"We have to have a way to launch our national security payloads into space," Carter stated. "One way to do that… is to continue to use the Atlas booster, including a limited but continuing number of RD-180 engines, notwithstanding the fact we don’t like the fact that they're made in Russia."
The Department of Defense is recommending this approach because replacing the RD-180 rocket engine would give it a bill of one billion dollars or more.
In 2014, US Congress passed a law demanding the United States phase out its reliance on the Russian-made RD-180 rocket engines.
However, in the two years after implementing a purchasing ban on the RD-180 engines, Congress has been forced to lift that ban to ensure the United States access to space.