Despite more than two decades of work, the US military's GPS modernization efforts are still so muddled that uninterrupted operation of a secure network of GPS satellites could be at risk. 

The US Government Accountability Office (GAO) released a report yesterday filled with phrases like "multiple delays" and "significant development challenges" to describe the Space Force-led effort to transition to military-code GPS. Also known as M-Code, the tech can be encrypted and is resistant to jamming and spoofing.

Adoption of M-Code GPS requires new equipment in three places: space, ground control, and user equipment. The Space Force has been working on all three, and 24 of the 31 satellites in the GPS constellation are now M-Code capable, but there's little hardware on the ground able to make use of the enhanced signals.

"GAO has reported on challenges DoD experienced developing these systems since 2009 and made many recommendations to improve those efforts," the report stated, noting that eight of nine recommendations made since 2022 had been met. The Space Force took responsibility for the DoD's GPS modernization efforts in August 2021, and the report doesn't mention recommendations made prior.

"GAO has issued many recommendations to DoD regarding GPS Modernization in the past reports which DoD is in the process of implementing, but results could take time," GAO Director of contracting and national security acquisitions Jon Ludwigson told The Register.

The compounding interest of program delays

The 31-satellite GPS constellation operates on a staggered replacement schedule, and the next generation of satellites to launch into orbit will be the GPS IIIF series. However, a number of issues with the IIIF series satellites have eaten up months of time, meaning the first GPS IIIF delivery has slipped from February to November 2026 - and that's if nothing else goes wrong between now and then.

"Using Space Force data, we found that if GPS IIIF satellites deliver at even the earliest date … the constellation's probability of providing 24 operational M-Code-capable satellites will fall short of a 95 percent confidence level from early 2028 through late 2032," GAO said.

The situation isn't much better in the ground segment, which the DoD has been working to modernize for M-Code signals since 2010. That project, the Next Generation Operational Control System (OCX), is also facing serious delays.

OCX underwent system-level testing in 2023 that uncovered "deficiencies that prevented uninterrupted execution of the testing," even though that test was conducted 14 months later than planned. Another round of testing in March 2024 resulted in an 88 percent pass rate, below the Space Force's reported 100 percent target pass rate.

Those challenges "pose a risk to the [OCX] program's projected December 2025 acceptance for operational use," GAO said. As of April 2024, a backlog of 292 critical deficiencies in OCX had grown.

"It is hard to be optimistic with estimated time frames, particularly with OCX given recent performance," Ludwigson told us, noting that the Defense Contracting Management Agency in particular has expressed concerns about the number of remaining deficiencies.

User hardware - everything from soldiers' hand units to the receivers in a fighter jet - has problems too.

The Army and Navy are making more progress than the Air Force in developing their own M-Code capable receivers, GAO found, but there's still a lot of work to be done.

Around 700 types of weapon systems need to be outfitted with M-Code capable GPS units, GAO said, which could mean more than a million receivers need to be purchased once all that M-Code kit is up and running. However, the DoD is having trouble finding enough ASICs for all its receivers. That's led to consideration of software-defined GPS receivers able to handle multiple types of signals, a project the US Air Force is working on, GAO said.

Whose fault is this?

It would be easy to point the blame at the Space Force for bungling the GPS modernization project, but they only took ownership of M-Code GPS implementation in 2021.

"Challenges with contractor efforts has been a consistent theme with the last few reports [issued annually since 2021], particularly regarding the development of OCX," Ludwigson said. "But this is also an issue with the development of the Air Force's M-Code capable receivers."

The end result of GAO's findings, Ludwigson told us, is that Congress will receive a report on the state of the program, "which it can use to inform funding, oversight, and any other legislative action necessary to move GPS modernization efforts forward."

Whether the program could be imperiled is unclear. The GAO report mentions how important it is to get secure, tamper-resistant GPS into the military, but Congress probably won't be happy with another set of issues with a Space Force-led GPS project.

The Register asked the Space Force to comment. ®

https://www.theregister.com//2024/09/10/gps_modernization_us_gao/