|Mission Timeline: Cruise
The Cruise phase begins soon after separation from the third stage of the Delta-II launch vehicle when the spacecraft completes the Launch phase. Cruise ends when the spacecraft is 45 days from entry into the martian atmosphere. Since the arrival of each rover is held constant no matter when they launch within the launch period, the end of the cruise phase also has specific dates set: November 20, 2003 for Rover A and December 11, 2003 for Rover B.
Both rover missions took "type I" interplanetary transfers to Mars. Type I transfer trajectories are the fastest possible. Since each spacecraft travels millions of miles to reach Mars, engineers have the option to perform three trajectory correction maneuvers during cruise to "tweak" the position of the spacecraft to ensure it arrives at Mars and lands at the planned location. (Three more trajectory correction maneuvers are also possible during the approach phase.)
During cruise, the spacecraft spins at 2 rpm and requires periodic spin axis pointing updates to maintain the antenna pointing toward Earth and the solar panels pointed to the sun as their relative positions change during flight.
Due to a wide separation between Sun and Earth relative to the early trajectories, both spacecraft use a cruise low-gain antenna (CLGA) for early cruise communications. After the first couple of months of cruise, as the Earth and Sun come closer together as viewed from the spacecraft, the spacecraft switches to a medium-gain antenna (MGA) for communications during the rest of cruise.
In short, the activities during this phase include:
- health checks and maintenance of the spacecraft in its cruise configuration
- monitoring and calibrating the spacecraft and subsystems
- attitude correction turns (aforementioned spins to maintain the antenna pointing toward Earth for communications and the solar panels pointed toward the sun for power)
- navigation activities, including trajectory correction maneuvers, for determining and correcting the vehicle´s flight path and for training navigators prior to approach
- preparation for entry, descent, and landing and surface operations, including X-band communication tests used during entry, descent, and landing