The president put aside $40m [£31m] for its creation as he signed off the country’s $738bn annual military budget on Friday.
“The space force will help us deter aggression and control the ultimate high ground,” he said during a ceremony at the Joint Base Andrews complex in Maryland.
“Space is the world’s new war-fighting domain. Amid grave threats to our national security, American superiority in space is absolutely vital.
“We’re leading, but we’re not leading by enough, but very shortly we’ll be leading by a lot.”
The force – which will come under the command of the US air force and eventually comprise 16,000 personnel – will not put troops into orbit.
But military chiefs say it will allow the country to use technology to protect its assets which are already there such as communications satellites.
Its creation comes after strategists had previously warned of China and Russia making advancements in the so-called final frontier.
A February report from the Pentagon concluded the US faced “serious and growing challenges to its freedom to operate in space”.
And vice president Mike Pence has said that both countries had lasers and anti-satellite missiles that the US could only counter by going into orbit.
“The space environment has fundamentally changed in the last generation,” he said. “What was once peaceful and uncontested is now crowded and adversarial.”
The new force – the country’s first since the army and air force were separated in 1947 – will be led by General Jay Raymond, who currently runs the existing US space command.
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