TIM FURNISS / LONDON
Armed with a suite of scientific instruments, a fleet of five international spacecraft will be on its way to the Red Planet by late June
This summer, five spacecraft will be heading for Mars, arriving in late 2003 and early 2004 to search for conditions that may be conducive to life. They will represent the largest armada of spacecraft heading to one planet at the same time.
The European Space Agency (ESA) launched its first mission to the Red Planet, the Mars Express orbiter, on 2 June. Together with a piggyback craft, the UK's Beagle 2 lander, the Mars Express is due to arrive in December this year. NASA is also launching two Mars Exploration Rovers (MER) in June, due to land in 2004.
The fifth craft, the Japanese Institute of Space and Astronautical Sciences' Nozomi, was launched in 1998, aiming for Mars orbit in 1999. But a thruster fault made the journey more protracted, and Nozomi is set to reach the planet in early 2004.
The focus of this onslaught of Martian expeditions is simple - the search for water and "life". Life, as we understand it, requires water. There is geological evidence that water once flowed over the Mars surface and measurements by NASA's Mars Odyssey orbiter show it might still exist beneath the surface.
"Meteorites from Mars that have been found on Earth show clear evidence that conditions appropriate to life did exist on the planet," says Professor Colin Pillinger, the UK Open University scientist spearheading the Beagle 2 effort. But the Mars "life" sensation sparked by NASA in 1996, when scientists claimed to have found evidence for ancient microbacterial life in a chunk of meteorite, was controversial. It was also assumed the meteorites came from Mars.
"We cannot be sure that organic matter found in the meteorites is the remnant of organisms that lived on Mars and not due to contamination on Earth," says Pillinger. "We need to repeat the experiments on rocks that never left the Red Planet." That is the Beagle lander's job.
Although none of the Mars craft will be able to detect life directly, they will offer information about the planet's atmosphere, chemistry, geology and environment. The main objective of the Beagle and the MERs is to confirm conditions were at one time conducive to life. The orbiters will support the global search for water.
Spacecraft capabilities
The 540kg (1,190lb) Nozomi has a suite of 14 instruments, some of which are studying interplanetary and solar radiation. Others include an imaging camera that will also take the first close-up images of the Martian moons Deimos and Phobos since the Viking orbiters in 1976. Instruments will measure magnetic, radiation and dust properties, which will indicate historic or current atmospheric conditions, volcanic activity and water circulation.
ESA's first Mars spacecraft, the 1,110kg Mars Express, will perform similar observations. Carrying the UK's Beagle 2 as a piggyback payload, it was launched on a Soyuz Fregat booster operated by Starsem from the Baikonur cosmodrome on 2 June.
Five days before arrival at Mars, Beagle 2 will be deployed for its independent landing mission. Mars Express will be inserted into an initial capture orbit by its retro-propulsion system and later will be moved into a near-polar orbit, with an inclination of 86° and eventual 10,107 x 298km (6,280 x 185 miles) parameters, with an orbital period of 6.7h.
Mars Express will carry seven instruments. The subsurface-sounding radar altimeter will be able to map the substructure to a depth of a few kilometres. "We should be able to measure the thickness of ice or permafrost or determine whether there are layers of sediment sitting on top of other materials," says principal investigator Giovanna Picardi.
A 10m (32ft)-resolution, three-dimensional camera will photograph selected targets within its swath simultaneously - including the Beagle 2 lander - with a 2m resolution, revealing the topography of selected targets on Mars in full colour. The visible and infrared mineralogical mapping spectrometer will build a map of surface composition in 100m squares, particularly the iron and water content of the surface, rocks and clay minerals and non-silicate materials, such as carbonates and nitrates.
Three other Martian atmosphere-measuring instruments will probe for gases and will measure atoms to "estimate how much atmosphere has been lost over the years", says Rickard Lundin of the Swedish Institute of Space Physics. A radio science experiment will measure variations in the gravitational field.
The diminutive 60kg Beagle 2 lander, protected by a heatshield, will enter the largely carbon dioxide atmosphere - 100th the density of the Earth's atmosphere - at 20,000km/h (12,420mph). When the speed has been reduced to 1,600km/h, parachutes will deploy and large gas bags will inflate to protect the lander as it bounces across the surface of Mars at Isidis Planitia, at 10.6°N, 270°W, on 25 December.
When the Beagle 2 comes to a halt, the gas bags will be released and its clam-like outer casing will spring open, deploying solar panels and a robot arm holding nine instruments. This is called the Payload Adjustable Workbench and includes the Mole, which will crawl across the surface at a rate of 1m/6s. It will burrow under rocks to collect samples in a cavity in its tip, or can be positioned to burrow vertically to a depth of 1.5m.
The UK government, led by science minister Lord Sainsbury, the University of Leicester and several participating companies, including prime contractor Astrium, have provided support for Beagle 2.
After landing
"The first few days will be spent running pre-programmed sequences, imaging the site [with two stereo cameras] and running the environmental sensors, preparing for when the lander will start doing dedicated rock and soil analysis," says Mark Sims, lander manager at Leicester University. Communications from Beagle will be relayed back to Earth via Mars Express.
Beagle 2's gas analysis package comprises 12 ovens which will heat rock or soil samples gradually in the presence of oxygen. The carbon dioxide generated at each temperature will be delivered to a mass spectrometer that will measure its abundance and the ratio of carbon-12 to carbon-13. A variety of environmental sensors on the lander will measure atmospheric pressure, air temperature, wind speed and direction, ultraviolet radiation and dust fall-out, having measured pressure during the descent.
The cameras will be used to provide a three-dimensional model of the area within the reach of the robot arm, which will be used to guide the instruments into position alongside target rocks and soil. A corer/ grinder consists of a drill bit which can be moved over the surface to remove weathered material or positioned in one spot to drill a core of pristine sample. A microscope will pick out features a few thousandths of a millimetre across on rock exposed by the grinder and will determine its texture and nature. A spectrometer will investigate the mineral content by irradiating exposed rock and soil with gamma rays emitted by cobalt-57 and measuring the reflected gamma rays. An x-ray spectrometer will measure the elemental composition of rocks by bombarding exposed surfaces with x-rays from four iron and cadmium radioactive sources, to help estimate the age of rocks.
The objective of NASA's twin MERs - both to be launched this month - is to determine "whether life ever arose on Mars". They will characterise the planet's climate and geology to "prepare for human exploration", says NASA. The craft will also investigate the use of soil and rock as potential in-situ resources, as well as test the operation of wheeled vehicles.
The landings next January will be targeted at the Gusaev Crater at 15°S and Meridiani at 2°S. A final decision on which MER will land at which site will be made about a month before arrival. "In choosing where to go, we need to balance science value with engineering safety considerations," says Ed Weiler, NASA's associate administrator for space science.
Principal investigator Steve Squyres adds: "Both sites show powerful evidence of past liquid water, but in very different ways. They are fabulous sites and they complement each other because they are so different." Both solar-powered craft are designed to operate for about 90 days. Each 1,060kg MER comprises the 185kg rover and a cruise stage, entry, descent and landing system based on previous Mars Pathfinder and Viking lander technology.
The aluminium honeycomb/carbonfibre aeroshell entry vehicle provides the heatshield, a parachute and pre-landing retro-rockets, which will position the MERs at a "dead stop" 10-15m above the surface. Vectran airbags will inflate immediately, protecting the MERs encased in their composite/metal "shells", while the spacecraft bounces to a stop on the surface.
Each "petal" of the shell has a rocket motor that can place the craft into an upright position whatever the orientation of the lander after the balloon release. The petals can drag the airbags toward the lander to get them out of the path of the rover if required and will later be opened and ramplets deployed to allow the MER to begin its journey to the surface.
The MER is equipped with electronics, computer and a temperature control system to cope with the contrasting +22°/-99°C temperatures expected at the landing sites. Its six wheels, each with an individual motor and delicate suspension system, will enable the MER to make a full 360° turn in place and tilt to 45° in any direction without overturning. A multi-panel solar array provides 140W of electricity and there are low- and high-gain steerable antennas that will transmit directly to NASA Deep Space Network dishes on Earth.
Atmosphere analysis
A 1.4m-high mast assembly will act as a periscope for instruments mounted inside the rover for thermal reasons, enabling the 360°-pan, high-resolution, colour CCD stereo-pair panoramic camera, and hazard and navigation cameras, to get the best views of the terrain. A miniature thermal emission spectrometer, fixed at the base of the mast, will measure temperature, water vapour and dust content.
The MER's robot arm will manoeuvre other instruments for close-up inspections of the surface samples. A microscopic imager, Mossbauer spectrometer, alpha particle spectrometer, magnet array and rock abrasion tool (RAT) will be manoeuvred for close inspections of the surface samples. The RAT, which holds an ingenious self-cleaning brush, is a powerful grinding tool that can create a 45mm diameter, 5mm deep hole in a rock, providing samples for the instruments to investigate.
Depending on the success of this latest armada to Mars, larger rovers and other landers are planned for the future, including a Martian sample-return mission, once scheduled for 2005 but now more likely to take place after 2012. Then, budgets and political will permitting, it will be time for the big one - a human expedition to Mars.
Source: Flight International
