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One of our rare visits to another world is about to begin. If all goes
well, the American Mars Observer spacecraft will enter orbit around Mars
next week. Its primary mission, to map the planet and study its atmospheric
and topographic variations, starts in about three months, and will last
one Martian year or 687 Earth days.

Space scientists are hoping that the arrival of the Mars Observer will
herald a new chapter in Martian exploration, after a long period in the
doldrums. Researchers from more than 20 nations are already preparing to
take advantage of future launch windows between now and the year 2000, confident
that they can meet the budgetary constraints imposed by their political
masters by using more off-the-shelf technology and by pooling scarce resources.
Numerous suggestions for follow-up missions, stretching well into the next
century, are already in the pipeline.

Even though interest in the Red Planet is greater than ever, cutbacks
caused by the world recession will ensure that any planetary exploration
during the second half of the 1990s is very different from the multimillion
dollar extravaganzas of past decades. The next mission, a Russian-led project
known as Mars 94, has already been scaled down, setting a precedent for
smaller, less expensive studies of Mars. The Russians intend to launch a
second craft in 1996, when Japan’s first orbiter will also lift off, and
the new, less ambitious American programme – probably in collaboration with
Europe – should see a series of stations on the surface of Mars early next
century.

Launch opportunities to Mars occur only about once every 780 days.
During this period our planet’s faster orbital velocity, because it is closer
to the Sun, allows it to catch up with and pass Mars on an inside track.
However, the highly elliptical Martian orbit means that the gulf between
the two planets as they pass can vary between 54 million and 97 million
kilometres. A spacecraft can take anything between about 7 and 11 months
to reach Martian orbit. With a limited number of opportunities to visit
Mars, scientists are understandably eager to make the most of each launch
window.

Much has been learned about Mars since the first spacecraft flew past
the planet in 1964. The American Mariner 9 orbiter, launched in 1971, and
the two Viking probes, launched in 1975, were notable successes, sending
back thousands of pictures from orbit and landing two scientific laboratories
on the surface. However, as any explorer will recognise, information from
two landing sites provides a far from complete picture of a world which
has a surface area equivalent to all the landmasses on Earth.

But the very success of the Viking probes resulted in almost two decades
of inactivity. With little political support for sending people to Mars,
there was no urgency to send robot scouts. Perhaps it would have been a
different story if the Viking landers had discovered evidence of life in
the Martian dust. But the ‘canals’ dug by intelligent beings to irrigate
‘vegetation’, which the American astronomer Percival Lowell was convinced
he had observed, turned out to be figments of his imagination. To the best
of our knowledge, there is no life on Mars. Despite this, some researchers
still hold onto their dreams that Mars, the planet most like our own, may
one day be colonised by humans.

Frozen wasteland

Any life form on Mars, human or otherwise, would need to be well prepared
for its hostile environment. With a diameter at the equator of 6794 kilometres,
about half that of Earth, Mars is a freezing barren desert with huge dry
canyons and towering volcanoes. At the surface, gravity exerts around one-third
the pull it does on Earth. The polar caps are thought to consist of frozen
carbon dioxide, and water is scarce. Even in midsummer near the equator,
temperatures rarely rise above zero. The atmosphere is very thin – at just
6 millibars of pressure it is 160 times less than on Earth – and consists
mainly of carbon dioxide. Yet, every Martian year, heat from the distant
Sun stirs up the tenuous gases, generating dust storms that may engulf the
entire planet. There is even a planet-wide ozone hole, so that the surface
is bathed in deadly ultraviolet radiation. Spectacular it may be, but the
reality of Mars no longer inspires the world’s governments to dip deep into
their rapidly emptying wallets.

It was not always like this. When the Mars Observer mission was conceived
in the mid-1980s, NASA was looking forward to the 1990s as a decade of Mars
exploration. In July 1989, President George Bush fuelled this enthusiasm
by announcing his Space Exploration Initiative, and proposing that the US
should aim to land the first humans on Mars in 2019 – the 50th anniversary
of Neil Armstrong’s ‘giant leap for mankind’. The Mars Observer, launched
in September last year, was to pave the way with a comprehensive global
survey, mapping the planet at high resolution from orbit at an altitude
of 378 kilometres, and taking a closer look at its climate, geology and
geophysics. The plan was to follow this mission with a series of robot
landers and rovers, and the programme’s ambitious climax would have been
a return mission to bring back a piece of Martian rock before the year 2000.

Times have changed. Far from exuding enthusiasm for another multibillion
dollar space adventure, Congress pulled the rug from beneath the presidential
initiative. After several years of minimal budgets, the politicians refused
to allocate any funds for the fiscal year 1993. As far as the Clinton administration
is concerned, the thought of allocating vast sums of public money to a
human expedition to Mars is tantamount to committing political suicide.

However, scientists around the world are still determined to make the
most of what funds are available. First in the pipeline is the Russian-led
Mars 94. The 6-tonne craft should reach Mars in August 1995, about 10 months
after liftoff. It will carry an array of instruments designed and paid for
by many nations. Apart from carrying out a survey of the planet, the orbiter
will send back information relayed from two small landing stations and two
penetrators which will be released from the craft between three and five
days before it goes into orbit around Mars.

Touchdown

When they hit the surface, the 33.5-kilogram landers will orient themselves
by opening out four panels laden with instruments. NASA is paying $1.5
million to put soil oxidation experiments on both stations, which should
reveal more about the unusual oxidising agents that were found by the Viking
probes. Other instruments will include a TV camera to send back pictures
of the surrounding terrain, a magnetometer to measure the magnetic field
of the planet and local rocks, and a spectrometer to study rock composition.
The stations will also carry various sensors to measure the atmosphere
and climate, including an optical depth sensor to assess the clarity of
the atmosphere by measuring dust levels within it. Unfortunately, the elliptical
orbit of Mars 94 is not ideal for receiving information from the surface
stations. So Mars Observer, which has a circular polar orbit allowing it
to receive transmissions from almost anywhere on the Martian surface, will
be used in preference if it is still working in 1995. If all goes well,
the two stations should operate continually for at least two years.

Mars 94’s dart-shaped penetrators will plunge into the rocky Martian
desert at around 5 kilometres per second. On impact, the nose and tail sections
will separate. Scientists hope that the impact will drive the penetrators
to a depth of between 6 and 8 metres. Then information about soil water
content and chemical composition will be relayed to the cone-shaped upper
section. An antenna for communication with the orbiter will send back data
from the penetrators and their TV cameras.

The original plan was to send two identical Soviet spacecraft during
the 1994 launch window, each carrying a balloon, two small penetrators,
two surface stations and a rover, but financial difficulties after the
break-up of the Soviet Union delayed work and led to cutbacks. Even now,
despite cash injections worth millions of dollars from the West, notably
France, the US, the European Space Agency (ESA) and Germany, the future
of the Mars 94 project is still uncertain.

Even greater uncertainty surrounds Mars 96, if only because its departure
is further in the future. But if all goes well, Russia’s second orbiter
will carry a balloon and roving vehicle to explore the Martian wastes. Design
of the balloon, by the Russians, the French space agency CNES and the California-based
Planetary Society, is already well under way. The aim is to inflate it during
descent using attached cylinders of compressed gas. This has only been attempted
once before, during the successful Soviet-French Vega mission to Venus in
1985-86. The compacted fabric will swell into a gigantic helium-filled cylinder,
42 metres long and 12 metres in diameter. Warmed by the rising Sun and by
energy reradiated from the Martian surface, the balloon and its gondola,
laden with instruments, will float at up to 3 kilometres over the rugged
terrain during the day, sending back close-up pictures and weather data.

During the freezing night, the balloon will descend to within 50 metres,
where its titanium ‘snake’ – a segmented tail packed with instruments –
will trail along the surface. This will measure rock composition, radioactivity,
hardness and temperature, and use radar scanning to collect information
about surface conditions. When the snake’s internal temperature reaches
-60 °C it switches to ‘sleep’ mode to conserve the precious lithium
battery used to power its instruments. Data collected during the night will
be stored and then transmitted the next day to the orbiting spacecraft via
the gondola. Russian scientists hope the battery will last up to 14 days.

The Planetary Society is also helping to develop the Russian-designed
Mars 96 rover, which has already proved itself on some of the Earth’s most
inhospitable terrain. Initial tests in the volcanic wastes of Kamchatka,
in the eastern part of the former Soviet Union, were last year followed
by extensive trials in Death Valley in California’s Mojave Desert. Each
of the rover’s six conical wheels, which taper towards the centre of the
vehicle to increase stability, has its own drive system. In addition, the
front and rear segments of the chassis are hinged, allowing them to extend
independently, establish a firm grip, and then pull the rest of the rover
along behind. Scientists from NASA’s Ames Research Center in Moffett Field,
California, are now developing hardware so they can drive the rover using
a video link and virtual reality techniques. The aim is to produce a vehicle
with a top speed of 0.5 kilometres per hour and a maximum range of 100 kilometres.

Meanwhile, engineers at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena
are interested in combining the exploration talents of their 7-kilogram
rover, Rocky IV, with its large Russian cousin (Technology, 12 September
1992). There is even a possibility that Mars 96 may carry tiny insect-like
rovers developed by researchers at the Massachusetts Institute of Technology.
These machines, weighing around 1 kilogram and using legs rather than wheels,
could act as scouts or extra sensors for the main rover.

By 2003 NASA hopes to have landed a series of surface stations of its
own on Mars, with the aim of comparing data from several sites on the planet.
Last year, NASA administrator Daniel Goldin requested a new approach to
planetary exploration. The Discovery programme is the administration’s response,
with each Discovery craft restricted to a three-year development period
and a budget of $150 million. NASA hopes to obtain funding for the first
of the Discovery missions to Mars, called Pathfinder, in its 1994 budget.
If successful, Pathfinder will depart for Mars two years later.

Like any craft landing on the planet’s surface, it faces a daunting
survival course before it can begin operation. Pathfinder will enter the
thin Martian atmosphere at a 20 degrees angle, speeding at 6.3 kilometres
per second towards an elliptical target area measuring 100 kilometres by
25 kilometres. Most of the deceleration from 22 000 kilometres per hour
to 900 kilometres per hour will be achieved through aerobraking – slowing
caused by friction between the blunt heat shield of the craft and the atmosphere.
Next, the aeroshell (a casing that protects the craft during this first
phase) is jettisoned, and a parachute slows the craft to around 125 kilometres
per hour. One second before impact, air bags inflate to cushion the landing.
Even so, the impact forces will be around 50 G.

The current JPL design consists of a tetrahedron, three sides of which
would open up like petals to right the lander regardless of its landing
position. Sensors on board will measure atmospheric conditions such as
temperature and humidity, and take measurements of surface material. A
360-degree panoramic view will be relayed to Earth, and the station may
also carry a seismometer. Wider-ranging studies could be made by the tiny,
six-wheeled Rocky IV.

A new generation

Pathfinder is so named because it is seen as the forerunner of a family
of 12 to 16 small landers which could make up NASA’s Mars Environmental
Survey (MESUR) by early next century. The administration hopes to deploy
the network of stations in three consecutive launch windows between 1999
and 2003. But NASA scientists, who are already struggling to keep within
the budgetary framework laid down by Goldin, are being forced to re-examine
the programme. According to Carl Pilcher of NASA’s Solar System Exploration
Division, the administration may have to settle for a combination of full-size
landers and separate, smaller weather stations. ‘We could still do good
science with about six landers,’ says Pilcher, ‘but this (small number)
is not very likely considering the amount of interest out there.’ One solution
may be to take advantage of a similar proposal currently under consideration
by the ESA.

Earlier this year, the ESA proposed its Marsnet programme to send three
landers to Mars. However, the agency cannot afford to go ahead without
collaboration, so integration into MESUR would benefit both the ESA and
NASA. The Marsnet craft closely resemble those planned for MESUR in the
systems they use for braking, atmospheric entry and landing, but the ESA’s
early designs suggest that the lander may comprise a cylinder resting on
a wide base. Power supply would come from solar cells on its upper surface,
and the scientific payload would include spectrometers to analyse surface
material, cameras, a seismometer and meteorological sensors.

ESA scientists have already chosen the Tharsis region on Mars for intensive
study because volcanoes there suggest it may be an area of considerable
scientific interest. The Tharsis plateau surrounds four of the largest volcanoes
in the Solar System, including the magnificent Olympus Mons, standing 27
kilometres high and 600 kilometres in diameter.

A Russian-built tethered mini-rover could also be used within a 12-metre
radius of the European landers, taking close-up pictures and soil measurements.
Data from both the European and American stations could be collected and
sent back to Earth via a data relay satellite which is currently under
study by the Italian company Alenia Spazio.

Pondering the next steps

Although the Marsnet proposal was rejected as premature at a recent
evaluation of candidates for ESA’s second medium-cost science mission, it
stands a good chance when the science committee makes its next choice in
two years. But even then, the ESA would not be able to launch a craft before
1999.

If the world’s planetary scientists get their way, the period from 1996
onwards promises to be a busy time for Martian exploration. The Japanese
Institute of Space and Astronautical Science near Tokyo, intends to launch
its first Mars probe, known as Planet-B, in August 1996. The main task of
the 300-kilogram orbiter will be to examine the interaction between Mars
and the solar wind. Information from previous spacecraft has been sparse,
but the Martian magnetic field seems to be so weak that charged particles
from the Sun penetrate deep into the atmosphere and even drive a considerable
part of the atmosphere away from the planet.

Like many other nations, the Japanese are still pondering their next
steps on the road to Mars. Certainly ‘intelligent’ rovers to wander the
barren deserts, collect specimens, and even return samples to Earth, are
under consideration by most space powers. Scientists in France and the ESA
are already working on the design of a nuclear-powered rover. Meanwhile,
in the US, NASA has received proposals for other small Discovery-class orbiter
missions.

One of the most original ideas comes from a group of scientists at the
Ames Research Center. They want to build a series of small landers, similar
to the Surveyors which so successfully photographed the lunar surface in
the 1960s. These would be able to take 100-metre hops around the Martian
wilderness, collecting pictures and data from a variety of sites within
the same locality.

Russian scientists have recently announced plans to fly a return mission
to Phobos, the larger of Mars’s two moons, in 1998 or 2003. The Russians
argue that their proposed mission would provide an excellent test-bed for
the technology needed to complete a similar trip to bring back a sample
of the planet’s own surface. The low gravity conditions on Phobos, which
is only about 23 kilometres in diameter, would mean that atmospheric entry,
soft landing and returning the spacecraft would not pose the problems that
would be faced on Mars itself.

Other innovative approaches to Martian exploration were aired in May
at the Case for Mars 5 conference at the University of Colorado. Among the
proposals for launch during the first half of the 21st century was the
Mars Aerial Platform, described by Robert Zubrin of Martin Marietta Astronautics,
an engineering company based in Denver, Colorado. He suggested releasing
as many as eight balloons into the Martian atmosphere from one spacecraft.
Taking advantage of the planet’s 60 kilometre per hour winds, the fleet
of balloons could circle the planet once every 10 to 30 days, making a detailed
survey of its sand dunes, volcanoes, dry river beds and polar ice caps.

How realistic is all of this? Certainly, landing a human on Mars is
technically feasible, but estimates of the cost range from $50 billion
to $500 billion – up to 20 times the cost of the Apollo Moon missions.
So the chances of landing humans on Mars by 2019 seem small, given the current
economic and political climate. There are still complaints that the missions
planned for the rest of this decade have overlapping objectives. As Jacques
Blamont, chief scientist at CNES, puts it: ‘All the world’s space agencies
are trying to do the same thing.’ But Roger Bourke from the Mars Advanced
Missions Office at JPL sees that this could be an advantage. He exemplifies
the renewed optimism among planetary scientists. ‘There’s worldwide interest
in Mars right now,’ he says. ‘Real money is being spent despite tough times.
If we could pool everybody’s money, we could do an enormous amount and avoid
unnecessary duplication.’

An important step on the road to rationalisation was taken at a workshop
in Wiesbaden, Germany, in May. There, representatives of the world’s space
agencies decided to form an international Mars exploration working group
to produce a strategy for the exploration of the Red Planet after the
year 2000. For the first time in 30 years of Martian exploration, the agencies
have agreed to coordinate their future plans. It now remains to be seen
whether the politicians will provide the support and funding needed to continue
exploring our intriguing planetary neighbour.

Peter Bond is a freelance writer. His latest book Reaching for the Stars
was published in July by Cassell, price £15.99.