March 27 (Reuters) - ​The U.S. Space Force's Space Systems Command said on Thursday it had awarded contracts to Rocket Lab USA RKLB.O and Stoke Space to expand its portfolio of launch systems for critical space capability.

Shares of Rocket Lab USA rose 9% in overnight trading after the announcement. The contract enables the company to compete for future U.S. national security launch missions.

Rocket Lab and Stoke Space will each receive a $5 million order to conduct initial capability assessment.

They will join companies including Elon Musk's SpaceX, Jeff Bezos' Blue Origin and United Launch Alliance in the U.S. Space Force's National Security Space Launch Phase 3 Lane 1 program, which is meant to bolster the United States' space launch capabilities by adding a broader range of service providers.

"Once Rocket Lab and Stoke Space complete their first successful launch, they will be eligible to compete for launch service task orders on Lane 1," said Lt. Col. Douglas Downs, SSC’s materiel leader for Space Launch Procurement.