0 a rocket on a spacecraft or an aircraft that fires in the opposite direction to the direction in which the vehicle is travelling, in order to slow it down --
As he plummeted downward, he saw what appeared to be two of the spent retrorockets pass across the periscope view after the retrorocket package had been jettisoned.
A backup was not needed since its supplies lasted for a 10-day flight, which would allow for reentry by orbital decay if the retrorocket failed.
The lander/rover will have its own small retrorocket, and, after being jettisoned from the tug, was projected to conduct a braking maneuver to land softly on the lunar surface.
The decision was made to leave the retrorocket pack in position during reentry.
The spacecraft was maneuvered into retrofire attitude and the first retrorocket fired.
A backup solid-fuel retrorocket was added to the top of the descent module.
At 250 m from the surface, the main retrorocket was turned off and the four outrigger engines were used to slow the craft.
White paint, gold and chrome plating, and a silvered plastic sheet encasing the retrorocket furnished thermal control.
