The final request for proposals for building the next batch of Global Positioning System (GPS) III satellites will be released on or near Dec. 7, the U.S. Air Force announced the week of Nov. 19.

The Air Force had previously indicated that it would issue the final RFP for “follow-on production” sometime in the current quarter. The service released the draft RFP in July.

While Lockheed Martin [LMT] is building the initial 10 GPS III satellites, the program has experienced cost overruns, schedule delays and technical problems. Boeing [BA] and Northrop Grumman [NOC] have both expressed interest in competing to produce the 11th satellite and beyond.

“We wouldn’t be doing a competition if we didn’t think there were viable alternatives to the Lockheed Martin system,” said Lt. Gen. John Thompson, commander of the Air Force Space and Missile Systems Center in California. “There are many vendors that are interested in that competition.”

In May 2016, the Air Force awarded contracts to Boeing, Lockheed Martin and Northrop Grumman to study the feasibility of producing the next block of satellites. Each company built a demonstration payload.

The Air Force wants to begin building the next block of satellites in fiscal year 2019. The contract for 22 satellites is expected to have a value of $10 billion, Thompson told reporters at the Pentagon Nov. 2.

Lockheed Martin continues to tout its active production line, announcing Nov. 27 that the third GPS III satellite, or space vehicle (SV03), is fully assembled and ready to begin environmental testing. Lockheed Martin expects SV04 to reach that marker in January. The company began assembling SV05 in August.

“GPS III is the most powerful and complex GPS satellite ever designed and built, and it’s now into a smooth production flow,” said Mark Stewart, Lockheed Martin’s vice president for navigation systems.

SV01 is in storage awaiting a 2018 launch. SV02 is undergoing ground testing and is slated to be delivered to the Air Force in 2018.