Mars Missions:

Since the 16th century, learned men have recognized Mars for what it is-a relatively nearby planet not so unlike our own. The fourth planet from the sun and Earth's closest neighbor, Mars has been the subject of modern scientists' careful scrutiny with powerful telescopes, deep space probes, and orbiting spacecraft. In 1976, Earth-bound scientists were brought significantly closer to their subject of investigation when two Viking landers touched down on that red soil. The possibility of life on Mars, clues to the evolution of the solar system, fascination with the chemistry, geology, and meteorology of another planet-these were considerations that led NASA to Mars. Project Viking's goal, after making a soft landing on Mars, was to execute a set of scientific investigations that would not only provide data on the physical nature of the planet but also make a first attempt at determining if detectable life forms were present.

Landing a payload of scientific instruments on the Red Planet had been a major NASA goal for more than 15 years. Two related projects-Mariner B and Voyager-preceded Viking's origin in 1968. Mariner B, aimed at placing a capsule on Mars in 1964, and Voyager, which would have landed a series of sophisticated spacecraft on the planet in the late 1960s, never got off the ground. But they did lead directly to Viking and influenced that successful project in many ways.

When the space agency was established in 1958, planetary exploration was but one of the many projects called for by scientists, spacecraft designers, and politicians. Among the conflicting demands made on the NASA leadership during the early months were proposals for Earth-orbiting satellites and lunar and planetary spacecraft. But man in space, particularly under President John F. Kennedy's mandate to land an American on the moon before the end of the 1960s, took a more than generous share of NASA's money and enthusiasm. Ranger, Surveyor, and Lunar Orbiter-spacecraft headed for the moon-grew in immediate significance at NASA because they could contribute directly to the success of manned Apollo operations. Proponents of planetary investigation were forced to be content with relatively constrained budgets, limited personnel, and little publicity. But by 1960 examining the closer planets with rocket-propelled probes was technologically feasible, and this possibility kept enthusiasts loyal to the cause of planetary exploration.


Viking Mission:

NASA's Viking Mission to Mars was composed of two spacecraft, Viking 1 and Viking 2, each consisting of an orbiter and a lander. The primary mission objectives were to obtain high resolution images of the Martian surface, characterize the structure and composition of the atmosphere and surface, and search for evidence of life.

The Viking Landers transmitted images of the surface, took surface samples and analyzed them for composition and signs of life, studied atmospheric composition and meteorology, and deployed seismometers. The Viking 2 Lander ended communications on April 11, 1980, and the Viking 1 Lander on November 13, 1982, after transmitting over 1400 images of the two sites.

The results from the Viking experiments gave our most complete view of Mars. Volcanoes, lava plains, immense canyons, cratered areas, wind-formed features, and evidence of surface water are apparent in the Orbiter images. The planet appears to be divisible into two main regions, northern low plains and southern cratered highlands. Superimposed on these regions are the Tharsis and Elysium bulges, which are high-standing volcanic areas, and Valles Marineris, a system of giant canyons near the equator. The surface material at both landing sites can best be characterized as iron-rich clay. Measured temperatures at the landing sites ranged from 150 to 250 K (what is this in Fahrenheit? click here), with a variation over a given day of 35 to 50 K. Seasonal dust storms, pressure changes, and transport of atmospheric gases between the polar caps were observed. The biology experiment produced no evidence of life at either landing site.

The Viking mission represented a careful melding of the demands imposed by the scientific mission and the high degree of reliability required of the spacecraft subsystems. Weight and volume considerations affected the size of each subsystem. After the Voyager program with plans for an 11,500-kilogram spacecraft was abandoned in 1967, a follow-on study concluded that a spacecraft weighing 3700 kilograms 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 (1195 kilograms). 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. While weight and volume limitations helped to shape the Viking lander, data about Martian atmospheric pressure obtained during the Mariner 9 mission were also influential.

Viking 1 was launched on August 20, 1975 and arrived at Mars on June 19, 1976 after a 10 month cruise to Mars. The orbiter began returning global images of Mars about 5 days before orbit insertion. The Viking 1 Orbiter was inserted into Mars orbit on 19 June 1976 and trimmed to a 1513 x 33,000 km, 24.66 hr site certification orbit on 21 June. Imaging of candidate sites was begun and the landing site was selected based on these pictures. The lander separated from the orbiter on 20 July 08:51 UT and landed at Chryse Planitia at 11:56:06 UT. The orbiter primary mission ended at the beginning of solar conjunction on 5 November 1976. The extended mission commenced on 14 December 1976 after solar conjunction. Operations included close approaches to Phobos in February 1977. The periapsis was reduced to 300 km on 11 March 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 7 August 1980 Viking 1 Orbiter was running low on attitude control gas and its orbit was raised from 357 x 33943 km to 320 x 56000 km to prevent impact with Mars and possible contamination until the year 2019. Operations were terminated on 17 August 1980 after 1485 orbits. The total cost of the Viking project was roughly one billion dollars.

Viking 2 was launched September 9, 1975 and entered Mars orbit on August 7, 1976 after a 333 day cruise to Mars. The Viking 2 Orbiter began returning global images of Mars prior to orbit insertion. The orbiter was inserted into a 1500 x 33,000 km, 24.6 hr Mars orbit on 7 August 1976 and trimmed to a 27.3 hr site certification orbit with a periapsis of 1499 km and an inclination of 55.2 degrees on 9 August. Imaging of candidate sites was begun and the landing site was selected based on these pictures and the images returned by the Viking 1 Orbiter. The lander separated from the orbiter on 3 September 1976 and landed at Utopia Planitia at 22:37:50 UT. Normal operations called for the structure connecting the orbiter and lander (the bioshield) to be ejected after separation, but because of problems with the separation the bioshield was left attached to the orbiter. The orbit inclination was raised to 75 degrees on 30 September 1976. The orbiter primary mission ended at the beginning of solar conjunction on 8 November 1976. The extended mission commenced on 14 December 1976 after solar conjunction. On 20 December 1976 the periapsis was lowered to 778 km and the inclination raised to 80 degrees. 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 placed in a 302 x 33176 km orbit and turned off on 25 July 1978 after returning almost 16,000 images in 706 orbits around Mars.


Viking Orbiter:

The primary objectives of the Viking orbiters were to transport the landers to Mars, perform reconnaissance to locate and certify landing sites, act as a communications relays for the landers, and to perform their own scientific investigations. The orbiter, based on the earlier Mariner 9 spacecraft, was an octagon approximately 2.5 m across. The total launch mass was 2328 kg, of which 1445 kg were propellant and attitude control gas. The eight faces of the ring-like structure were .4572 m high and were alternately 1.397 and 0.508 m wide. The overall height was 3.29 m from the lander attachment points on the bottom to the launch vehicle attachment points on top. There were 16 modular compartments, 3 on each of the 4 long faces and one on each short face. Four solar panel wings extended from the axis of the orbiter, the distance from tip to tip of two oppositely extended solar panels was 9.75 m. The power was provided by eight 1.57 x 1.23 m solar panels, two on each wing. The solar panels were made up of a total of 34,800 solar cells and produced 620 W of power at Mars. Power was also stored in 2 nickel-cadmium 30-amp-hr batteries.

The main propulsion unit was mounted above the orbiter bus. Propulsion was furnished by a bipropellant (monomethyl hydrazine and nitrogen tetroxide) liquid-fueled rocket engine which could be gimballed up to 9 degrees. The engine was capable of 1323 N thrust, translating to a delta-V of 1480 m/s. Attitude control was achieved by 12 small compressed-nitrogen jets. An acquisition Sun sensor, a cruise Sun sensor, a Canopus star tracker and an inertial reference unit consisting of 6 gyroscopes allowed three-axis stabilization. Two accelerometers were also on board. Communications were accomplished through a 20-W S-band (2.3 GHz) transmitter and 2 20-W TWTA's. An X-band (8.4 GHz) downlink was also added specifically for radio science and to conduct communications experiments. Uplink was via S-band (2.1 GHz). A 2-axis steerable high-gain parabolic dish antenna with a diameter of approximately 1.5 m was attached at one edge of the orbiter base, and a fixed low-gain antenna extended from the top of the bus. Two tape recorders were each capable of storing 1280 Mbits. A 381 MHz relay radio was also available.

Scientific instruments for conducting imaging, atmospheric water vapor, and infrared thermal mapping were enclosed in a temperature controlled, pointable scan platform extending from the base of the orbiter. The scientific instrumentation had a total mass of approximately 72 kg. Radio science investigations were also done using the spacecraft transmitter. Command processing was done by two identical and independent data processors, each with a 4096-word memory for storing uplink command sequences and acquired data.


Viking Lander:

Mariner 9's occultation experiment indicated that the atmospheric pressure at the surface of Mars ranged from 4 to 20 millibars, rather than 80 millibars as estimated earlier. This information had a definite impact on the aerodynamic shape of the Mars entry vehicle being designed, since weight and diameter would influence the craft's braking ability. Langley engineers had determined that aerodynamic braking was the only practical method for slowing down a lander as large as Viking for a soft touchdown. The entry vehicle would have a diameter of 3.5 meters, an acceptable ballistic coefficient that would help ensure Viking's safe landing on Mars.

Since electrical power requirements were thought of in terms of the weight that the power apparatus would add to the spacecraft, the design engineers sought creative means for getting maximum results from a minimum amount of power. Low-power integrated circuits were used extensively both to conserve energy and to keep the package small. In addition, power switching techniques were devised to reduce energy requirements. As John D. Goodlette, deputy project director at Martin Marietta, noted, the design rule was "turn off unneeded consumers." When power had to be used, the equipment was designed with multiple power levels, or states, so [that only the minimum power required to achieve the immediate function would he consumed.

Once separated from the orbiter with its 700-watt solar panels, only 70 watts of radioisotope-thermoelectric-generated power would support the long mission on the surface. Because of this limitation on landed power, the radio transmitters could be used only sparingly, a factor that in turn controlled the amount of data that could be sent to Earth.

The Viking lander was a highly automated spacecraft for a number of reasons. Since there was only a 20-minute one-way communications opportunity between Earth and Mars during the landings, control of the lander from Earth from separation to touchdown was not practical. The entire function of navigation-from obtaining an inertial reference to locating a local surface reference-had to be accomplished by the onboard computer. After landing, the spacecraft would be out of direct communication with Earth for about half of each Martian day. And because of electrical power limits, the communications between lander and mission control in California would amount to only a short time each day. The lander, therefore, had to be capable of carrying out its mission unattended by Earth. Mission specialists could send the lander new assignments or modify preprogrammed ones, but for the most part the craft was on its own as it did its day-to-day work.

The lander consisted of a 6-sided aluminum base with alternate 1.09 m and 0.56 m long sides, supported on three extended legs attached to the shorter sides. The leg footpads formed the vertices of an equilateral triangle with 2.21 m sides when viewed from above, with the long sides of the base forming a straight line with the two adjoining footpads. Instrumentation was attached to the top of the base, elevated above the surface by the extended legs. Power was provided by two radioisotope thermal generator (RTG) units containing plutonium 238 affixed to opposite sides of the lander base and covered by wind screens. Each generator was 28 cm tall, 58 cm in diameter, had a mass of 13.6 kg and provided 30 W continuous power at 4.4 volts. Four wet-cell sealed nickel-cadmium 8-amp-hour, 28 volt rechargeable batteries were also onboard to handle peak power loads.

Propulsion was provided for deorbit by a monopropellant hydrazine (N2H4) rocket with 12 nozzles arranged in four clusters of three that provided 32 N thrust, giving a delta-V of 180 m/s. These nozzles also acted as the control thrusters for translation and rotation of the lander. Terminal descent and landing was achieved by three (one affixed on each long side of the base, separated by 120 degress) monopropellant hydrazine engines. The engines had 18 nozzles to disperse the exhaust and minimize effects on the ground and were throttleable from 276 N to 2667 N. The hydrazine was purified to prevent contamination of the martian surface. The lander carried 85 kg of propellant at launch, contained in two spherical titanium tanks mounted on opposite sides of the lander beneath the RTG windscreens, giving a total launch mass of 657 kg. Control was achieved through the use of an inertial reference unit, four gyros, an aerodecelerator, a radar altimeter, a terminal descent and landing radar, and the control thrusters.

Communications were accomplished through a 20 W S-band transmitter and two 20 W TWTA's. A 2-axis steerable high-gain parabolic antenna was mounted on a boom near one edge of the lander base. An omnidirectional low-gain S-band antenna also extends from the base. Both these antennae allowed for communication directly with the Earth. A UHF (381 MHz) antenna provided a one-way relay to the orbiter using a 30 W relay radio. Data storage was on a 40 Mbit tape recorder, and the lander computer had a 6000 word memory for command instructions.

The lander carried instruments to achieve the primary scientific objectives of the lander mission: to study the biology, chemical composition (organic and inorganic), meteorology, seismology, magnetic properties, appearance, and physical properties of the martian surface and atmosphere. Two 360-degree cylindrical scan cameras were 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 are 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 flourescence 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.

Cylindrical projection of topography in the Tharsis rise (left) and Chryse region (right). The spatial resolution of the grid is about 3.75 km and the vertical accuracy is approximately 5 m.

Obvious on the map are the major Tharsis volcanoes: Olympus Mons (18 N, 228 E), Alba Patera (40 N, 250 E) and the volcanic chain consisting of Ascraeus, Pavonis and Arsia montes. Note that Olympus Mons sits off to the west of the Tharsis rise and Alba Patera is separated from the main dome that contains the Tharsis montes. Note that at the high elevations of the volcanoes the color scale saturates -- those are NOT snow-capped peaks!

The grid also shows improved detail in Valles Marineris (in the center) and verifies our earlier observation that the eastern part of the canyon is about a kilometer in elevation below the mouth of the Chryse outflow channels. The westward dip of the eastern part of the canyon seems to be controlled by the intersection of pre-existing Noachian (old!) terrain with the canyon at a longitude of about 300 E. The fact that this structural control is older than the canyon suggests that the westward dip was not due to a late-stage tectonic uplift.

The map also clarifies aspects of early water transport on Mars. In the Chryse region (330 E) there is detailed structure where outflow channels debouch into the northern plains that indicates that water flowed well beyond the channel mouths into what previously appeared to be relatively featureless (from a topographic standpoint) plains. The map also shows considerable detail regarding past flow out of the Hebes Chasma (2 S, 282 E) and into the Kasei Valles (25 N, 290 E).


Lander Site #1:

The Viking 1 Lander touched down in western Chryse Planitia at 22.697 deg N latitude and 48.222 deg W longitude at a reference altitude of -2.69 km relative to a reference ellipsoid with an equatorial radius of 3397.2 km and a flatness of 0.0105 (22.480 deg N, 47.967 deg W planetographic) at 11:53:06 UT (4:13 p.m. local Mars time). Approximately 22 kg of propellants were left at landing. 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. Otherwise, all experiments functioned nominally. The Viking 1 Lander was named the Thomas Mutch Memorial Station in January 1982 in honor of the leader of the Viking imaging team. It operated until 13 November 1982 when a faulty command sent by ground control resulted in loss of contact.

The above is a Viking 1 Lander image of Chryse Planitia looking over the lander. The large white object at lower left and center, with the American flag on the side, is the radiothermal generator (RTG) cover. The high-gain S-band antenna is at upper right. The view, from 22 N, 50 W, is to the northwest. Chryse Planitia is a wide, low plain covered with large rocks and loose sand and dust. The image was taken on 30 August 1976, a little over a month after landing.

The Viking 1 Lander sampling arm created a number of deep trenches as part of the surface composition and biology experiments on Mars. The digging tool on the sampling arm (at lower center) could scoop up samples of material and deposit them into the appropriate experiment. Some holes were dug deeper to study soil which was not affected by solar radiation and weathering. The trenches in this ESE looking image are in the "Sandy Flats" area of the landing site at Chryse Planitia. The boom holding the meteorology sensors is at left.


Lander Site #2:

The Viking 2 Lander touched down about 200 km west of the crater Mie in Utopia Planitia at 48.269 deg N latitude and 225.990 deg W longitude at a reference altitude of 4.23 km relative to a reference ellipsoid with an equatorial radius of 3397.2 km and a flatness of 0.0105 (47.967 deg N, 225.737 deg W planetographic) at 22:58:20 UT (9:49:05 a.m. local Mars time). Approximately 22 kg of propellants were left at landing. 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 Viking 2 Lander operated on the surface for 1281 Mars days and was turned off on April 11, 1980 when its batteries failed.

Viking 2 Lander image of the spacecraft and Utopia Planitia looking SSW. At the center of the image is the pole for the S-band high gain antenna. In the foreground left is the radiothermal generator (RTG) and to the right is the other. The camera test target grids are visible near the center. Note the dark gray rocks littering the plain are partly covered with orange dust. The image covers about 70 degrees azimuth and was taken at 9:29 local time.

Viking 2 Lander close-up of the surface of Mars. The metal cylinder at right is the shroud for the surface sampler instrument, which was ejected after landing. To the left of it are trenches dug by the sampling arm, and at lower right part of a footpad can be seen. Note the holes in the rocks, which appear to be vesicles produced by gas bubbles when the rocks first solidified from lava. The camera is looking due east and local time is 19:47. The shroud is about 30 cm long.


Viking Search for Life:

The Viking landers each containing three experiments to search for life:

  1. Pyrolytic release - an experiment to test for photosynthesis, where a small amount of martian soil was placed in a CO2 gas, using carbon -14, illuminated for a time, then baked. If living organisms ingest the CO2, then the soil would contain traces of the isotope.
  2. Label release - an experiment to look for metabolism, where a small amount of martian soil is moistened with nutrients tagged with carbon-14. If living organisms exist they would release the carbon-14 as waste.
  3. Gas exchange - an experiment to test for respiration, where a sample of soil is given nutrients in a controlled atmosphere. The atmosphere is monitored for changes.
The first two experiments showed rapid changes in the martian soil, but too fast for most living processes. The martian soil is rich in oxides, and the reactions seen where chemical in nature.


Pathfinder:

Mars Pathfinder was originally designed as a technology demonstration of a way to deliver an instrumented lander and a free-ranging robotic rover to the surface of the red planet. Pathfinder not only accomplished this goal but also returned an unprecedented amount of data and outlived its primary design life.

Mars Pathfinder used an innovative method of directly entering the Martian atmosphere, assisted by a parachute to slow its descent through the thin Martian atmosphere and a giant system of airbags to cushion the impact. The landing site, an ancient flood plain in Mars northern hemisphere known as Ares Vallis, is among the rockiest parts of Mars. It was chosen because scientists believed it to be a relatively safe surface to land on and one which contained a wide variety of rocks deposited during a catastrophic flood.

The lander, formally named the Carl Sagan Memorial Station following its successful touchdown, and the rover, named Sojourner after American civil rights crusader Sojourner Truth, both outlived their design lives the lander by nearly three times, and the rover by 12 times.

From landing until the final data transmission on September 27, 1997, Mars Pathfinder returned 2.3 billion bits of information, including more than 16,500 images from the lander and 550 images from the rover, as well as more than 15 chemical analyses of rocks and soil and extensive data on winds and other weather factors. Findings from the investigations carried out by scientific instruments on both the lander and the rover suggest that Mars was at one time in its past warm and wet, with water existing in its liquid state and a thicker atmosphere.

The entry, descent and landing (EDL) process for Mars Pathfinder began days before landing when controllers at JPL sent commands to the spacecraft to tell it precisely when and how to begin the complex autonomous series of steps necessary to safely land on the surface of Mars. These commands are sent periodically right up to a few hours before landing, when controllers on the Earth had the most precise knowledge of where the spacecraft is relative to Mars (the effect of Mars' gravity well is not felt until the spacecraft is less than 48 hours away).

Landing was at about 3:00 am local time on Mars, which is 10:00 am PDT on Friday, July 4, 1997. From an hour and a half before landing until about 3 and a half hours later, the spacecraft is under control of autonomous on-board software that precisely controls the many events that must occur. The fast-paced approach of Pathfinder at Mars begins with venting of the heat rejection system's cooling fluid about 90 minutes prior to landing. This fluid is circulated around the cruise stage perimeter and into the lander to keep the lander and rover cool during the 7 month cruise phase of the mission.

Its mission fulfilled, the cruise stage is then jettisoned from the entry vehicle about one-half hour prior to landing at a distance of 8500 km from the surface of Mars. Several minutes before landing, the spacecraft begins to enter the outer fringes of the atmosphere about 125 km. (80 mi.) above the surface. Spin stabilized at 2 rpm, and traveling at 7.5 km/sec, the vehicle enters the atmosphere at a shallow 14.8 deg angle. A shallower entry angle would result in the vehicle skipping off the atmosphere, while a steeper entry would not provide sufficient time to accomplish all of the entry, descent and landing tasks. A Viking-derived aeroshell (including the heatshield) protects the lander from the intense heat of entry. At the point of peak heating the heatshield absorbs more than 100 megawatts of thermal energy. The martian atmosphere slows the vehicle from 7.5 km/sec to only 400 m/sec (900 mph).

Then entry deceleration of up to 20 gees, detected by on-board accelerometers, sets in motion a sequence of preprogrammed events that are completed in relatively quick succession. Deployment of the single, 24-ft. diameter parachute occurs 2-3 min. after atmospheric entry at an altitude of 5-11 km. (3-7 mi.) above the surface, eventually slowing the vehicle down to 65 meters/sec. The parachute is similar in design to those used for the Viking program but has a wider band around the perimeter which helps minimize swinging.

The heatshield is pyrotechnically separated from the lander 20 sec. later and drops away at an altitude of 2-9 km. (3-6 mi.). The lander soon begins to separate from the backshell and "rappels" down a metal tape on a centrifugal braking system built into one of the lander petals. The slow descent down the metal tape places the lander into position at the end of a braided Kevlar tether, or bridle, without off-loading the parachute or placing excessive loads on the backshell. The 20 m bridle provides space for airbag deployment, distance from the solid rocket motor exhaust stream and increased stability. Once the lander has been lowered into position at the end of the bridle, the radar altimeter is activated and aids in the timing sequence for airbag inflation, backshell rocket firing and the cutting of the Kevlar bridle.

The lander's Honeywell radar altimeter is expected to acquire the surface about 32 sec. prior to landing at an altitude of about 1.5 km. The airbags are inflated about 8 sec. before landing at an altitude of 300 meters above the surface. The airbags have two pyro firings, the first of which cuts the tie cords and loosens the bags. The second, 0.25 sec. later, and 4 sec. before the rockets fire, ignites three gas generators that inflate the three 5.2 m (17-ft) dia. bags to a little less than 1 psi. in less than 0.3 sec. The conical backshell above the lander contains three solid rocket motors each providing about a ton of force for over 2 seconds. They are activated by the computer in the lander. Electrical wires that run up the bridle close relays in the backshell which ignite the three rockets at the same instant.

The brief firing of the solid rocket motors at an altitude of 80-100 meters is intended to essentially bring the downward movement of the lander to a halt some 12 meters (10 m) above the surface. The bridle separating the lander and heatshield is then cut in the lander, resulting in the backshell driving up and into the parachute under the residual impulse of the rockets, while the lander, encased in airbags, falls to the surface. Because it is possible that the backshell could be at a small angle at the moment that the rockets fire, the rocket impulse may impart a large lateral velocity to the lander/airbag combination. In fact the impact could be as high as 25 m/sec (56 mph) at a 30 deg grazing angle with the terrain.

It is expected that the lander may bounce at least 12 m about the ground and soar 100-200 m between bounces. (Tests of the airbag system verified that it was capable of much higher impacts and longer bounces.) Once the lander has settled on the surface, pyrotechnic devices in the lander petal latches are blown to allow the petals to be opened. The latches locking the sturdy side petals in place are necessary because of the pulling forces exerted on the lander petals by the deployed airbag system. In parallel with the petal latch release, a retraction system will begin slowly dragging the airbags toward the lander, breaching vent ports on the side of each bag, in the process deflating the bags through a cloth filter. The airbags are drawn toward the petals by internal lines extending between attachments within the airbags and small winches on each of the lander sides. It takes about 64 minutes to deflate and fully retract the bags.

There is one high-torque motor on each of the three petal hinges. If the lander comes to rest on its side, it will be righted by opening a side petal with a motor drive to place the lander in an upright position. Once upright, the other two petals are opened. About 3 hours is allotted to retract the airbags and deploy the lander petals. In the meantime, the lander's X-band radio transmitter will be turned off for the first time since before launch on December 4, 1996. This saves battery power and will allow the transmitter electronics to cool down from being warmed up during entry without the cooling system. It also allows time for the Earth to rise well above the local horizon and be in a better position for communications with the lander's low-gain antenna later in the morning.

Normal digital data transmissions will cease near the time of cruise stage separation due to the dynamics of EDL. Instead, the transmitter's carrier signal and sidebands will be recorded by the Deep Space Network's Madrid station so that the effects of the many events on the signal may be discerned. The digital data downlink will automatically resume 3.5 hours after landing, long after the airbags have been retracted and the petals opened.

The mosaic of the landscape constructed from the first images revealed a rocky plain (about 20 percent of which was covered by rocks) that appears to have been deposited and shaped by catastrophic floods. This was what we had predicted based on remote-sensing data and the location of the landing site (19.13 degrees north, 33.22 degrees west), which is downstream from the mouth of Ares Vallis in the low area known as Chryse Planitia. In Viking orbiter images, the area appears analogous to the Channeled Scabland in eastern and central Washington state. This analogy suggests that Ares Vallis formed when roughly the same volume of water as in the Great Lakes (hundreds of cubic kilometers) was catastrophically released, carving the observed channel in a few weeks. The density of impact craters in the region indicates it formed at an intermediate time in Mars' history, somewhere between 1.8 and 3.5 billion years ago. The Pathfinder images support this interpretation. They show semi-rounded pebbles, cobbles and boulders similar to those deposited by terrestrial catastrophic floods. Rocks in what we dubbed the Rock Garden a collection of rocks to the southwest of the lander, with the names Shark, Half Dome, and Moe are inclined and stacked, as if deposited by rapidly flowing water. Large rocks in the images (0.5 meters or larger) are flat-topped and often perched, also consistent with deposition by a flood. The Twin Peaks, a pair of hills on the southwestern horizon, are streamlined. Viking images suggest that the lander is on the flank of a broad, gentle ridge trending northeast from Twin Peaks; this ridge may be a debris tail deposited in the wake of the peaks. Small channels throughout the scene resemble those in the Channeled Scabland, where drainage in the last stage of the flood preferentially removed fine-grained materials.

Taking all the results together, scientists have deduced that Mars was once more Earth-like than previously appreciated. Some crustal materials on Mars resemble, in silicon content, continental crust on Earth. Moreover, the rounded pebbles and the possible conglomerate, as well as the abundant sand- and dust-sized particles, argue for a previously water-rich planet. The earlier environment seems to have been warmer and wetter, perhaps similar to that of the early Earth. In contrast, since the time that floods produced the landing site 1.8 to 3.5 billion years ago, Mars has been a very un-Earth-like place. The site appears almost unaltered since it was deposited, indicating very low erosion rates and therefore no water in relatively recent times.


Spirit/Opportunity/Curosity:

NASA's Mars Exploration Rover Mission (MER) is an ongoing robotic space mission involving three rovers, Spirit, Opportunity and Curosity, exploring the planet Mars. It began in 2003 with the sending of the two rovers: MER-A Spirit and MER-B Opportunity to explore the Martian surface and geology.

The mission's scientific objective was to search for and characterize a wide range of rocks and soils that hold clues to past water activity on Mars. The mission is part of NASA's Mars Exploration Program, which includes three previous successful landers: the two Viking program landers in 1976 and Mars Pathfinder probe in 1997.

Curiosity is a car-sized robotic rover exploring Gale Crater on Mars as part of NASA's Mars Science Laboratory mission (MSL). Curiosity was launched from Cape Canaveral on November 26, 2011, at 10:02 EST aboard the MSL spacecraft and successfully landed on Aeolis Palus in Gale Crater on Mars on August 6, 2012, 05:17 UTC. The Bradbury Landing site was less than 2.4 km (1.5 mi) from the center of the rover's touchdown target after a 563,000,000 km (350,000,000 mi) journey.

The rover's goals include: investigation of the Martian climate and geology; assessment of whether the selected field site inside Gale Crater has ever offered environmental conditions favorable for microbial life, including investigation of the role of water; and planetary habitability studies in preparation for future human exploration.

Goals for Curiosity:

Biological

Geological and geochemical

Planetary process

Surface radiation


Questions:

  • Why was Mars considered an interesting planet?
  • What was the Viking mission?
  • What was the Pathfinder mission?
  • What were the results from the Mars rover missions?