Mars Climate Observer

Credit: NASA

The second launch of three in the 1998-99 launch window was of the Mars Climate Orbiter (MCO; formerly the Mars Surveyor '98 Orbiter), the second of three spacecraft in the Mars Surveyor program, the first being Mars Global Surveyor (launched in November 1996) and the third being the Mars Polar Lander (formerly the Mars Surveyor '98 Lander). MCO was designed to arrive at roughly the same time as Mars Polar Lander and conduct simultaneous investigations of Mars's atmosphere, climate, and surface. MCO was also designed to serve as a communications relay for the Mars Polar Lander and other future NASA and international lander missions to Mars.

After the Lander's three-month mission, MCO would have performed a two-year independent mission to observe and study dust storms, weather systems, clouds and dust hazes, ozone, distribution and transport of dust and water, the effects of topography on atmospheric circulation, atmospheric response to solar heating, and surface features, wind streaks, erosion, and color changes. It would also take daily pictures of the planet's surface to construct an evolutionary map of climatic changes. Scientists hoped that such information would aid in reconstructing Mars' climatic history and provide evidence of buried water reserves.

MCO was launched on December 11, 1998 by a Delta 7425 rocket. The spacecraft reached Mars on September 23, 1999, and executed a 16 minute, 23 second orbit insertion main engine burn. MCO passed behind Mars and was to re-emerge and establish radio contact with Earth 10 minutes after the burn was completed. However, contact was never re-established and no signal was ever received from the spacecraft. Findings of the failure review board indicate that a navigation error resulted from some spacecraft commands being sent in English units instead of being converted to metric. This caused the spacecraft to miss its intended 140 - 150 km altitude above Mars during orbit insertion, instead entering the Martian atmosphere at about 57 km. The spacecraft would have been destroyed by atmospheric stresses and friction at this low altitude.

The above photograph is one of the very few taken by MCO, and was the first photograph of Mars taken by the MCO's Mars Color Imager (MARCI). The photograph was taken on September 7, 1999 when the spacecraft was approximately 4.5 million km (2.8 million miles) from the planet. This full-scale medium angle camera view is the highest resolution possible at this distance from Mars.

Nozomi

Credit: MIC onboard NOZOMI / ISAS

The 1998-99 launch window was an ambitious one, with three spacecraft launched toward Mars; unfortunately, all three suffered failures.

The first of the three to be launched was Nozomi ("Hope"), the first (and, to date, only) Japanese spacecraft to be sent toward Mars.

Its mission was to conduct long-term investigations of the planet's upper atmosphere and its interactions with the solar wind, and to track the escape trajectories of oxygen molecules from Mars' thin atmosphere. The spacecraft also was to take pictures of the planet and its moons from its operational orbit of 300 x 47,500 kilometers. During perigee, Nozomi was to perform remote sensing of the atmosphere and surface; while close to apogee, the spacecraft would have studied ions and neutral gas escaping from the planet. Although designed and built by Japan, the spacecraft carried a set of fourteen instruments from Japan, Canada, Germany, Sweden, and the United States.

Nozomi was launched by an M-V (M-5), a Japanese solid fuel rocket, on July 3, 1998. After entering an elliptical parking orbit around Earth, Nozomi was sent on an interplanetary trajectory that involved two gravity-assist flybys, once around the Moon on September 24th, and once around the Moon and the Earth on December 18th and December 20th, respectively. However, on the December 20th flyby, a malfunctioning valve resulted in a loss of fuel and left the spacecraft with insufficient acceleration to reach its planned trajectory. Two course correction burns were made on December 21st, but the burns used more propellant than planned, leaving the spacecraft short of fuel.

A new mission was then devised, whereby Nozomi would remain in a heliocentric orbit for an additional four years, including two Earth flybys in December 2002 and June 2003, and encounter Mars at a slower relative velocity in December 2003. On April 21, 2002, as Nozomi was approaching Earth for the gravity-assist maneuver, powerful solar flares damaged the spacecraft's onboard communications and power systems. An electrical short was caused in a power cell used to control the attitude control heating system, allowing the hydrazine fuel to freeze. The fuel thawed out as the craft approached Earth and maneuvers to put the craft on the correct trajectory for its Earth flyby were successful.

The second Earth flyby occurred on June 19, 2003. The fuel had completely thawed out for this maneuver because of the spacecraft's proximity to the Sun. However, on December 9, 2003, efforts to orient the craft to prepare it for a December 14, 2003 main thruster orbital insertion burn failed, and efforts to save the mission were abandoned. The small thrusters were fired on December 9, moving the closest approach distance to 894 km so that the probe would not inadvertently impact on Mars and possibly contaminate the planet with Earth bacteria, since the orbiter had not been intended to land and was therefore not properly sterilized. Nozomi flew by Mars on December 14, 2003 and went into a roughly 2-year heliocentric orbit. Though its mission has been abandoned the spacecraft is still active.

The above photograph, of the Earth and Moon, was the first picture taken by Nozomi, on July 18, 1998.

Results from Mars Pathfinder

Credit: NASA

Although Mars Pathfinder was expected to operate any time between a week to a month, it eventually lasted for almost three months. The final contact with Pathfinder was at 10:23 UTC on September 27, 1997, on sol 83. Although mission planners tried to restore contact during the following five months, the mission was terminated on March 10, 1998. The Lander's silver-zinc battery was only capable of being recharged about 40 times; as a consequence, after about sol 40, the battery was not able to keep the Lander warm at night. The exact reason for the final failure of the Lander is not certain, but it was probably due to an electronics failure due to the very cold night-time temperatures that were experienced in the final weeks of the mission. After sol 92, the automatic backup procedures should have instructed Sojourner to return to the Lander and circle it while attempting to re-establish communications. This behavior would have continued until hardware failure.

Mars Pathfinder returned 16,500 images from the lander and 550 images from the rover, as well as more than 15 chemical analyses of rocks and soil, plus extensive data on winds and other weather factors. Among the scientific findings were:

The APXS analysis of "Barnacle Bill" showed its origin to be consistent with the Martian meteorites. The rock is about 60% felsic, 40% mafic, roughly 1/3 quartz, 1/3 feldspar, and 1/3 orthopyroxene. This would classify it as an andesite (a type of rock found in the Andes mountain) if it is an igneous rock, a highly differentiated quartz-rich rock compared to the Martian meteorites, which are classified as basalts. This would indicate that Mars has been more thermally active in its past than was previously thought, producing at least some highly remelted and differentiated rocks. "Barnacle Bill" could also be a mixture of basalt or granite mixed in a sedimentary rock or impact melt. However, results from spot reflectance spectra compared with spectral results from fresh volcanic earth rocks strengthen the case that it is a volcanic andesite.

Preliminary analysis of the APXS data returned for "Yogi" suggested it was very different from Barnacle Bill. If Yogi is of volcanic origin, it appeared to be basalt, a primitive, unprocessed rock type. However, a thin covering of dust on the rock indicates there is probably a soil component mixed in these measurements. Rough estimates have been made of the contribution of the soil component. Subtracting this out gives a composition of Yogi similar to that of Barnacle Bill.

The rock "Scooby-Doo" appears to be a sedimentary rock composed primarily of compacted soil. The APXS analysis of Scooby-Doo shows only minor differences from the local soils analyzed.

Images from Pathfinder are consistent with the earlier results from Viking Orbiter images that Ares Vallis was the site of a massive flood about one to three billion years ago, and with measurements by the Viking Landers showing large quantities of iron oxides in the soil.

The analysis of soil samples by the APXS shows a very close match to soils examined by the Viking Landers. There are some differences, however. Soils at the Mars Pathfinder site generally have higher aluminum and magnesium, and lower iron, chlorine, and sulfur than those studied by Viking.

Preliminary analysis indicates the possibility that all Martian dust is at least slightly magnetic. The dust is believed to contain maghemite, a strongly magnetic mineral formed in environments of scarce oxygen.

Temperatures measured from the top of the 1 meter mast on Mars Pathfinder varied from daily highs of about 260 K (+8 F) to lows of 196 K (-107 F).

Imaging of the sky and the sun at different elevations above the horizon showed the atmosphere to be moderately dusty, consistent with what was seen by the Viking Landers. The optical depth indicates that about 35% of the direct sunlight at noon is scattered or absorbed by dust. Visibility tends to be about 30 km. The dust appears to be spread vertically high into the atmosphere and is globally distributed. The sky is hazy and salmon-colored, as it was for Viking.

Extensive water-ice clouds have been imaged in the pre-dawn hours by the Lander camera. The clouds moved from the NE at about 7 meters per second (15 mph) and disappeared right around sunrise. The clouds are thought to consist of frozen water condensed around dust particles.

The above photo was taken by the left-side camera on the Mars Pathfinder Lander. The Lander carried a stereoscopic camera on an extendable pole that allowed "3-D" images to be taken. The photo shows the "Rock Garden" in the foreground and "Twin Peaks" in the background. The "Twin Peaks" are modest-sized hills to the southwest of the Mars Pathfinder landing site. The peaks were discovered on the first panoramic photos taken by Pathfinder's camera on July 4, 1997, and subsequently identified in Viking Orbiter images taken over 20 years ago. The peaks are approximately 30-35 meters (100 feet) tall. North Twin is approximately 860 meters (2,800 feet) from the lander, and South Twin is about a kilometer away (3,300 feet). The scene includes bouldery ridges and swales or "hummocks" of flood debris that range from a few tens of meters away from the lander to the distance of the South Twin Peak.

Sojourner

Credit: NASA

On July 4, 1997, Mars Pathfinder landed on Mars using a combination of an entry capsule, a parachute, solid rockets, and large airbags. About 21.5 meters above the surface of the planet, the lander and rover, protected by a 5.2-meter "bubble" of airbags, detached from the parachute and bounced onto the surface of the planet. The lander and rover bounced a total of 15 times (the first bounce went up 12 meters into the air), rolling approximately a kilometer from the initial impact site. The lander deflated the airbags, then opened up three "petals" that surrounded the rover, the petals being covered with solar panels to generate electricity. Ninety-eight minutes after landing, Pathfinder began signaling Earth with the data it had accumulated during the descent and landing.

The heart of the mission was the tiny rover, Sojourner, named after the American abolitionist and women's rights activist Sojourner Truth (1797-1883). Sojourner was very small, measuring 65 cm long, 48 cm wide, 30 cm tall, and weighing 10.6 kg. (In comparison, the Mars Exploration Rovers Spirit and Opportunity are both 1.6 meters long, 2.3 meters wide, 1.5 meters tall, and weigh 180 kg.)

While the Mars Pathfinder mission was primarily concerned with engineering and budgetary hurdles (namely, proving the "faster, better and cheaper" program by sending a simple system to another planet at 20% of the cost of the Viking missions), the lander and Sojourner did carry a number of scientific instruments. The lander carried a stereoscopic camera on an extendable pole, plus a meteorological station that measured air pressures, temperatures, and wind speeds and directions. Sojourner carried an Alpha Proton X-ray Spectrometer (APXS) that was used to analyze the components of the rocks and soil. The rover also had three cameras, two black and white and one for color images, plus a number of other experiments.

In the above image, Sojourner is taking Alpha Proton X-ray Spectrometer (APXS) measurements of the rock named "Yogi." The image clearly shows the "two-toned" surface of this large rock. The nature of this color difference is not known; however, it might consist of wind-blown dust accumulated on the surface (the rock is leaning into the prevailing wind) or it might be evidence of a break from a larger boulder as it was deposited in the ancient flood that scoured this area.

Pathfinder

Credit: NASA

[My apologies for the break over the past three days. While I've never promised that Areology would be a "Mars Picture of the Day"-type blog, I've tried to keep that type of schedule since the beginning. Unfortunately, this past weekend was rather busy, and I hadn't had time to prepare posts in advance. This type of break may happen from time to time in the future, but I'm hoping that the occurrences will be few and far between. Now, back to our continuing series of missions to Mars.]

The third and final launch of the 1996 launch window (Mars Global Surveyor had been the first) was of the Mars Pathfinder mission. On December 4th, Pathfinder lifted off on a Delta II rocket, and arrived seven months later, on July 4, 1997, on Ares Vallis. Ares Vallis is a channel that flows out of Margaritifer Terra, through the Xanthe Terra highlands, and into a delta-like region of Chryse Planitia. Ares Vallis was chosen as the landing site because it is an ancient flood plain that was theorized to contain a wide variety of rocks deposited during a possible catastrophic flood. Upon the successful landing of Pathfinder's lander, the landing site was named "The Carl Sagan Memorial Station" in honor of the late astronomer; Sagan had died 16 days after the launch of Pathfinder. (Asteroid 2709 Sagan is also named after Carl Sagan.)

The mission of Pathfinder was primarily one of testing new and cheaper technologies. Pathfinder was the second in a series of mission in the Discovery Program that NASA sponsored to launch low-cost spacecraft frequently under the motto, "cheaper, faster and better," which itself was a reaction to the loss of Mars Observer. Among the new technologies tested on this mission were large airbags used to cushion the impact of landing of the lander (as opposed to the much heavier and more expensive rocket-landing system used on the two Viking missions), an automated obstacle avoidance system (currently being used by the two Mars Exploration Rovers, Spirit and Opportunity) and, of course, Pathfinder's tiny rover, Sojourner.

The above image is the first photo taken from the Pathfinder Lander.

Mars 96 - The Last Russian Mission to Mars

Credit: NASA

Nine days after the launch of Mars Global Surveyor, Russia launched Mars 96, aka "Mars 8." This was an extremely ambitious mission, and was the heaviest interplanetary spacecraft ever launched. Intended subjects of investigation included the Martian surface and atmosphere, the inner structure of the planet, solar plasma studies (especially of the sun's and Mars' magnetic fields), and astrophysical studies, including the study of cosmic gamma ray bursts. Mars 96 had several components, including an orbiter based on the Phobos orbiter design, two surface stations that were to land in separate locations on the northern hemisphere of Mars, and two penetrators, which would separate into two pieces upon impact. Both pieces had scientific equipment in them. The forebody was to penetrate up to 5-6 meters beneath the surface, while the afterbody would remain near the surface and transmit back the data.

Mars 96 lifted off on November 16, 1996 on a Proton 8K82K/11S824F rocket. This is a four stage rocket in a configuration that had flown only twice before, launching the two Phobos spacecraft. The rocket performed properly up to parking orbit. However, the planned second burn of the Block D-2 fourth stage shut down prematurely after a 20 second burn. Mars 96 and its Fregat module then automatically separated from the Blok D-2. The latter seems to have fired (as planned earlier), placing Mars 96 into an orbit that deposited the spacecraft into the Earth's atmosphere. Mars 96 burned up, falling somewhere in the vicinity of Chile, Bolivia or the Pacific Ocean off the Chilean or Bolivian coast. The Block D-2 re-entered on a later orbit.

Mars 96 is, to date, the last Mars mission undertaken by Russia/Soviet Union. The Soviet Union tried to send a total of 18 missions to Mars and the Russian Federation, one. Of all nineteen missions, none could be considered a complete success and only five a partial success. Even of those five, it is difficult to say which was the most successful mission.

The above image is a NASA computer-generated model of the Mars 96 (Mars 8) Orbiter.

The Martian North Pole by MOLA

Credit: NASA

Yesterday, I briefly discussed the Mars Orbiter Laser Altimeter (MOLA) that was carried on board the Mars Global Surveyor (MGS). MOLA allowed scientists to determine the altitudes of all points on the Martian surface. To give an idea of how valuable a tool MOLA was, I'm highlighting today the first 3-D view of the Martian north polar region using MOLA's data. From the NASA press release (6 December 1998):

Measurements by a laser altimeter instrument orbiting aboard NASA's Mars Global Surveyor spacecraft are providing striking new views of the north pole of the red planet and the processes that have shaped it. This first three-dimensional picture of Mars' north pole enables scientists to estimate the volume of its water ice cap with unprecedented precision, and to study its surface variations and the heights of clouds in the region for the first time.

The elevation measurements were collected by the Mars Orbiter Laser Altimeter (MOLA) aboard Global Surveyor during the spring and summer of 1998, as the spacecraft orbited Mars in an interim elliptical orbit. MOLA sends laser pulses toward the planet and measures the precise amount of time before the reflected signals are received back at the instrument. From this data, scientists can infer surface and cloud heights.

Approximately 2.6 million of these laser pulse measurements were assembled into a topographic grid of the north pole with a spatial resolution of .6 miles (one kilometer) and a vertical accuracy of 15-90 feet (5-30 meters). A peer-reviewed paper based on the measurements will be published in the Dec. 11 issue of Science magazine.

The topographic map reveals that the ice cap is about 750 miles (1,200 kilometers) across, with a maximum thickness of 1.8 miles (3 kilometers). The cap is cut by canyons and troughs that plunge to as deep as 0.6 miles (1 kilometer) beneath the surface. "Similar features do not occur on any glacial or polar terrain on Earth," said Dr. Maria Zuber of the Massachusetts Institute of Technology and NASA's Goddard Space Flight Center, Greenbelt, MD. "They appear to be carved by wind and evaporation of ice."

The MOLA data also reveal that large areas of the ice cap are extremely smooth, with elevations that vary by only a few feet over many miles. In some areas the ice cap is surrounded by large mounds of ice, tens of miles across and up to half a mile in height. "These structures appear to be remnants of the cap from a time when it was larger than at present," Zuber said. Impact craters surrounding the cap appear to be filled with ice and dust that was either deposited by wind or condensation, or perhaps remains from an earlier period when the ice cap was larger.

The shape of the polar cap indicates that it is composed primarily of water ice, with a volume of 300,000 cubic miles (1.2 million cubic kilometers). The cap has an average thickness of 0.64 miles (1.03 kilometers) and covers an area 1.5 times the size of Texas. For comparison, the volume of the Martian north polar cap is less than half that of the Greenland ice cap, and about four percent of the Antarctic ice sheet.

The estimated volume of the north ice cap is about 10 times less than the minimum volume of an ancient ocean that some scientists believe once existed on Mars. If a large body of water once existed on the red planet, the remainder of the water must presently be stored below the surface and in the much smaller south polar cap, or have been lost to space. But such a large amount of unaccounted-for water is not easily explained by current models of Martian evolution.

During its mapping of the north polar cap, the MOLA instrument also made the first direct measurement of cloud heights on the red planet. Reflections from the atmosphere were obtained at altitudes from just above the surface to more than nine miles (approximately 15 kilometers) on about 80 percent of the laser profiles. Most clouds were observed at high latitudes, at the boundary of the ice cap and surrounding terrain.

Clouds observed over the polar cap are likely composed of carbon dioxide that condenses out of the atmosphere during northern hemisphere winter. Many clouds exhibit dynamic structure probably caused by winds interacting with surface topography, much as occurs on Earth when winds collide with mountains to produce turbulence.

Animations of a flyover of the Martian north pole may be found here.

Mars Global Surveyor

Credit: NASA

Four years after the launch of the two Phobos spacecraft, the U.S. resumed its exploration of Mars with the Mars Observer spacecraft. This was the first spacecraft the U.S. had launched toward Mars in seventeen years (and sixteen days). Mars Observer was designed to study the geoscience and climate of Mars. However, three days prior to orbital insertion, Mission Control lost contact permanently with the spacecraft for unknown reasons. Whether Mars Observer went into orbit around Mars or flew by the planet, going into heliocentric orbit, is unknown. One possible reason for the loss of contact may have been an explosion in a propellant line during pressurization procedures just before the orbital insertion engine burn. Hypergolic fuel may have leaked past valves in the system during the cruise to Mars, allowing the fuel and oxidizer to combine prematurely before reaching the combustion chamber. The engine was not designed to lie dormant for months before being fired. Despite the loss of the spacecraft, several science instruments originally developed for Mars Observer are (or were) being used by three other orbiters, the Mars Global Surveyor, Mars Odyssey and the Mars Reconnaissance Orbiter.

Two launch windows later, on November 7, 1996, the U.S. followed up by launching Mars Global Surveyor (MGS). The primary mission of MGS was to map the surface of Mars; however, it also carried a laser altimeter (Mars Orbiter Laser Altimeter or MOLA) that allowed the spacecraft to determine the altitudes of all points on the Martian surface. The data from MOLA has resulted in a very colorful and popular map of Mars (see the image above). MGS was also used to track the Martian weather and act as a communications relay for the Mars Exploration Rovers, Spirit and Opportunity.

After a series of aerobraking maneuvers that lowered the apoapsis (highest point of the orbit) from 54,026 km to 450 km, MGS began its primary mission of mapping the surface of Mars. The spacecraft circled Mars once every 117.65 minutes at an average altitude of 378 kilometers (235 miles). It was in a near-polar orbit (inclination = 93°) which was almost perfectly circular, moving from the south pole to the north pole in just under an hour. The altitude was chosen to make the orbit sun-synchronous, so that all images taken by the spacecraft of the same surface features on different dates would be under identical lighting conditions. After each orbit, the spacecraft viewed the planet 28.62° to the west because Mars had rotated underneath it. In effect, it was always 14:00 for MGS as it moved from one time zone to the next. After seven sols and 88 orbits, the spacecraft would approximately retrace its previous path, with an offset of 59 km to the east. This ensured an eventual full coverage of the entire surface.

MGS Mission Control lost contact with the spacecraft on November 2, 2006 after being ordered to perform a routine adjustment of its solar panels. The spacecraft reported a series of alarms but, in a final transmission, indicated it had stabilized. According to NASA, the MGS loss was likely due to faulty computer code uploaded five months before that ultimately caused one of the spacecraft's battery to overheat. The spacecraft had reoriented to an angle that exposed one of its two batteries to direct sunlight. The battery overheated and, over the course of 11 hours, depleted the other battery as well. An incorrectly oriented antenna prevented the spacecraft from communicating its status to controllers. The board investigating the loss of MGS concluded that the MGS team followed existing protocols correctly, but that the procedures were insufficient to spot the errors that occurred.

The contribution MGS made to our understanding of Mars is enormous. Using the Mars Orbiter Camera, MGS took over 212,000 images. I hope to highlight a number of the accomplishments MGS made in future posts. Of all the spacecraft sent to Mars, MGS was in operation the longest, having survived five days short of ten years since its launch.

Phobos 1 & 2

Credit: Russian Academy of Sciences/Don P. Mitchell

And then began the long wait...

As Oliver Morton wrote in his book, Mapping Mars, "The failure to find any trace of life on Mars in the 1970s was as harsh a blow to science fiction as it was to science. It had almost always been the Martians, rather than their planet, on which the fiction had focused. From the mid-1970s to the mid-1980s there was remarkably little new science fiction about Mars." (p. 136)

The dearth in Mars-oriented science fiction went hand in hand with the dearth in missions to Mars. From 1975 through 1988, no new missions were launched by any country. Granted, the various Viking Orbiters and Landers remained operational from 1976 through 1982, providing a diminishing flow of new data as the Landers and Orbiters eventually went silent. However, from November 1982, when the Viking 1 Lander died, through January 1989, there were no working spacecraft on or orbiting Mars. Moreover, there were no attempts in the various launch windows in all those years, in contrast to the eleven missions launched in the past six launch windows, since 1996 (with seven missions successful, five missions still operational, and one, the Phoenix Mars spacecraft just launched).

In July 1988, the Soviet Union sent their first mission to Mars since 1973, when they had launched the four spacecraft, Mars 4 through 7. These two spacecraft, Phobos 1 and Phobos 2, were the first to focus primarily on the Martian moon, Phobos, in addition to Mars. Each spacecraft was a combination orbiter-lander (although, in the case of Phobos 2, there were two landers). The objectives of the Phobos Program were to: conduct studies of the interplanetary environment, perform observations of the Sun, characterize the plasma environment in the Martian vicinity, conduct surface and atmospheric studies of Mars, and study the surface composition of the Martian satellite Phobos.

Phobos 1 was launched on July 7, 1988 and was operating normally through September 2nd, when mission controllers were unable to contact the spacecraft. A few days earlier, on August 29th and 30th, some software had been uploaded that accidentally deactivated the attitude thrusters. Phobos 1 lost its lock on the Sun and could no longer orient its solar arrays properly, depleting its batteries.

Phobos 2 was launched five days later, on July 12th, and entered Mars orbit on January 29, 1989. The spacecraft was able to take a total of 38 different pictures using a number of different cameras, including a video-spectrometric complex (VSK), three CCD cameras and a optical-mechanical linear camera that operated simultaneously in red/near-infrared light (600 - 950 nm) and far thermal infrared (8.5 - 12 μ), using a cryogenically cooled detector. As mentioned above, Phobos 2 also carried two landers. Both were to land on Phobos, one being a stationery platform and the other a mobile "hopper." However, on March 29th, as Phobos 2 neared its namesake satellite, communications was lost. The cause of the failure was determined to be a malfunction of the on-board computer.

The above picture is a near infrared scan of Mars, taken during the daytime on March 26, 1989. Starting on the left, the large circular feature is the southern-most of the three prince volcanoes, Arsia Mons. Moving to the right, the large triangular region made up of a maze of deep, steep-walled valleys is Noctis Labyrinthus ("The Labyrinth of the Night"). Across the center of the image is the vast Valles Marineris, ending in the Eos Chasma to the right. In the darkness at the far right is Margaritifer Terra. The area directly south of Valles Marineris is Sinai Planum, and the area to the northeast of Valles Marineris (and northwest of Margaritifer Terra) is Xanthe Terra.

Viking 2

Credit: NASA

Viking 2 was launched on September 9, 1975 using a Titan/Centaur rocket. After a 333 day cruise to Mars, the Viking 2 Orbiter entered Mars orbit on August 7, 1976. The Lander detached from the Orbiter on September 3rd. While normal operations called for the structure connecting the Orbiter and Lander (the bioshield) to be ejected after separation, the bioshield was left attached to the Orbiter because of problems with the separation.

The Viking 2 Lander touched down about 200 km west of the crater Mie in Utopia Planitia at 48.269º North, 225.990º West at 22:58:20 UT (9:49:05 a.m. local Mars time). Due to radar misidentification of a rock or highly reflective surface, the thrusters fired an extra time 0.4 seconds before landing, cracking the surface and raising dust. The lander settled down with one leg on a rock, tilted at 8.2 degrees. The cameras began taking images immediately after landing.

The Orbiter's primary mission ended at the beginning of solar conjunction on November 8, 1976. The extended mission commenced on December 14, 1976 after the solar conjunction. On December 20th, 1976 the periapsis was lowered to 778 km. Operations included close approaches to Deimos in October 1977, and the periapsis was lowered to 300 km and the period changed to 24 hours on 23 October 1977. The Orbiter developed a leak in its propulsion system that vented its attitude control gas. It was turned off on July 25, 1978 after returning almost 16,000 images in 706 orbits around Mars.

As for the Viking 2 Lander, it operated on the surface for 1,281 Mars days, and was turned off on April 11, 1980 when its batteries failed.

The above picture is the second image of the Martian surface taken by the Viking Lander 2, shortly after touchdown on September 3, 1976. The picture sweeps around 330°, starting from northwest at the left through north (above the sampler arm housing) past east, where the sky is bright at the center, and southeast toward the right above the radioisotope thermoelectric generator cover. The surface is strewn with rocks out to the horizon, ranging in size up to several meters across. Some pitted rocks resemble fragments of porous volcanic lava. Other rocks have grooves that may have been eroded by windblown sand and dust. Although fine-grained material is seen between the boulders, no sand dunes are evident. The dip in the eastern horizon at the center is an illusion caused by an 8° tilt of the Lander toward the west. Actually, the terrain is more level than that at the Viking 1 site. The horizon toward the left of the panorama (northwest) appears featureless, indicating that it may be several kilometers distant. The sky at the center (east) is bright because the sun was above but out of the picture at 10 a.m. Mars time. Toward the right (southeast), the rocks that are silhouetted against the skyline indicate that the horizon is much nearer, probably because of a slight rise in that area of the terrain. The circular high-gain antenna at the right has clots of fine-grained material adhering to the lower half, some of which appeared to have been sliding downward while the camera was scanning the area. At the extreme right, the banded appearance resulted because the camera continued to scan while it was no longer moving in azimuth. Any motion or other variation in the scene would show up as a change in successive lines.

Viking 1

Credit: NASA

Viking 1 was launched on August 20, 1975 using a Titan/Centaur rocket. Ten months later, the orbiter began taking photos of Mars five days prior to Mars orbit insertion, which occurred on June 19, 1976. The landing of the Viking 1 Lander was originally planned for July 4, 1976, the United States Bicentennial, but photos of the primary landing site showed that it was too rough for a safe landing. The landing was delayed until July 20th, when a safer site had been found.

The Lander and its aeroshell separated from the orbiter at 8:51 (UT) on July 20th. After a few hours, at about 300 km altitude, the Lander was reoriented for atmospheric entry. The aeroshell with its ablative heat shield slowed the craft as it plunged through the atmosphere. During this time, entry science experiments were performed. At 6 km altitude, traveling at about 250 meters per second, the Lander's parachutes were deployed. Seven seconds later the aeroshell was jettisoned, and eight seconds after that the three lander legs were extended. At 1.5 km altitude, retrorockets on the lander itself were ignited and, 40 seconds later, at about 2.4 meters per second, the Lander arrived with a relatively light jolt. The Viking 1 Lander is located in the western Chryse Planitia at 22.697° North, 48.222° West.

The landing rockets used an 18 nozzle design to spread the hydrogen and nitrogen exhaust over a wide area. It was determined that this would limit surface heating to no more than 1 degree Celsius and that no more than 1 mm of the surface material would be stripped away. Since most of Viking's experiments centered on this surface material a more straightforward design would not have served. This system was never used again on a Martian landing. It was relatively heavy and cumbersome, and the system used now - surrounding the probe with airbags for a bouncing landing - has been in use ever since.

Transmission of the first surface image began 25 seconds after landing. The seismometer failed to uncage, and a sampler arm locking pin was stuck and took 5 days to shake out. All the other experiments functioned nominally. In January 1982, the Viking 1 Lander was named the Thomas Mutch Memorial Station in honor of the leader of the Viking imaging team.

The Orbiter's primary mission ended at the beginning of the solar conjunction on November 5, 1976. The extended mission commenced on 14 December 1976 after the solar conjunction. Operations included close approaches to Phobos in February 1977. The periapsis (lowest point of the orbit) was reduced to 300 km on March 11, 1977. Minor orbit adjustments were done occasionally over the course of the mission, primarily to change the walk rate — the rate at which the planetocentric longitude changed with each orbit, and the periapsis was raised to 357 km on 20 July 1979. On August 7, 1980, the Viking 1 Orbiter was running low on altitude control gas and its orbit was raised to prevent the Orbiter impacting with Mars (and possible contamination of the planet) until the year 2019. Operations were terminated on August 17, 1980 after 1,485 orbits.

The Lander operated for 2,245 sols, until November 13, 1982, when a faulty command sent by ground control resulted in loss of contact. The command was intended to uplink new battery charging software to improve the Lander's deteriorating battery capacity, but the software inadvertently overwrote data used by the antenna pointing software. Attempts to contact the lander during the next four months, based on the presumed antenna position, were unsuccessful. In 2006 the Viking 1 lander was imaged on the Martian surface by the Mars Reconnaissance Orbiter.

The above picture is the first panoramic view by Viking 1 from the surface of Mars. The out of focus spacecraft component toward left center is the housing for the Viking sample arm, which was not yet deployed. Parallel lines in the sky are an artifact and are not real features. However, the change of brightness from horizon towards zenith and towards the right (west) is accurately reflected in this picture, taken in the late Martian afternoon. At the horizon to the left is a plateau-like prominence much brighter than the foreground material between the rocks. The horizon features are approximately three km (1.8 miles) away. At left is a collection of fine-grained material reminiscent of sand dunes. The dark sinuous markings in the left foreground are of unknown origin. Some unidentified shapes can be perceived on the hilly eminence at the horizon towards the right. A horizontal cloud stratum can be made out halfway from the horizon to the top of the picture. At left is seen the low gain antenna for the receipt of commands from the Earth. The projections on or near the horizon may represent the rims of distant impact craters. In the right foreground are color charts for the calibration of the Lander camera, a mirror for the Viking magnetic properties experiment, and part of a grid on the top of the Lander body. At upper right is the high gain dish antenna for direct communication between landed spacecraft and Earth. Toward the right edge is an array of smooth, fine-grained material which shows some hint of ripple structure and may be the beginning of a large dune field off to the right of the picture, which joins with dunes seen at the top left in this 300° panoramic view. Some of the rocks appear to be undercut on one side and partially buried by drifting sand on the other.

Viking 1's First Picture

Credit: NASA

The above photo is the first picture from the surface of Mars, taken by Viking 1 on July 20, 1976.

The camera began scanning the scene 25 seconds after touchdown and continued to scan for five minutes. The picture was assembled from left to right during the 20 minutes it took to transmit the data from the Orbiter relay station to Earth. The first segment to be displayed was a narrow strip at the far left. About all that could be determined was the presence of bright and dark areas in the scene, but even that was cause for elation. Ironically, some viewers were more impressed by the picture of the footpad than by the view of the martian surface, marveling at the fidelity with which the rivets were displayed.

The lower edge of the picture is at a slant range of about 1.5 m, the upper edge about 2 m. The larger rocks are about 10 cm across...

The vertical streaking in the left quarter of the picture stimulated a variety of explanations. Those of us familiar with camera operation doubted that it represented a camera malfunction. Instead, something was causing the light levels to vary during the first 1 1/2 minutes following touchdown. It was suggested that clouds were passing in front of the Sun, or, more improbably, that the deployed parachute was casting a shadow as it drifted between the Sun and the Lander. It seemed most likely that dust, kicked up at the time of the landing, was briefly entrained in the lower atmosphere between the camera and the surface. This argument was strengthened by the observation of a sizable accumulation of dirt in the upper concave part of the footpad. Demonstration of the transient nature of the effect is provided by a later picture of the same area taken with the same approximate lighting. Note that the streaks have disappeared.
-- The Martian Landscape - The First Picture

Viking Landers

Credit: NASA

The heart of the Viking Program was the two landers, which constituted about 80 to 90 percent of the program. The primary mission of the Viking landers was to determine, if possible, whether there was any life on the surface of Mars. "The lander should include an ensemble of complementing experiments relevant to the possible existence of life on Mars, since no single experiment is either completely definitive or unambiguous.'' Coupled but dissimilar experiments would be one satisfactory approach, such as a mass spectrometer that could detect carbon-containing compounds and a life detector that could search for signs of grossing organisms with a carbon base. Other lander experiments the panel suggested included mass spectrometry for determining atmospheric composition, x-ray fluorescent examination of soil composition, and determination of subsurface water vapor, among others.

Once the lander's mission and its method of landing was settled (a soft landing was chosen), weight and volume constraints began to affect the construction of the lander and its various subsystems. After the Voyager Program with plans for an 11,500 kg spacecraft was abandoned in 1967, a follow-on study concluded that a spacecraft weighing 3,700 kg could he transported to Mars by a Titan-Centaur-class launch vehicle. The lander and its flight capsule would account for more than a third of this weight (1,195 kg). At the start of the mission, the orbiter and lander would be housed in a 4.3-meter shroud atop the Titan-Centaur. The landed spacecraft would be 3 meters at its widest point and 2 meters tall from the footpads to the tip of the large disk S-band high-gain antenna.

Instrumentation included two 360° cylindrical scan cameras mounted near one long side of the base. From the center of this side extended the sampler arm, with a collector head, temperature sensor, and magnet on the end. A meteorology boom, holding temperature, wind direction, and wind velocity sensors extended out and up from the top of one of the lander legs. A seismometer, magnet and camera test targets, and magnifying mirror were mounted opposite the cameras, near the high-gain antenna. An interior environmentally controlled compartment held the biology experiment and the gas chromatograph mass spectrometer. The X-ray fluorescence spectrometer was also mounted within the structure. A pressure sensor was attached under the lander body. The scientific payload had a total mass of approximately 91 kg. The lander was then enclosed into a bioshield and baked for decontamination so as to prevent the contamination of the Martian surface by terrestrial organisms.

The above photograph is a model of the Viking Lander.

Viking and Its Orbiters

Credit: NASA

By the 1975 launch window, the USSR had mostly given up on Mars. Since October 1960 they had launched a total of 16 missions, with only very limited success for all of their efforts. They would not launch any more spacecraft to Mars until the summer of 1988.

The 1975 launch window is known for two amazingly successful missions to Mars: Viking 1 and Viking 2. Until the mid-90s, most of the information humanity had learned about Mars came from the Viking Program. To be honest, the amount of data and photographs available from the two Viking missions alone could probably keep this blog running for years: by itself, the Viking 2 Orbiter took almost 16,000 images. So, while one blog post is not enough to present a brief synopsis of the Viking missions, we will spend a few days discussing these two spacecraft and their results before resuming our history of missions to Mars.

As mentioned yesterday, the Viking Program grew out of the canceled Voyager Mars Program.but also had its roots in the Mariner Program. In fact, the Viking Orbiter was originally based on the Mariner 9 spacecraft. However, with the decision to have both a lander and an orbiter, the size and complexity of the orbiter quickly grew. The orbiter would now transport the lander to Mars, provide a platform for the Viking imaging system so that proposed landing sites could be surveyed and certified, relay lander science information (pictures and other data in an electronic format) to Earth, and conduct scientific observations in its own right. Moreover, the orbiter would not only have to transport the lander, it would also have to carry an increased supply of propellant for longer engine firings during the Mars orbit insertion, longer than those planned for the 1971 Mariner mission. And an upgraded attitude control system with greater impulse, plus a larger supply of attitude control propellant, would be required to control the combined spacecraft. Additionally, the orbiter would have to provide power to the lander during the flight to Mars, especially during the periodic checkups on the lander's health and during occasional updates of the landers computerized memory. These additional energy requirements made it necessary to increase significantly the solar panels, from 7.7 square meters to 15.4.

Scientific instruments aboard the Viking Orbiters included cameras for visible light imaging and for infrared thermal mapping. The orbiter could also study the water vapor in Mars' atmosphere, and radio science investigations could be made through the spacecraft's transmitter.

The above photograph is a model of the Viking Orbiter.

The Voyager Mars Program

Credit: NASA

Starting in 1960, NASA began working on a series of unmanned probes to Mars (and Venus) that was named the Voyager Program. This program (not to be confused with Voyager 1 and Voyager 2, which were sent toward the outer planets) was planned to set the stage for manned landings on Mars in the 1980s.

Originally NASA had proposed a direct lander using a variant of the Apollo Command Module launched atop a Saturn 1B rocket with a Centaur upper stage. With the discovery by Mariner 4 in 1965 that Mars had only a tenuous atmosphere, the mission was changed to have both an orbiter and lander. The orbiters would have been a modified Mariner probe identical to that employed for Mariner 8 and Mariner 9, while the landers were to be modified Surveyor moon probes that landed through the use of aeroshells and a combination parachute/retro-rocket landing systems.

Politics involving the use of specific boosters played a role in the unravelling the program. As mentioned above, Voyager was to be launched originally on a Saturn 1B-Centaur combination. In mid-October 1965, NASA announced that development of the Saturn 1B-Centaur would be terminated, with Voyager being launched on a Saturn V booster instead. The Titan IIIC was looked at as an alternative booster, but was determined to be too weak to carry the payload weight.

And yet, the Saturn V was too powerful a rocket for just one Voyager mission. JPL, which had been managing the program since the beginning, had operated under the assumption that it would launch a fly-by test mission in 1969 and two complete missions in 1971 and 1973. The use of a Saturn V booster would mean that the two missions would have to be launched together on the same rocket. Moreover, the program would become too costly because the increased payload capability of the Saturn V booster would "escalate the cost of the spacecraft," and it would be too big a technological leap over the Mariners that were then being planned and launched.

On December 22, 1965, JPL was notified that there would be no 1971 mission; the earliest Voyager would now fly would be 1973. According to this plan, both spacecraft would orbit Mars and release large landing capsules that would search for evidence of Martian life. Work on the Voyager spacecraft would "go on a low back burner basis for the next year and a half to two years before [it was picked] up again." JPL would continue design work on landing capsules with support from Langley and Ames, but the next phase of the procurement cycle would be delayed "for some time."

In 1968, funding was cut for the Voyager Mars Program (along with the larger Apollo Applications Program, of which the Voyager Mars Program was only a part). $150 million had been requested in the 1967 budget to begin hardware development for Voyager. However, only $10 million was allocated, largely because the Apollo and Surveyor programs were reaching critical periods in their maturation, which left the planetary mission budgets taking the largest cuts. In essence, there was not enough money for both the moon and the planets. In 1971, the mission was cancelled completely, primarily on the grounds that launching both probes on the same rocket was both expensive and risky.

Despite the cancellation, the trials and tribulations of the Voyager Mars Program laid the foundation for the very successful Viking Program of the 1970s.

The above diagram shows the proposed Voyager lander as of September 1966. The lander's design was quite similar to that of the Viking landers, which would reach Mars in 1976. Similar elements included the tripod landing gear, large direct-link high-gain antenna, smaller relay antenna, and radioisotope thermoelectric generators. The 1966 design already had a boom soil sampler and a television camera, but the scientific experiments would need more definition for a biological mission. The plan across the legs of the Voyager lander was nearly twice that of the Viking; likewise, the proposed weight was about twice that of Viking.

Mars 4 - 7

Credit: Russian Academy of Sciences/Don P. Mitchell

The 1973 launch window was dominated solely by the Soviet Union, which launched four spacecraft, Mars 4 through 7. NASA, at this time, was busy preparing for the Viking missions, which lifted off in the next launch window, in 1975.

The four Mars spacecraft was the Soviet Union's political attempt to steal the United State's thunder by soft-landing two landers onto Mars two years prior to Viking. To accomplish these plans, the four Mars spacecraft each carried separate pieces needed for the whole mission. Mars 4 and 5 were designed to orbit Mars and return information on the composition, structure, and properties of the Martian atmosphere and surface. The spacecraft were also designed to act as communications links for the Mars 6 and 7 landers. These latter two landers were carried by orbiter-style buses that didn't carry enough fuel to enter orbit. This split-up between the four spacecraft was done because the 1973 Mars launch window was inefficient, and the Proton rockets couldn't deliver the same amount of mass to Mars as they were able to do in 1971.

Mars 4 was launched on July 21, 1973, and arrived at Mars on February 10, 1974. Due to a flaw in a computer chip, resulting in degradation of the chip during the voyage to Mars, the retro-rockets designed to slow the craft into Mars orbit didn't fire, and Mars 4 flew by the planet at a range of 2200 km. It returned one swath of pictures and some radio occultation data, which constituted the first detection of the nightside ionosphere on Mars. It continued to return interplanetary data from solar orbit after the flyby.

Mars 5 was launched four days later, on July 25th, and arrived on February 12th. The spacecraft was able to achieve an elliptical orbit that took 24 hours, 53 minutes to complete, with an inclination of 35.3°. Nearly synchronized with the rotation of the planet, its two photo-television cameras could take up to 12 pictures during each close approach. The "Vega" camera used a wide area 52mm lens with color filters; the "Zulfar" camera used a telescopic 350mm lens and a long-pass orange filter. Images were transmitted in a rapid 220-line mode, and then selected pictures were retransmitted at 880 or 1760 line resolution. Mars 5 collected data for 22 orbits until a loss of pressurization in the transmitter housing ended the mission. About 60 images were returned over a nine day period showing swaths of the area south of Valles Marineris, from 5° North, 330° West to 20° South, 130° West.

Mars 6 was launched on August 5th, and arrived at Mars on March 12th. The descent module separated from the bus at a distance of 48,000 km from Mars. The bus continued on into a heliocentric orbit after passing within 1600 km of Mars. The descent module entered the atmosphere at 09:05:53 UT at a speed of 5.6 km/s. The parachute opened at 09:08:32 UT after the module had slowed its speed to 600 m/s by aerobraking. During this time the craft was collecting data and transmitting it directly to the bus for immediate relay to Earth. Contact with the descent module was lost at 09:11:05 UT in "direct proximity to the surface," probably either when the retrorockets fired or when it hit the surface at an estimated 61 m/s. Mars 6 landed in the Margaritifer Terra region of Mars (23.90° South, 19.42° West). The descent module transmitted 224 seconds of data before transmissions ceased, the first data returned from the atmosphere of Mars. Unfortunately, much of the data were unreadable due to a flaw in a computer chip, leading to a degradation of the system during its journey to Mars.

The final spacecraft, Mars 7, was launched four days after Mars 6, on August 9th, and arrived three days prior, on March 9th. Due to a problem in the operation of one of the on-board systems (attitude control or retro-rockets) the landing probe separated prematurely (4 hours before encounter) and missed the planet by 1300 km. The early separation was probably due to a computer chip error which resulted from degradation of the systems during the trip to Mars. The intended landing site was 50° South, 28° West, in the Noachis Terra region, east of Argyre Planitia. The Mars 7 lander and bus continued on into heliocentric orbits.

The above image is a composite of three photos taken by the Mars 5 "Vega" camera on February 23, 1974. Frame 9 was taken with a green filter, frame 10 was taken with a red filter, and frame 11 was taken with a blue filter. Unfortunately, I do not know the location of these three pictures. However, the image does give a decent indication of the quality of the Soviet camera technology at the time.

Olympus Mons Caldera

Credit: ESA / DLR / FU Berlin (G. Neukum)

Earlier this week, we compared Mariner crater as it had been photographed by three separate spacecraft. Today, I thought I'd compare the Olympus Mons caldera. Yesterday, I highlighted a photograph taken by Mariner 9 in 1972 of the caldera. Today's picture was taken by Mars Express on January 21, 2004. This is the first high-resolution color image of the complete caldera of Olympus Mons. The image was taken from a height of 273 km in orbit 37 by Mars Express's High Resolution Stereo Camera (HRSC). The view is centred at 18.3° North and 227° East. The image is about 102 km across with a resolution of 12 m per pixel, South is up (i.e., the image is upside down compared to yesterday's image).

Mariner 9

Credit: NASA

The last mission to Mars launched in 1971 was Mariner 9, which lifted off on May 30th, two days after Mars 3. However, due to a tighter trajectory, Mariner 9 reached Mars on November 14th, shortly before both Mars 2 and Mars 3, which reached Mars on November 22nd and December 2nd, respectively.

Mariner 9 was designed to continue the atmospheric studies begun by Mariner 6 and 7, and to map over 70% of the Martian surface from the lowest altitude (1500 km) and at the highest resolutions (1 km per pixel to 100 m per pixel) of any Mars mission up to that time. An infrared radiometer was included to detect heat sources as evidence of volcanic activity. Mariner 9 was also to study temporal changes in the Martian atmosphere and surface as well as Phobos and Deimos.

Upon arrival, Mariner 9 observed that a great dust storm was obscuring the whole globe of the planet. Ground controllers sent commands to the spacecraft to wait until the dust had settled and the surface was clearly visible before compiling its global mosaic of high-quality images of the Martian surface. The storm persisted for a month, but after the dust cleared, Mariner 9 proceeded to reveal a very different planet than expected -- one that boasted gigantic volcanoes and a grand canyon stretching 4,800 km (3,000 miles) across its surface. This canyon, Valles Marineris, Latin for the "Valley of the Mariner," was named after Mariner 9.

Mariner 9 exceeded all primary photographic requirements by photo-mapping 100 percent of the planet's surface. The spacecraft also provided the first closeup pictures of the two small, irregular Martian moons: Phobos and Deimos.

The Mariner 9 mission was concluded on October 27, 1972, when the spacecraft ran out of altitude control gas. Mariner 9 remains in orbit around Mars where it is expected to survive until the year 2022, when it may finally crash onto the Martian surface.

The above photo is of the Olympus Mons caldera. This photo was taken in 1972 on Mariner 9's 230th orbit, approximately 4,000 km above the Martian surface. The basic morphology is similar to terrestrial calderas, although the scale is much larger. The smallest (and youngest) collapse pit, at right, is 30 km across. Concentric fractures and terraces are visible in the larger parts of the caldera. The caldera is about 29 km above the mean Martian surface. North is at 7:00.

Mars 2 & 3

Credit: Russian Academy of Sciences/Don P. Mitchell

A total of five spacecraft were launched in 1971 with the intention of going to Mars. This post will cover the first four.

On May 8, the US launched Mariner 8. This satellite was to orbit Mars for a minimum of 90 days, during which time the spacecraft would gather data on the composition, density, pressure and temperature of the atmosphere, and the composition, temperature and topography of the surface. However, during liftoff, the upper stage of the Atlas-Centuar rocket began to tumble out of control. The Centaur stage of the rocket and Mariner 8 separated and re-entered the Earth's atmosphere approximately 1500 km downrange, falling into the Atlantic Ocean about 560 km north of Puerto Rico.

Two days later, on May 10th, the Soviet Union launched Cosmos 419. There is uncertainty over whether this spacecraft was to have been a combined orbiter and lander (as the next two spacecraft discussed, Mars 2 and 3, were) or if it was to be a single orbiter like Mariner 8. Regardless, Cosmos 419 failed to separate from the fourth stage of its Proton rocket, and fell back to earth two days later. The stage 4 timer was originally set to fire 1.5 hours after reaching its parking orbit; however, the timer was actually set to fire 1.5 years later.

Mars 2 and Mars 3 represented a partial triumph for the Soviet Union's space program. These two missions to Mars, the 11th and 12th overall that the Soviet Union had attempted, were the most successful of any to that point in time. Both missions used identical spacecraft, consisting of an orbiter and a lander. The orbiters' primary scientific objectives were to image the Martian surface and clouds, determine the temperature on Mars, study the topography, composition and physical properties of the surface, measure atmospheric properties, monitor the solar wind and the interplanetary and Martian magnetic fields, and act as communications relays to send signals from the landers to Earth. The landers, which would descend to the surface by parachute and retro-rockets, contained several instruments, including two television cameras and a mass spectrometer. They also contained a small rover that would move about on two wide, flat skis after being placed on the surface by a manipulator arm. The rover was attached to the lander by a 15 meter umbilical.

Mars 2 successfully entered Martian orbit on November 27, 1971, orbiting once every 17.96 hours with a closest approach of 1,380 km. The lander had separated from the orbiter 4.5 hours prior to reaching orbit. While plummeting through the atmosphere, the descent system on the lander malfunctioned, possibly because the angle of entry was too steep. The descent system did not operate as planned and the parachute did not deploy. The lander crashed at 4° North, 47° West (per Wikipedia; according to NASA, the lander crashed at 45° South, 313° West). Mars 2 was the first manmade object to reach the surface of Mars.

Mars 3 was not quite as lucky as Mars 2. By the time of its orbital insertion, the orbiter did not have enough fuel to put itself into a planned 25 hour orbit. As a result, the orbiter swung into a long 12 day, 19 hour orbit. The closest point of the orbit was 1,500 km, but the farthest point was 211,400 km (in comparison to Mars 2's 24,940 km apoapsis). Like the Mars 2 lander, the Mars 3 lander was released about 4.5 hours prior to reaching orbit. However, unlike the other lander, the Mars 3 lander successfully soft-landed onto the Martian surface (45° South, 158° West) and began operations. Unfortunately, 20 seconds later, transmission on both data channels stopped for unknown reasons and no further signals were received from the Martian surface. It is not known whether the fault originated with the lander or the communications relay on the orbiter. A partial panoramic image returned showed no detail and a very low illumination of 50 lux. The cause of the failure may have been related to the extremely powerful Martian dust storm taking place at the time, which may have induced a coronal discharge, damaging the communications system. The dust storm would also explain the poor image lighting.

The two orbiters, however, worked as planned and transmitted most of their data between December 1971 and March 1972, although both orbiters continued transmissions through August 1972. On August 22, the Soviet Union announced that both missions had been completed; Mars 2 had completed 362 orbits, with 20 orbits by Mars 3. A total of 60 photographs were sent back. The images and data revealed mountains as high as 22 km, atomic hydrogen and oxygen in the upper atmosphere, surface temperatures ranging from -110 C to +13 C, surface pressures of 5.5 to 6 mb, water vapor concentrations 5000 times less than in Earth's atmosphere, the base of the ionosphere starting at 80 to 110 km altitude, and grains from dust storms as high as 7 km in the atmosphere. The images and data enabled the creation of surface relief maps, and gave information on the Martian gravity and magnetic fields.

The photo above is a composite image from the Mars-3 52 mm camera, using its program of cycling red, green and blue glass filters.

Mariner 6 and 7

Credit: NASA

To continue our history...

Two days after the launch of Mariner 4, the Soviets launched Zond 2. However, during some maneuvering, Zond 2 lost contact with Earth on May 5, 1965. Operating on limited power, most probably due to a solar panel not having deployed properly, the spacecraft continued on and is believed to have flown by Mars on August 6.

During the next launch window, in spring 1969, four spacecraft lifted off for Mars. The two Soviet craft, Mars 1969A and Mars 1969B, were both lost during the launch. The third stage of the Proton rocket carrying 1969A exploded, causing the rocket and spacecraft debris to be strewn over the Altai mountains; likewise, the first stage of 1969B's Proton rocket malfunctioned and crashed to the ground 41 seconds after liftoff, approximately 3 km from the launch site.

The American spacecraft were Mariner 6 and 7 (Mariner 5 was sent to Venus). This was a dual mission: Mariner 6 was launched 31 days before Mariner 7; however, because Mariner 7 traveled a tighter path to Mars, it flew by Mars only four days after Mariner 6. The mission's goals were to study the surface and atmosphere of Mars during close flybys to establish the basis for future investigations, particularly those relevant to the search for extraterrestrial life, and to demonstrate and develop technologies required for future Mars missions and other long-duration missions far from the Sun. Mariner 6 also had the objective of providing experience and data which would be useful in programming the Mariner 7 encounter.

On July 29, 1969, less than a week before the closest approach, JPL lost contact with Mariner 7. They regained the signal via the backup low-gain antenna and were able to start using the high gain antenna again shortly after Mariner 6's close encounter. It was later determined that a battery onboard Mariner 7 had exploded. Based on the observations made by Mariner 6, Mariner 7 was reprogrammed in flight to take further observations of areas of interest and actually returned more pictures than Mariner 6, despite the explosion. Both Mariners took a total of 198 photos, 143 pictures of Mars as the two spacecraft approached the planet, and 55 close-up pictures. Mariner 6 flew past the equatorial region of Mars, while Mariner 7 flew over the southern polar region.

Mariner 6 and 7 revealed cratered deserts, as well as depressions with no craters, huge concentrically terraced impact regions, and collapsed ridges. However, both spacecraft missed the giant northern volcanoes and Valles Marineris, the equatorial grand canyon, discovered later. Their approach pictures did, however, photograph about 20% of the planet's surface (compared with 1% of the planet's surface by Mariner 4), showing the dark features long seen from Earth, but none of the canals mistakenly observed by ground-based astronomers.

The above image, number 6N21, was taken by Mariner 6. The dark area to the left is Sinus Sabaeus and the lighter area is Deucalionis Regio. A careful crater count in both regions shows that there is no significant difference in the crater distribtions between the dark and light areas.

Mariner Crater from 1964 through 1999

Credit: NASA/Malin Space Science Systems

Before we move on, now would be a good time to show just how good the optics have become on the various missions to Mars. Yesterday, we showed a photo taken of Mariner crater by Mariner 4. Malin Space Science Systems, which helped to build the Mars Orbiter Camera (MOC) on board Mars Global Surveyor (MGS), has an interesting comparison using Mariner crater over a 34-year span. This first picture is of Mariner crater taken by Mariner 4; Malin has added a white arrow to the photo that references the third picture (below).



Our second picture is of Mariner crater taken by the Viking 1 Orbiter back in February 1978. As you can see, the crater detail is crystal clear, especially of that linear ridge (part of Sirenum Fossae) that cuts diagonally across the bottom of the crater.



The last photo is some detail of the rim of Mariner crater taken by the MOC on March 18, 1999; remember, this is that tiny point indicated by the white arrow in the first photo above. The resolution of this photo to the first above is almost 400 times greater than what was capable back in the mid 60s. This view of the Mariner crater floor has a spatial resolution of 1.5 meters (5 feet) per pixel and covers an area only 1.5 km (0.9 mi) wide by 2.2 km (1.4 mi) long, whereas Mariner crater as a whole is 151 km wide.