The US Department of Energy has agreed to provide more funds for the building of the National Ignition Facility (NIF) at the Lawrence Livermore National Laboratory in California. It will contribute an extra $200 million–$250 million over the next two years, and will extend the construction schedule by four years, to 2008.

Confirming the worst predictions of the project's critics (see Nature 403, 469; 2000), Thomas Gioconda, assistant secretary of energy for defence programmes, said last week that the cost of the troubled project is now expected to exceed the original estimate of $1.2 billion by between $750 million and $1 billion.

The NIF is the world's largest laser project, and aims to cause fusion by firing 192 huge lasers at a tiny deuterium target. The project is central to the US government's stockpile stewardship programme, which will maintain nuclear weapons — and the army of scientists and engineers that work with them — in the absence of nuclear testing.

Just how much the NIF is over budget will be confirmed in the next few weeks, when the General Accounting Office publishes a report on the project. But the scale of the cost overrun has shocked staff and members of Congress, where the Department of Energy's plan to complete the NIF must win approval.

Gioconda said that the money to complete the programme will come from the rest of the nuclear weapons research budget, and “predominantly” from the Livermore laboratory's $1 billion annual budget. Previously, Bill Richardson, the energy secretary, had said that it would all come from Livermore's other programmes.

Under the new decision, announced on 3 May, a first phase of the NIF, with 96 working lasers, will be completed in 2004, with the rest becoming operational by 2008. The facility would aim to reach ignition — the point at which it produces a self-sustaining fusion reaction — in 2011.

Richardson's choice falls short of an alternative favoured by the Livermore laboratory, which would inject an extra $390 million over the next two years to bring the project back on schedule. The laboratory says that it will now support Richardson's plan.

Despite the extraordinary scale of the cost overruns at the NIF, the indications are that Washington will continue to support the project, say administration and congressional staff.