Rocket Girls

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 

Two shows about a more contemporary, realistic, unglamorous side of space travel. Their protagonists generally do mundane jobs in Earth's orbit and work for departments with few resources and even less respect, although they all wind up getting involved with larger adventures by the end of their stories. Both shows have similar aesthetics and senses of realism but also veer into wacky comedy from time to time. Rocket Girls clearly has more of a moe influence, but other than the character designs of its leads and their ages (and generally age-appropriate personalities and behavior), one could easily see the two series taking place in the same universe at different points in time. read more