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Vol.
XXVIII No. 02
January 11,
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Rovers
On Mars: Anyone Out There?
Raghu
AN
important milestone in space exploration was reached on January 4 when the
American space agency NASAs 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 NASAs success was further highlighted by the recent
failure of the European Space Agency (ESA) missions 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, NASAs 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 humanitys 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
Pandoras 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 Beagles 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 Earths 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 rovers 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 NASAs 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 missions
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
NASAs
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, NASAs twin Viking landers and the Mars Pathfinder. The
failure of the European Beagle-2 is fresh in everyones memory. Perhaps people
have forgotten, or have not registered, the failure of Japans 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 Earths 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 NASAs 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 NASAs 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!
