A number of real-life terms relating to air and space travel that are still in common use are borrowed or adapted from nautical terms. Since we still call people who steer airplanes “pilots”, the places where airplanes load and unload “airports”, and people who travel through outer space “astronauts”, I don’t think it’s outdated or silly for science fiction authors to invent similar terms.
Actually, I’ve been nursing a pet theory that the Manticoran 8th Fleet, which was doing deep-strike raids against Havenite industrial bases, might have been a reference to the USAAF 8th Air Force, famous for their daylight bombing campaign against Occupied Europe and Germany (along with the 12th and 15th Air Forces, but alas, they don’t get as many movies made about them).
EDIT: Although did you notice how the early FTL comm relays were basically telegraphs?
What’s the alternative- laser musket? 
The Atomic Rockets website suggests the term “espatiers”
Laser…longarm? Lightlock?
That’s a different branch. 
Do it right and they’ll hit like a plank.
Carbine.
There’s not that many “Space Marines” as such though I think. There’s Marines who are in space, but most aren’t called Space Marines; they’re just called Marines or something like “Colonial Marines”. The three groups actually named Space Marines I can think of are the Warhammer 40k supersoldiers, the Grayson Space Marines, and Orz Space Marines.
Photon slingshot!
Well, most sci-fi energy weapons aren’t called lasers, so we’re not necessarily dealing with beams of light. Maybe the “barrel” of the weapon contains part of the machinery that generates the energy blast. Maybe the weapon doesn’t have to be that shape, but it does need to be that bulky, so they may as well build it that shape so it’s easier to aim. Maybe the “barrel” modifies the energy blast in a way that improves the weapon’s range and accuracy, so the people who use them call them rifles out of inertia.
Can’t see this sort of thing happening in real life. Not at all. Nobody would call an energy weapon a rifle in the real world. No sirree.
Taser: Thomas A. Swift’s electric rifle.
The guys in Starship Troopers weren’t called “Space Marines”, but Heinlein did use the term in several other stories (including Space Cadet and various short stories in his “Future History”). H. Beam Piper also had Space Marines in his “Future History” (including the Fuzzy novels). The name seems to show up fairly frequently in your more space-opera-ish science fiction from maybe the Thirties through the Sixties.
Per TV Tropes (it’s been so long since I read the book I can’t remember myself), the troopers in Starship Troopers were arguably more like Space Paratroopers than Space Marines. Drop them into hostile territory, let them cause disproportionate damage and chaos scattered behind enemy lines (an early engagement in the book, described as a pretty typical raid, had the troopers a few kilometers apart, IIRC)
And yes, laser musket was suggested. My friends were fun that way.
How about “shield”? I suppose police still use them, but soldiers mostly don’t, yet every space cruiser worth its salt has “shields”, and is in danger of “losing the shields” or “losing a shield”. In fact, the “shields” for spaceships might better be termed “force armor”–“armor” is arguably a less archaic term than “shields”, for both vehicles and personnel, and more closely describes your typical science fiction “deflector shield” in use and behavior–but I can’t think of any science fiction examples that use the term “armor” to refer to some kind of force field. (Star Trek: Enterprise did have “hull plating”, but IIRC that was actual plating that had had its polarity reversed or some such.)
Just as an aside: we still say “dial” for telephones, so it’s not surprising that old language would continue even when outmoded by technology.
Quite a number of SF novels set in the future still use the word ‘tape’ to describe digital storage media.
What, like for Space Cavalry?
Many of them are from when that was the only rewritable storage media, tho.
Well, there’s GalaxyQuest, with the plasma armor.
(Crewman Guy asks if they should return fire; Jason replies “no, divert all energy to the armor” before telling Sarris it doesn’t take a great actor to recognize a bad one; Gwen says the armor’s almost gone, Sarris berates the fool for failing to realize that, “with your armor gone, my ship will tear through yours like tissue paper…”)
A carbine is just a short-barreled rifle. Like the M4 is the carbine version of the M16.
I suppose “laser gun” would be the appropriate term for portable laser weapon. “laser pistol” and “laser carbine” would also be appropriate if they came in different sizes.
Actually, I think the Colonial Space Marines from Aliens would be analogous to modern Armored Cavalry, if they were part of the Army.
Actually I wish to modify my earlier statement. I could imagine some future space fleet borrowing historic terms from the Air Force and Navy rather than just making up new words. I’m just pretty sure that future space wars won’t be fought George Lucas Battle of Midway in Space style.
Well in every space setting, a ship is said to have a “captain”. Interestingly, Russia, the US and China have used the designation “commander” for the astronaut incharge of a spacecraft.