III - The Ten Instruments Mars Rover Curiosity Carries: MEDLI
Engineers have a lot to worry about during Curiosity's descent through the atmosphere--as advertised by their "seven minutes of terror" video. But during that descent, Curiosity will already be working, gathering data for the next set of missions to Mars.
The MSL Entry, Descent and Landing Instrumentation (MEDLI) will monitor the heat and pressure it undergoes upon entry. It's actually made up of two kinds of instruments: MISP (MEDLI Integrated Sensor Plugs) and MEADS (Mars Entry Atmospheric Data System). Seven of each type sit on Curiosity's heat shield. (The system is the black box in the left of the photo.)
MISP will measure just how hot things get when it's burning through the atmosphere. (Short answer: really hot. Slightly less short answer: three times hotter than a space shuttle going through Earth's atmosphere.) Curiosity's thermal protection system will actually burn off, and MISP will measure the rate of burning, known as "recession."
MEADS will take a measurement of the atmospheric pressure during descent. Arranged in a cross pattern, the seven sensors will allow engineers to determine Curiosity's orientation as a function of time. Once they know that, they can grade Curiosity's descent against their predictions, then improve them for next time.