People's Democracy

Rovers On Mars: Anyone Out There?

  Raghu

AN important milestone in space exploration was reached on January 4 when the American space agency NASA’s mobile robotic probe, named Spirit, successfully landed on Mars and started sending back spectacular images of the red planet. More than two-thirds of all attempts to land probes on Mars have miscarried one way or another, and NASA’s success was further highlighted by the recent failure of the European Space Agency (ESA) mission’s roving platform Beagle-2, which was to have landed on Mars on Christmas day, to send back even a “landed safely” signal leaving everyone wondering about its fate.

The present Mars mission by NASA, costing all of 800 million dollar (Rs 3840 crore) is the latest of several endeavours to explore Mars undertaken over the past three decades or more. Apart from early fly-by attempts, NASA’s Viking missions landed two stationary probes on Mars in the early ‘70s but subsequent US attempts were plagued by errors and misfortune, as indeed have most efforts by other space-faring nations, earning for Mars the nickname “the death planet”.

This time, if all goes to plan, Spirit --- so named by a third standard student who won a “name the rovers” contest --- will be joined by a second rover, named Opportunity, on January 25 but at a totally different location on the other side of Mars, giving scientists an opportunity to study two quite dissimilar terrains on Mars. 

Scientists are eagerly awaiting the information from this mission which has been described by Steve Squyres, principal investigator for the Mars Exploration Rovers project, as “humanity’s first great voyage of exploration of this century”. The excitement can be understood since the goal of the mission is to study the presence and role of water on Mars. Scientists are now fairly certain that Mars has a substantial quantity of water trapped in its soil and that the planet once had plenty of water. The question really is, how much water was there and, perhaps more important, how long was it there? If sufficient water was there, life may have begun and if the water was there long enough, life could have become self-sustaining.           

Answers to these questions could, therefore, also perhaps provide some answers to that eternal and profound question: is there life outside Earth? The only life humankind knows is that on Earth and, if life is discovered on Mars, a Pandora’s box gets opened. Going from life on one planet to life on two is not just an increment of one: it immediately opens up the possibility of life in innumerable places in the universe and would pronounce unequivocally, once and for all, that WE ARE NOT ALONE!

THE MISSION

The Spirit was boosted off Earth on a Boeing Delta-2 rocket which took seven months to complete a 485 million kilometre voyage to Mars.

The Spirit, mounted on a landing craft or lander, was then released from the rocket to descend through the Martian atmosphere in a terrifying 6 minutes at speeds close to 20,000 kmph, its heat shield acting as a brake to slow the craft down while also protecting it from the extreme high temperatures caused by the friction.

When the craft was about 10,000 metres above the Martian surface, a supersonic parachute was deployed for the last 2 minutes of its descent. The heat shield was then jettisoned and Spirit moves down a tether or rope made of a special synthetic material called Zylon thus making room for its rockets to fire for accurate positioning of the craft and to allow for deployment of the airbags which will cushion its landing.

A camera aboard Spirit then took photographs of the surface below to locate the best landing spot and fire its transverse or horizontally-oriented rockets for safe landing avoiding big sharp rocks which could puncture the airbags leading to damage to the craft on landing (a possible cause for the Beagle’s failure). Similarly, an on-board radar kept taking soundings or readings of the distance to the Martian surface as Spirit descended, based on which retro-rockets were fired vertically to control descent speed.

Once the right position and descent speed were determined, the airbags inflated and Spirit left its backshell which stayed attached to the parachute.  From this point on, an UHF (ultra high frequency) antenna on Spirit started transmitting pre-coded tones conveying specific information on flight status to the orbiting Mars Global Surveyor spacecraft which was timed to pass overhead at precisely this time. This link to the Mars Surveyor enabled Spirit to pass on additional information to the orbiter which then relayed the same to Earth, the first time such relay information-passing had been achieved.

This achievement was another tribute to the precision of the mission since only 7 minutes were available for such a linkage, with the orbiter due to set below the Martian horizon after this period.

The mission as a whole has been characterised by a very high degree of precision which has set an exemplary standard for all future missions. The final position of the spacecraft above the Martian atmosphere before it commenced its descent was within 200 meters of the original target despite the long journey and the numerous uncertainties along the way. This was achieved by, and have in turn contributed to, tremendous advances in navigation methods and computer software, measurement systems based on radio signals linked with Deep Space Network (DSN) of antennae on Earth located at 120 degrees intervals, and precise calculations of Mars’ and Earth’s tilts, revolutions around its own axis and orbits around the sun.   

The rover, protected by the lander structure and the airbags, must have bounced several times perhaps as high as a three or four-storeyed building, and then rolled maybe as much as 1 kilometre across the Martian surface before it came to a complete stop, these last being the only imprecise and unpredictable manoeuvers of the Mission.

Despite this lack of exactness at the fag end of an otherwise high-precision mission, this method of landing the probe was worked out and successfully tried during the 1997 Pathfinder mission in preference to the technique used in earlier missions to the Moon and to Mars, involving rockets, guidance and control systems and complex manoeuvers all with very small margins of error.

As it turned out, the landing was perfect and the dramatic first photographs showed a fairly even terrain surrounding the landing site with relatively small rounded rocks, ideal terrain for the rover’s explorations. The airbags deflated and detached, the three petal-like shields covering Spirit on the lander opened out. 

Once all checks are complete, and mission control is fully satisfied with the status in four to five days after the landing, Spirit will detach itself  from the lander and commence its exploratory movement along the Martian surface for a targeted 90 days. 

ROVERS AND SEARCH FOR WATER

Both Spirit and its twin, Opportunity, are equipped with a high-resolution panoramic camera and an associated infra-red camera for identifying minerals nearby. Pictures from both these cameras will be used by controllers to identify spots or objects for closer examination by the rover.

For such close observations, the rovers’ robot arm carries microscopic cameras, two spectrometers to measure the chemical composition of selected samples and a rock abrasion tool or RAT which will grind selected rocks to reveal their interior structure and composition.

The rovers are solar-powered and fully mobile, with six independently steerable wheels, stereoscopic vision and powerful computer software to help it move around even when it is out of contact with ground controllers. The rovers are programmed and equipped to avoid and go around obstacles larger than 10 inches high and simply go over smaller objects. While NASA’s earlier robotic probe on Mars, the Sojourner, sent to Mars on the 1997 Pathfinder mission (also covered in these columns) was relatively small and rather cute, these rovers are about 8 times as large weighing in at about 400 kg.  

Commands and information will be beamed directly to and from the rovers during relatively short communications sessions during the start of each Martian day. Scientific data gathered by the rovers will be relayed back to Earth twice each afternoon via radio links with the Mars Global Surveyor and the Mars Odyssey spacecraft currently orbiting the planet.

The landing sites for Spirit and Opportunity were selected from a list of over 150 potential locations. The assessment was made keeping in mind the mission’s water-centred objectives of study, and based on photographs and other available data on Mars.

Spirit landed in the extensive Gusev Crater, 15 degrees south of the Martian equator. The crater has what is fairly surely reckoned to be a large dried up river bed leading into it, leading to the probability that the crater was once a lake. If so, water must have been standing for relatively extended periods of time, leaving sediments which would have preserved and therefore represent an environmental history of the planet.

Opportunity is slated to land in quite a different terrain, 5 degrees south of the Martian equator on the other side of Mars. This site is known to have a high concentration of a substance known as grey haematite or iron oxide which is usually associated with the geological action of liquid water on minerals.

By doing such geological studies, the rovers would be acting, in the words of one NASA scientist, as “a time machine to take us back into the past and to tell us was water there long enough and perhaps warm enough to have supported life.”

DIFFICULTIES OF SPACE EXPLORATION

NASA’s Mars Exploratory Rovers mission and the successes it has achieved even at this early stage, is itself a lesson, for all those nations or groupings seeking to embark on similar adventures, on just how difficult, time-consuming and expensive space exploration is.

Only 12 of the 30 US and Soviet/Russian Mars missions attempted over the past four decades have succeeded. Of eight attempts to land a spacecraft on Mars, only three succeeded, NASA’s twin Viking landers and the Mars Pathfinder. The failure of the European Beagle-2 is fresh in everyone’s memory. Perhaps people have forgotten, or have not registered, the failure of Japan’s Nozomi (hope) mission which sought only to orbit the red planet, not even to land on it, but could not achieve even this limited goal.

Nozomi was scheduled to arrive at Mars in October 1999 but a technical problem in its rockets in December 1998 made it miss the window to transfer to an orbit around Mars. In order to conserve fuel, a new orbital plan was developed including two additional Earth swing-bys to use Earth’s gravity to “sling-shot” it towards Mars timed for it to arrive at Mars in January 2004. But on December 9, 2003, Japan gave up hope on inserting the spacecraft into Mars orbit and allowed it to drift off into space.

Spirit and Opportunity are the result of almost an overhaul of NASA’s Mars exploration programme. Despite the early successes in the ‘70s Viking programme, NASA itself suffered two devastating failures in 1999. The Mars Polar Lander crashed into the planet because of a programming error in the software which resulted to the engine shutting down prematurely and ruining the planned trajectory for a soft landing. More embarrassingly for NASA, the Mars Climate Orbiter burned up in the Martian atmosphere due to an unforgivable error in converting between metric (kg-metre) units and the British (pound-feet) units used even today by the US but less so by the British due to their EU affiliation. An independent investigation commissioned by NASA concluded that both failures were essentially due to overly aggressive development schedules and tight budgets, both major ingredients of NASA’s “faster, better, cheaper” approach to planetary exploration.

Persons occupying exalted positions in India who speak quite lightly of moon-landings and colonies on Mars --- please take note!