So much for the idea that private companies can’t do big acquisitions. SpaceX’s $17 billion proposed purchase of a much-coveted chunk of wireless spectrum from EchoStar on Monday is a big step towards Elon Musk’s ambitions for offering satellite-to-cell phone services globally. But the fact that SpaceX is paying half the price with its own stock is a big step forward for those entrepreneurs who want to keep their companies private long term. Conventional wisdom holds that one good reason for companies to go public is to get a currency for acquisitions, as the shares can be very easily valued—just look at the stock price. That’s still true, although with a company as big as SpaceX, which regularly does tender offers to let employees sell their shares, gut-checking valuation isn’t difficult. Count this as another reason why you shouldn’t expect to see SpaceX going public anytime soon, if ever. space.com/space-explorati..