InSight will be going around 13,000 miles per hour as it first enters the Martian atmosphere.
The heat shield will get as hot as 2500 degrees Fahrenheit—hot enough to melt steel. It will stay this hot for about 3.5 minutes, until it is time for the parachute to deploy. The chute will stay full for 30 seconds, at which point InSight will drop its heat shield.
Immediately after this, InSight's onboard radar will activate and will begin pinging the planet. With each radar bounce the spacecraft will take a measurement of not only how far away it is from the surface, but how fast it's going.
About 40 seconds before touchdown InSight will jettison all of this paraphernalia, then spend about a minute in free-fall. It will spin itself away from the tumbling parachute and heat shield to avoid damage.
Seconds before InSight touches down it will fire its thrusters in preparation for contact. In just under seven minutes the lander will have gone from 13,000 mph to just 5 mph.