Billionaire Elon Musk's SpaceX has confidentially filed for an initial public offering in what could be the largest stock market debut ever, according to Bloomberg and the Wall Street Journal.The space exploration company submitted a draft IPO filing to the Securities and Exchange Commission that puts it on track for a June listing, the news outlets reported, citing people familiar with the matter. SpaceX did not immediately respond to a request for comment. As part of the IPO process, the Texas-based company is aiming to raise as much as $75 billion and could seek a valuation of $1.75 trillion, according to Bloomberg. Saudi Aramco, Saudi Arabia's…