LONDON - Seven years in the making, costing £9.3 billion ($14.5 billion) and featuring 10,490 athletes, the London Olympics opens Friday with 302 gold medals to be won and hard-fought reputations at stake.The Olympic Stadium and Aquatics Centre in London's East End will host Beijing super-heroes Usain Bolt and Michael Phelps, who tore up the history books in 2008. On the other side of the city, Roger Federer, Novak Djokovic and Serena Williams will be the headline acts as Wimbledon welcomes the heavyweight tennis talent.In between, Horse Guards Parade, within walking distance of Downing Street and the Houses of Parliament, hosts beach volleyball and Wembley Stadium will stage the football final. Even Lord's, the home of cricket, gets involved, opening its doors to the world's best archers.On the track, Bolt, a triple gold-medallist in Beijing in the 100m, 200m and 4x100m relay, faces a mouthwatering showdown with Jamaican team-mate Yohan Blake in the 100m final on August 5.Bolt holds the world record of 9.58sec but Blake is the world champion and the in-form sprinter this season, getting the better of his senior partner in the Jamaican trials last month. In the pool, Phelps, whose eight golds in Beijing took his medal tally to 14, needs five more to surpass the all-time record of 18 set by Soviet gymnast Larisa Latynina between 1956 and 1964."Obviously, we always want to do our best and swim the fastest, they are the main objectives," said Phelps, who will compete in seven events. Like Bolt, the 27-year-old Phelps also faces a national rival in the shape of Ryan Lochte, a triple Olympic champion, who can put a huge hole in his rival's dreams when the two clash in the 200m and 400m medleys.Elsewhere in the pool, eyes will also be on precocious Missy Franklin, just 17 and also racing seven events, and Australian sensation James Magnussen. Dubbed 'The Missile', Magnussen is the 100m freestyle world champion and earlier this year swam that event's fastest ever time without the aid of the now-banned, drag-reducing 'super suits'.Other athletics stars include Russian polevault queen Yelena Isinbayeva, Kenya's David Rudisha in the 800m and Ethiopia's Kenenisa Bekele, the 5,000m and 10,000m champion in Beijing. South Africa's Oscar Pistorius, known as 'Blade Runner' because he runs with carbon fibre prosthetic running blades, will make history as the first double amputee athlete to compete at an Olympics.At the velodrome, Bradley Wiggins, fresh from his historic Tour de France triumph, will fire up home hopes. Zara Phillips, the grand-daughter of Queen Elizabeth, adds a little royal lustre to the equestrian at Greenwich. Federer, having won a record-equalling seventh Wimbledon title, returns to the All England Club in south-west London looking to add singles gold to the doubles he won with Swiss compatriot Stanislas Wawrinka four years ago.His rivals will be Djokovic and Andy Murray but there will be no defending champion Rafael Nadal, who pulled out to rest his ongoing knee problems. The United States will be comfortable favourites in the men's basketball with a Dream Team boasting LeBron James and Kobe Bryant but not the injured Dwyane Wade or Derrick Rose.The build-up to the Games has been relatively trouble-free, although organisers had to summon 3,500 troops for the showpiece after private security firm G4S admitted they couldn't provide a full contingent of guards. Amid gripes about security and transport, colourful London mayor Boris Johnson hit out at critics of the Olympics, saying the city was about to stage the greatest show on Earth."Oh come off it, everybody -- enough whimpering," Johnson wrote in The Sun newspaper. "Cut out the whingeing. And as for you whingers, put a sock in it -- fast." However, one subject the British enjoy discussing -- the weather -- continues to be at the forefront. After a wet and chilly summer, temperatures are expected to reach the high twenties by the time the Games officially get underway with Friday's opening ceremony.Before that, the first action will take place in Wales on Wednesday when the Great Britain women's football team tackle New Zealand at Cardiff's Millennium Stadium.