The Trump representative said detailed plans were being drawn up to help retain the dominance of the US in outer space following concerns that China and Russia are catching up.
Mr Mattis said: “Our competitive edge in every domain of warfare — air, land, sea, space, and cyberspace — is eroding.
International tensions have risen in recent months with the Doomsday Clock striking closer to midnight this week, after the world’s leading scientists announced their concerns for the safety of the world.
The ominous clock is now two minutes from midnight after researchers from The Bulletin of the Atomic Scientists unveiled just how close humanity has come to ending the world.
Mr Mattis implied the next big war could be fought over spacecraft.
In a speech, he said: “Space is like any other domain of war.”
“Military uses of space are emerging.
“During a conflict, attacks against our critical defence, government, and economic infrastructure must be anticipated.”
However, the US Government official added any war for control of space was likely to happen on Earth rather than in outer-atmosphere.
He said: “It’s not about what you might think, guns in space shooting at each other.”
There are a number of important satellites in space that help countries with everything from predicting the weather to monitoring flights of enemy planes.
In a warning threat to any countries that may consider launching an attack on the US’s assets above the Earth the Defence Secretary added: “Don’t try it.”
As part of the plans announced the US is said to be considering investing in cheaper satellites that can quickly replace any space equipment taken out by an enemy force.
He said: “For every satellite up, we’ll have a hundred more that could launch as fast as they’re taken out.”
Continuing in his announcement on how the US would approach any military threat in space he said there was a need to come to an agreement on arms control.
Mr Mattis explained: “In space we will do our best to deter.
“But for right now, it’s about sizing up the problem and making certain that our diplomats will be negotiating from a position of strength.
“We’ll come up with arms control agreements at some point, and we’ll start getting this under control.”