You are right that the ideal gas law doesn't describe real gases but it can be a reasonable approximation for some applications, even at fairly low temperatures, provided the density isn't high.
Helium is the closest thing we have to and "ideal gas" as far as the ideal gas law goes when it's at STP.
It can still somewhat behave as an ideal gas as low as 50K or so granted it is not under pressure.
Once you increase the pressure the ideal gas law breaks down pretty much completely, and is not applicable to liquid helium at about 6000PSI.
People also forget that the tank is made out usually titanium or aluminum (i think aluminum can't hold helium but am not sure about that) wrapped in a composite material usually Kevlar/Epoxy or some sort of carbon fiber composite, extreme low temperatures are well a bit tricky for these materials.
NASA had issues with that during the shuttle program, and it seems that even the new Orion has encountered issues with the effects of low temperature on COPV's which required them to develop new resins and composites http://www.compositesworld.com/articles/orion-composite-tank...
It can still somewhat behave as an ideal gas as low as 50K or so granted it is not under pressure.
Once you increase the pressure the ideal gas law breaks down pretty much completely, and is not applicable to liquid helium at about 6000PSI.
People also forget that the tank is made out usually titanium or aluminum (i think aluminum can't hold helium but am not sure about that) wrapped in a composite material usually Kevlar/Epoxy or some sort of carbon fiber composite, extreme low temperatures are well a bit tricky for these materials.
NASA had issues with that during the shuttle program, and it seems that even the new Orion has encountered issues with the effects of low temperature on COPV's which required them to develop new resins and composites http://www.compositesworld.com/articles/orion-composite-tank...