

Karen James describes the sights and sounds of the final space shuttle launch, witnessed from Nasa's press site
The space shuttle Atlantis, STS-135 lifts off from launch pad 39A at the Kennedy Space Center
The space shuttle Atlantis lifts off from Cape Canaveral, Florida, on Friday. Photograph: Gary Hershorn/Reuters

It begins when the white noise of nervous chatter around me gradually coalesces into a ragged chant. "Ten! Nine! Eight!" Then the chant becomes clearer and louder. "Seven! Six! Five!"

Someone to my left shouts, "main engine start!" I focus hard on the launchpad three miles away. For a second nothing happens and it's as if I'm looking at a still photograph, or even the wrong spot (the launchpad could be empty if it weren't for a hint of orange – the top of Atlantis's external fuel tank – peeking above grey scaffolding).

What happens next erases all doubt: a white cloud of smoke and steam appears, growing fast from the bottom right side of the pad. This is the plume from Atlantis's main engines. Then an even bigger cloud jets out to the left, this one from the solid rocket boosters (SRBs). Slowly at first, a colossal weight of metal levitates into view above the scaffolding. When the familiar shape of the space shuttle appears, my thoughts lurch towards the four humans on board, their courage and their vulnerability.

As the "stack" (the shuttle together with the external tank and the SRBs) speeds upwards, the flame coming from the main engine and the SRBs is unexpectedly bright – brighter, it seems to me, than the sun. It's a tremendous explosion, after all, and only barely controlled, as the Challenger disaster so tragically brought home.

Accelerating towards the thin cloud layer above, the stack rolls over so that Atlantis is obscured, from my vantage point at Nasa's press site, by the external tank and SRBs. It is a planned manoeuvre that positions the shuttle in a heads-down attitude, to achieve orbit but also to minimise the stress of acceleration to Atlantis and her crew.

Only when the stack nears the clouds does the sound arrive. It's a rumble at first, corresponding to main engine start; it's loud but not overwhelming. When the sound of the SRBs arrives, however, I not only hear it, I feel the percussive roar on the skin of my face, my chest, my arms. I am physically connected to Atlantis now.

All too fast for me, but right on schedule for Atlantis, she pierces the clouds. For a few seconds I can still see the bright spot even through the thin layer, but as that fades, I start to become aware of the column of smoke tracing the shuttle's ascent. It's drifting to the left of the launch pad but, remarkably, maintains its shape right down to individual billows.

As my bubble of attention continues to expand, I notice a dark line lengthening from the point where the column of smoke meets the clouds. I realise this is the shadow of the portion of the column that is above the clouds, and that I can monitor the shuttle's progress by watching the shadow extend further and further to the left. I can even see it curving slightly as the shuttle begins to curve towards its orbital track.

I start to notice the other people around me again. I'm reassured to see I'm not the only one catching my breath and wiping away tears. The excited chatter returns, this time mixed with sniffles and sighs. Friends hug and pat each other on the back and I hear snatches of conversation: "Godspeed Atlantis," "I can't believe it's over" and even a heartbreaking "my job is now obsolete".

I poke my head into the Nasa Tweetup tent where the official Nasa feed is up on the big screen. A cheer goes up to celebrate the announcement of "MECO", or main engine cut off. Atlantis and her crew are now in orbit around the Earth, travelling at a speed of nearly 28,000 kilometres per hour.

In two days' time, they will rendezvous with the International Space Station and get to work on the objectives of their mission to stock the station with a final delivery of supplies and equipment. The final space shuttle mission is not over, it has only just begun.

Watch live and archived video coverage of the launch and mission on Nasa's website