For nearly 50 years, our civilization has been attempting to send
spacecraft to Mars. By the beginning of the 21st century, only 10
missions out of 33 tries had been a complete success. Journey with us
down the rocky road of Mars exploration.
Mars Polar Lander/ Deep Space 2: Jan. 3, 1999
Slice into a martian polar cap and you might see alternating bands of
color ranging from pristine white to murky orange. These bands are a
record of the ice and dust that have been laid down over time. Like
growth rings of a tree, the alternating layers may help reveal what
environmental conditions were like when they were formed and offer clues
to past climates on Mars. The Mars Polar Lander (MPL) was designed to
unearth these clues by landing on layered terrain near the planet's
south pole.
MPL was scheduled to touch down on the surface of Mars on December 3,
1999. It was to gather images of the icy terrain, as well as probe the
polar cap with a suite of five instruments. The science payload was
called MVACS, Mars Volatiles and Climate Surveyor. Volatiles are
substances that can evaporate easily. At the poles of Mars, carbon
dioxide and water are considered volatiles because they change from
vapor to ice (or visa versa) in one season. MVACS was to study the
surface-to-atmosphere cycle of carbon dioxide and water on Mars by
measuring the amounts of these substances in the atmosphere, in the ice,
and in the soil.
The MVACS package included a Meteorological Package (MET), which was a
weather station; the Surface Stereo Imager (SSI), which would take
multi-color images of Mars; the Thermal and Evolved Gas Analyzer (TEGA),
which would look for water, carbon dioxide, and water-bearing minerals
in the soil; the Robotic Arm (RA), to dig trenches and collect soil
samples for TEGA to study; and the Robotic Arm Camera (RAC), to take
images of the trenches made by the RA.
The lander also carried a camera that would photograph the surface
during descent (the Mars Descent Imager -- MARDI), and a
Light
Detection and Ranging
instrument (LIDAR) built by the Russians to measure dust and haze in the
atmosphere. A
microphone
was aboard to record the sounds of Mars.
Riding piggyback on the Mars Polar Lander was another mission named Deep
Space 2. Two "microprobes" were mounted on the MPL's cruise stage for
release during descent. The probes were designed to use the force of a
hard impact to penetrate up to 2 meters into the south pole of Mars.
Each probe consisted of two parts -- a short cylinder that would remain
above the surface of Mars for radio communications, and a long, thin
cylinder that would plunge underground. The subsurface cylinder
included a temperature sensor, a soil sample chamber, and ice and water
vapor detection equipment. The goal of the Deep Space 2 mission was to
demonstrate the new microprobe technology and its ability to search for
water ice beneath the surface of Mars.
None of the instruments in either mission would have a chance to return
data.
At about 12 minutes before the Mars Polar Lander was scheduled to land,
the spacecraft was healthy and ready to enter the martian atmosphere.
The spacecraft turned its antenna away from Earth, as planned, and it
was never heard from again. Engineers struggled for weeks to find a
radio signal, but without success. MPL's Entry, Descent, and Landing
system underwent extensive scrutiny. Much of the system was inherited
from the Mars Pathfinder mission, but MPL did not inherit the airbag
method of landing. Instead, it was to achieve a pinpoint landing via
retro-rockets and legs, much like the Viking landers did 20 years
earlier. A press release dated March 28, 2000 states:
"… the most probable cause of the failure (of MPL) was the generation of
spurious signals when the lander legs were deployed during descent. The
spurious signals gave a false indication that the spacecraft had landed,
resulting in a premature shutdown of the engines and the destruction of
the lander when it crashed on Mars."
Following the failure of both the Mars Climate Orbiter and the Mars
Polar Lander, NASA conducted an in-depth review of its entire Mars
exploration program. The next lander mission, which was scheduled for
launch in 2001 and carried the Athena Precursor Experiment (APEX), was
canceled. Its spacecraft was a near-twin of the Mars Polar Lander. The
2001 launch window would only see an orbiter, Mars Odyssey, begin a
journey to the Red Planet.
Mars Climate Orbiter: Dec. 11, 1998
In the three years preceding the launch of the Mars Climate Orbiter,
America had successfully lofted several spacecraft into the heavens.
Cassini was on its way to Saturn; the NEAR (Near Earth Asteroid
Rendezvous) probe was closing in on asteroid Eros; and Deep Space 1 was
on target for a flyby of two asteroids and a comet. By 1998, America
had found success at Mars as well. The Mars Pathfinder mission had
placed a rover on the Red Planet, and the Mars Global Surveyor orbiter
would soon begin its mapping operations.
On the heels of these successes came the Mars Surveyor '98 program. It
included an orbiter — the Mars Climate Orbiter, and a lander — the
Mars Polar Lander. They would launch separately, but both shared the
common science goal of studying water on Mars.
Mars Climate Orbiter (MCO) was a weather satellite that was designed to
monitor the daily and seasonal weather patterns on Mars. Just like
weather satellites in Earth orbit, MCO was to take pictures of martian
clouds, look for storms, and monitor winds. It was to gather information
about water vapor and dust in the martian atmosphere, explore climate
processes that trigger dust storms; and search for evidence of past
climate changes.
Two science instruments would do the job. The Mars Color Imager (MARCI)
included a wide angle and medium angle CCD camera to gather daily
images. From these images, scientists would garner a season-to-season
weather portrait of Mars. The other instrument was the Pressure
Modulator Infrared Radiometer (PMIRR). It would scan the planet's thin
atmosphere to measure temperature, water vapor, and dust. This was a
duplicate of the infrared radiometer that flew on the failed Mars
Observer mission.
The Mars Climate Orbiter's initial task was to serve as communications
relay for the Mars Polar Lander (MPL). The plan was that after MPL's
surface operations ended, the orbiter's science mission would begin and
continue for one martian year (687 Earth days). The mission's projected
completion date was December 1, 2004, but it ended much sooner.
On September 23, 1999, MCO fired its main engine to slow its speed for
orbit insertion. Information received from the spacecraft up to that
time looked normal. The engine burn happened as planned and the orbiter
passed behind Mars. Then the nightmare began. Flight controllers could
not find a signal. MCO was not where it was expected to be. A frantic
scan of the sky with the Deep Space Network's giant antennas was met
with silence.
Failure review teams would later find that the problem was "the failed
translation of English units into metric units in a segment of
ground-based, navigation-related mission software." This software was
critical to placing the spacecraft on the correct path for Mars orbit
insertion. The Mars Climate Orbiter should have approached the planet
at an altitude of about 150 km (93 miles). But data indicated that the
actual approach altitude had been much lower — too low for the
spacecraft to survive the stresses and friction in the atmosphere. What
was once a robust spacecraft had become a fireball.
Scientists and engineers comforted themselves with the knowledge that
Mars Polar Lander would be arriving at Mars in a little more than two
months. It was to touch down near the south pole of the planet on
December 3, 1999. But Mars was not ready for visitors.
Nozomi: July 4, 1998
By 1998, Japan’s Institute of Space and Astronautical Science (ISAS) and
its predecessor, the Institute of Space and Aeronautical Science, had
launched several scientific satellites. Nozomi (which means “Hope”)
would be the institute’s first probe to another planet and the first
spacecraft sent to Mars by a country other than the United States and
Russia. It would prove to be a challenging mission.
Nozomi was launched exactly one year after the Mars Pathfinder landing.
Its objective is to study the motion and structure of the martian upper
atmosphere and how it is affected by the solar wind. Knowledge about
the mechanisms of the atmosphere may help scientists solve the mystery
of why Mars lost its liquid water. The orbiter was scheduled to arrive
at Mars in October of 1999, but the 15-month journey stretched to five
years when mission engineers found themselves in a battle to keep the
spacecraft alive.
The original plan was for Nozomi to stay in an elliptical orbit around
the Earth for four months after launch, use two swing-bys of the Moon in
1998 to tweak its elliptical path, and then pass by the Earth in
December of that year for a gravitational boost into a trajectory for
Mars. But a thruster malfunctioned and the boost was not enough.
Propellant had to be used to keep Nozomi on target. These unscheduled
course corrections left the lightweight spacecraft short on fuel – fuel
that would be needed at the other end of the trip to enter an orbit
around Mars.
Mission engineers crafted a new trajectory. The plan called for Nozomi
to stay in an orbit around the sun for four more years. There would be
two more Earth flybys in December 2002 and June 2003. However, as
Nozomi orbited the Sun, the spacecraft was bombarded with a powerful
solar flare in April of 2002. The burst of radiation damaged
communications and power systems. Mission engineers struggled to regain
control of the spacecraft and were able to salvage the Earth flyby in
December of that year.
The June 2003 swingby of the Earth will insert Nozomi into the proper
orbit for its journey to Mars. Arrival at Mars will be sometime between
mid-December 2003 and early January, 2004. The exact date depends on
the extent of the orbital correction maneuvers that have to be performed
following the final Earth flyby.
When Nozomi finally reaches the Red Planet, its 14 science instruments
will gather data about the martian atmosphere and ionosphere; search for
a magnetic field and take precise measurements of its strength; anlayze
how dust storms are generated; monitor changes in the polar ice caps;
take images of martian weather, as well as the moons Phobos and Deimos;
and search for a dust ring along the orbit of Phobos. The international
mission includes a spectrometer from Sweden, a plasma analyzer from
Canada, a dust counter from Germany, a camera developed in collaboration
with France, and a spectrometer and radio science hardware from the
United States.
The Nozomi mission was designed to last for at least two years (one
martian year). Fuel will be the critical factor. The length of time
the orbiter will operate depends on the amount of fuel that is consumed
when it is maneuvered into an orbit around Mars.
Mars Pathfinder: Dec. 4, 1996
The greatest danger to the Mars Pathfinder mission was not the hazard of
a rocket launch, space travel, or operations in a hostile planetary
environment, but rather the threat of being canceled before it ever got
off the ground. Work on Pathfinder began in 1992. By 1995, its
reviewers saw the mission as too risky and many experts said it would
never work. These critics began to take steps to cancel the mission.
But the Pathfinder team demonstrated that it was able to meet each
challenge and created one of the most successful technology missions
ever sent to Mars.
Pathfinder was designed to be an engineering mission to demonstrate new
spacecraft technologies that could take America back to the surface of
Mars for dramatically less than the cost of the
Viking missions.
However, Pathfinder’s critics were quick to point out that the mission’s
technical problems seemed overwhelming. Viking was 20 years in the
past. Many of the people who knew how to put a lander on Mars had
retired. Mars Observer would have provided helpful data, but its demise
left Pathfinder engineers combing through old Viking records for
information on expected surface and atmospheric conditions. Time and
fate made the situation difficult, especially since the Pathfinder team
was operating under NASA's new Discovery Program dictate of "faster,
better, cheaper." They had to make their mission work at one-fifth the
cost of Viking.
One of the major problems faced by Pathfinder engineers was to develop
an entry, descent, and landing (EDL) system that was cheaper than that
used by Viking, but still reliable. An idea was borrowed from Soviet
landers. They had used airbags to cushion landings on the Moon and
Venus. This eliminated the need for the extensive use of costly fuel to
control braking rockets for a pinpoint landing. Following this lead,
Pathfinder’s tetrahedral lander was wrapped in a cluster of resilient
airbags. The new EDL system was not an immediate success, however.
When dropped on a platform of jagged, Mars-like rocks, initial impacts
left the airbags with gaping holes. The fabric was reinforced and the
design was tweaked until future tests proved successful.
An additional technology and
science component of the Pathfinder mission was the inclusion of a small
rover. The Sojourner Rover would be the first rover to put its wheels
in martian soil. But its addition to the mission created several more
problems for the Pathfinder team. How would the rover be able to get
around a rocky martian landscape without getting stuck? Where should
Pathfinder land to allow the rover to drive safely and make the best use
of its science potential? And how could something the size of a
microwave oven do any real science?
Engineers went to work designing a new mobility system that put the
rover’s wheels on levers. This
“rocker-bogie”
suspension allowed Sojourner to
move up and down over rough terrain without tipping over. This
capability was also critical to the rover’s power supply. The solar
panels on top of Sojourner had to be kept level to receive the most
sunlight.
To save fuel and money, Pathfinder would not orbit Mars before it
landed, but rather would make a direct entry into the martian
atmosphere. Unlike Viking, Pathfinder engineers would not have the
luxury of changing their minds about a landing site after launch. The
decision would have to be final. The process of finding an appropriate
landing site to satisfy landing safety and scientific interest took more
than two years. One of Pathfinder's science goals was to study a
variety of rocks. But too many rocks pose a landing hazard for the
airbags. Ultimately, an outflow channel in a location called Chryse
Planitia, not far from the Viking 1 landing site, was chosen. Named
Ares
Vallis, it appeared to be
the site of a catastrophic flood on Mars -- good for a geologic mission,
but critics worried that the region had too many rocks to be safe for an
airbag landing.
The Sojourner Rover may have been small, but it carried out some
significant science investigations. It was equipped with three cameras
and an Alpha-Proton-X-Ray Spectrometer (APXS) to analyze martian rocks.
The rover communicated its findings to Earth through the lander, which
also carried its own science instruments. The Pathfinder lander had a
stereo camera, a weather station with pressure, temperature, and wind
speed instruments, and magnets to study the properties of dust in the
martian atmosphere.
|
Mars Pathfinder launched on Dec. 4, 1996 after two delays due to weather
and computer problems. It landed safely on Mars on July 4, 1997. The
airbags survived the landing, bouncing more than 16 times and as high as
15 meters (50 feet) on initial contact with the martian surface. The
lander, formally named the Carl Sagan Memorial Station after touchdown,
returned spectacular images of Mars. Sojourner was commanded to leave
the lander on the second day of the mission. The small rover used its
APXS to make chemical analyses of nearby rocks and used its cameras to
image the rocks and soils up close. The public became enraptured with
the "little rover that could."
The Pathfinder mission was designed to last one month, but the lander
and rover actually operated for 83 Mars days, or Sols. During that
time, a wealth of images and other data were returned to Earth. There
was information from the lander’s weather station that revealed rapid
pressure and temperature variations on Mars; evidence that martian dust
includes magnetic, composite particles; evidence of dune-shaped deposits
which indicate the presence of sand on Mars; a distribution of rocks
that appeared to be caused by flooding; and the possible identification
of rounded pebbles that could have been formed in running water on a
warmer and wetter Mars.
 |
|
Credit: NASA/JPL
A Pathfinder panorama of Mars taken at sunset.
|
Pathfinder had done its job well. A mission that was nearly canceled
had become an enormous success and captured the world's attention. Most
importantly, Pathfinder demonstrated some key technologies and
operations procedures that could be used for future missions. Plans
were put into motion for another rover to visit the surface of the Red
Planet. These plans would later give rise to the Mars Exploration Rover
mission.
Mars 96: Nov. 16, 1996
Dramatic changes had occurred in Russia since the time of the Phobos
missions in the late 1980s. The old Soviet Union was dissolved, and the
republics that had formed the USSR became independent nations. Russia
took over the Soviet space program, and struggled to keep it going
during difficult economic times. The Buran, a twin to America's Space
Shuttle, was scrapped in 1993. As the cold war faded, the United States
and Russia began to work together in space. Cosmonauts rode the American
space shuttle, and astronauts worked on the Russian Mir space station.
Still, money for Russian planetary missions was very tight. A new
mission to Mars that was to launch in 1994 had to be postponed. The
result was a very ambitious project called Mars 96.
The goal of the Mars 96 mission was to perform extensive studies of the
atmosphere, surface and interior of Mars. The spacecraft was created
using experience and knowledge gained from Russia's successful missions
to Venus and failed missions to Mars. It carried an orbiter based on
the Phobos design with more than 20 science instruments. It also
carried two small landers packed with additional science equipment, and
two surface penetrators with several sensors.
The Mars 96 landers were designed to separate from the main spacecraft
and fly on their own to selected landing sites. They were to survive an
entire martian year (687 Earth days) so that science instruments could
gather information about seasonal changes in the atmosphere, study
martian soils, measure magnetic fields, and record any seismic activity.
Each lander also carried a panoramic camera to view the nearby
landscape.
The two surface penetrators were also designed to last one martian year.
Impact with the surface would drive the tip of each probe deep into the
soil. One section of the penetrator would remain on the surface, but
stay connected by wires to the deeper probe. Instruments were located in
both sections of the device. They included a television camera,
spectrometers, seismometers and a neutron detector.
Mars 96 was scheduled to reach the Red Planet on Sept. 12, 1997, but it
never left Earth orbit. A failure during the second ignition of the
Proton rocket's upper stage sent the spacecraft tumbling into the
Pacific Ocean. A review board was convened, but was unable to determine
the exact cause of the failure. To date, there have been no more Russian
missions to Mars.
Mars Global Surveyor: Nov. 7, 1996
From the ashes of the failed Mars Observer mission came an orbiter that would find extreme success. It was designed with knowledge
gleaned from Observer's failure reports and built using many spare parts from that mission. It was also tailored to fit cost-cutting
measures that became mandatory during NASA's new era of "faster, better, cheaper." The result was a robust spacecraft far less
expensive than its predecessor. The Mars Global Surveyor (MGS) has not
only surpassed its goals, it has returned a wealth of information about Mars, and continues to examine the Red Planet today.
However, the mission was not without its problems. Shortly after launch, one of the orbiter's two solar panels did not deploy properly.
It unfolded, but did not lock because of debris lodged in a hinge. The problem would later haunt engineers.
As MGS approached the point where the Mars Observer had been lost, tensions ran high. There was a collective sigh of relief when
engines fired successfully. The craft went into a highly elliptical orbit around Mars to begin its
aerobraking phase. Aerobraking is a method of
slowing the spacecraft by dipping into the Martian atmosphere and using solar arrays to create drag. Like a mainsail taut with wind,
aerobraking places a strain on the solar arrays. The jammed solar panel resurfaced as a concern. Would the maneuver cause it to snap
off? Engineers resorted to a gentler method of aerobraking which meant that MGS would take at least a year longer to arrive at its
nearly-circular orbit around Mars. Mapping the planet did not begin until March of 1999, but would continue far longer than the
anticipated January, 2001 end date.
The objectives of the Mars Global Surveyor mission were similar to that of the Mars Observer -- conduct an extensive two-year study of
Mars to gather detailed measurements of its surface and atmosphere. Most of the instruments MGS carries are flight spares from the Observer
mission. They are a magnetometer and electron reflectometer to study the planet's
magnetic field; a camera to image the surface; a
laser altimeter to map the height of surface features;
thermal emission spectrometer to investigate surface and atmospheric properties by
measuring radiated heat; and an oscillator for radio science
to study the Martian gravity field and track atmospheric pressure and temperature.
The orbiter is also equipped with a relay system so that information from spacecraft on the surface of Mars can be relayed to Earth. Anticipating that
MGS still will be functioning in 2004, its relay system will be used to transmit information gathered by the Mars Exploration Rovers.
The Mars Global Surveyor has returned more information about the surface, atmosphere and interior of Mars than all other Mars missions combined.
MGS achievements include a detailed global topographic map of Mars; global models of the Martian crust; evidence that Mars once had a magnetic
field which is lacking today; the discovery of hematite deposits; information about the role of wind and dust in the Martian climate; and possible
evidence for recent liquid water on Mars. The Mars
Orbiter Camera continues to capture spectacular views of the surface of Mars, adding to an archive of more than 100,000 images.
Currently, MGS in its third extended mission and is aiding in the selection of landing sites for the Mars rovers. Its daily activities also include
monitoring Martian storms and weather patterns, searching for changes in surface features, and observing new areas of interest to science.
Mars Observer: Sept. 25, 1992
Seventeen years had passed since America sent a spacecraft to Mars. It was an expanse of time that saw the Soviet Union continue to explore Venus, the United States send probes of its own to that planet, Voyager 1 and 2 journey to the gas giants, the Space Shuttle come into being, European and Japanese probes study Halley's Comet, the rise of Russia's Mir Space Station, the Galileo spacecraft travel to Jupiter, and the launch of the Hubble Space Telescope. America was ready to return to Mars.
Mars Observer was a massive orbiter that was similar to Earth-orbiting satellites of its day. It was designed to remotely probe the Red Planet's surface, atmosphere, and interior in fine detail over the course of one Martian year (687 Earth days). Equipment on the rectangular bus included computers, a radio system, tape recorders, and fuel tanks. Four of seven science instruments were mounted on a panel that would always face the planet. They were a camera to image the entire surface of Mars, a laser altimeter to create topographic maps, an infrared radiometer to monitor the atmosphere, and a thermal emission spectrometer to determine the properties of rocks and soils. Two other instruments were located on booms so their readings would not be affected by emissions from the spacecraft. They were the magnetometer/electron reflectometer to search for magnetic fields, and the gamma-ray spectrometer to identify chemical elements. Mars Observer's radio system was considered to be a seventh instrument. Scientists planned to use it to map the Martian gravity field.
The journey to Mars took 11 months and, during that time, there was no hint of the tragic events to come that would doom the mission. On August 21, 1993, only three days before the spacecraft was scheduled for orbit insertion, Mars Observer fell silent. It happened just as a command was executed that should have pressurized the propulsion system that was to slow the spacecraft as it approached the planet. Engineers sent backup commands and made frantic efforts to find a signal, but contact was never reestablished. Mars had refused visitors once again.
In the months that followed, an investigation board tried to piece together the very little information they had in order to find a reason for the loss. It finally concluded that ruptured tubing in the propulsion system caused Mars Observer to spin out of control. A liquid-propellant rocket mixes fuel and an oxidizer in a combustion chamber to get the high-pressure stream of gases needed to propel or slow a spacecraft. The board surmised that, during the long, cold journey to Mars, nitrogen tetroxide (an oxidizer) had seeped into and condensed in the fuel lines. When the fuel hit the liquid oxidizer, the resulting combustion caused a rupture in the tubing instead of in the combustion chamber. The board's findings included remarks that there had been too much reliance on a design taken from Earth orbiting satellites. Even though the orbiter had been modified for Mars, the long duration cold soak of interplanetary travel is very different from a low Earth orbit. Still, the board was careful to state that there could be no exact determination for the failure of Mars Observer.
The demise of the Mars Observer spacecraft triggered a restructuring of NASA's entire Mars program. Too many expensive instruments had flown on one spacecraft. "Faster, better, cheaper" became NASA's catchphrase for the next phase of Mars exploration.
Web content editor/writer: Pamela R. Smith
