ESA Science & Technology - Cruise Phase

The long interplanetary cruise

Prelaunch M.Heschler, a mission analyst, described the next challenge: "To avoid the Fregat upper stage also ending up on Mars, we may decide to off-target the launcher slightly. The Fregat will have a very precise guidance system which will automatically remove errors introduced during the firing of its large rocket engine. Even so, there will be a small deviation between the trajectory reached and the one we want. So the next task will be to determine precisely which trajectory Mars Express is following."

ESA ground stations in Perth, Australia and Kourou, Guiana achieved this by repeatedly sending radio signals to the spacecraft and measuring the time taken for them to return. Two days and 600 000 km later, ground control sent a message to Mars Express to re-target its trajectory onto a collision course with Mars. All it took was a burn of the small thrusters for a few minutes to produce the desired effect.

Mars Express was now hurtling through interplanetary space with an absolute velocity of 116 800 kmh^-1 and a velocity relative to Earth of 10 800 kmh^-1.

For the first month, detailed checks of each payload instrument were carried out before switching them off for this phase of the mission.  The cruise phase was the lull between the rush of launch and orbit insertion.  Operations entered a rountine housekeeping phase with contact to ground control kept to daily health checks and minor course corrections.  At two points along the way the HRSC instrument was activiated to capture imags of the Earth and Moon and then Mars - from a distance of just 5.5 million km.

Release of Beagle 2

One month before arrival, preparations began for the separation of the Beagle 2 lander. "Once more the small thrusters will be fired to put Mars Express onto a trajectory that will allow Beagle 2, which has no propulsion of its own, to enter the Martian atmosphere and drift down to the correct landing site on the surface," described Hechler before launch.

In reality he was correct and at 08:31 UT 19 December 2003 the pyrotechnic mechanisms on Mars Express were activated to release the probe towards the surface of the red planet. This operation took place as late as possible to give scientists the best possible chance of calculating the landing site.

Mars captures the orbiter

At the same time that Beagle 2 was scheduled to reach the surface Mars Express fired its main engine for the first time since launch.  This was the start of the orbit insertion manoeuvre.  An engine burn lasting 37 minutes was required to place the spacecraft into a highly elliptical orbit several thousand kilometres above the surface of the planet at apocentre.  Of the following days the orbit was gradually corrected bring it ever closer to the operational scientific orbit.

On 30 December 2003 the first major correction took place.  This positioned the spacecraft into a polar orbit: pericentre 300 km, apocentre 10 000 km, inclination 86° .

Journey facts at a glance