During the 1980s I received as a present a hardback comic book (of the typical Christmas style annals) that covered a whole raft of space stories, fact and fiction, including several episodes of a comic strip featuring a space cadet.
The two stories I can think of involved three aliens (completely human) who infiltrate the academy as part of a plan to steal the best ship humans have, so they can see if a planned invasion would work. The hero cadet follows after the stolen ship in a standard vessel and forces the stolen ship to crash in the arctic - he lands and rescues the pilot, but the stolen ship sinks. Before he can leave in the standard vessel, an alien ship arrives and takes it on board. The aliens think the ship they have is the best tech the humans have and immediate order the invasion, but the hero cadet works out they can block the "carrier wave" the alien fleet is traveling on and prevent the invasion.
The second story begins with the cadet and his friends taking part in a space race, but when the cadet leaves the lazy bully in charge one shift, the bully causes a near fatal crash. The hero cadet, being the captain of the ship, is disgraced and dismissed from the service. We next meet him as a steward on board a luxury liner, which is then hijacked by pirates. The liners crew and passengers are left aboard an old soviet ship, which they manage to get moving and land on a planet populated by giants - after years of being used as curiosities (living chess pieces etc) they are helped by the king to return home, where the hero cadet is reinstated due to his courageous acts.