Since the other two companies associated with Elon Musk have publicly traded shares, one might think that it only makes sense that they be joined by the third, rocket maker Space Exploration Technologies, better known simply as SpaceX.

SpaceX Falcon

But Musk, CEO of SpaceX, put the dampers on that moon shot of an idea Tuesday faster than you can say 3-2-1-blastoff.

SpaceX, best known as having won the contract to resupply the International Space Station, will remain private, Musk told shareholders of Tesla Motors, where he is CEO.

The problem, he explained, is that SpaceX’s goals are long term. They are longer than the quarterly whims of the stock market where long-term is usually considered to be only several years. Since those inconsistent long-range goals would not be “super loved by the markets,” it doesn’t make sense to take the Hawthorne, Calif.-based company public.

Yet SpaceX would seem like a strong candidate for investors. It has had a string of successful launches of its Falcon 9 rocket and is working on its Dragon capsule for NASA.

So how soon? “It will go public once we have regular flights to Mars,” he told investors. Musk is a proponent of exploration of the red planet.

Besides Tesla, solar power installer Solar City, where Musk is chairman, is also a public company.