Guardian Unlimited | Special reports | Nasa chiefs 'repeatedly ignored' safety warnings

Fears of a catastrophic shuttle accident were raised last summer with the White House by a former Nasa engineer who pleaded for a presidential order to halt all further shuttle flights until safety issues had been addressed.



In a letter to the White House, Don Nelson, who served with Nasa for 36 years until he retired in 1999, wrote to President George W. Bush warning that his 'intervention' was necessary to 'prevent another catastrophic space shuttle accident'.



During his last 11 years at Nasa, Nelson served as a mission operations evaluator for proposed advanced space transportation projects. He was on the initial design team for the space shuttle. He participated in every shuttle upgrade until his retirement.



Listing a series of mishaps with shuttle missions since 1999, Nelson warned in his letter that Nasa management and the Aerospace Safety Advisory Panel have failed to respond to the growing warning signs of another shuttle accident. Since 1999 the vehicle had experienced a number of potentially disastrous problems: