NASA says it will now cost almost $US9 billion to build and launch the James Webb space telescope, a replacement for the Hubble space telescope. That's $US2 billion more than previous estimates.
James Webb is regarded as the successor to Hubble and will carry technologies capable of detecting the light from the first stars to shine in the Universe.
But delays and cost overruns have dogged the project and some now politicians want JWST cancelled.
The House Appropriations Committee put forward a draft 2012 budget for the US space agency last month that would terminate funding for the observatory.
However, the equivalent committee in the Senate is yet to have its say.
NASA has fiercely defended the telescope, with senior officials describing it as one of their top priorities.