I am having trouble recalling a space-based Role Playing Game that we tried after we first tried Traveller. Our usual D&D group didn't care for Traveller as much as I (and the DM/GM) did.
- The rules were one book.(Unlike Traveller, which had three in the original box).
I don't recall there being a box. The cover was silver/gray, and the art of people in space gear was black ink drawings.
The size of the book was about the size of a Traveller book (in terms of LxW, but it was a lot thicker).
My most vivid memory is of one game session that included one of our players using a weapon called an "ion chatter" (something like a submachine gun) to clear out a bar in a rough part of the spaceport where we started. (I recall mostly using grenades myself).
What space based RPG were we playing? There were not many sessions, as we went back to D&D shortly after that.
I can't find it
My various web searches for "ion chatter" do not have any weapons show up, and I have some images from Google under "ion chatter" that are ion weapons from WH40K which is not the game we were playing.
The game I am remembering was published in the mid-to-late 1970's, IIRC before 1980 but after Traveller came out.
There weren't that many space-based games, and it was not a TSR product.
This timeline suggests only a few possible games.
What RPG were we playing?
As recommended by @nitsua60, these appear to be a few games we were not playing:
Based on the timeline and some comments, I was able to eliminate Ken St Andre's Starfaring (cover wrong) and a game called Space Patrol (only 24 page rule book). Further commenting indicates that Space Opera came about a year later than I recall playing (based on life events like us all being out of college by that point, and because the cover was wrong).