuz in great detail -- namely because I haven't been able to find a fraction of the detail on it that I have the Gemini and Apollo designs. However, I can make some reasonable guesses based on the data I have found and on what I learned while researching capsules in general.<br /><br />- The Soyuz has no cryogenics to boil off.<br />- The orbital module has solar panels to provide long-term power. The Soyuz doesn't require <b>nearly</b> as much power as the shuttle, so these panels can provide full power to the systems essentially indefinitely.<br />- In space, <b>generally</b> you have a bigger problem with too much heat rather than too little, as the electronics & crew generate more heat that must be radiated to space. This isn't true of the shuttle because it's so flipping huge (more radiating area and heat-generating equipment more dispersed). With the solar panels, equipment on board the Soyuz can be kept running (if necessary) to generate enough heat to keep the H2O tanks/etc. from freezing. Alternately -- they may have tuned the exterior of the Soyuz for heat absorption/radiation such that it maintains a reasonable temperature simply from solar flux.<br />- The Soyuz has both a primary space radiator and a pair of sequencing space radiators on the propulsion module. These will be used to radiate heat when the crew is onboard and the electronics are running nominally. While the Soyuz is docked, these radiators can be either shut down or run at a much lower rate to retain more heat.<br /><br />What it really boils down to is that the Soyuz was designed to stay on orbit for months and the orbiters weren't. Had it been a design criteria, there are probably ways that the short-poles could have been handled: zero-boil-off tanks for the fuel cells, putting heat-sources near cold-damagable components, usin