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/M...0UZJND_1.html]
Separation of Beagle 2. Credits: All rights reserved Beagle 2

[Image 2:
http://www.esa.int/export/SPECIALS/M...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