SpaceX is deepening its ties with U.S. intelligence and military agencies, winning at least one major classified contract and expanding a secretive company satellite program called Starshield for national-security customers.

The Elon Musk-led company entered into a $1.8 billion classified contract with the U.S. government in 2021, according to company documents viewed by The Wall Street Journal. SpaceX said in the documents that funds from the contract were expected to become an important part of its revenue mix in the coming years. It didn’t disclose the name of the government customer.

The size and secrecy of the agreement illustrate a growing interdependence between SpaceX—a dominant force in the space industry—and the national-security establishment.

SpaceX’s work for U.S. defense clients has long included blasting off classified and military satellites. The Pentagon has more recently done business with SpaceX’s Starlink broadband service, including agreements to pay for Ukrainian internet links during Ukraine’s war with Russia.