Mars Reconnaissance Orbiter

The Mars Reconnaissance Orbiter (MRO, English for Mars exploration satellite) is a NASA spacecraft to explore the planet Mars, which was broken up on 12 August 2005 to the Red Planet, and on 10 March 2006 reached their goal. Since the Viking landers of 1975, it was the heaviest U.S. Mars probe. At the start she weighed ( with drive and fuel) over 2 tons. The total cost of the mission amounted to about 720 million U.S. dollars, of which 450 million on the development and manufacture of the probe and its instruments, 90 million on the launch vehicle and 180 million for the mission of the five and a half years planned primary mission.

With the arrival of MRO on Mars were active simultaneously along with Mars Global Surveyor, Mars Odyssey and Mars Express orbiter in the first four Mars orbit.

• 4.1 Start
• 4.2 flight phase
• 4.3 arrival
• 4.4 Entry into the target orbit
• 4.5 Primary Mission
• 4.6 After the end of the primary mission

Mission Objectives

The primary goal of the probe is the mapping of the surface of Mars: The Mars Reconnaissance Orbiter brings the hitherto highest resolution camera in a Mars orbit. It reaches an improved horizontal resolution of one meter per pixel, whereas earlier recordings still had several meters per pixel. Because of the limitation of the amount of data that can be transmitted to Earth, only selected parts of the planet can be detected at the highest resolution.

The recordings are intended to identify smaller geological structures, such as hydrothermal vents, near which (fossil ) life is suspected. So you also enable a more targeted selection of interesting landing sites for other Mars missions, as for the 25 May 2008 arrived at the Mars Phoenix Lander and the Mars Science Laboratory in August 2012.

Furthermore, the MRO examined with radar after just below the Martian surface water present and ice, especially at the polar caps. Finally, the probe for future landing missions is to serve as a relay station.

Technology

Originally, the Mars Reconnaissance Orbiter should an Atlas III rocket is launched and have a launch mass of 1,975 kg. But after the recent Atlas V rocket had its maiden flight successfully in 2002, a decision was made to launch the probe with her, since it allows more payload III the price of an Atlas. This allows the starting mass of the probe increased to 2180 kg, with the unladen mass of the probe is 1031 kg and 1149 kg (including 139 kg instruments ) accounted for the fuel to be carried. The supporting structure of the probe without any equipment weighs 220 kg and is made of light but resistant materials such as titanium, carbon fiber composites and aluminum honeycomb core in a sandwich - design. The structure must start accelerations of 5 g can withstand what (ie 10.9 thousand kg ) equal to five times their own weight of the probe.

Energy supply

The power supply of the orbiter carried long and 2.53 m wide only by two each 5.35 m solar collectors. The solar panels can be independently moved up and down both are rotated as well to its own axis. On the front of each collector 9.5 m2 each covered with 3,744 individual solar cells. The highly efficient triple -junction solar cells have an efficiency of 26%, which means that they can convert 26% of the energy of incident sunlight into electricity. The solar cells are connected so that they deliver a constant voltage of 32 V, to which the instruments of the probe are designed. The total energy yield of the solar collectors in Mars orbit is about 2,000 watts ( in Earth orbit would be the energy yield due to the smaller distance to the sun at 6,000 watts).

The Mars Reconnaissance Orbiter performs two rechargeable nickel -metal hydride batteries with a capacity of 50 Ah (ampere hours) on board with. The batteries are used to power during the flight phases in which the solar collectors provide no electrical energy. This happens for example at the start, when swinging in the Mars orbit, at the aerobraking maneuvers or when the probe enters Mars shadows. Since the available voltage to the progressive discharge of the batteries falls and the on-board computer switches off at a voltage drop to about 20 V, the probe can only use about 40 % of the battery capacity.

Electronics

The heart of the MRO - board computer is a 133 MHz faster, from 10.4 million transistors of existing, 32 -bit RAD750 processor. The processor is basically a hardened against radiation PowerPC G3 750 and is the successor of RAD6000 processor, which is used for example in the Mars rovers Spirit and Opportunity. Although the speed of the processor at 133 MHz compared to today's home PCs appears to be very low, which is currently the fastest processor - far away from the protection of the magnetic field and the Earth's atmosphere - can still work reliably.

For data storage, the MRO has 20 GB, which are distributed to more than 700 individual flash memory chips with a capacity of 256 Mbps ( = 32 MB ). The storage capacity of the probe is compared to an image of the HiRISE camera, which can be up to 3.5 GB in size, not particularly high.

The on-board computer uses a VxWorks real-time operating system, which is known for its speed and reliability, and in many space missions, such as in Spirit and Opportunity, was used.

Communication

For communication with the earth of the MRO has a directional antenna ( high gain Antenna - HGA ) with a diameter of three meters, with data transfer rates of up to 6 Mbit / s can be achieved. The antenna is movable and can be accurately aligned on the ground. The probe transmits the X-band at a frequency of 8 GHz, with a power of 100 Watt, is also an experimental communication in the Ka band planned 32 GHz and 35 watts. At the higher transmission rate, a higher data transfer rate can be achieved. If the communication in Ka-band prove, future space probes are equipped with the new transmission technology. The probe has two amplifier for the X-band (the second, in the case that the first fail), and an amplifier for the Ka-band. After the end of the primary mission to the antenna has been transferred to the scientific data to Earth about 34 terabits (this is more than the amount of data of all previous planetary space probes together ), with a day around 10-11 hours long data transfer with an average data rate of 0.6 to 5 Mbit / s takes place (depending on the distance between Earth and Mars). The receiver on earth is a 34 - m DSN antenna. For comparison: The transmitter had to MGS and Odyssey / have an electrical output of 25/15W and a data transfer rate of 20-80/14-120 kbit / s - more than an order of magnitude less than MSP.

For the case that the directional antenna can not be used, has the MRO two low gain antennas ( low gain antenna - LGA). The antennas are located on the HGA - bowl, one on the front and one on the back. To communicate with the earth, the low gain antennas do not need to be aligned with it, but reached it only low data rates. Since the probe has two of these antennas (each one covers a full hemisphere from ), it can be any position signals for both transmit and receive. The antennas are used during startup and when entering the Mars orbit, but also are used to protect the communication in an emergency.

In addition, the MRO has an Electra UHF communications system, by which the probe can communicate with other Mars probes, both the Phoenix lander as well since 2012 with the Mars Science Laboratory. Thus, the data of the country emissions by the MRO can be forwarded to the earth. In addition, it can be determined on the Martian surface by the measurement of signal propagation times the exact position of the Lander.

Drive system

The MRO uses a drive system that burns catalytically decomposed hydrazine as the only fuel, and therefore carries no oxidizer. Composed of titanium tank of the probe with a volume of 1,175 liters can hold up to 1187 kg of fuel, but only 1149 kg of fuel to be carried, so as not to exceed the maximum payload of the launch vehicle. This amount of fuel would be sufficient to change the speed of the probe is 1.551 m / s. About 70 % of the fuel consumed when swinging in the Mars orbit, since the probe had to be greatly slowed down to be captured by the attraction of Mars. To set the fuel under pressure, helium gas is used, which is stored in a separate tank under high pressure.

The drive system of the probe consists of 20 engines in three different sizes:

• Six large MR - 107N engines, each producing 170 N thrust ( a total of 1,020 N). These engines are used for the first course correction maneuvers, as well as for the injection into the Mars orbit.
• Six medium-sized MR - 106E engines, each producing 22 N of thrust. These engines are used to correct the trajectory and the probe to keep the bullet in the Mars orbit on the right track.
• Eight small MR - 103D engines, which each produce 0.9 N of thrust. They are used for the position control of MRO both during normal operation time as well as during entry into the Martian orbit and during trajectory corrections.

In addition, four reaction wheels are used for precise position control, especially in high-resolution images, where already the slightest movement causes a blur in the image. Each wheel is used for one axis of motion, the fourth wheel is a spare, should one of the other three fail. A single momentum wheel weighs 10 kg, and can rotate up to 6,000 revolutions per minute.

Navigation system

Navigation systems and sensors provide information about the position, course and orientation of the probe during the flight. These data are crucial in order to perform precise maneuvers on the way to Mars and to keep aligned to the solar panels on the sun and the antenna on the ground. Moreover, the position of the probe must be checked very carefully in order to make unverschwommene high-resolution images of the Martian surface can. For these purposes, the navigation system has multiple sensors and instruments:

In addition, the MRO has with Optical Navigation Camera on an experiment for optical navigation for a more accurate bullet in the Mars orbit. For this purpose, the Mars moons Phobos and Deimos are photographed 30 until two days before the arrival of the probe on Mars, so as to determine the exact position of the probe. The Optical Navigation Camera is not necessary for safe entry of the MRO in orbit. If this experiment, however, provide positive results, this type of navigation is used in future landing missions, the need to arrive at Mars with a very high precision in order not to miss the very well-defined landing sites.

Instruments

Are both six scientific instruments as well as some technical experiments, such as the Ka - band communication, the Electra communication system and the optical navigation camera aboard the MRO. The technical experiments were described in the section technique, here the scientific instruments are presented.

Functioning of the mission

The first proposals, one equipped with a powerful camera Orbiter in 2003 to send to Mars, appeared at NASA in 1999. The space probe to the Mars Surveyor Orbiter provisional designation should both gain expected by the lost Mars Climate Orbiter scientific data and in addition are looking for signs of water on Mars. The probe should approximately match the size of the Mars Global Surveyor launched in 1996 and would therefore have to be manufactured and launched relatively cheap. For the same launch window is also sighted the start of a larger Mars Rovers. In July 2000, NASA finally decided, the rover project to grant preferential and the rover to send to Mars in 2003 (later the dual mission of the two rovers, Spirit and Opportunity, it was ). The launch of the orbiter was then postponed by two years to 2005 and expanded its mission: it should now be a larger and correspondingly more expensive Orbiter, equipped with powerful instruments developed. In autumn 2000, the new project was launched under the name Mars Reconnaissance Orbiter. In October 2001, Lockheed Martin was awarded a contract from NASA to build the probe.

Start

The Mars Reconnaissance Orbiter to be launched on 10 August 2005 with an Atlas V ( 401) rocket from Cape Canaveral. Due to technical problems with the launcher of the launch was initially postponed to August 11. This start date could not be held due to problems with the Centaur upper. The launch took place then on the third attempt on August 12 at 11:43 UTC clock. The spacecraft was separated 57 minutes and 54 seconds after the start of the Centaur upper stage, and three minutes later a Japanese antenna are manufactured in Uchinoura Space Center of the contact to the probe. 14 minutes after disconnecting the extension of the large solar panels has been completed successfully.

Flight phase

After the successful launch and activation of the probe was transferred to the "cruise mode" in which it was until about two months before arrival at Mars. This phase of the mission involved daily monitoring of the subsystems of the probe, determination and correction of the trajectory as well as testing and calibration of the instruments. On 15 August, the MARCI instrument was tested, for which recordings of the earth and the moon were made. On September 8, followed by tests of HiRISE, CTX and Optical Navigation Camera, what the instruments looked back to the now 10 million kilometers distant moon. All tests were successful.

The about 500 million mile journey to Mars took about seven months. In order to control the spacecraft on its way, five course correction maneuvers were planned. The first 15 seconds long maneuver (TCM -1) took place on August 27, 2005 using all six major 170 N thrusters. Previously fired six smaller engines for 30 seconds, in order to position the fuel in the tank for a better flow rate. During the maneuver, a change in speed of 7.8 m / s was achieved. The remaining course corrections use the smaller 22 N thrusters, the 20 seconds long second course correction maneuver (TCM -2) took place on November 17th and a change in velocity of 0.75 m / s achieved. The third course correction maneuver (TCM -3) should be held 40 days prior to arrival, but was canceled because the probe was already at an optimal price. The fourth course correction maneuver (TCM -4) was scheduled for February 28, but was also canceled for the same reason. Also, the optional fifth maneuver (TCM -5), which should take place in the Mars orbit 24 to six hours before admission, has been canceled.

Arrival

To ease in the Martian orbit (Mars Orbit Insertion MOI ) should, the big engines of the probe from 21:24 bis 21:51 clock clock UTC for about 26.8 minutes ( 1606 seconds ) are fired on March 10, 2006. Due to an unexpectedly poor performance of the engines of the computer of the MRO burning but had to be extended by 35 seconds. Since the spacecraft was at the end of the braking maneuver behind Mars, and therefore could not communicate with the earth, it was not until 23:16 clock a signal from the probe, and a few minutes later, the confirmation of the successful entry into the Mars orbit. In the braking maneuver, the velocity of the probe at 1000.48 m was / s (about 18% of the approach speed ) - planned were 1000.36 m / s - reduced so that it was captured by the pull of Mars and in an elliptical 426 × 43,500 km orbit occurred. The first test images of the HiRISE camera of the spacecraft was received on March 24. The expectations were fully met. From a distance of 2489 km, which is far above the later working distance, images were obtained with a resolution of 2.5 meters per pixel. After another test patterns on 25 March, the camera was turned off until the beginning of the scientific work in November 2006. At the same time the Context Imager and the Mars Color Imager were tested, the obtained images were not published until later.

Entry into the target orbit

On 30 March 2006 began the aerobraking maneuvers in the Martian atmosphere, the orbit gradually to about 255 × 320 km high in almost polar sun-synchronous path should be reduced with an orbital period of 112 minutes. For this, the MR - 106E engines of the probe were ignited for 58 seconds, making the martian next point of the orbit was reduced to 333 km. By further braking maneuver was brought to the lowest point of the orbit within the very thin upper atmosphere of Mars, which exerted a further drag on the orbiter. The two large solar panels of the MRO were placed in a position in which they produced a higher air resistance. In order not to endanger the spacecraft by the generated due to air friction heat, each dipping process could last only a limited time and thus reduce only a fraction of the airspeed. Therefore, it was estimated at the beginning of the mission, the number of required immersions to around 500 by the aerobraking about 600 kg of fuel could be saved, the MRO would otherwise have to carry around with the aid of its own engines to achieve the same target orbit.

The aerobraking maneuvers were successfully concluded on 30 August 2006 after 426 immersion processes in the atmosphere. On this day the spacecraft their MR - 106E engines fired for six minutes, and thus brought the mars nearest point of the orbit at 210 km altitude, which is well above the top of the atmosphere ( during the Aerobrakings he averaged 98 to 105 km). On September 11, followed by another - and 12.5 min burn time the longest after Mars orbit insertion - trajectory correction maneuver, which at 250 × 316 km took the train level and the lowest point of the orbit in the vicinity of the South Pole as well as the highest in the vicinity of the North Pole placed.

On 16 September 2006, the 10 m long antenna of the SHARAD radar was deployed ( a similar operation was preparing for the European Mars Express spacecraft numerous problems ). On September 27, the removal of the protective cover and the calibration of the CRISM instrument followed.

On October 3, the HiRISE camera made ​​recordings from Victoria Crater, on whose edge was located at the time of the Opportunity rover. The high-resolution photographs can clearly see the rover and its tracks in the Martian soil detect even the shadow of the rover camera mast is visible.

From October 7 to November 8, 2006, was the planet Mars in a Sonnenkonjunktion. During this period, the sun was directly between the Earth and Mars, so that could only take place limited communication of the orbiter with the earth. After Sonnenkonjunktion the Mars Reconnaissance Orbiter other smaller function tests has undergone and is available since November 2006 for scientific work available.

Primary mission

The primary mission of the probe on Mars lasts four years, of which Mars has been mapped to both the HiRISE camera during the first two years from November 2006 to December 2008, and studied with the other instruments. For the following two years was provided that the Orbiter serves as a platform for communication between future land emissions and the earth. Recordings from a gully on the dune slope of the so-called Russell Crater, made between November 2006 and May 2009, rendered the view of researchers of the Institute of Planetology, University of Münster evidence that there is on Mars at certain seasons of liquid water. In August 2009, the orbiter put himself after problems with the software in a safety mode. On 8 December 2009, it succeeded then NASA, return the probe according to one taking place in several stages, update the software, return to the normal operating state. On 19 May 2010 HiRISE was able to photograph a crater, which did not exist in the previous overflight in March 2008. Logging was near subsurface water ice was exposed. Another photo may show the parachute of Mars 3, a Soviet space probe, which was to explore the Mars using a Landers 1971.

The primary mission ended on December 31, 2010. Upon completion of the primary mission, the onboard fuel should be sufficient to operate MRO least another five years as a communications platform.

After the end of the primary mission

On 6 August 2012, the Mars Reconnaissance Orbiter made ​​with the HiRISE camera photos from the probe's descent Curiosity while they hung on the parachute.