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What is Cruise?
The cruise phase is the voyage between Earth and Mars. It begins after
the spacecraft completes the launch phase
and ends slightly before the spacecraft slows down to be captured into
Mars' orbit during Mars Orbit Insertion.
What Happens During Cruise?
During the cruise phase, the main task is navigation. Tracking data will
determine where the spacecraft is in the solar system, and engineers will
use this data to execute any trajectory correction maneuvers to make
sure the spacecraft gets to Mars. To adjust the spacecraft's path, engineers
will rely on on-board propulsion for trajectory correction maneuvers.
Corrections will be achieved by firing two or more of the eight
10-Newton* thrusters that are attached to each corner of the spacecraft
and are fuelled by the same bi-propellant mixture as the main engine.
The main engine is pretty powerful, and is used to decelerate the
spacecraft to go into orbit around Mars. By the time Mars Express gets to its
final orbit, most of the propellant will be used up. The main engine, attached
to the underside of the spacecraft bus, is capable of delivering a force of
400 Newtons.* It uses a mixture of two propellants that are contained in
two tanks, each with 267 liter (71 gallon) capacity. Fuel is fed into the
engine using pressurized helium from a 35-liter (9-gallon) tank.
(*A Newton is a unit of force required to accelerate a mass of one kilogram one meter per second squared).
NASA Participation During Cruise
While the main responsibility for navigation belongs to the European
Space Operations Center (ESOC) located in Darmstadt, Germany, engineers
at NASA's Jet Propulsion Laboratory with many years of experience in
navigating missions to Mars will work collaboratively with their European
colleagues. Together, they must validate software that determines
spacecraft trajectories and compare solutions using real data from other
The JPL team will start regular navigation operations during the
approach to Mars. Solutions will be compared against those computed
by the ESOC navigation team on a regular basis for accuracy. JPL's
involvement in the navigation of Mars Express will formally end once the
spacecraft has reached a safe orbit around Mars.