Update for 10 p.m. ET: SpaceX has successfully launched the 10-satellite Iridium-4 mission in a spectacular evening launch. See our launch wrap story with video and photos here: Used SpaceX Rocket Launches 10 Communications Satellites Once Again
Two rockets are scheduled to launch within 1 minute of each other tonight (Dec. 22), and you can catch the back-to-back spaceflight action live.
A Japanese H-2A rocket will lead things off with a liftoff from Tanegashima Space Center at 8:26 p.m. EST Friday (0126 GMT; 1:26 a.m. local Japan time on Dec. 23). One minute later, a two-stage SpaceX Falcon 9 rocket with a pre-flown first stage is scheduled to rise from California's Vandenberg Air Force Base.
You can watch both launches live here at Space.com, courtesy of the Japan Aerospace Exploration Agency (JAXA) and SpaceX, respectively.
The Falcon 9 will carry aloft 10 communications satellites for the Iridium Next commercial constellation, marking the second such mission for the rocket's first stage: That booster was part of the Falcon 9 that launched 10 Iridium Next satellites this past June.
The communications company Iridium is therefore poised to become the first SpaceX customer ever to fly multiple missions with the same Falcon 9 first stage.
Today's liftoff will be the last one for this particular first stage, however: SpaceX does not plan to bring it down for a landing, company representatives have said.
To date, SpaceX has landed first stages 20 times during Falcon 9 launches and has reflown four of these landed boosters.
The H-2A, meanwhile, is topped with two JAXA payloads — the Global Change Observation Mission-Climate (GCOM-C) satellite and the Super Low Altitude Test Satellite (SLATS). GCOM-C will monitor global water circulation and climate change from orbit for at least 10 years; and SLATS will test an efficient ion-engine technology developed to help satellites operate at altitudes below 190 miles (300 kilometers), where air resistance is significant, JAXA officials said.