Dan Goldin and the 1997 Mars Pathfinder rover
US space agency administrator Dan Goldin is to step down after nine years in the job - a longer tenure than any other chief in the history of Nasa.
His resignation has been expected for some time; the White House has been looking for another candidate since George W Bush took up the presidency. Goldin's announcement has come just one day after Nasa's associate administrator for space flight, Joseph Rothenberg, announced his retirement.
The departures occur amid a growing crisis at Nasa over the funding of the ISS and talks of further cutbacks as a result of the cost of America's "war on terrorism" - Operation Enduring Freedom.
Faster, better, cheaper
"For nearly a decade, it has been my honour to serve the American people by leading our nation's space programme and its dedicated personnel," Goldin said in a letter to the president.
"It was the highlight of my life when your father asked me in 1992 to serve as America's ninth administrator for the National Aeronautics and Space Administration."
Dan Goldin, 61, took up the position of Nasa chief on 1 April, 1992, and became the agency's longest-serving administrator on 5 March, 2001, surpassing James Fletcher's previous record of nearly nine years achieved across two separate terms.
During Goldin's tenure, Nasa launched 171 missions, of which 160 were successful. Goldin believed his "faster, better, cheaper" philosophy allowed the agency to deliver missions of high value without sacrificing safety.
But he was criticised for making big cuts in Nasa's spending. He reduced annual budgets by a cumulative total of $40bn.
His supporters countered that he initiated a more balanced space programme, by reducing human space flight funding from nearly half of Nasa's total budget to about a third. This permitted him to increase funding for science missions.
Obsessed by Mars
Analysts said that one of Goldin's major achievements was to cut the time required to develop Earth- and space-science spacecraft by 40%, and reduce the cost by two-thirds, while increasing the average number of missions launched per year by a factor of four.
But he has also been criticised for being too vigorous a proponent of increased exploration of Mars. Some said he had become fixated with the search for life on the Red Planet, at the expense of a return mission to the Moon and the exploration of distant worlds, such as Jupiter's moon Europa and the planet Pluto.
Goldin said: "Nasa's mission of discovery will continue. Humanity will continue to benefit from the fruits of this journey and I am proud and deeply humbled by the opportunity that was given me. The people of Nasa have my unconditional respect and eternal gratitude."
Goldin officially leaves his post on 17 November - and Nasa's new administrator, who should be named before that date, will have to face up to some severe problems.
The ISS is expected to go $5bn over budget in the next few years and Nasa has already had to abandon a crew habitation module and an emergency return vehicle, or "lifeboat", to cut costs.
A panel of outside experts has also been looking into Nasa's operations and its findings should be released in about a month. Nasa officials who have been interviewed by the panel expect the report to be devastating.