WASHINGTON — U.S. Senate appropriators said the ground control system for the next-generation of GPS satellites “remains in jeopardy” and that as a result, the Air Force should slow its launch cadence for future GPS satellites and terminate development efforts for latter parts of the new system.

Combined the two moves led the Senate Appropriations Committee to strip more than $600 million from the Air Force’s budget request for fiscal year 2017. The committee passed a $515.9 billion defense appropriations bill May 26 by a 30-0 vote to send the spending plan to the Senate floor.

In report language accompanying the bill, the committee said it is “concerned” that the Operational Control Segment, or OCX, program “cannot correct course” and meet deadlines.

OCX is expected to offer improved information assurance and cyberprotection while automating various GPS 3 satellite operating functions. The full OCX program, which encompassed two blocks, and includes further modernization, is not expected to be completed sooner than 2021. In the meantime, the program has been described by Air Force leaders as the most troubled development effort in the Defense Department, and is expected to cost about $4.2 billion according to a Defense Department report released in March.

The delays on OCX have been a sore point for Air Force leaders, who say that because of the lag they will be unable to immediately leverage the full capabilities of the GPS 3 satellites, which include better accuracy and higher-power signals.

Raytheon is the program’s prime contractor.

Senate appropriators proposed two steps to help remedy the OCX problems in their version of the spending bill.

First, they suggested the Air Force spend about $163 million on the program in fiscal year 2017, significantly less than the $393 million the White House requested.

The Senate appropriators’ bill would cancel the two latter parts of the OCX program: Block 1, which will provide command and control of the GPS 3 and earlier generation satellites, and Block 2, which helps provide operational control of the new international civil signal aboard the GPS 3 satellites.

Instead, under the Senate appropriators’ plan, the Air Force would only rely on OCX to handle GPS 3 satellite launch and on-orbit checkout, a set of capabilities known as Block 0.

The Senate committee then set aside $30 million for enhancing the current operational control system (OCS), which runs the GPS 2F generation of satellites, to serve as the primary GPS 3 ground control system. Lockheed Martin built that system.

The Air Force should “turn its focus toward ensuring that the interim OCS solution succeeds, on schedule and on budget,” the report language said.

The Pentagon’s chief weapons tester told the Defense Secretary in a January 2016 memo that the Air Force’s backup plan for using OCS in place of OCX is “grossly optimistic and unrealistic.” Raytheon officials have warned that the Air Force’s contingency operations plan do not offer all of the capabilities of the full OCX system.

Second, the Senate committee said because of problems with OCX, the Air Force does not need to launch the GPS 3 satellites as quickly as it had planned. The Air Force expected to launch nine GPS 3 satellites before 2021, the report said. Senate appropriators provided funding for the Air Force to buy three launches in fiscal year 2017, not the five launches the White House had requested.

The Air Force plans to seeks bids next year from SpaceX and United Launch Alliance for two GPS 3 launches, but Senate appropriators stripped at least $395 million from the Air Force’s $1.5 billion request for its Evolved Expendable Launch Vehicle program and called for delaying the competition for those launches past 2017.

“The committee sees no justification for launching so many satellites without a system in place to operate them,” report language accompanying the bill said.

Earlier this month, the Senate Armed Services Committee said it would prohibit the Air Force from spending any money on OCX next year until the Defense Secretary Ash Carter makes the case the program should not be canceled.

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.