Nasa has purchased two reusable solid rocket motors from ATK Launch Systems to provide a launch-on-need rescue capability for the final planned space shuttle mission.

The reusable solid rocket motors are the propellant-loaded sections of the solid rocket boosters that provide thrust for the first two minutes of a shuttle flight.

The $64.6m modification brings the total value of the contract, which was awarded in October 1998, to $4.1bn and covers work begun in February to produce and transport the two motors.

Work will be performed at the ATK plants in Utah, and facilities at Nasa’s Marshall Space Flight Center and Kennedy Space Center.

The final shuttle mission is scheduled for September 2010.