The entry, descent, and landing (EDL) begins when the spacecraft reaches the Martian atmosphere, about 80 miles (about 128 kilometers) above the surface, and ends with the lander safe and sound on the surface of Mars six minutes later.
For InSight, this phase includes a combination of technologies inherited from past NASA Mars missions such as NASA’s Phoenix Mars Lander. This landing system weighs less than the airbags used for the twin rovers or the skycrane used by the Mars Science Laboratory. The lean landing hardware helps InSight place a higher ratio of science instruments to total launch mass on the surface of Mars.
Compared with Phoenix, though, InSight’s landing presents four added challenges:
InSight enters the atmosphere at a lower velocity — 12,300 miles per hour (5.5 kilometers per second) vs. 12,500 miles per hour (5.6 kilometers per second).
InSight has more mass entering the atmosphere — about 1,340 pounds (608 kilograms) vs. 1,263 pounds (573 kilograms).
InSight lands at an elevation of about 4,900 feet (1.5 kilometers) higher than Phoenix did, so it has less atmosphere to use for deceleration.
InSight lands during northern hemisphere autumn on Mars, when dust storms are known to have grown to global proportions in some prior years.
Some of the changes in InSight’s entry, descent and landing system, compared to the one used by Phoenix, are:
InSight uses a thicker heat shield, partly to handle the possibility of being sandblasted by a dust storm.
InSight’s parachute suspension lines use stronger material.
The entry, descent and landing sequence breaks down into three parts:
Entry – The spacecraft is controlled by small rockets during descent through the Martian atmosphere, toward the surface.
Parachute Descent – The InSight spacecraft slows by a large parachute, jettisons its heat shield and extends its three shock-absorbing legs.
Powered Descent – Once the lander separates from its backshell and parachute, 12 descent engines on the lander begin firing and the onboard guidance software slows down the spacecraft until touchdown.