Boeing's new heavy-lift Delta 4 rocket has finally flown from Cape Canaveral, Florida, after several days' delay.
The rocket may carry astronauts one day
It was the first outing for the 70m-tall (230ft) vehicle, and it put a dummy payload and two university research satellites into orbit.
The rocket is booked for military use but currently has no commercial orders.
Commentators say the vehicle could eventually be modified to form the basis of the launcher system that succeeds the shuttle when it retires.
Three in one
The rocket lifted clear of the US Air Force Station Complex 37B pad at 2150GMT.
The flight marked a critical milestone for the vehicle, which features three core boosters strapped side-by-side.
Each Rocketdyne-built RS-68 engine burns a tonne of propellant every second, producing 2,891 kiloNewtons (650,000lbs) of thrust at lift-off.
Tuesday's launch made for a very impressive sight.
"Nobody could be disappointed seeing this; it was majestic," said Jim Harvey, from the Delta 4 programme management. "I'm beside myself. This is a great Christmas present."
It was not a complete success, however. An underperformance on the first stage meant the 6.1-tonne "Demosat" failed to reach its intended near-circular orbit at an altitude of 36,340km (22,580 miles).
A statement from Boeing released on Wednesday did not state how short of the intended orbit the deployment had fallen.
Tuesday's launch brought to an end what had been a frustrating period for the Boeing and US Air Force teams working on the project.
They had seen three launch days scrubbed at the beginning of the month because of bad weather, minor technical glitches and competition for flight time from Lockheed Martin who wanted to send up their Atlas 5 rocket.
When that vehicle completed a successful mission on Friday, it left the Delta clear for a fresh attempt. And despite some cautious holds in Tuesday's countdown, the rocket got away well within the set window.
The Delta 4-Heavy can lift 23 tonnes into a low-Earth orbit, a capability not dissimilar to the space shuttle. But with modifications, Boeing believes it can more than double that payload capacity.
And the company is trying to persuade the US space agency that this would offer the sort of capacity it is looking for to launch astronauts and equipment into orbit.
It envisions derivatives of the Delta 4-Heavy being used to take people back to the Moon and possibly even on to Mars.
The rocket has been booked for two military launches but has attracted no commercial interest from the satellite sector.
This market has been flat for a number of years now, and the prospects for growth are not improved by a glut of different launcher systems all competing for a small number of contracts.
The commercial market leader, Europe's Arianespace, will test its heavy-launch vehicle, the Ariane 5-ECA, next month.
It will be a second launch for the ECA; its first ended in an explosive failure in December 2002.