Enlarge / United Launch Alliance's final Delta IV Heavy rocket, seen here in December when ground crews rolled it to the launch pad at Cape Canaveral Space Force Station, Florida. (credit: United Launch Alliance )

This is the rocket that literally lights itself on fire before it heads to space. It's the world's largest rocket entirely fueled by liquid hydrogen, a propellant that is vexing to handle but rewarding in its efficiency.

The Delta IV Heavy was America's most powerful launch vehicle for nearly a decade and has been a cornerstone for the US military's space program for more than 20 years. It is also the world's most expensive commercially produced rocket, a fact driven not just by its outsized capability but also its complexity.

Now, United Launch Alliance's last Delta IV Heavy rocket is set to lift off Thursday from Cape Canaveral Space Force Station, Florida, with a classified payload for the National Reconnaissance Office, the US government's spy satellite agency.

Enlarge / A US Army soldier lifts the hydraulic launching system on the new Long-Range Hypersonic Weapon (LRHW) during Operation Thunderbolt Strike at Cape Canaveral Space Force Station, Florida, on March 3. (credit: Spc. Chandler Coats, US Army )

Airspace and maritime navigation warnings released to pilots and mariners suggest the US military might launch a hypersonic missile this week on a test flight from Cape Canaveral, Florida.

This test could be one of the final milestones before the US Army fields the nation's first ground-based hypersonic weapon, which is more maneuverable and more difficult for an enemy to track and destroy than a conventional ballistic missile. Russia has used hypersonic in combat against Ukraine , and US defense officials have labeled China as the world's leader in emerging hypersonic missile technology.

That has left the US military playing catch-up, and the Army is on the cusp of having its first ground-based hypersonic missiles ready for active duty. If informed speculation is correct, the test launch from Cape Canaveral Space Force Station this week—performed in partnership between the Army and the Navy—could be a full-scale test of the new solid-fueled hypersonic missile to propel a hypersonic glide vehicle to high speeds over the Atlantic Ocean.

Enlarge / A Falcon 9 rocket streaks into the sky over Cape Canaveral, Florida, on a mission Sunday night to deploy 22 more Starlink internet satellites. (credit: SpaceX )

The late-night liftoff of a Falcon 9 rocket with another batch of Starlink Internet satellites on Sunday set a new record for the most flights by a SpaceX launch vehicle, with a first-stage booster flying for a 16th time. SpaceX now aims to fly its reusable Falcon 9 boosters as many as 20 times, double the company’s original goal.

The flight followed several months of inspections and refurbishment of SpaceX’s most-flown rocket, a process that included a “recertification” of the booster to prove, at least on paper, that it could fly as many as five more times after completing its 15th launch and landing last December.

Sunday night’s mission got the booster’s extended life off to a good start.