To ensure a successful entry, descent, and landing, engineers begin intensive preparations 45 days before the spacecraft enters the Martian atmosphere. They call this preparation period the approach phase. It lasts until the spacecraft enters the Martian atmosphere, which extends 3522.2 kilometers (2,113 miles) as measured from the center of the red planet.
The mission team switches to "Mars time" during this phase. (The martian day, or sol, is about 40 minutes longer than an Earth day, so the team needs to synchronize their schedules to the rovers.) The activities that engineers are focused on during the approach phase include:
the final three 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 is substantially increased to allow engineers to determine more accurate trajectory solutions in the final weeks before arrival at Mars. This tracking supports the safe delivery of the spacecraft to the surface of Mars. The Deep Space Network's 34-meter and 70-meter antennas are able to provide tracking coverage of the spacecraft during the approach phase.
