Jeff Bezos may be No. 1 in the world in Amazon rankings and was the richest person in the world until being dethroned by Bill Gates in January, but that doesn't mean the sky's the limit for the billionaire.

Bezos, who owns about 18 percent of Amazon, has seen his net worth decline by $4.1 billion in the past 11 days as the Seattle-based tech giant's stock price has continued to slide after a post-earnings sell-off. Bezos' net worth is now at $157.4 billion.

Bezos set up the Blue Origin rocket program to fly tourists to the edge of space, but the company has had some issues so far. In 2018, Bezos' rocket company lost a bid to win a contract to launch a spy satellite into space for the U.S. military.

Competition for such lucrative military contracts, in particular, is heating up. Elon Musk's SpaceX has launched rockets bound for the International Space Station, and Boeing launched a communications satellite bound for the space station in December. Last year, SpaceX won a contract to launch satellites for an Asian satellite company.

"If we had applied all of our effort to winning the Air Force Satellite Launch competition, we probably would have lost it. But we didn't," Bezos told staff members at Blue Origin earlier this month in an email obtained by the Financial Times.

Bezos' email offered encouragement to employees and said the company was "optimistic" about its future. Blue Origin and SpaceX are both ramping up launches of their rockets as they compete to work on the military's most expensive satellites, which can cost around $150 million each.