Updated March 5 at 2:59 p.m. EST

WASHINGTON — NASA is mulling how it will keep the International Space Station in orbit past 2024 if Russia follows through on plans to detach the orbital outpost’s Russian modules and form a new space station.

“We are responsible for the day-to-day operations and control of the international space station [but] they [Russia] provide propulsion,” NASA Administrator Charles Bolden said March 5 during a House Appropriations commerce, justice, science subcommittee hearing. “[W]e are planning right now for them to at some point to take away the propulsion module.”

Bolden did not elaborate on the agency’s plans, and NASA spokesman Allard Beutel, reached by email March 5, had no immediate comment.

The hearing, called to discuss the $18 billion budget the White House requested for NASA in 2016, took place about a week after the Russian space agency, Roscosmos, said it would remain a part of the ISS program until 2024 and then reuse at least some of Russia’s modules to form a new space station in low Earth orbit.

NASA relies on Russia to keep ISS orbiting at between 350 and 460 kilometers above the Earth. Although Russia’s unmanned Progress cargo ships have handled most of the orbit-raising duties, Russia’s Zvezda service module — one of the three original ISS components — is equipped to boost station’s orbit. Visiting space shuttle orbiters and Europe’s now-retired ATV cargo tug have also given ISS a boost before undocking.

Russia’s Feb. 24 statement did not identify Zvezda as one of the modules it wants to use post-2024 for its new station. However, Bolden’s testimony suggests NASA is preparing for a future in which it cannot rely on the Russian propulsion module.

Bolden’s acknowledgement that NASA is indeed planning for a possible Russian secession came amid a sometimes-tense exchange with new subcommittee chairman Rep. John Culberson (R-Texas).

During the hearing, Culberson lamented NASA’s dependence on Russia’s Soyuz system to transport NASA astronauts to and from ISS and said Russian President Vladimir Putin is “reminiscent of Joseph Stalin.”

Despite worsening diplomatic relations over Russia’s annexation of Ukraine’s Crimean peninsula, Bolden said relations between NASA and Roscosmos remain strong.

“While our political and diplomatic relations are not very good … the indications are that the rhetoric on the political side is not the same as when you talk about space exploration,” Bolden said.

Bolden authorized NASA last month to reserve six more seats on Soyuz flights in 2018 in case spacecraft being developed under the agency’s commercial crew program by Boeing Space Exploration of Houston and SpaceX of Hawthorne, California, are not ready in 2017 as planned.

Soyuz is currently the only crewed space system that can take anyone to ISS, Bolden reminded Culberson. Even if crewed Chinese spacecraft could integrate with ISS, NASA is legally barred from cooperating with Beijing.

The reality of the Soyuz monopoly reignited an old, partisan argument over the current gap in U.S. crewed spaceflight capability.

Bolden pointed out that Congress has repeatedly appropriated more money for the Space Launch System (SLS) heavy-lift rocket and Orion deep space crew capsule than NASA says it needs while at the same time underfunding the agency’s commercial crew requests.

“Had we gotten the funding that was first requested when I became the NASA administrator [in 2009], we would have been all joyously going to the Kennedy Space Center later this year to watch the first launch of some commercial spacecraft with our crew members on it,” a frustrated Bolden told Culberson.

Culberson, as he did in a budget hearing last April, blamed the gap on the Obama administration’s decision to cancel the Constellation moon exploration program in 2010. Under Constellation, Orion was to have launched to ISS atop Ares 1, an a solid-fueled rocket derived from the space shuttle’s side-mounted boosters.

“Had not NASA canceled the Constellation program, we’d be ready to fly in 12 months,” Culberson said.

Rep. Chakka Fattah (D-Pa.), the subcommittee’s ranking Democrat, reminded lawmakers that the Constellation program the George W. Bush administration established in the wake of the 2003 Space Shuttle Columbia accident called for retiring the shuttle fleet and relying on Soyuz for as long as it took NASA to field an alternative.

Bolden said March 5 the alternative should be ready by late 2017: Either SpaceX’s crewed Dragon capsule, launched on the company’s Falcon 9 rocket, or Boeing’s CST-100, launched by United Launch Alliance’s Atlas 5.

NASA plans to use SLS for the first time to launch an uncrewed Orion on a test flight to lunar space in 2018 and repeat the feat in 2021 with a crew onboard.

Bolden all but promised March 5 that even if Congress again appropriates more money for crewed deep-space missions than the White House requested, humans will not venture beyond low Earth-orbit before 2021.

“We have a program in place that calls for them to fly at a particular date and we’re not going to change that appreciably with more money,” Bolden said.

More money, Bolden said, would be better spent on procuring hardware for the third and fourth SLS/Orion flights.

“If you gave me more money … I would buy down risk,” Bolden said. “When you go to SpaceX and look on their floor, there are engines all over the place. There are engines for flights they don’t have yet. That’s the way they buy down risk. That’s the way industry does it. You put assets in place so that you can carry out a program years in advance. That’s what I would do.”