Princess Projectra of the planet Orando was a member of the
Legion of Super-Heroes. After her planet was attacked by the
Legion of Super-Villians, Projectra moved her planet out of this plane of existence to protect it from further "corruption" by the 30th century.
The ruling Council of Orando decided that Projectra should be punished for bringing the Legion of Super-Villians to Orando through her ties to the Legion, so the stripped her of her title and sent her back to our plane of reality. She returned to the Legion, but by the judgment of the Council, she was not allowed to let her former teammates know who she was. Masked and in a different costume, Projectra joined the Legion as Sensor Girl, by the recommendation of Saturn Girl, who Projectra had taken into her confidence.
Due to an augmentation of her power, Sensor Girl could not only create illusions, but also had the ability to percieve beyond the normal spectrum and pierce illusions and see beyond them. This gave her the equivalent of super-hearing and x-ray vision. Because of the recent loss of Supergirl and her resemblence to Supergirl, it was believed for a while by members of the team, especially Brainiac 5 that she was Supergirl returned. Her identity was finally revealed during a battle with the Fatal Five.
Sensor Girl was married to Karate Kid, prior to his death.