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Mars Express – Europe Raises The Bar

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This first short section is direct from the European Space Agency’s Mars Express Website:

“Mars Express is the first fully European mission to any planet.
It is an exciting challenge for European technology.”

Rudi Schmidt, Mars Express Project Manager, ESTEC.

From the Greeks more than two thousand years ago to Eugene Antoniadi in the mid 1900s, Europeans have made many important observations of Mars with the naked eye and through Earth-bound telescopes. They have even contributed their fair share of speculation and fantasy about the planet in a fine tradition beginning in 1897 with the publication of The War of the Worlds by H.G. Wells in which hostile Martians invade Earth.

Europe, however, has never sent its own spacecraft to Mars – that is until now. The European Space Agency’s Mars Express orbiter and its lander, Beagle 2, will play a key role in an international exploration programme spanning the next two decades.

Research institutes throughout Europe provided the instruments on board the orbiter. Some were first developed for the ill-fated Russian spacecraft, Mars ’96. Now upgraded, they will provide remote sensing of the atmosphere, ground and up to 5 kilometres below the surface, to a degree of accuracy never before achieved.

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The Journey

Launched in June of 2003, the Euorpean Space Agency’s Mars Express was boosted towards Mars aboard a Russian Soyuz/Fregat four stage rocket. Three stages to place the spacecraft into high orbit, and the final stage to insert the craft into a Mars rendezvous trajectory. Six days before arrival to Mars orbit, Mars Express ejected the Beagle 2 lander which was to have made its own way to the correct landing site on the surface.

The orbiter successfully entered Martian orbit on 25 December. First it maneuvered into a highly elliptical capture orbit from which it moved into its operational near polar orbit later in January 2004. Mars Express will remain in orbit around the Red Planet for at least one Martian year, 687 Earth days, which is the nominal mission lifetime. During this time, the point of the orbit closest to Mars (pericentre) will move around to give the scientific instruments coverage of the entire Martian surface from a variety of viewing angles.

Last week the spacecraft unfolded its Sub Surface Sounding Raday Altimiter, a device that will provide imaging and measurments below the surface of Mars.

Here is an overview of the spacecraft and her instruments:

The Lander

Beagle 2 was planned to descend to the surface, entering the atmosphere at more than 20 000 kilometres per hour. A heat-resistant shield would have protected it as friction with the upper atmosphere slowed it down.

When its speed had fallen to about 1600 kilometres per hour, a parachute would have deployed to slow it further. Finally, large gas-filled bags inflate to protect it as it bounced to a halt on the chosen landing site. As soon as the lander came to a halt, the gas bags would have been jettisoned, its clam-like outer casing sprung open, its solar panels unfurled, the robotic arm deployed and its cameras started to take in the view.

Unfortunately, the Beagle 2 lander was declared lost after it failed to make contact with orbiting spacecraft and Earth-based radio telescopes. There has been no contact with the lander, or any indication as to the final fate of the Beagle 2.

The Onboard Equipment

High Resolution Stereo Camera (HRSC)

The HRSC is imaging the entire planet in full colour, 3D and with a resolution of about 10 metres. Selected areas will be imaged at 2-metre resolution. One of the camera’s greatest strengths will be the unprecedented pointing accuracy achieved by combining images at the two different resolutions. Another will be the 3D imaging which is revealing the topography of Mars in full colour.


Serious Canyons On Mars

OMEGA Visible and Infrared Mineralogical Mapping Spectrometer

OMEGA is building up a map of surface composition in 100 metre squares. It will determine mineral composition from the visible and infrared light reflected from the planet’s surface in the wavelength range 0.5-5.2 microns. As light reflected from the surface must pass through the atmosphere before entering the instrument, OMEGA will also measure aspects of atmospheric composition.

“We want to know the iron content of the surface, the water content of the rocks and clay minerals and the abundance of non-silicate materials such as carbonates and nitrates,” says Jean-Pierre Bibring, OMEGA PI from the Institut d’Astrophysique Spatiale, Orsay, France

SPICAM Ultraviolet and Infrared Atmospheric Spectrometer

SPICAM is determining the composition of the atmosphere from the wavelengths of light absorbed by the constituent gases. An ultraviolet (UV) sensor will measure ozone, which absorbs 250-nanometre light, and an infrared (IR) sensor will measure water vapour, which absorbs 1.38 micron light.

“Over the lifetime of the mission, we should be able to build up measurements of ozone and water vapour over the total surface of the planet for the different seasons,” says Jean-Loup Bertaux, SPICAM PI from the Service d’Aeronomie du CNRS, Verrières-le-Buisson, France

Planetary Fourier Spectrometer (PFS)

The PFS is determining the composition of the Martian atmosphere from the wavelengths of sunlight (in the range 1.2-45 microns) absorbed by molecules in the atmosphere and from the infrared radiation they emit.

In particular, it will measure the vertical pressure and temperature profile of carbon dioxide which makes up 95% of the martian atmosphere, and look for minor constituents including water, carbon monoxide, methane and formaldehyde.

ASPERA Energetic Neutral Atoms Analyser

ASPERA is measuring ions, electrons and energetic neutral atoms in the outer atmosphere to reveal the numbers of oxygen and hydrogen atoms (the constituents of water) interacting with the solar wind and the regions of such interaction.

Constant bombardment by the stream of charged particles pouring out from the Sun, is thought to be responsible for the loss of Mars’s atmosphere. The planet no longer has a global magnetic field to deflect the solar wind, which is consequently free to interact unhindered with atoms of atmospheric gas and sweep them out to space. “We will be able to see this plasma escaping the planet and so estimate how much atmosphere has been lost over billions of years,” says Rickard Lundin, ASPERA PI from the Swedish Institute of Space Physics in Kiruna, Sweden

MARSIS Sub-Surface Sounding Radar Altimeter

MARSIS will map the sub-surface structure to a depth of a few kilometres. The instrument’s 40-metre long antenna will send low frequency radio waves towards the planet, which will be reflected from any surface they encounter. For most, this will be the surface of Mars, but a significant fraction will travel through the crust to be reflected at sub-surface interfaces between layers of different material, including water or ice.

Propulsion
Most of the energy needed to propel Mars Express from Earth to Mars was provided by the four-stage Soyuz/Fregat launcher. The Fregat upper stage separated from the spacecraft after placing it on a Mars-bound trajectory. The spacecraft used its on-board means of propulsion solely for orbit corrections and to slow the spacecraft down for Mars orbit insertion.

The main engine on the underside of the spacecraft body (or ‘bus’) is capable of delivering a force of 400 Newtons, which will reduce the speed of the spacecraft by 2880 kilometres per hour in 30 minutes (400 Newtons is equivalent to the force needed on Earth to suspend a 40 kilogram weight above the ground). Eight attitude thrusters attached to each corner of the spacecraft bus can deliver 10 Newtons each.

Electrical power
This is provided by the spacecraft’s solar panels which were deployed shortly after launch. When Mars is at its maximum distance from the Sun (aphelion), the solar panels are still be capable of delivering 650 Watts which is more than enough to meet the mission’s maximum requirement of 500 Watts, equivalent to just five ordinary 100 Watt light bulbs! When the spacecraft’s view of the Sun is obscured by Mars during a solar eclipse, a lithium-ion battery (67.5 Amp hours), previously charged up by the solar panels, takes over the power supply.

Communications
The circular dish attached to one face of the spacecraft bus is a 1.6-metre diameter high-gain antenna for receiving and transmitting radio signals when the spacecraft is a long way from Earth. When it is close to Earth, communication is via a 40 centimetre-long low-gain antenna, which protrudes from the spacecraft bus.

Data storage
As scientific data cannot be transmitted back to Earth as soon as it is collected, they will be stored on the spacecraft computer until transmission is possible. The computer has 12 Gbits of solid-state mass memory.

Control
The on-board computers control all aspects of the spacecraft functioning including switching instruments on and off, assessing the spacecraft orientation in space and issuing commands to change it.

Navigation
Three on-board systems help Mars Express maintain a very precise pointing accuracy, which is essential to allow the spacecraft to communicate with a 34-metre dish on Earth up to 400 million kilometres away. They are two star trackers; six laser gyros; two coarse Sun sensors.

Thermal control
The spacecraft must provide a benign environment for the instruments and on-board equipment. Two instruments, PFS and OMEGA, have infrared detectors that need to be kept at very low temperatures (about -180°C). The sensors on the camera (HRSC) also need to be kept cool. But the rest of the instruments and on-board equipment function best at room temperatures (10-20°C).

The spacecraft is encapsulated in thermal blankets made from gold-plated aluminium-tin alloy (which gives it that distinct “Doritos Nacho Cheese” look, in the first picture), to keep the interior at 10-20°C. The instruments that need to be kept cold are thermally insulated from the warm interior of the spacecraft and attached to radiators that lose heat to space, which is very cold (about -270°C).

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Even if the Mars Express was limited to the stunning pictures it has already sent back to earth, I would be happy. But this craft is just beginning its primary mapping mission, and the scientific data it sends will fire research and discovery for many years to come.

Three cheers go out to the ESA, for a job very well done.

Also posted at VERMONT SPACE
(ESA sez “Oh yeah!”)

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About Bennett Dawson