with lunar orbit. Such missions began on a lunar impact trajectory instead. Descent and braking – the spacecraft fires its engines until it is no longer in orbit. If the engines were to stop firing entirely at this stage the spacecraft would eventually impact the surface. During this stage, the spacecraft uses its rocket engine to reduce overall speed Final approach – The spacecraft is nearly at the landing site, and final adjustments for the exact location of touchdown can be made Touchdown – the spacecraft achieves soft landing on the Moon Touchdown Lunar landings typically end with the engine shutting down when the lander is several feet above the lunar surface. The idea is that engine exhaust and lunar regolith can cause problems if they were to be kicked back from the surface to the spacecraft, and thus the engines cut off just before touchdown. Engineers must ensure that the vehicle is protected enough to ensure that the fall without thrust does not cause damage. The first soft lunar landing, performed by the Soviet Luna 9 probe, was achieved by first slowing the spacecraft to a suitable speed and altitude, then ejecting a payload containing the scientific experiments. The payload was stopped on the lunar surface using airbags, which provided cushioning as it fell. Luna 13 used a similar method. Airbag methods are not typical. For example, NASA's Surveyor 1 probe, launched around the same time as Luna 9, did not use an airbag for final touchdown. Instead, after it arrested its velocity at an altitude of 3.4m it simply fell to the lunar surface. To accommodate the fall the spacecraft was equipped with crushable components that would soften the blow and keep the payload safe. More recently, the Chinese Chang'e 3 lander used a similar technique, falling 4m after its engine shut down. Perhaps the most famous lunar landers, those of the Apollo Program, were robust enough to handle the drop once their contact probes detected that landing was imminent. The landing gear was designed to withstand landings with engine cut-out at up to of height, though it was intended for descent engine shutdown to commence when one of the probes touched the surface. During Apollo 11 Neil Armstrong however touched down very gently by firing the engine until touchdown; some later crews shut down the engine before touchdown and felt noticeable bumps on landing, with greater compression