[pvaldes]

I wonder if NASA machines could include small "3D printers" able to use sand and other local matherials so they could just print small glass objects in situ. That could improve some of the weight problems.

You could make an "unlimited" suply of high quality lenses to replace broken ones, replace small pieces or even fix small cracks in space hatches. If you can make a glass table in situ you don't need to pack it. You can just pack a set of legs for a small table and made it extensible to fit a bigger surface later (Metallic spacial furniture should be printed as a mess of spongy filaments in any case to reduce weigth without losing resistence). And another important matherial that will be needed at some time is the optical fiber, of course.

I assume that heating sand to 1400 degree would be expensive but possible in a combustion chamber with modified pressure and all rockets have some kind of this.

The need to cool the melted glass fast to harden it should not be a problem in Mars. Just put it outside. And there is plenty of sand available.

[pvaldes]

I see... How interesting. That would deserve a separate post:

https://en.wikipedia.org/wiki/In_situ_resource_utilization