This is (again) something from the back of my head, that I am looking for right now. I think that in 2008, I saw a presentation on foamed / expanded aluminium for structural components (1). The promise was to enable roughly 10 times lighter structures in aluminium as compared to a structure with an equivalent strength made from solid aluminium. It was at an ESA meeting, so it should come from either somewhere in Europe or Canada. I can not find it and actually I do not know how it is called. Foam does not seem to be the term. It was about really small bubbles of some sort, similar to or smaller than in foam plastic. I do not know about outgassing in this context, maybe the bubbles were evacuated. It would be interesting to find out more. There are some composites / polymers in use in space, for which foam has at least been investigated, but this is sort of not what I am looking for.
(1) EDIT: I need to specify this. I am talking about structural components of space crafts or satellites. Think of structures in terms of skeletons. Launchers are interesting, but not the scope of this question. It also means, that I prefer a source, which talks about the use in space (longer duration, weeks, months, years), space applications (proposals for or documentation of structural component xyz of mission abc) or space qualification of the material (an analysis of its mechanical properties plus [thermal] vacuum tests is probably most interesting in this case).