Mars Reconnaissance Orbiter

Overall picture

MRO will lead its scientific expedition during one two years period, after being placed on a circular orbit thanks to the technique of atmospheric braking (or Aérofreinage), that NASA starts to control. This technique consists in gradually slowing down the vessel thanks to the upper atmosphere of Mars to return the orbit of a circular vessel. The scientific expedition itself will start only when all the technical tests are carried out (in November 2006). After its two years of mission, the probe will most probably continue its scientific observations, while continuing to be used as relay of communication.

The Mars Reconnaissance Orbiter probe will thus prepare the ground for future missions already envisaged by NASA, in particular for the lander called Phoenix, selected to be sent during the launching appropriateness of 2007, but also for a mobile robot called Mars Science Laboratory, which will be developed to benefit from the launch window of 2009. The cameras of MRO will make it possible to choose the best sites of amarsissage for these robots, by making the best compromise between possible hazards and scientific harvest awaited on the known as sites. The higher capacities of probe MRO as regards data transmission will make it possible to provide an essential relay of communication for the missions present at the ground. MRO will be also able to provide essential data during the amarsissage of these probes.

Course of the mission

Mars Reconnaissance Orbiter was launched the August 12th 2005, since the space complex of Cap Canaveral, on board a rocket Atlas V, was equipped with the upper floor Centaur . It profited daily from a launch window two hours between the August 10th and the August 30th. 56 minutes after takeoff, the stage Centaur entirely burned its fuel in order to place probe MRO on its orbit of interplanetary transfer in direction of Mars.

MRO sailed in space during 7 months and half before reaching Mars. Four corrections of trajectory could be possibly realized, so that the probe can carry out without problem its orbital insertion once arrived closest to Mars.

Orbital insertion occurred when probe MRO approached Mars, for the first time the March 10th 2006. The probe passed under the southern hemisphere of planet, at an altitude ranging between 370 and 400 kilometers (190 miles). The 6 principal engines of the probe burned their fuel during 27 minutes, in order to reduce the speed of the probe of 2900 m/s (6500 miles per hour) to 1900 m/s (4250 miles per hour)

This orbital insertion placed the probe on a polar Orbite very elliptic. The Périapse, i.e. the point where the probe approaches the most surface, is of 300 kilometers (180 miles). The Apoapse, the most distant point of surface, is of 45.000 kilometers (28 000 miles). The probe then spends 35 hours to carry out a complete orbit.

Atmospheric braking ( Aerobraking in English) began shortly after this orbital insertion, to give to the probe a lower orbit and more rapid. This braking makes it possible to save fuel (almost 50%). Atmospheric braking proceeded in three stages:

MRO lowered its périapse gradually by using its engines. The ideal altitude of atmospheric braking was at the proper time given, it depended on the smoothness of the atmosphere (let us recall that the atmospheric pressure varies according to the seasons over Mars). This first stage was carried out in 5 orbits, that is to say one week terrestrial.

MRO remained then at a sufficiently low altitude to use atmospheric braking during 5 months and half, is less than 500 orbits. The engineers of NASA used the engines of the probe to carry out occasional corrections of the périapse, so that the probe does not disintegrate in the thin atmosphere. Thanks to this braking, the apoapse should be reduced with 450 kilometers (280 miles).

to finish the atmospheric sequence of braking, probe MRO used its engines so that its périapse is located out of the Martian atmosphere (at the end of the month of August 2006).

After this phase of braking, the engineers will carry out additional adjustments of the orbit, during one or two weeks, thanks to the engines. These corrections will be probably carried out before a solar conjunction which will take place between on October 7th and on November 8th, 2006. Indeed, to this period, Mars will pass behind the Sun for the terrestrial observers. After this phase of atmospheric braking, the scientific operations will be able to start. The orbit of work will oscillate between 255 kilometers (with the top of the south pole) and 320 kilometers (with the top of the north pole of Mars).

The scientific operations will proceed during one two years nominal period. After that, the wide mission will begin. The probe will be used of communication network and navigation for the landers and the rovers present at the ground.

Instrumentation

The principal goals of the mission of Mars Reconnaissance Orbiter are the search for possible aquiferous resources, the characterization of the atmosphere and Martian geology.

Six scientific instruments are embarked on board vessel, as two instruments which use the data collected by the subsystems of the vessel, to collect scientific data. Three technological demonstrations are also included, to be possibly used at the time of future missions.

Cameras

HiRISE ( High Resolution Imaging Science Experiment )
CTX ( Context Camera )
MARCI ( Color Mars To color )

Spectrometer

CRISM ( Compact Recognition Imaging Spectrometer for Mars )

Radiometer

MCS ( Mars Climate Sounder )

Radar

SHARAD ( Shallow Radar )

Scientific instrumentation

HiRISE

The Caméra HiRISE (in English High Resolution Imaging Science Experiment ) consists of a reflective telescope of 0,5 Mètre, largest ever used in a space mission. This camera has an angular resolution corresponding to 0,3 meter on the ground since height a 300 kilometers. It will take stereotypes in 3 bands of colors: in blue-green, in red and in the infra-red.

To facilitate the cartography of potential sites of amarsissage, the HiRISE camera can produce stereo images. One will be able to thus estimate the topography of a site with an accuracy of 0,25 meter.

CTX

The camera of context (in English Context Imager whose acronym is CTX ) will provide stereotypes Monochrome S, being able to cover up to 40 km of width, with a resolution of 8 Mètre S by pixel. Instrument CTX must function in a synchronous way with the two other cameras present on the probe, to provide (as its name indicates it) charts making it possible to replace the images of HiRISE and MARCI in their total context.

MARCI

The Color Mars To color , also called MARCI , will provide images in 5 bands of visible colors, and in 2 bands Ultraviolet your. MARCI will be used to carry out a total chart of Mars, in order to characterize the variations day laborers, seasonal and annual of the climate Martian. MARCI will provide also bulletins weather days laborer.

CRISM

The instrument CRISM is a Spectromètre working in the Infrarouge and the visible Lumière. It will produce detailed charts of the Minéralogie of Martian surface. This instrument has a resolution of 18 meters, at an orbital distance of 300 km. It will operate in wavelengths ranging between 400 Nm and 4050 Nm, measuring their spectrum thanks to 560 Canaux of 6,55 Nm of width each one. In English language, CRISM is the Acronyme of: Compact Recognition Imaging Spectrometers for Mars

MCS

The Mars Climate Sounder (acronym MCS ) is a spectrometer of 9 channels, equipped with a broad band channel functioning of the ultraviolet close relation to the infra-red close relation (0.3 to 3.0 µm), and eight channels functioning in the average infra-red (12 to 50 µm). The various channels will make it possible the instrument to measure the temperature, the pressure, the steam and the levels of dust present at surface.

It will observe the atmosphere while being interested in the horizon of visible planet since the probe. This instrument will split this image of the horizon, in order to finely analyze the various layers of the atmosphere. The MCS will be able to visualize separate layers of the atmosphere of 5 km (either 3 miles).

Taken measurements will be assembled to carry out charts day laborers and total of the temperature showing the atmospheric variations over Mars.

SHARAD

The experimentation Shallow Subsurface Radar , called SHARAD , is conceived to probe the internal structure of the Martian Polar icecap, but also to gather information on the layers of Glace underground present over Mars, the Roche S and to detect (which knows!), of the liquid water which could be accessible from surface.

Other scientific investigations

Study of the field of gravity

The variations of the gravitational field Martian can generate variations speed for probe MRO. The swiftness of the probe will be measured by using the shift Doppler of the orbitor, whose signal is returned towards the Earth.

Study of the structure of the Martian atmosphere

Very sensitive Accéléromètre S are integrated into the orbitor. They will make it possible to determine by deduction the atmospheric density. It is not known yet if this experiment will proceed only during the atmospheric phase of braking (when MRO is located at a lower altitude, in denser zones of the atmosphere), or during all the mission.

Technological demonstrations

Electra

Electra is an antenna UHF with high Fréquence, conceived to communicate with the futures landers as of their amarsissage. Thanks to Electra, the arrival and the localization of probes over Mars would be more precise.

Optical camera of navigation

The optical camera of navigation will take stereotypes of the moons of Mars, Phobos and Déimos with stars in background, in order to determine the orbit of MRO with more precision. This experiment is not essential to the good performance of the mission, it was included so that the engineers can test novel methods of location in space. In the future, insertions in orbit and the amarsissages could be more precise.

Data of engineering

Structure of the probe

The employees of Lockheed Martin Space Systems assembled the structure of the vessel in Denver, and the scientific instruments grafted to him. The scientific material was built in Tucson, by the Université of Arizona; in Laurel, in Maryland, at the physics laboratory applied John Hopkins , but also in Europe, in Rome, with the Space agency Italian (ASI); like in San Diego, in California, with the Malignant Space Science Systems and with JPL.

The vessel is mainly made up of carbon (a material Composite containing Graphite reinforced plastic ), as well as alveolate plates in Aluminum. The payload of the orbitor depends on the weight of the fuel tank, which occupies most of the structure of the vessel, it is out of titanium.

the total mass is lower than 2,180 Kilogram S.
the empty weight (without fuel) is of less than 1,031 kilograms.

In the beginning, the orbitor weighed 2,180 kilograms (either 4,806 pounds), but the engineers succeeded in reducing the weight of the probe of 51 kilograms (or 112 pounds). This lightening of the structure will make it possible to add a supplement of Hydrazine, in order to extend the lifespan of the probe up to 2014.

Electric feeding system

The electrical energy of the Mars Reconnaissance Orbiter probe comes only from its two solar panels. Each panel can swivel independently around two axes (rotation top to the bottom, or from left to right). Each solar panel has a surface of approximately 100 square meters, and contains 3744 solar cells distinct. These cells consist of three layers, they make it possible more effectively to convert solar energy into electricity. In the case of MRO, these cells are able to convert more than 26% of energy of the Sun into electricity, and connected together, they are able to deliver a tension of 32 V. Over Mars, the two solar panels will provide approximately 1000 Watt S to the probe.

Mars Reconnaissance Orbiter will use two refillable batteries with the Nickel metal hydride. The batteries are used as energy source when the solar panels do not make vis-a-vis the Sun (as during launching, orbital insertion or atmospheric braking), or at the time of the passages in the shade of Mars. Each battery a capacity of 50 Ah, but the probe not needing all this energy, the battery will be probably used at the beginning towards 40% of its capacity. This capacity decreases with their wear and that of the solar panels. When the remaining tension falls under 20 V, the trip computer will cease functioning.

Embarked electronics

The principal computer of Mars Reconnaissance Orbiter is a processor 32-bit RAD750, including/understanding 10.4 million Transistor S, and whose internal clock is given rhythm with 133 MHz. This processor is a special version of the processor PowerPC 750 also called G3, but this version is hardened to resist the space Radiation S. A specific Mother chart was carried out for the occasion. Processor RAD750 is the successor of RAD6000. Of course, this processor can appear obsolete if one compares it with a PC or a Macintosh, but this processor is particularly reliable in space, it can even function at the time of the solar storms.

The scientific data are stored in a memory flash of 160 Gigabit S (20 Giga-octet S), consisted of approximately 700 memory chips, each chip having a capacity of 256 Mo. This storage capacity is not very important if it is considered that acquired volumes of data will weigh heavy. Indeed, only one image of the HiRISE camera will be able to occupy up to 28 Gigabits of data.

The operating system of the vessel, VxWorks has many tools making it possible to carry out a monitoring vessel. Many protocols included in VxWorks enable him to diagnose possible errors precisely.

Navigation systems

The navigation systems and of the sensors will provide data to the engineers (position of the vessel, course and altitude).

Sixteen solar sensors (of which eights of help) are placed all around the vessel, to measure the position of this one compared to the Sun.
Two “star hunters” will be used to provide a pointing of precision to the orbitor, in order to determine his orientation and its altitude. These “star researchers” are simple numeric cameras used to recognize the already catalogued star position in an autonomous way.
Two central inertial is also present at edge (of which one of help). They will provide data at the time of the movements of the vessel. Each inertial unit consists of three Accéléromètre S and three Gyroscope S of the type Gyroscope-laser ( RLG: Laser boxing ring Gyroscope ).

System of telecommunications

The subsystem dedicated to telecommunications uses a large antenna to transmit its data to the frequency usually used for the interplanetary probes (either the Bande X, at the frequency of 8 GHz). MRO will innovate by using in an experimental way the Bande Ka, to 32 Ghz, in order to transmit data to high-flow. The transmission speed of the data could reach 6 Mbit /s, according to the forecasts. This rate of transfer of information is ten times higher than for the preceding orbiteurs Martians. Two Amplificateur S will be used for the radio frequency in band-X (emitted power of 100 Watt S, the second amplifier being an apparatus of help). An amplifier in band-Ka consumes 35 Watts. On the whole, the probe conveys two Transpondeur S.

Two smaller antennas, into weak profit, are also integrated into the probe, for the communications with low flow (they will be used in the event of critical situations, during launching or of insertion in Martian orbit). These antennas do not need to be pointed towards the Earth, they can transmit and emit in any direction.

System of propulsion

A fuel tank of 1175 Liter S is filled with 1187 kg with Hydrazine, a Monergol. The pressure inside the tank is controlled by gas (pressurized helium) present in another dedicated tank. Nearly 70% of the fuel will be used for orbital insertion.

The probe is equipped with 20 engines of push.

6 engines of strong push, mainly intended for insertion in orbit. Each engine produces 170 newtons of push; that is to say a total of 1020 newtons of push.

6 intermediate engines, to carry out operations of correction of trajectory, but also to control the angular position, as well as the rotation of the probe during orbital insertion (in English, one speaks about the attitude control to indicate all the apparatuses which make it possible to determine the orientation of the orbitor). Each one of these intermediate engines product 22 newtons of push.

8 small engines of push, also present to determine and correct the orientation of the space vehicle (control of the angular position, the rotation of the orbitor). These auxiliary engines will also be useful for all the other operations when the probe functions in a nominal way. Each engine of weak push produces 0,9 newtons.

Four Gyroscope S are also included, in order to direct the satellite finely, such as for example during the frame grabbing to very high-resolution, where least “clumsy movement” of the orbitor could make the image fuzzy. Each gyroscope is used for an axial movement. The fourth gyroscope will be able to replace does not import lequelle of the three others in the event of possible failure. Each gyroscope weighs 10 kg, and can turn very quickly (up to 6000 turns per minute).

See too

Exploration of the planet Mars

References

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