The US Congress armed services committee voted to double the purchase of Russian-made rocket engines in a Thursday vote, US media reported. The United States has been relying on Russia-made RD-180 rocket engines to put its national security satellites into orbit, despite efforts to reduce dependence on Russian technology in the use of launch vehicles.

"[I'm] aware of the need to end our reliance to Russian rocket engines, but not at the expense of the required of assured access," author of the amendment, Republican Congressman Mike Coffman from the state of Colorado, said as quoted by The Hill.

Coffman stressed ahead of a voice vote to allow the purchase of 18 RD-180s instead of nine that "assured access to space is indispensable for our national security."

Supporter of the amendment Adam Smith, Democrat from Washington, argued that "the purpose of buying these engines is that there's an alternative."

"The number of 18 is pulled pretty much out of thin air... Though the 18 isn't perfect, I will support that bridge of 18," Smith explained.

Opponents, including California Republican Duncan Hunter claimed that the vote to buy 18 rocket engines would "literally contribut[e] $540 million to Russia's military modernization."

In 2014, US Congress passed a law demanding the United States phase out its reliance on the Russian-made RD-180s. Two years after implementing a procurement ban, Congress was forced to lift the measure to ensure the United States maintained access to space.

The RD-180 engines are used for the first stage of the United Launch Alliance's - a Lockheed Martin and Boeing joint venture - Atlas V rocket space launches.