Ahead of today's opening free practice session, the air temperature is 25 degrees C, while the track temperature is 29 degrees. It is bright and sunny, with similar conditions expected for the remainder of the weekend.

Much has happened since the Hungarian GP, most notably Romain Grosjean is replacing Nelson Piquet, while Ferrari test driver Luca Badoer is standing in for Felipe Massa. Also, BMW has announced that it is withdrawing from F1 at the end of the season, though it is hoped that, like Honda, a buyer will be found in order to allow the Swiss-German outfit to continue.

The lights go green and first out is Vettel, who has just extended his contract with Red Bull until 2012. He is followed by Buemi Kubica, Badoer, Glock and Alguersuari. No doubt Badoer and Grosjean will be keen to get in as many laps as possible today.

While most drivers return to their pits having completed the obligatory installation lap, Heidfeld remains out on track for an extra lap before he too returns to base.

Eight minutes into the session, Button heads down the pitlane leaving Trulli and Barrichello as the only drivers yet to make an appearance. Brawn GP really need a result this weekend if they are to keep their championship(s) hopes alive. Red Bull has taken serious points off of the British team in the last couple of races, and now McLaren and Ferrari are showing clear signs of improvement.

In the Ferrari garage Badoer chats with Michael Schumacher, both men looking as cool as cucumbers.

Shortly after Barrichello comes out to complete his installation lap, Trulli heads down the pitlane to get his weekend off to a start.

As the Italian returns to his garage, Alguersuari heads back out for his second run of the day. As teammate Buemi heads down the pitlane, Alguersuari crosses the line to post the first time of the weekend, a 1:50.229.

As Hamilton leaves the pits, Buemi posts a 46.458. This weekend, unlike previous race weekends, all the updates are on Kovalainen's car, these include a new floor and a massively revised front wing.

Buemi improves with a 44.998 while his teammate posts 46.487, elsewhere, Grosjean and Trulli are back on track.

Grosjean goes third with his first lap, improving to second with 46.124 next time around. Moments later he's bumped down to third when Trulli posts 46.051. Buemi remains quickest.

Half-an-hour into the session, Badoer heads down the pitlane. The Italian has said that his main aim this weekend is to finish the race, he isn't expecting any miracles. At the end of his first lap he goes sixth with a 52.982, just over 8s off the pace of Glock who has just gone quickest with a 44.804. Next time around Badoer improves to 52.058. Early days.

Heidfeld, Nakajima, Rosberg and Raikkonen all on track as Alguersuari complains of a lack of grip.

On his second flying lap, Rosberg goes quickest (44.468), ahead of Glock, Buemi and Raikkonen. Badoer now tenth quickest, 4.539s off the pace.

A 44.577 sees Heidfeld go second, both the German and his team needing to make a good impression this weekend and in the weeks ahead.

Alonso gets it all wrong at the entry to Turn 2, the Spaniard needing to make full use of the ultra-wide run off.

It's a Williams 1-2 as Nakajima posts 44.084 to go quickest. Raikkonen moves up to third, 0.202s off the pace.

Heidfeld takes the top spot with a 44.040 but this is almost instantly eclipsed by Rosberg who crosses the line at 43.746. However, the Williams driver is short-lived as local hero Alonso takes the top spot with a 43.413 and Nakajima goes second (43.617).

Coming up to half-time, only twelve drivers have posted times, with Vettel, Webber, Button and the McLaren duo amongst those who have yet to complete a flying lap.

As Alonso consolidates the top spot with a 43.345, Badoer is clearly struggling for grip, the back end of the car getting out of shape at all manner of corners. It might be costing him precious time but it looks spectacular. The Italian is now just 2.682s off the pace.

At half-time, it's: Alonso, Kubica, Nakajima, Raikkonen, Rosberg, Heidfeld, Glock, Webber, Buemi and Grosjean.

As Barrichello goes fifth, he complains that his brakes seem "very hot", though the team assure him there's nothing abnormal.