Watch SpaceX launch 21 'data transport' satellites for US military today

Starship won't be the only SpaceX rocket flying today, if all goes according to plan.

A Falcon 9 rocket is scheduled to launch from California's Vandenberg Space Force Base today (July 16), carrying 21 satellites for the U.S. military's advanced new "Tranche 1 Transport Layer" (T1TL) constellation to orbit.

Liftoff will take place during a 22-minute window that opens at 4:22 p.m. EDT (2022 GMT; 1:22 p.m. local California time). You can watch it live via SpaceX beginning about 10 minutes before launch.

SpaceX's Starship megarocket — the biggest and most powerful launch vehicle ever built — is slated to make its 13th test flight shortly thereafter. It will lift off from the company's Starbase site in South Texas during a 90-minute window that opens at 6:45 p.m. EDT (2245 GMT; 5:45 p.m. local Texas time).

SpaceX will stream that mission live as well, and Space.com will carry the feed. Coverage will begin about half an hour before launch.

Today's Falcon 9 flight will help assemble the T1TL, a network in low Earth orbit (LEO) that will be operated by the U.S. Space Force's Space Development Agency (SDA).

The T1TL "will provide global communications access and deliver persistent regional encrypted connectivity in support of warfighter missions around the globe," SDA officials wrote in a explainer.

The T1TL will eventually consist of 126 satellites, which will be built by York Space Systems, Lockheed Martin and Northrop Grumman. Forty-two of the spacecraft have reached orbit to date, on two Falcon 9 launches from Vandenberg — one last September and another last October.

These 126 spacecraft will be part of a larger LEO network that the SDA calls the Proliferated Warfighter Space Architecture.

The PWSA is "a proliferated constellation of hundreds of optically linked small satellites, in low-Earth orbit (LEO), delivering capability at speed to the warfighter," SDA officials wrote in a Tranche 1 fact sheet.

"SDA leverages spiral development to deploy and proliferate new capability into a new generation of the PWSA every two years, called a 'tranche,' to continually increase capability used by the warfighter," they added.

If everything goes according to plan today, the Falcon 9's first stage will come back to Earth about 8.5 minutes after liftoff for a landing in the Pacific Ocean, on the drone ship "Of Course I Still Love You." According to a SpaceX mission description, it will be the fourth flight for this particular booster, which is designated 1103.

The Falcon 9's upper stage will haul the 21 satellites to LEO. We don't know when or exactly where they'll be deployed; the SpaceX mission description doesn't provide that information, likely at the request of the SDA.