Live coverage: 400th Proton rocket takes off with Russian satellite

The most powerful version of United Launch Alliance’s Atlas 5 rocket lifted off from Cape Canaveral at 10:30 a.m. EDT (1430 GMT) today on a three-hour flight to deploy a U.S. Navy mobile communications satellite into orbit. Follow the mission in our live journal.

SpaceX is preparing this week for the second flight of the upgraded “Block 5” version of the company’s Falcon 9 rocket, and a hold-down firing of the booster was accomplished Wednesday at Cape Canaveral ahead of a middle-of-the-night launch this weekend with a Canadian-owned commercial communications satellite. The static fire test occurred at 5 p.m. EDT (2100 GMT) Wednesday.

Khrunichev and International Launch Services, the team behind Russia’s Proton rocket, are developing two scaled-down versions of the booster in a bid to capture a wider share of the commercial launch market, the companies announced last week.