SpaceXfounder Elon Musk is on a mission to seal court documents in his Texas child custody court battle because he’s concerned for his life and the lives of his children, RadarOnline.com can exclusively reveal. The stunning court admission is the first time the opinionated tech billionaire has revealed in innermost fears as he battles the mother of their three children, Canadian singer and artist Grimes, whose real name is Claire Boucher. In court documents obtained by RadarOnline.com, theX owner told a Travis County family court judge he has a target on his back both here in the United States…