Crucial moments on the way to Mars (Forwarded)

ESA News
http://www.esa.int

3 December 2003

Crucial moments on the way to Mars

Mars Express, ESA's first probe to Mars, still has some challenges to face.

The spacecraft has successfully come through its first power test after the 
gigantic solar flare on 28 October.

Since 17 November the on-board software has been 'frozen' after several updates 
and the spacecraft is now quietly proceeding to its destination. The next major 
task, starting on 19 December, will be to safely release the Beagle 2 lander.

Separation

To deliver Beagle 2 where planned, Mars Express has been put on a collision 
course with Mars, since Beagle 2 does not have a propulsion system of its own 
and must therefore be aimed precisely at its destination.

Intense activity will begin six days before the arrival at Mars on 25 December 
with the release of Beagle 2. The orbiter will follow Beagle 2 for a while 
until, three days before arrival at Mars, ground controllers must make it change 
trajectory to avoid crashing onto the planet.

This will be the first time that an orbiter delivers a lander without its own 
propulsion onto a planet and attempts orbit insertion immediately afterwards.

Orbit insertion

The spacecraft speed will be reduced from about 11 kilometres per second to 9 
kilometres per second. At that speed, the planet's gravitational field will be 
enough to 'capture' Mars Express and put it into Martian orbit.

Several manoeuvres will follow to set the spacecraft into its final operational 
orbit. This orbit is a highly elliptical polar orbit, taking Mars Express as 
close as 260 kilometres from the Martian surface, and out to more than 11,000 
kilometres away at its furthest from the planet.

This is another crucial moment, as it is the first time after the launch that 
the orbiter's propulsion system comes into action. On top of this, the 
deployment of the radar booms will take place -- one of the most critical 
instrument activities.

Landing

The landing itself is another very complicated and challenging operation. Beagle 
2 will enter the Martian atmosphere at 20,000 kilometres per hour, but friction 
with the thin atmosphere will slow it down. Once its speed has decreased to 
about 1600 kilometres per hour, two parachutes will be deployed in sequence.

Finally, large, gas-filled bags will inflate to protect the lander as it bounces 
on the surface. Once Beagle 2 comes to a halt, the bags are ejected and the 
lander can open up and start operating.

Any one of these operations could go wrong. An incorrect alignment of the lander 
could mean it burns up in the atmosphere. The parachutes could fail to deploy, 
plunging Beagle 2 into the surface at great speed. The balloons could become 
detached, or get punctured, again possibly causing Beagle 2 to crash.

If the lander does not land on the planned spot, then this is less serious. The 
landing area is not one 'spot' but a large 'ellipsis', 300 kilometres long and 
100 kilometres wide.

It has been calculated taking into account the density of the Martian 
atmosphere, the winds and many other factors. So the risk of missing the landing 
site is very small. If the winds are stronger than calculated, for instance, 
they may 'push' Beagle 2 a little further away, but still within the selected area.

Top-class science

On the orbiter, if one or more of the instruments fail, then the mission could 
still carry on. All seven instruments on board are designed to work 
independently. So even some instruments fail, it would still be possible to 
perform top-class science.

Past missions to Mars have been lost due to a variety of problems, ranging from 
trivial errors in calculations to system problems. Errors can always happen, but 
all aspects of the Mars Express mission have been tested as much as possible to 
be confident that there will be no errors due to trivial mistakes. Mars Express 
has been developed in a record-breaking time, but there have been no compromises 
in testing.

* Europe goes to Mars
  http://www.esa.int/SPECIALS/Mars_Express/index.html

More about ...

* Mars Express overview
  http://www.esa.int/esaSC/120379_index_0_m.html

Related articles

* The search for life
  http://www.esa.int/esaSC/SEMAGE1P4HD_exploring_0.html
* Interplanetary trajectories
  http://www.esa.int/esaSC/SEM8USS1VED_index_0.html

Related links

* Beagle 2 lander homepage
  http://www.beagle2.com

IMAGE CAPTIONS:

[Image 1:
http://www.esa.int/export/SPECIALS/Mars_Express/SEM5Z0UZJND_1.html]
Separation of Beagle 2. Credits: All rights reserved Beagle 2

[Image 2:
http://www.esa.int/export/SPECIALS/Mars_Express/SEM5Z0UZJND_1.html#subhead1]
Deployment of the 40m long MARSIS radar antenna. Credits: ESA

[Image 3:
Credits: All rights reserved Beagle 2]
Beagle parachute deployed. Credits: All rights reserved Beagle 2