WASHINGTON — Despite warnings from NASA that any cuts to commercial crew funding would delay the program, Senate appropriators slashed nearly $350 million from the agency’s request because they believed the program was already suffering delays.

The Senate Appropriations Committee approved June 11 a 2016 spending bill for NASA and other agencies that provides $900 million for NASA’s commercial crew program. That amount is $344 million below the administration’s original request and $100 million less than what the House approved June 3.

In a report accompanying the bill, appropriators argued that the current round of commercial crew contracts was already suffering delays. “To date, milestones intended to show progress in the development of the ISS Crew capability have already begun to be delayed,” the report states. “More technically challenging milestone completion dates are about to be reached or may be potentially postponed further.”

NASA awarded Commercial Crew Transportation Capability (CCtCap) contracts to Boeing and SpaceX last September. The contracts feature a series of milestones, with payments attached to each, similar to earlier commercial crew awards carried out under Space Act Agreements. Redacted versions of the contracts released by NASA in March listed 23 milestones in Boeing’s award and 18 in SpaceX’s, each with a planned completion date.

A schedule of milestones published by NASA in an April presentation to the NASA Advisory Council showed that some of the milestone dates have shifted for both companies. A readiness review for tests of a structural test article in Boeing’s contract, originally planned for April, was scheduled for August in the presentation slides, while some other milestones shifted by one to two months.

The updated schedule for SpaceX features longer delays in its milestones. A “delta” critical design review, scheduled for June in the contract, is planned for December in the updated schedule. Similarly, an uncrewed flight test of the Dragon spacecraft moved from March to November of 2016.

However, both NASA and industry officials said the moving milestones did not represent program delays, but rather updates to take into account developments after the companies submitted their CCtCap proposals in early 2014. The updated schedule still calls for both companies to have their vehicles certified by September 2017.

NASA spokeswoman Stephanie Schierholz said June 18 that the agency considers those schedule adjustments “changes, not delays,” citing testimony by NASA’s associate administrator for human exploration and operations, William Gerstenmaier, before the House Science Committee in February.

“It is likely that there will be a relatively large number of changes because the original contract milestones were established over a year ago when the companies submitted their CCtCap proposals,” Gerstenmaier said in his prepared remarks. “These changes will not be indicative of poor contractor performance, but rather the significant maturity and advancement that has occurred on the partner designs since the proposals were submitted.”

Boeing spokeswoman Kelly Kaplan said June 17 she was unaware of any significant delays in its CCtCap contract. The company had made some minor adjustments to the milestones in its original contract, she said, including splitting a safety review originally planned as a single milestone into three parts. Boeing also moved a pad abort test from before an uncrewed test flight of its CST-100 spacecraft to after it.

Those arguments, however, did not sway Senate appropriators. A committee aide confirmed that the cut in commercial crew funding in the Senate bill was linked to the delayed milestones, coupled with the belief that schedules would slip further once companies got past initial review milestones and into hardware development.

An additional factor in the committee’s decision is NASA’s intent to procure Soyuz seats for flights to the International Space Station in 2018, a year after the commercial crew vehicles are scheduled to enter service. Those plans, the appropriations report stated, indicate that NASA “does not have confidence that even with significant financial and technical support, the availability of a reliable domestic ISS crew capability by 2017 is guaranteed.”

The committee aide suggested NASA could solve its commercial crew funding shortfall by diverting funding from Soyuz seats. Unlike the administration’s request and the House bill, which fund commercial crew out of NASA’s exploration account, the Senate bill moves the program to space operations, which also pays for Soyuz and commercial cargo flights.

All sides acknowledged the debate about the 2016 budget is far from over. The full Senate has yet to take up the spending bill, and if it passes, it will have to be reconciled with the House version.

“It’s too early to tell what the end of the budget process will look like at this point,” Eric Stallmer, president of the Commercial Spaceflight Federation and an advocate for full funding of the commercial crew program, said June 18. “CSF and our members will continue to work with the Congress to find a way to responsibly fund commercial crew.”