Jack makes his first attempt to go back in time using: SCIENCE! I'm sure anyone with a scientific background is cringing at this episode (explosions in space, special relativity goes boink, and who knows how those bugs are getting around in a vacuum), not to mention the fact that Jack falls through the earths atmosphere and crashes straight into the ground in one big BOOM and manages to walk it off like he just bruised his knee (man that space suit must have been strong).
However, this will most likely blow over the heads of anyone younger than a teenager, leaving the rest as a decent enough episode with Jack nobly defending the space ship from Aku's minions, sacrificing his "one chance" (ha, little did he know how many ways there were to travel back in time, and how many chances he'd get) at returning home to allow the escapists to...escape. Still beats me why they couldn't have waited for Jack to just, you know, fight off the minions, and then get into his pod? But I guess "Darn it! There's no time!" I'm sure there could be an explanation drudged up from somewhere about that, probably about fuel or engaging near-light speed travel...or something.
Jack's still on his way North to find the magical jewel the Woolies spoke of at this point, so you aren't missing any plot by skipping this episode.