Blender 3D is a free, open source option. It's considered the best free 3D modeling software out there, and is fully capable of modeling humans as well as rigging them for animation, and creating the animations as well. To my knowledge, there's no 3D Modeling software specifically geared towards a singular task. There's a number of ways to model the human form. There is an extensive wiki as well as numerous youtube/vimeo videos on blender modeling. You can watch my introduction video here:
MakeHuman is great, and has a sort of "complete exchange file system" that exports the rigging (to be able to animate and pose the model), the Lip Sync poses (to make the model speak, which is obviously not needed here), and so on. You'll have to design the space suit around it, but to provide custom human meshes, it is good at it.
To design space suit however, there's no such utilities as this. You'll have to make your own. Take some NASA spacewalk pictures from a quick Google Image search and apply them as background images.
Blender is one powerful 3D suite that can easily be compared to 3DS Max (I'm not even joking, the two can compete now, it's just that 3DSM is more known and more used in the cinema business), so it is a bit complex; but take a bit of your time to learn it and I'm sure it will be worth it.