SpaceX is aiming to file its initial public offering prospectus with regulators later this week or next week, according to a person with direct knowledge of the plans. The confidential filing will formalize the IPO plans for Elon Musk’s rocket and telecom company as it targets a June public listing.

The offering will test investor appetite for what is gearing up to be the biggest U.S. IPO of all time—by a wide measure. Advisers involved in the preparation predict the company could try to raise more than $75 billion in the IPO, higher than a previously reported estimate of $50 billion, according to the person. The company, last valued at $1.25 trillion, won’t decide the actual size of the offering and a valuation until a few weeks before the IPO.