The National Aeronautics and Space Administration (NASA) said it would have to spend 235 million dollars by the end of next year on alterations to the launch system. Another 45 million dollars would be spent on a new engineering and safety centre.
The most expensive changes will be to the external fuel tank that was at the centre of the Columbia disaster on February 1.
A piece of isolation foam on the tank came off during launch and pierced the shuttle's protective skin, letting in boiling gases that led to the vessel's breakup as it re-entered the Earth's atmosphere. All seven crew were killed.
The modifications to the fuel tank will cost 65 million dollars.
Another 57 million dollars will be spent on changes to allow astronauts to carry repairs while the shuttle is in orbit. Forty-four million dollars will be spent on a camera system to monitor possible problems after launch.
The 280 million dollars does not take account of changes already decided by NASA, which was strongly criticised by the official inquiry into the accident.
The agency hopes to resume shuttle flights in September 2004.