This experiment will measure the microstructure of Amorphous Solid Water (ASW), a porous material that can be formed by vapour-depositing water onto a cold plate, an excellent analogue of the ice found in star- and planet-forming regions of our galaxy. The thermal and temporal evolution of this metastable condensed-matter material has major implications in the physical and chemical role ices play in astrophysical environments. Our previous work on ISIS NIMROD has shown that the ASW has very small-scale porosity, and hints at larger scale structure of the material. With NIMROD data alone we are unable to elucidate whether the pores collapse or aggregate, a "hot" debate in the ice literature. This experiment tests ASW porosity scales and exploits the broad Q-range of SANS2d, with higher Q data providing a direct overlap to our earlier results obtained on NIMROD.