It is unclear if a rocket will actually fly around the Gherkin as part of Loncon 2014.
The convention will be held at the Excel Conference Centre in the London Docklands from Thursday 14 to Monday 18 August 2014. As well as numerous panels and programme items, the convention will also play host to the Hugo Awards. Guests of honour at the convention will include novelists Iain M. Banks and Robin Hobb.
There is a new website for the convention here, if accessible (it had crashed from weight of traffic the last time I checked it).