A rendering of Hypersonic missile from RAND Corp. Source: Rand Corp.

As the Pentagon looks to implement a new service branch devoted to space, Air Force Gen. Paul Selva explained Friday how emerging Russian and Chinese hypersonic threats could significantly challenge U.S. forces in that domain. Selva, vice chairman of the joint chiefs of staff, noted that an endgame defense for defeating a hypersonic weapon would be difficult without space-based assets. His remarks came a day after Vice President Mike Pence laid out President Donald Trump's vision for creating the Space Force by 2020. "What was once peaceful and uncontested is now crowded and adversarial. Today, other nations are seeking to disrupt our space-based systems and challenge American supremacy in space as never before," Pence said Thursday at the Pentagon. Selva echoed Pence's speech at the Capitol Hill Club on Friday and described the nature of these new breed of weapons the U.S. could face off with in space.

"If you think missile defense is easy, think again, you're shooting a bullet with a bullet, and that's as good as it gets. It gets worse when the bullet is going 13 times the speed of sound and can maneuver and that is what hypersonics is," Selva explained. What's more, he added that when an object flies faster than Mach 7, or hypersonic speeds, it becomes nearly impossible to track with the current technology the U.S. has deployed. Read more: Russia and China are 'aggressively developing' hypersonic weapons — here's what they are and why the US can't defend against them In short, a hypersonic weapon can travel further, faster, for longer and can maneuver itself which makes it all the more difficult to track and target. Additionally, some hypersonic weapons can be outfitted with nuclear weapons. Earlier this year, Russian President Vladimir Putin's boasted about new nuclear and hypersonic weapons, which he described as "invincible" during a state of the nation address. The Kremlin's hypersonic glide vehicle, dubbed Avangard, is designed to sit atop of an intercontinental ballistic missile. Once launched, it uses aerodynamic forces to sail on top of the atmosphere. According to sources with direct knowledge of American intelligence reports, Russia successfully tested the weapon, which could carry a nuclear warhead, twice in 2016.

In this video grab provided by RU-RTR Russian television via AP television on Thursday, March 1, 2018, a computer simulation shows the Avangard hypersonic vehicle en route to target. RU-RTR Russian Television via AP

"We ought to say to all of our potential adversaries if that object is a nuclear weapon we will respond in kind and inflict harm on you commensurate with the harm you inflicted on us and that is not negotiable," Selva said. "So don't do it." Of the six weapons Putin debuted in March, CNBC has learned that two of them will be ready for war by 2020, according to sources with direct knowledge of U.S. intelligence reports. Currently, the Pentagon has nearly a dozen programs tasked with developing and defending against the new breed of weapons. The Air Force awarded Lockheed Martin a $928 million contract in April for an undefined number of hypersonic strike weapons.

WATCH: Pentagon's hypersonic weapons program shrouded in secrecy