Stratos 4

The similarities lie in the choice of characters and setting. In both series, the protagonists are high schoolers who are chosen to undergo pilots'/astronauts' training. The setting is on a sub-tropical island for both, with a remarkably similar choice of supporting characters (a slightly slutty but fearsome female instructor, a chinese inn where the protagonists stay, some otaku (not anime) at the base where they are stationed). That is not to say that they are entirely the same, though. For instance, Rocket Girls is far more realistic depicting the technical aspect of the show (bar a few nonsensical things), while Stratos 4 sometimes foregoes technical accuracy for dramatic effect (which is all well and good, but it might tick off sticklers like me for a bit). read more 

Both anime feature all-girl military/mecha squads who have to stop meteors from falling to Earth. Anyone who likes the concept will get something out of either of these.