WASHINGTON — Contractors in the hunt to build the GPS satellites the U.S. Air Force will launch next decade are already touting their work on a fully digital navigation payload, an upgrade lawmakers want the Air Force to include when it finally places a follow-on order for the GPS 3 satellites now being built.

Most recently, on July 20, Boeing announced it completed a “breakthrough” toward that effort by generating digital signals from its version of a navigation payload. Boeing, which built a dozen GPS 2F satellites the Air Force expects to finish deploying early next year, is among at least three companies angling for a multibillion-dollar contract to build a second batch of GPS 3 satellites.

Both Boeing and Northrop Grumman are looking to replace Lockheed Martin Space Systems as prime contractor when the Air Force awards a production contract two or three years from now for nearly two dozen more GPS 3 satellites.

Under a roughly $3.6 billion contract awarded in 2008, Lockheed Martin is building at least eight and as many as 12 GPS 3 satellites. The Air Force has told Congress it expects Lockheed to build at least 10.

But Lockheed’s GPS 3 satellites­ — the first of which is expected to launch in 2017 — are running about two years behind schedule. Air Force leaders primarily attribute the delays to difficulties with the non-fully digital navigation payload that Harris Corp.’s recently acquired Exelis team is building for at least the first batch of GPS 3 satellites. Those problems have led the Air Force to seek out alternate designs with varying degrees of seriousness in recent years, but industry continues to invest in the capability.

Harris Corp. said in a July 22 email to SpaceNews that the company demonstrated digital signal capability to preliminary design level maturity in 2013 and continues to invest in development of a fully digital navigation payload.

Northrop Grumman has not specifically discussed its work on a digital payload, but will compete for the GPS contract. “The systems the nation will build for this program will be operational well into the 2040’s so it needs to be forward looking,” Lon Rains, a Northrop Grumman spokesman, said in a July 24 email to SpaceNews. “We have designed, built and tested an extraordinarily compelling solution.”

In April, the Air Force revamped its acquisition plan for the next batch of GPS 3 satellites. As part of that plan, it wants to explore whether there is a business case for industry to invest in GPS payload development and then recover those costs over the course of a large production contract. Gen. John Hyten, commander of Air Force Space Command, has said the service eventually needs to move a digital payload.

The Air Force said in June 2014 it would hold a competition in 2017 or 2018 for a fixed-price contract potentially worth billions of dollars to build up to 22 GPS 3 satellites beyond the eight to 12 Lockheed is already under contract to build. The Air Force said the first of the new batch of satellites would need to be ready to launch in 2023.

While early versions of the Air Force’s acquisition strategy explicitly called for an alternative to the current non-fully digital navigation payload, the most recent plan did not.

However, lawmakers are pushing the Air Force to commit to switching to a fully digital navigation payload when it places its next GPS 3 satellite order. Senate appropriators included $80 million in a 2016 defense spending bill to put the digital payload on a development timetable that would get it done in time to fly on the 11th GPS 3 satellite. That would be the first of the new batch if the Air Force ends Lockheed’s production run at 10.

“The GPS 3 spacecraft was designed with pre-planned evolution in mind, having additional size, weight and power capabilities to be able to seamlessly integrate new payloads as new technology is available,” Mark Stewart, vice president of Lockheed Martin’s Navigation Systems, said in a July 23 email to SpaceNews. In fall 2013, Lockheed Martin issued a request for information on a new navigation payload that included options for a fully digital payload.

Ellen Mitchell, a spokeswoman for Harris, noted that a fully digital payload is not a current requirement for the GPS 3 competition, but added, “Harris is committed to continuing our legacy of innovation in GPS navigation payloads, and will continue to invest in this technology, ensuring we are well positioned to meet evolving GPS program and warfighter needs.”

In a July 20 press release, Boeing said it has demonstrated it can generate GPS navigation signals from a digital payload. “Boeing is developing the digital waveform generator in support of a U.S. Air Force solicitation for GPS 3 alternate sources,” the company said in the release. “The demonstration validated that the basic GPS signals can be generated digitally in different code combinations with variable power levels and meet stringent signal requirements.”

Boeing spokesman Addrian Brooks, citing the Air Force’s pending request for proposals, declined to discuss a timeline for the development of the payload or any of the specific milestones for the work.

The Air Force plans on awarding multiple contracts worth up to $6 million this year for companies to demonstrate their ability to build the satellites. On July 20, the Air Force posted a special notice to the Federal Business Opportunities website asking for industry comments on the proposal.

The Air Force has said it expects to issue a formal request for proposals for the competition by the end of September with contract awards in early 2016.

Mike Gruss covers military space issues, including the U.S. Air Force and Missile Defense Agency, for SpaceNews. He is a graduate of Miami University in Oxford, Ohio.