A full list of space related minifigures can be found on Bricklink here as well as under the Town theme. If you count fantasy themes there are also many astronaut minifigures under Alien Conquest, Blacktron, Life on Mars, Mars Mission, Space Police, etc...
There is also the Spaceman from the 1st Collectible Minifigure series.
It's not a Star Wars set, it's most of the main part from "70704 Vermin Vaporizer" from the Galaxy Squad theme.
The word "pressure" on the green tile hints that it's not Star Wars, as that would normally be in Aurebesh - the written script you see in the films.
It turns out the curved white roof tile (Circle 90G 6X6 Roof Tile) at the front was only used in ...
It's hard to answer this definitively without a picture identifying the exact parts you have, but this sounds a lot like the set Rocket Base (358-1) from 1973:
That was one of the first space themed sets. The round parts are similar to what you've described. It looks like an obvious tribute to the Apollo program, though it isn't licensed or branded that ...
At this time, there has been no announcement of a scheduled unlicensed LEGO Space theme. LEGO is not going to make an announcement that "We forever and ever retired LEGO Space, and it will never-ever come back." It's just not going to happen. In addition, they don't reveal what they are working on, until it is time for an official announcement - usually ...
What you have there is a 6118 Wheel Hard Plastic Small (22mm D. x 24mm), and this wheel is pretty common, it features in 39 sets, but luckily for you only in 4 sets in the color White. These sets are:
1704-1 Ice Planet Satellite Plow - this set has 6 of these wheels.
6983-1 Ice Station Odyssey - this set has 10 of these wheels.
6814-1 Ice Tunnelator - ...
928 was the original set number of the Galaxy Explorer - so the numbering of that one is following the LEGO tradition of using the set number.
As Joubarc points out, at that time the sets were branded LegoLand, which is where the LL comes from (in recent years LEGO often uses the Designer's initials).
I'd say that as Benny is a rather well used Classic ...
Although the stand-alone, unlicensed Space theme technically remains discontinued, LEGO has recently released an unlicensed Space sub-theme under their City theme.
While these builds seem to be more "near future" than the classic Space sets, they can be whatever you want them to be. This is LEGO we are talking about, use your imagination to figure out how ...
Some of the places you can buy old (discontinued) sets include:
Generic on-line toy stores that carry old stock
Some LEGO discussion forums have areas for buying and selling
Toy shops and LEGO stores sometimes carry old stock
Stands at exhibitions and shows
Not sure if you would include the Futuron Astronaut or Classic Space Astronaut in this list (image courtesy of http://www.toplessrobot.com/2009/05/the_30_greatest_lego_minifigs_of_all_time.php?page=2):
I had several of these as a kid - I remember black, blue, yellow, and red variants.
They also used the following helmet variation in Series 1 of the Minifigures set:
I also have the limited edition orange Lego Universe Spaceman that can be seen here:
Neither of these came with backpacks.
There is also now the Minifigures "Galaxy Patrol" style spaceman which started appearing in Series 8:
This combined a new helmet with the much enhanced ...
Couple of observations:
Neither of these pictures shows complete sets
The parts you show in each picture most likely do not all come from the same set
From what I can see, you have the following parts of sets in the pictures, clockwise from top left:
Parts of a Y-wing (likely 9495 Gold Leader's Y-wing Starfighter ) plus parts of 7166 Imperial Shuttle