Surface & atmosphere
Mars Express, which has now been in orbit around Mars for over a year, is a great success for the European scientific community which was disappointed by the loss of the Russian Mars-96 mission. This mission carried several European instruments, including French ones.
In 1997, ESA decided the Mars-Express mission in order to recover partially the objectives of the Mars-96 mission, and to offer a new opportunity to European experiments.
The main scientific objectives of the mission for the orbiter are:
- the high resolution (10 m/pixel) global cartography of the surface in colour and in stereoscopy and the imaging of selected areas with a 2 m/pixel resolution;
- the global and high resolution (100 m/pixel) mineralogical cartography of the surface;
- the radar sounding of the Martian subsurface, to detect solid or liquid water reservoirs;
- the determination of the atmosphere's composition, the study of its circulation and its interaction with the surface, the solar wind, and the interplanetary medium;
- a radioscience experiment to sound the neutral and ionized atmosphere to determine the surface's dielectric properties and the planet's gravity field.
The small Beagle 2 lander (69 kg including 33 kg landing on the Martian surface), under British responsibility, aimed to discover traces of past or present life. No contact could be made with Beagle after its release.
7 Months to Reach Mars
Mars Express was launched on 2 June 2003 at 17:45:26 TU from the Baïkonur cosmodrome in Kazakhstan.
2003 was particularly favourable to the launch of a spacecraft to Mars because Mars was passing at less than 56 million kilometres of the Earth, which only happens every 15 or 17 years. This enabled Mars Express to meet the Red Planet in seven months instead of the usual 9 to 12 months.
Mars Express was launched by a Soyuz launcher, with an upper Fregat stage which injected the spacecraft onto its Martian trajectory. Then the satellite deployed its solar panels, supplied a health status of its equipment to the Earth, and began the long journey to Mars.
During this cruise, the satellite was followed by the New Norcia ground station (Australia) and received instructions to correct the trajectory by firing for a few minutes its attitude thrusters. At this stage of the flight, the health status of the scientific instruments was verified.
Beagle 2 release
On 16 December, the operations leading to the Beagle 2 lander release began. The satellite positioned itself voluntarily on a Mars collision course, to enable Beagle 2 release in the direction of its landing site. This manoeuvre was critical because the lander had neither attitude control nor thrusters. On 19 December, Beagle 2 was then released by the satellite on a ballistic trajectory aimed at Mars. If the trajectory was not correct, either Beagle 2 bounced on the Martian atmosphere and continued its cruise in the interplanetary medium, or the small lander entered the atmosphere with too high an incidence and burned. No contact could be made with Beagle after its release.
Immediately after the release, Mars Express fired for the first time its main thruster to modify its trajectory and retargeted for orbit insertion to enable the capture of the orbiter by the gravity field of Mars.
Mars Orbit Insertion
To reach the Mars Orbit Insertion, the main thruster was fired to slow the satellite down to a speed lower than the speed of liberation from the planet (5.2 km/s, speed enabling a spacecraft to escape from the Martian attraction).
Mission success depended on this critical phase. At this instant of the mission, it took 10 minutes for the telecommands to reach the satellite. The Martian insertion took place entirely automatically; the satellite had to manage alone its "destiny".
Mars Express orbit
After several manoeuvres, Mars Express was positioned on an elliptical orbit (250 x 10142 km) with a quasi-polar inclination (86.35°) and a duration of 6.75 hours.
The mission lifetime is a Martian year, i.e. approximatively two terrestrial years. However the Mars Express resources are anticipated to enable the achievement of a mission extended by one Martian year.
Besides operating the on-board scientific instruments, Mars Express must also be the telecommunication relay for the Beagle 2 lander, which was not designed to communicate directly with the Earth.