ULA's Vulcan rocket returns to flight after 9 months

United Launch Alliance builds rockets for the government and private companies. Its newest rocket, Vulcan Centaur, hasn't flown since February. A problem with its solid rocket boosters grounded it for nine months. Today, if everything goes to plan, Vulcan lifts off from Cape Canaveral carrying 40 satellites for Amazon. They're part of Amazon's new internet service, Leo, built to rival SpaceX's Starlink.

ULA doesn't have many other rockets left to fly. Its older Atlas and Delta rockets are being retired. The government and companies like Amazon are counting on Vulcan to fly often and reliably. That matters most for big national security payloads. A nine-month grounding over a booster issue is exactly the kind of delay ULA can't afford right now. For Amazon, the stakes are just as real. SpaceX's Starlink already has thousands of satellites in orbit. Amazon's Leo network is only just getting started.

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Does today's launch actually go off without a hitch? ULA already slipped the date once, from Friday to Saturday, after a ground equipment problem. A clean flight would be a real relief for both ULA and Amazon. A scrub, or worse, a repeat of the booster issue, would raise harder questions. It would ask whether Vulcan is ready for the busy launch schedule everyone is counting on. Over the next year, how often Vulcan flies, and how smoothly, will say a lot. That will show whether Amazon can realistically challenge Starlink in orbit.