About 70 minutes before entering the Martian atmosphere each spacecraft orients its heat shield forward. From this point onwards, the rover uses solar panels to power itself. Fifteen minutes before entering the Martian atmosphere, the protective aero shell enclosing the lander and rover separates from the cruise stage.
Both the rovers enter the Martian atmosphere at a flight path angle of about 11.5 degrees and a velocity of about 5.4 kilometers per second.
Mars has a much thinner atmosphere than Earth. But still the friction of traveling through it will heat and slow the spacecraft. By 4 minutes after atmospheric entry, speed will decrease to about 430 meters per second. At 8.5 kilometers above the ground, the spacecraft will deploy its parachute. Within 2 minutes the spacecraft will be on the surface of mars.
In those two minutes the following actions are to be performed
- Twenty seconds after parachute is deployed, the spacecraft will jettison the bottom half of its protective shell, the heat shield, exposing the lander inside.
- Ten seconds later, the back shell, still attached to the parachute, will begin lowering the lander on a tether like bridle about 20 meters long. Spooling out the bridle to full length will take 10 seconds.
- Almost immediately, a radar system on the lander will begin sending pulses toward the ground to measure its altitude. Radar will detect the ground when the craft is about 2.4 kilometers above the surface, approximately 35 seconds before landing.
- There are tools to avoid excessive horizontal speed during ground impact in case of strong winds near the surface. One is a downward-looking camera mounted on the lander. Once the radar has sensed the surface, this camera will take three pictures of the ground about 4 seconds apart and automatically analyze them to estimate the spacecraft's horizontal velocity. The other tool is a set of three small transverse rockets mounted on the back shell that can be fired in any combination to reduce horizontal velocity.
- Eight seconds before touchdown, gas generators will inflate the lander's airbags.
- Two seconds later, the three main deceleration rockets on the back shell and, if needed, one or two of the transverse rockets will ignite.
- After 3 more seconds, when the lander should be about 15 meters (50 feet) above ground and have zero vertical velocity, its bridle will be cut, releasing it from the back shell and parachute.
- The airbag-protected lander will then be in free fall for a few seconds as it drops toward the ground.
The first bounce may take the airbag-protected lander back up to 15 meters or more above the ground. Bouncing and rolling could last several minutes.
Twelve minutes after landing, motors will begin retracting the airbags, a process likely to take about an hour. Then the lander petals will open. No matter which of the four petals is on the bottom when the folded-up lander stops rolling, the petal-opening action will set all four faces up, with the rover's base petal in the center.
After the safe landing of the lander, rover emerges out of it and starts performing operations on mars as it is programmed to do. Let us now study the rover in detail: