The cruise phase lasts for approximately 10 months as Phoenix makes its way to Mars. During the cruise phase, the spacecraft verifies the health of its scientific instruments and performs trajectory correction maneuvers (TCMs). The Deep Space Network (DSN) is used to communicate with the spacecraft

Up to six trajectory correction maneuvers are planned to keep Phoenix on track to its landing area. (Image Credit: Phoenix Mission, University of Arizona)

during these operations. The massive antennas of the DSN are also used to obtain information about the spacecraft's flight path. Often times, the spacecraft will be observed from DSN sites in different parts of the world simultaneously to find its exact trajectory. These measurements are crucial for planning (TCMs).

The initial launch trajectory is intentionally pointed away from Mars so that the jettisoned third stage from the launch vehicle does not impact Mars. The first TCM, performed just 10 days after launch, places the spacecraft on a trajectory towards Mars. The subsequent
Five minutes before Phoenix enters the martian atmosphere, the cruise stage is jettisoned. (Image Credit: Phoenix Mission, University of Arizona)
TCMs are planned to take place much later in cruise phase to correct small errors in the first TCM (see image at right). These errors come from a multitude of sources, including imperfections in the flight model and slight inaccuracies in the DSN measurements. This type of deep space navigation has been used by many other NASA missions, including Mars Odyssey and the recent Mars Exploration Rovers.

Entering Atmosphere
In this artist's rendition, Phoenix is hurtling towards Mars at 16,000 mph and is minutes away from entering the atmosphere. (Image Credit: Phoenix Mission, University of Arizona)

During the last two weeks before Phoenix enters the martian atmosphere, the DSN will be tracking the spacecraft even closer than before. Two TCMs are scheduled to be performed within the last three days. Just before entry, flight path data is sent to Phoenix that is used by the onboard computers during the descent and landing to guide the spacecraft to its landing site. The cruise assembly, which consists of solar panels and other components that are only necessary for the cruise phase of the journey, is jettisoned five minutes prior to entry.

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