SAN FRANCISCO / BOSTON, April 23 : SpaceX is telling prospective investors its board will not need a majority of directors who are independent of the company, according to an excerpt of its IPO filing reviewed by Reuters, underscoring how founder Elon Musk is retaining control of the rocket and artificial intelligence maker. In a departure from the vast majority of public companies, SpaceX said it would maintain "controlled company status" after its $1.75 trillion IPO, expected this summer.