Former astronaut and retired U.S. Navy Captain Mark Kelly on Thursday said a separate military branch devoted to space was redundant and wasteful, and that while Pence was right about the threats in outer space, the military was already handling them.
Sen. Bill Nelson is among the lawmakers opposed to the idea. The United States will have a Space Force as a separate branch of the military. The second phase requires Congress to combine these components into the sixth branch of the armed forces.
In the meantime, White House officials have been working with national security leaders to aggressively move ahead without Congress.
"Initially the Department will recommend that the Air Force Space Command commander be dual-hatted as commander of the unified command", the report said.
The steps towards establishing a Space Force are creating a Space Development Agency, a Space Operations Force and a United States Space Command, the White House added.
However Mattis has since echoed support for Trump's position, saying Tuesday that he was "in complete alignment with the president's concern about protecting our assets in space that contribute to our security, to our economy".
Pence said President Donald Trump - who first touted the creation of what would be the sixth branch of the U.S. military, despite skepticism from military brass - wanted Congress to authorize $8 billion over the next five years to launch the effort.
But, earlier this week, Mr Mattis said he is in "complete alignment" with Mr Trump's concerns about U.S. space assets.More news: Hurricane John absorbs tropical storm off Mexico
As the US continues to stave off competition and threats from both Russian Federation and China, the White House has decided it will create the US Space Force as a sixth, separate military service by 2020.
President Donald Trump, who regularly touts the Space Force in his rallies to loud cheers from his supporters, tweeted: "Space Force all the way!" after Pence's speech.
"China and Russian Federation have been conducting highly sophisticated on-orbit activities that could enable them to maneuver their satellites into close proximity of ours, posing unprecedented new dangers to our space systems", he said.
The Pentagon's role in space has been under scrutiny because of a recognition that the United States is increasingly reliant on satellites that are hard to protect in space. "So now, we have to adjust and make sure that we can defend what we do in space and deter anyone from challenging us there".
In 2007, China blew up a dead weather satellite with a missile, creating a massive debris cloud in orbit.
"Both nations are also investing heavily in what is known as hypersonic missiles created to fly up to five miles per second at such low altitudes that they could potentially evade detection via our missile defence radars". On Thursday, Pence said that the administration will work with Congress on the plan, and will outline a budget next year.
"Peace only comes through strength", Pence said.
Hawaii senator Brian Schatz branded the Space Force a "silly but risky idea" as he instead urged the expansion of the "Medicaid" health programme.