Elon Musk Buys X.COM, Elon started X.com way back in 1999, his second-ever company.
It was an online bank that would go on to become PayPal. In 2001, he stepped aside, leaving behind both X.com the company and X.com the domain name.

Now, over 16 years later, Musk and X.com are back together: PayPal confirms with Business Insider that Elon Musk has repurchased the X.com domain name. The news was first reported by Domain Investing.

Could this be in relation with Elon's Musk project SpaceX,

The following was reported on Bloomberg recently, Interesting times?
Before Elon Musk started SpaceX, he held a series of salons in Los Angeles and Silicon Valley, asking experts in the field for ideas on what a new-age rocket company should look like. A handful of people advising Musk urged him to make small, cheap rockets that would bring the cost of getting something into orbit down to $5 million from the going rate of about $100 million. In the years that followed, Space Exploration Technologies Corp.did manage to lower launch prices drastically, but it stuck to making bigger spaceships instead of pursuing the radical approach that some of Musk's advisers desired.
A couple of these space dreamers, who helped get SpaceX off the ground, have now turned up with their own rocket startup called Vector Space Systems. They have radical plans and then some. Vector's goal is to make a $1.5 million rocket that can carry small satellites into orbit. It expects to conduct 100 launches per year—a figure that would match the annual capacity of the entire aerospace industry.