By Paul Rincon
BBC News science reporter, Baikonur
As the Soyuz rocket carrying Venus Express climbed steadily into the morning sky, big grins broke out on the faces of delegates who had come to watch the launch from Baikonur Cosmodrome in Kazakhstan.
And the grins kept getting wider throughout the morning, as the spacecraft successfully completed a number of steps needed to send it on its way from Earth orbit to our nearest planetary neighbour.
The textbook launch came as a much needed boost to the European Space Agency (Esa) after the failure of its eagerly awaited Cryosat explorer.
This spacecraft, which was to have shed light on the response of Arctic ice to climate change, crashed into the sea following a malfunction at lift-off.
Venus Express also aims to study the effects of greenhouse warming, albeit on another planet.
As with its "sister" spacecraft, Mars Express, the launch took place at Baikonur, the historic spaceport in Kazakhstan.
This is where Sputnik, Earth's first artificial satellite, and Yuri Gagarin, Earth's first spaceman, blasted off into orbit.
"This is where space began. If you have the slightest sense of wonder at being able to get off the planet, Baikonur is the place to be," said David Southwood, Esa director of science.
This is by no means the first Venus mission to launch from Baikonur. It was from here that the Soviets launched their Venera and Vega missions in the '60s, '70s and '80s.
It is as remote a location as it is possible to be in. The flat, arid steppe stretches for as far as the eye can see and far beyond; this is a spot chosen for secrecy, not ease of access.
Since it was opened to commercial launches, Baikonur has received an influx of funding to upgrade facilities.
Venus shines in the sky above Baikonur Cosmodrome
But much else here harks back to another era, such as the old brick buildings and the diesel locomotives that set off at 0730 on the dot to ferry rockets to the launch pad, a tradition established decades ago by the Soviets' celebrated chief rocket designer, Sergei Korolev.
"The flight director who gives the go for launch has 551 launches behind him. There isn't anyone in the world with such experience," said Jacques
Louet, head of science projects at Esa.
Venus will be centre stage when the spacecraft begins its capture by the planet's gravity in six months.
But it made sure everyone saw it waiting in the wings, twinkling brilliantly through an indigo sky in the pre-dawn hours.
Foreign visitors began arriving to see the launch after 0800. At just over 1km from the launch pad, the viewing site is unusually close.
And when the Soyuz rocket began climbing into the sky on a grey plume, the orange glow was piercing and the roar was ear-shattering - almost drowning out the cheers from the assembled spectators.
When the rocket's lower stage was seen to separate successfully, there was a palpable sense of tension being lifted.
It would be another two hours, though, before the spacecraft began transmitting signals to tell ground controllers it was healthy and on its way to Venus.
The launch comes just four years after the announcement of a project opportunity by Esa and is the agency's fastest ever turnaround of a space mission.
"There were people who said we really couldn't make it by 2005, we'd have to wait until 2007. I invited one or two of them to the launch just to prove it
isn't faked on TV," David Southwood told me.
Jean Dauphin, business development head for the spacecraft's main contractor EADS-Astrium, added:
"Most of the core team has been switched from one project to the other.
"It has been a little bit tight, but today is a great day for us."
Venus Express is being billed as a mission to study the runaway greenhouse warming that has turned Venus into the hottest planet in the Solar System, with a view to learning lessons about how climate change will shape Earth.
But to many of those working on the mission it is about the advancement of knowledge, full stop.
"Earth is halfway between Venus and Mars. When the data is put together with that from Mars Express, it will really teach us about all three planets," Professor Manuel Grande, from the Rutherford Appleton Laboratory in
Oxfordshire, UK, told me just after the launch.
"We'll be keeping our fingers crossed for the next six months."