I was pointed at this va PN... native speaker here.
Raum = Space (actually, the more correct term would be "Weltraum", that is just usually abbreviated and never used with things like Raumjäger or Raumschiff. "Raum" has two other meanings, too: A room in a house, and a general meaning of volume, of space in the more earthly sense. When in doubt, use Weltraum to make sure you are talking about the Great Void..
Stern = Star
Jäger = Hunter (or "Ranger", but the term is also traditionally used for fighter aircraft - though not modern ones, as we don't have dedicated anti-aircraft aircraft in the Luftwaffe these days, only multi-role combat planes).
Krieg = War
Kämpfer = Fighter
Flugzeug = Airplane (lit. "Flying stuff" or "flying fixings")
Schiff = Ship
Boot = Boat
Korvetten = Corvettes (singular Korvette)
Fregatten = Frigates (singular Fregatte)
Zerstörer = Destroyers (singular and Plural is both "Zerstörer")
Schlachtschiff Battleship, plural is Schlachtschiffe.
I recommend using
http://dict.leo.org/englisch-deutsch/ for translations.
Some additional stuff:
Raumschiff - space ship (you guessed it).
Raumflotte - space fleet. Note that using the literal German translation of "space navy" would be "Raummarine" (Or "Sternenmarine", which is almost used in 2300 AD), which does not at all make sense, etymologically. Marine is, obviously, derived from the Latin word "mare", sea, and is limited to water. No German would say that, in science fiction, "Raumflotte" is used (or "Sternenflotte", but that is limited to that one franchise where the reverse translation into English also applies) . The English word derives from the Latin word "navis", for ship, so in English "space navy" does perfectly make sense, But not in German.
Gasriese Gas giant. Literally.
Curiously, the 2300 AD PDF from Mongoose uses weird rank titles for the German space navy, because the ranks used are a bad mixture of German navy and army/airforce ranks. I#d recommend to either go all Luftwaffe or all German navy. Being ex-navy myself, my preference is clear:
Matrose (only during basic training)
Gefreiter/Obergefreiter/Hauptgefreiter/Stabsgefreiter (regular crewmen)
Maat / Obermaat (lowest enlisted with leadership or highly qualified specialist function)
Bootsmann / Oberbootsmann
Hauptbootsmann
Stabsbootsmann
Oberstaabsbootsmann
Kadett (Seekadett in the navy, you might want to make it "Raumkadett" for the space fleet, legally this is a Maat with higher seniority)
Fähnrich (Navy rank is "Fähnrich zur See", literally, "Ensign at sea", "Fähnrich" without the "at sea" is also used in the army and the air force" legally it is equivalent to a Bootsmann with higher seniority). This is actually what English-speaking navies call a Midshipman.
Oberfähnrich: The actual ensign, navy specialty is, again with a "zur See" added.
Leutnant (equivalent to a 2nd lieutenant/Lt jg.), "zur See" for the navy, without such, it is army or air force.
Oberleutnant (same as above, 1st lieutenant/full lieutenant in english-speaking forces/navies).
Kapitänleutnant (equivalent to an army or air force captain (which is "Hauptmann")).
Korvettenkapitän (Major)
Fregattenkapitän (Lieutenant Colonel, which is called "Oberstleutnant" in the army and air force.)
Kapitän zur See: Full navy captain, equivalent to a full colonel in english-speaking forces (which is a Oberst in German), but you only get to this rank if you have proven to be capable of flag officer duty. For a space navy, you might want to drop the "at sea" and either just skip it or replace it with "im Raum" or "im Weltraum".
Flottillenadmiral
Konteradmiral
Vizeadmiral
Admiral