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27 December 2003: Propelled by thrust from Lampoldshausen, ESA's Mars
Express probe successfully entered a safe and precise polar
orbit around Mars - ESA's first visit to another planet in
the solar system. En route, Mars Express released the Beagle
2 lander on 19 December.
Mars Express has successfully achieved its operational orbit
of between 260 and 11,000 km from the surface of Mars, mapping
the red planet, exploring for water and mineral resources
and providing images of objects down to two meters.
At an altitude of 260 km, Mars Express will overfly the landing
site where NASA's Spirit Rover touched down at the Gusev Crater.
Using its powerful camera and two spectrometers, Mars Express
will help NASA spot minerals formed in water that may be present
at Spirit Rover's landing site and elsewhere.
Mission scientist Albert Haldermann said the collaboration
between the US space agency's (NASA) Spirit and Mars Express
would be an "historic" opportunity and a "co-ordinated
observation that is international in nature."
Mars Express was launched on 2 June 2003 from Baikonur by
Soyuz-Fregat and was released from the Fregat upper stage
after injection into a Mars bound trajectory.
Five days before its arrival at Mars, the Beagle 2 probe
was released from the Mars Express orbiter. The orbiter then
changed its Mars collision trajectory into a highly eccentric
capture orbit on 25 December. From there, it performed several
deceleration manoeuvres to descend into its final operational
orbit around Mars in January.
The Mars Express main engine was used to slow down the spacecraft
to enable Mars orbit insertion and for orbit correction manoeuvres.
Orbital insertion was a critical moment that had to be performed
flawlessly and precisely on time. A failure could have resulted
in Mars Express overshooting Mars into a heliocentric orbit
around the sun.
Based on existing, flight proven hardware with excellent
heritage credentials, a bi-propellant propulsion system, was
selected for Mars Express to meet the requirement for a high-performance,
low-cost propulsion system with minimum mass.
The Mars Express propulsion system comprises a 400 N main
engine and eight 10 N thrusters. Oxidiser and fuel is supplied
from two propellant tanks, having a total volume of 540 litres.
The propellants are pressure-fed using helium stored in a
35 litre pressure vessel.
For trajectory correction manoeuvres during the interplanetary
cruise phase, the propulsion system was designed to operate
in a pressure-regulated mode using only the 10 N thrusters.
The 400 N main engine remained dormant throughout the 7 month
journey to Mars.
A few days before Mars orbit insertion, the main engine
was activated and its thrust calibrated by making specific
manoeuvres. This ensured that the engine was prepared and
could be used safely for the Mars orbit insertion manoeuvre
as well as acquisition of the operational orbit. In the event
of a main-engine failure at this critical phase, the 10 N
thrusters would have been used to carry out the capture manoeuvre.
In this event, only a degraded orbit around Mars would have
been established, although aerobraking could help to achieve
the nominal orbit.
During its 30 minute deceleration burn, the 400 N main engine
reduced the velocity of Mars Express from about 11 kilometres
per second to 9 kilometres per second. At this velocity, the
planet's gravitational field was sufficient to 'capture' Mars
Express into the Martian orbit. Precision orbit correction
manoeuvres were performed using the 10 N thrusters, to place
Mars express into its final operational orbit.
Since Mars Express is now within its final orbit, The 400
N main-engine and its pressure control assembly have been
isolated. The rest of the mission will now be performed using
just the 10 N thrusters in blow-down mode.
More information about Mars Express and Beagle 2 can be found
at:
Mars Express: Official
ESA website
Beagle Lander: Official
website
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