After a joint journey of 250 million miles (400 million km), the British-built Beagle 2 spacecraft and the European Space Agency's Mars Express orbiter should now have parted and gone their separate ways.
At 8.31 GMT, software on Mars Express was scheduled to send the command for the Beagle 2 lander to separate from the orbiter. This would fire a pyrotechnic device that would slowly release a loaded spring and gently push Beagle 2 away from the mother spacecraft at around 1 ft/s (0.3 m/s).
If all goes according to plan, the release mechanism will also cause Beagle 2 to rotate like a spinning top, stabilising its motion during the final stage of its flight towards Mars.
Since Beagle 2 does not have a propulsion system of its own, it must be carefully targeted at its destination. With Mars Express acting as a champion darts player aiming at a bullseye, Beagle 2 should be placed on a collision course with the planet, following a precise ballistic path that will enable it to hit a specific point at the top of the Martian atmosphere in six days' time.
Initial confirmation that the separation manoeuvre has been successful is expected at 10.40 GMT, when the European Space Operations Centre (ESOC) in Darmstadt, Germany, should receive X-band telemetry data from Mars Express. Further information from Mars Express and Beagle 2 telemetry confirming separation should be returned by 11.10 GMT.
In addition, it is hoped that the orbiter's onboard Visual Monitoring Camera (VMC) will provide pictures showing the lander moving slowly away. The images are expected to be available within hours of the separation event.
However, after six months in space, during which the spacecraft were buffeted by solar storms, the manoeuvre is not without risk. Although it has been tested many times on Earth, there is always the outside possibility that something may go wrong during the all-important separation.
Even if the separation is successful, Beagle 2 must rely on its own battery, which cannot last beyond 6 days, until its solar arrays are fully deployed on the surface. This means that Mars Express must release Beagle 2 at the last possible moment in order to ensure that the lander has enough power for the rest of its journey to the rust-red Martian plains.
This will be the first time that an orbiter has delivered a lander without its own propulsion onto a planet and then attempted orbit insertion immediately afterwards.
Meanwhile, Mars Express will follow Beagle 2 for a while until, three days before arrival at Mars, ground controllers will have to fire its thrusters and make it veer away to avoid crashing onto the planet. Early on 25 December, Beagle 2 should plunge into the atmosphere before parachuting to its planned landing site, a broad basin close to the Martian equator, known as Isidis Planitia. Later that day, Mars Express should enter orbit around Mars.
Beagle 2 has no propulsion system of its own so it is carried to Mars by the Mars Express spacecraft which will go into orbit around the planet for remote sensing purposes.
The Beagle 2 Spin-Up & Ejection Mechanism (SUEM) was designed and developed by INSYS Ltd. of Ampthill, Bedford, UK.
The SUEM has two elements: the first, the launch clamp mechanism, will provide a secure mounting system to withstand loads applied during ground handling and lift-off. During the launch phase, three matched cup and cones transfer the launch loads from the probe to the orbiter. Each cup and cone is preloaded by the use of a "Frangibolt®" which uses a memory metal collar, which when heated expands and fractures each bolt. Release of the Frangibolts® was initiated a few days after launch, shortly after insertion of Mars Express into its transfer trajectory between Earth and Mars. The second element, the ejection mechanism, releases the probe for its descent to Mars. This is accomplished by means of a pyrotechnic protractor that releases a ball cage locking device. This allows a spring within the SUEM to push the probe from Mars Express. A helical guide groove induces a linear velocity of 0.3 m/s (1 ft/s) and an angular velocity of 14 rpm into the probe.
Materials provided by Particle Physics & Astronomy Research Council. Note: Content may be edited for style and length.
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