I've been trying to find the name of this live-action TV series for years.
I used to watch it on French TV during the 90s. The show is probably American. It was about a team of teenagers/kids doing missions in space. I think most of the action would happen in the spaceship, not much exploring or space battles, but I might be wrong.
The main character, who was the captain of the ship was living a double life:
1) spaceship's captain
2) teenager having dinner with his family on Earth without them knowing about his other life. I think he would get on the spaceship by teleportation.
In one of the episodes the bad guys are messing with the captain's timeline so he starts fading away...
The opening was kinda rocky with lyrics sung by a man.