I got the feeling I just saw the whole movie...
Difficult to believe someone hasn't seen the original, as it's one of the most important animes introduced to America (we know it as "Star Blazers").Long story short, a distant planet named Gamilon bombards Earth with radioactive meteors in order to colonize it after our misfortune. Star Force sends the reconditioned Yamato to Iscandar to get a machine that will scrub the radiation on a planatery scale. Mission accomplished.
Anonymous - the original Space Battleship Yamato was very hard to get here in the UK before the interwebs. If it was ever shown (and a quick Google makes me think it might have only been in the cinema for a short time), it certainly didn't have the following it gathered in the States. Generally anime was hard-to-come by here until the early '90s. We never got the stuff that was available in the US during the 80s :-(
Ah, memories. That was the series that got me into anime in the first place, way, way back in the 20th century. There's also a live action version, by the way: http://youtu.be/6fQoh6AIgNE