To buy into SpaceX’s audacious $1.5 trillion valuation in a listing next year, investors will need to have faith in Elon Musk’s equally galactic vision for his rocket and satellite maker, from orbital data centers to lunar factories to human settlements on Mars. SpaceX is planning an initial public offering that may be the world’s biggest ever. Its revenue is forecast to be between $22 billion to $24 billion in 2026, largely fueled by its Starlink satellite-internet unit, according to people familiar with ...