To ensure a successful entry, descent, and landing, engineers began intensive preparations during the approach phase, 45 days before the spacecraft entered the Martian atmosphere. It lasted until the spacecraft entered the Martian atmosphere, which extends 3522.2 kilometers (2,113 miles) as measured from the center of the red planet.

    The activities that engineers typically focus on during the approach phase include:

    • the final trajectory correction maneuvers, which are used to make final adjustments to the spacecraft's incoming trajectory at Mars
    • attitude pointing updates, as necessary, for communications and power
    • frequent "Delta DOR" measurements that monitor the spacecraft's position and ensure accurate delivery
    • start of the entry, descent, and landing behavior software, which automatically executes commands during that phase
    • entry, descent, and landing parameter updates
    • spacecraft activities leading up to the final turn to the entry attitude and separation from the cruise stage
    • the loading of surface sequences and communication windows needed for the first several sols (a "sol" is a martian day)

    During the approach phase, the amount of requested tracking by the Deep Space Network was substantially increased to allow engineers to determine more accurate trajectory solutions in the final weeks before arrival at Mars. This tracking supported the safe delivery of the Mars Science Laboratory landing system to the surface of Mars. The Deep Space Network's 34-meter and 70-meter antennas provided tracking coverage of the spacecraft during the approach phase.