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Mars Reconnaissance Orbiter
Mars Reconnaissance Orbiter spacecraft
Mission typeMars orbiter
OperatorNASA / Jet Propulsion Laboratory
COSPAR ID2005-029A Edit this at Wikidata
SATCAT no.28788
Websitemars.nasa.gov/mro/
nasa.gov/mission_pages/MRO/main/index.html
Mission duration20 years, 2 months and 19 days from launch (19 years, 7 months and 21 days (6983 sols) at Mars)
Spacecraft properties
ManufacturerLockheed Martin / University of Arizona / Applied Physics Laboratory / Italian Space Agency / Malin Space Science Systems
Launch mass2,180 kg (4,810 lb)[1]
Dry mass1,031 kg (2,273 lb)
Payload mass139 kg (306 lb)
Power600–2000 watts
Start of mission
Launch dateAugust 12, 2005, 11:43:00 (2005-08-12UTC11:43Z) UTC
RocketAtlas V 401
Launch siteCape Canaveral SLC-41
ContractorLockheed Martin
Orbital parameters
Reference systemAreocentric
RegimeSun-synchronous[2]
Inclination93 degrees[2]
Period111 minutes
Mars orbiter
Orbital insertionMarch 10, 2006, 21:24:00 UTC
MSD 46990 12:48 AMT
Mars Reconnaissance Orbiter insignia
Official insignia of the Mars Reconnaissance Orbiter mission

The Mars Reconnaissance Orbiter (MRO) is a spacecraft designed to search for the existence of water on Mars and provide support for missions to Mars, as part of NASA's Mars Exploration Program. It was launched from Cape Canaveral on August 12, 2005, at 11:43 UTC and reached Mars on March 10, 2006, at 21:24 UTC. In November 2006, after six months of aerobraking, it entered its final science orbit and began its primary science phase.

Mission objectives include observing the climate of Mars, investigating geologic forces, providing reconnaissance of future landing sites, and relaying data from surface missions back to Earth. To support these objectives, the MRO carries different scientific instruments, including three cameras, two spectrometers and a subsurface radar. As of July 29, 2023, the MRO has returned over 450 terabits of data, helped choose safe landing sites for NASA's Mars landers, discovered pure water ice in new craters and further evidence that water once flowed on the surface on Mars.[3]

The spacecraft continues to operate at Mars, far beyond its intended design life. Due to its critical role as a high-speed data-relay for ground missions, NASA intends to continue the mission as long as possible, at least through the late 2020s. As of October 31, 2025, the MRO has been active at Mars for 6983 sols, or 19 years, 7 months and 21 days, and is the third longest-lived spacecraft to orbit Mars, after 2001 Mars Odyssey and Mars Express.

Pre-launch

[edit]

After the failures of the Mars Climate Orbiter and the Mars Polar Lander missions in 1999, NASA reorganized and replanned its Mars Exploration Program. In October 2000, NASA announced its reformulated Mars plans, which reduced the number of planned missions and introduced a new theme, "follow the water". The plans included the Mars Reconnaissance Orbiter (MRO), to be launched in 2005.[4]

On October 3, 2001, NASA chose Lockheed Martin as the primary contractor for the spacecraft's fabrication.[5] By the end of 2001 all of the mission's instruments were selected. There were no major setbacks during the MRO's construction, and the spacecraft arrived at John F. Kennedy Space Center on April 30, 2005, for launch preparations.[6][7]

Mission objectives

[edit]
Components of MRO

MRO has both scientific and "mission support" objectives which were carried out during the mission's phases. The Primary Science Phase lasted until November 2008, at which time NASA declared the mission a success.[8]: 18  The Extended Science Phase, lasting from 2008 to 2010, was initially planned to support the Phoenix lander and the Mars Science Laboratory, but they were uncontactable and delayed respectively, freeing up the MRO to further study Mars.[8]: 19–20 After 2010, the mission consisted of Extended Mission (EM) phases, each lasting two years up to EM4, and three years from then on.[8]: 28  As of 2024, the MRO is on its 6th extended mission.[8]: 13 

The formal science objectives of MRO are to observe the present climate, particularly its atmospheric circulation and seasonal variations; search for signs of water, both past and present, and understand how it altered the planet's surface; map and characterize the geological forces that shaped the surface.[9]

To support other missions to Mars, the MRO also has mission support objectives. They are to provide data relay services from ground missions back to Earth, characterize the safety and feasibility of potential future landing sites and Mars rover traverses, and capture data from the entry, descent and landing phase of rovers.[9][8]: 12 

MRO played a key role in choosing safe landing sites for the Phoenix lander in 2008, Mars Science Laboratory / Curiosity rover in 2012, InSight lander in 2018, and the Mars 2020 / Perseverance rover in 2021.[10][11][12]

Launch and orbital insertion

[edit]
Launch of Atlas V carrying the MRO, 11:43:00 UTC August 12, 2005
Transfer orbit from Earth to Mars. TCM-1 to TCM-4 denote the planned trajectory correction maneuvers.
Animation of MRO's trajectory around Mars from March 10, 2006, to September 30, 2007
   MRO ·   Mars
Artwork of MRO aerobraking

On August 12, 2005, MRO was launched aboard an Atlas V-401 rocket from Space Launch Complex 41 at Cape Canaveral Air Force Station.[13] The Centaur upper stage of the rocket completed its burns over a 56-minute period and placed MRO into an interplanetary transfer orbit towards Mars.[14]

MRO cruised through interplanetary space for seven and a half months before reaching Mars. While en route, most of the scientific instruments and experiments were tested and calibrated. To ensure proper orbital insertion upon reaching Mars, four trajectory correction maneuvers were planned and a fifth emergency maneuver was discussed.[15] However, only three trajectory correction maneuvers were necessary,[16] which saved 27 kilograms (60 lb) of fuel that would be usable during MRO's extended mission.[17]

MRO began orbital insertion by approaching Mars on March 10, 2006, and passing above its southern hemisphere at an altitude of 370–400 kilometers (230–250 miles). All six of MRO's main engines burned for 27 minutes to slow the probe by 1,000 meters per second (3,300 ft/s). The burn was remarkably accurate, as the insertion route had been designed more than three months prior, with the achieved change in speed only 0.01% short from the design, necessitating an additional 35-second burn time.[18]

Completion of the orbital insertion placed the orbiter in a highly elliptical polar orbit with a period of approximately 35.5 hours.[19] Shortly after insertion, the periapsis – the point in the orbit closest to Mars – was 426 km (265 mi) from the surface[19] (3,806 km (2,365 mi) from the planet's center). The apoapsis – the point in the orbit farthest from Mars – was 44,500 km (27,700 mi) from the surface (47,972 km (29,808 mi) from the planet's center).[20]

When MRO entered orbit, it joined five other active spacecraft that were either in orbit or on the planet's surface: Mars Global Surveyor, Mars Express, 2001 Mars Odyssey, and the two Mars Exploration Rovers (Spirit and Opportunity). This set a new record for the most operational spacecraft in the immediate vicinity of Mars.[21]

On March 30, 2006, MRO began the process of aerobraking, a three-step procedure that halved the fuel needed to achieve a lower, more circular orbit with a shorter period. First, during its first five orbits of the planet (one Earth week), MRO used its thrusters to drop the periapsis of its orbit into aerobraking altitude. Second, while using its thrusters to make minor corrections to its periapsis altitude, MRO maintained aerobraking altitude for 445 planetary orbits (about five Earth months) to reduce the apoapsis of the orbit to 450 kilometers (280 mi). This was done in such a way so as to not heat the spacecraft too much, but also dip enough into the atmosphere to slow the spacecraft down. Third, after the process was complete, MRO used its thrusters to move its periapsis out of the edge of the atmosphere on August 30, 2006.[22][23][24]

In September 2006, MRO fired its thrusters twice more to adjust its final, nearly circular orbit to approximately 250 to 316 km (155 to 196 mi) above the surface, with a period of about 112 minutes and a polar inclination of around 93°.[25][26][8]: 6  The SHARAD radar antennas were deployed on September 16. All of the scientific instruments were tested and most were turned off prior to the solar conjunction that occurred from October 7 to November 6, 2006. This was done to prevent charged particles from the Sun from interfering with signals and potentially endangering the spacecraft.[27] After the conjunction ended the "primary science phase" began.[28]

Timeline

[edit]
Tectonic fractures within the Candor Chasma region of Valles Marineris, Mars, retain ridge-like shapes as the surrounding bedrock erodes away.
The Curiosity rover during atmospheric entry as seen by HiRISE on August 6, 2012. Supersonic parachute and backshell visible
Image taken by HiRISE of Acidalia Planitia on May 17, 2015, where the novel The Martian and its film adaptation take place
Comparison of Mars with and without the dust storm that caused the end of the Opportunity rover, taken by MARCI in 2018
Main article: Timeline of Mars Reconnaissance Orbiter

On September 29, 2006 (sol 402), MRO took its first high resolution image from its science orbit. This image is said to resolve items as small as 90 cm (3 feet) in diameter. On October 6, NASA released detailed pictures from the MRO of Victoria crater along with the Opportunity rover on the rim above it.[29] In November, problems began to surface in the operation of two MRO spacecraft instruments. A stepping mechanism in the Mars Climate Sounder (MCS) skipped on multiple occasions resulting in a field of view that was slightly out of position. By December, normal operations of the instrument had been suspended, although a mitigation strategy allows the instrument to continue making most of its intended observations.[30] Also, an increase in noise and resulting bad pixels has been observed in several CCDs of the High Resolution Imaging Science Experiment (HiRISE). Operation of this camera with a longer warm-up time[a] has alleviated the issue. However, the cause is still unknown and may return.[32]

On November 17, 2006, NASA announced the successful test of the MRO as an orbital communications relay. Using the NASA rover Spirit as the point of origin for the transmission, the MRO acted as a relay for transmitting data back to Earth.[33] HiRISE was able to photograph the Phoenix lander during its parachuted descent to Vastitas Borealis on May 25, 2008 (sol 990).[34]

The orbiter continued to experience recurring problems in 2009, including four spontaneous resets, culminating in a four-month shut-down of the spacecraft from August to December.[35] Though engineers were not able to determine the cause of the recurrent resets, they suspected a piece of electronics had been affected by radiation. While investigating, the engineers discovered and fixed a flaw that could have deleted all critical information onboard the MRO.[8]: 7  Another spontaneous reset occurred in September 2010.[36]

On March 3, 2010, the MRO passed another significant milestone, having transmitted over 100 terabits of data back to Earth, which was more than all other interplanetary probes sent from Earth combined.[37]

In December 2010, the first Extended Mission began. Goals included exploring seasonal processes, searching for surface changes, and providing support for other Martian spacecraft. This lasted until October 2012, after which NASA started the MRO's second Extended Mission, which lasted until October 2014.[36] As of 2023, the MRO has completed five missions, and is currently on its sixth.[38]

On August 6, 2012 (sol 2483), the orbiter passed over Gale crater, the landing site of the Mars Science Laboratory mission, during its EDL phase. It captured an image via the HiRISE camera of the Curiosity rover descending with its backshell and supersonic parachute.[39] In December 2014 and April 2015, Curiosity was photographed again by HiRISE inside Gale Crater.[40]

Another computer anomaly occurred on March 9, 2014, when the MRO put itself into safe mode after an unscheduled swap from one computer to another. The MRO resumed normal science operations four days later. This occurred again on April 11, 2015, after which the MRO returned to full operational capabilities a week later.[36]

NASA reported that the MRO,[41] as well as the Mars Odyssey Orbiter[42] and MAVEN orbiter[43] had a chance to study the Comet Siding Spring flyby on October 19, 2014.[44][45] To minimize risk of damage from the material shed by the comet, the MRO made orbital adjustments on July 2, 2014, and August 27, 2014. During the flyby, the MRO took the best ever pictures of a comet from the Oort cloud and was not damaged.[40]

In January 2015, the MRO discovered and identified the wreckage of Britain's Beagle 2, which was lost during its landing phase in 2003 and was thought to have crashed. The images revealed that Beagle 2 had actually landed safely, but one or two of its solar panels had failed to fully deploy, which blocked the radio antenna.[40][46] In October 2016, the crash site of another lost spacecraft, Schiaparelli EDM, was photographed by the MRO, using both the CTX and HiRISE cameras.[40]

On July 29, 2015, the MRO was placed into a new orbit to provide communications support during the anticipated arrival of the InSight Mars lander mission in September 2016.[47] The maneuver's engine burn lasted for 75 seconds.[48] InSight was delayed and missed the 2016 launch window, but was successfully launched during the next window on May 5, 2018, and landed on November 26, 2018.[49]

Due to the longevity of the mission, a number of MRO components have started deteriorating. From the start of the mission in 2005 to 2017, the MRO had used a miniature inertial measurement unit (MIMU) for altitude and orientation control. After 58,000 hours of use, and limited signs of life, the orbiter switched over to a backup, which, as of 2018, has reached 52,000 hours of use. To conserve the life of the backup, NASA switched from MIMUs to an "all-stellar" mode for routine operations in 2018. The "all-stellar" mode uses cameras and pattern recognition software to determine the location of stars, which can then be used to identify the MRO's orientation.[50] Problems with blurring in pictures from HiRISE and battery degradation also arose in 2017 but have since been resolved.[51] In August 2023, electronic units within the HiRISE's CCD RED4 sensor began to fail as well, and are causing visual artifacts in pictures taken.[52]

In 2017, the cryocoolers used by CRISM completed their lifecycle, limiting the instrument's capabilities to visible wavelengths, instead of its full wavelength range. In 2022, NASA announced the shutdown of CRISM in its entirety, and the instrument was formally retired on April 3, 2023, after creating two final, near global, maps using prior data and a more limited second spectrometer that did not require cryocoolers.[40][53][54]

As of January 2024, the MRO has around 132 kg of fuel remaining, enough to support operations until 2035.[8]: 3 

Instruments

[edit]
aaa
High Resolution Imaging Science Experiment (HiRISE)
bbb
CRISM
bbb
Mars Color Imager (MARCI)
bbb
Context Camera (CTX)
bbb
Mars Climate Sounder (MCS)

Three cameras, two spectrometers and a radar are included on the orbiter along with three engineering instruments and two "science-facility experiments", which use data from engineering subsystems to collect science data. Two of the engineering instruments are being used to test and demonstrate new equipment for future missions.[55] The MRO takes around 29,000 images per year.[56]

HiRISE

[edit]
Main article: HiRISE

The High Resolution Imaging Science Experiment (HiRISE) camera is a 0.5 m (1 ft 8 in) reflecting telescope, the largest ever carried on a deep space mission, and has a resolution of 1 microradian, or 0.3 m (1 ft 0 in) from an altitude of 300 km (190 mi). In comparison, satellite images of Earth are generally available with a resolution of 0.5 m (1 ft 8 in).[57] HiRISE collects images in three color bands, 400 to 600 nm (blue–green or B–G), 550 to 850 nm (red) and 800 to 1,000 nm (near infrared).[58]

Red color images are 20,264 pixels across (6 km (3.7 mi) wide), and B–G and NIR are 4,048 pixels across (1.2 km (0.75 mi) wide). HiRISE's onboard computer reads these lines in time with the orbiter's ground speed, and images are potentially unlimited in length. Practically however, their length is limited by the computer's 28 Gb memory capacity, and the nominal maximum size is 20,000 × 40,000 pixels (800 megapixels) and 4,000 × 40,000 pixels (160 megapixels) for B–G and NIR images. Each 16.4 Gb image is compressed to 5 Gb before transmission and release to the general public on the HiRISE website in JPEG 2000 format.[26][59] To facilitate the mapping of potential landing sites, HiRISE can produce stereo pairs of images from which topography can be calculated to an accuracy of 0.25 m (9.8 in).[60] HiRISE was built by Ball Aerospace & Technologies Corp.[61]

CTX

[edit]

The Context Camera (CTX) provides grayscale images (500 to 800 nm) with a pixel resolution up to about 6 m (20 ft). CTX is designed to provide context maps for the targeted observations of HiRISE and CRISM, and is also used to mosaic large areas of Mars, monitor a number of locations for changes over time, and to acquire stereo (3D) coverage of key regions and potential future landing sites.[62][63] The optics of CTX consist of a 350 mm (14 in) focal length Maksutov Cassegrain telescope with a 5,064 pixel wide line array CCD. The instrument takes pictures 30 km (19 mi) wide and has enough internal memory to store an image 160 km (99 mi) long before loading it into the main computer.[64] The camera was built, and is operated by Malin Space Science Systems. CTX had mapped more than 99% of Mars by March 2017 and helped create an interactive map of Mars in 2023.[65][66]

MARCI

[edit]
Main article: Mars Color Imager

The Mars Color Imager (MARCI) is a wide-angle, relatively low-resolution camera that views the surface of Mars in five visible and two ultraviolet bands. Each day, MARCI collects about 84 images and produces a global map with pixel resolutions of 1 to 10 km (0.62 to 6.21 mi). This map provides a weekly weather report for Mars, helps to characterize its seasonal and annual variations, and maps the presence of water vapor and ozone in its atmosphere.[67] The camera was built and is operated by Malin Space Science Systems. It has a 180-degree fisheye lens with the seven color filters bonded directly on a single CCD sensor.[68][69] The same MARCI camera was onboard Mars Climate Orbiter launched in 1998.[70]

CRISM

[edit]
Main article: CRISM

The Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) instrument is a visible and near infrared spectrometer that is used to produce detailed maps of the surface mineralogy of Mars.[71] It operates from 362 to 3920 nm, measures the spectrum in 544 channels (each 6.55 nm wide), and has a resolution of 18 m (59 ft) at an altitude of 300 km (190 mi).[71][72] CRISM is being used to identify minerals and chemicals indicative of the past or present existence of water on the surface of Mars. These materials include iron oxides, phyllosilicates, and carbonates, which have characteristic patterns in their visible-infrared energy.[73] The CRISM instrument was shut down on April 3, 2023.[53]

MCS

[edit]

The Mars Climate Sounder (MCS) is a radiometer that looks both down and horizontally through the atmosphere in order to quantify the atmosphere's vertical variations. It has one visible/near infrared channel (0.3 to 3.0 μm) and eight far infrared (12 to 50 μm) channels selected for the purpose. MCS observes the atmosphere on the horizon of Mars (as viewed from MRO) by breaking it up into vertical slices and taking measurements within each slice in 5 km (3.1 mi) increments. These measurements are assembled into daily global weather maps to show the basic variables of Martian weather: temperature, pressure, humidity, and dust density.[74] The MCS weighs roughly 9 kg (20 lb) and began operation in November 2006.[75][76] Since beginning operation, it has helped create maps of mesospheric clouds,[77] study and categorize dust storms,[78] and provide direct evidence of carbon dioxide snow on Mars.[79]

This instrument, supplied by NASA's Jet Propulsion Laboratory (JPL), is an updated version of a heavier, larger instrument originally developed at JPL for the 1992 Mars Observer and 1998 Mars Climate Orbiter missions,[80] which both failed.[81]

SHARAD

[edit]
Main article: SHARAD
An artist's concept of MRO using SHARAD to "look" under the surface of Mars

The Shallow Radar (SHARAD) sounder experiment onboard MRO is designed to probe the internal structure of the Martian polar ice caps. It also gathers planet-wide information about underground layers of regolith, rock, and ice that might be accessible from the surface. SHARAD emits HF radio waves between 15 and 25 MHz, a range that allows it to resolve layers as thin as 7 m (23 ft) to a maximum depth of 3 km (1.864 mi). It has a horizontal resolution of 0.3 to 3 km (0.2 to 1.9 mi).[82] SHARAD is designed to complement the Mars Express MARSIS instrument, which has coarser resolution but penetrates to a much greater depth. Both SHARAD and MARSIS were made by the Italian Space Agency.[83]

Engineering instruments and experiments

[edit]

In addition to its imaging equipment, MRO carries three engineering instruments. The Electra communications package is a UHF software-defined radio that provides a flexible platform for evolving relay capabilities.[84] It is designed to communicate with other spacecraft as they approach, land, and operate on Mars. In addition to protocol controlled inter-spacecraft data links of 1 kbit/s to 2 Mbit/s, Electra also provides Doppler data collection, open loop recording and a highly accurate timing service based on an ultra-stable oscillator.[85][86] Doppler information for approaching vehicles can be used for final descent targeting or descent and landing trajectory recreation. Doppler information on landed vehicles allows scientists to accurately determine the surface location of Mars landers and rovers. The two Mars Exploration Rover (MER) spacecraft utilized an earlier generation UHF relay radio providing similar functions through the Mars Odyssey orbiter. The Electra radio has relayed information to and from the MER spacecraft, Phoenix lander and Curiosity rover.[87]

An image of Phobos taken by HiRISE on March 23, 2008, from a distance of around 6,800 kilometres (4,200 mi)[88]

During the cruise phase, the MRO also used the Ka band Telecommunications Experiment Package to demonstrate a less power-intensive way to communicate with Earth.[89]

The Optical Navigation Camera images the Martian moons, Phobos and Deimos, against background stars to precisely determine MRO's orbit. Although this is not critical, it was included as a technology test for future orbiting and landing of spacecraft.[90] The Optical Navigation Camera was tested successfully in February and March 2006.[91] It was subsequently turned off, but was turned back on in 2022 to collect data for a potential NASA-ESA Mars Sample Return mission.[8]: 11 

Two additional science investigations are also on the spacecraft. The Gravity Field Investigation Package measures variations in the Martian gravitational field through variations in the spacecraft's speed. Speed changes are detected by measuring doppler shifts in MRO's radio signals received on Earth. Data from this investigation can be used to understand the subsurface geology of Mars, determine the density of the atmosphere and track seasonal changes in the location of carbon dioxide deposited on the surface.[92] Due to decreased budgets, data collection ended in 2022.[8]: 8 

The Atmospheric Structure Investigation used sensitive onboard accelerometers to deduce the in situ atmospheric density of Mars during aerobraking. The measurements helped provide greater understanding of seasonal wind variations, the effects of dust storms, and the structure of the atmosphere.[93]

Spacecraft systems

[edit]
Size comparison of MRO with predecessors

Structure

[edit]

Workers at Lockheed Martin Space Systems in Denver assembled the spacecraft structure and attached the instruments. Instruments were constructed at the Jet Propulsion Laboratory, the University of Arizona Lunar and Planetary Laboratory in Tucson, Arizona, Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, the Italian Space Agency in Rome, and Malin Space Science Systems in San Diego.[94]

The structure is made mostly of carbon composites and aluminum-honeycombed plates. The titanium fuel tank takes up most of the volume and mass of the spacecraft and provides most of its structural integrity.[95] The spacecraft's total mass is less than 2,180 kg (4,810 lb) with an unfueled dry mass less than 1,031 kg (2,273 lb).[96]

Power systems

[edit]
The MRO solar panel

MRO gets all of its electrical power from two solar panels, each of which can move independently around two axes (up-down, or left-right rotation). Each solar panel measures 5.35 m × 2.53 m (17.6 ft × 8.3 ft) and has 9.5 m2 (102 sq ft) covered with 3,744 individual photovoltaic cells.[97][85] Its high-efficiency solar cells are able to convert more than 26% of the energy it receives from the Sun directly into electricity and are connected together to produce a total output of 32 volts. Whilst orbiting Mars, the panels together produce 600–2000[b] watts of power;[98][85][9] in contrast, the panels would generate 6,000 watts in a comparable Earth orbit by being closer to the Sun.[97][85]

MRO has two rechargeable nickel-hydrogen batteries used to power the spacecraft when it is not facing the Sun. Each battery has an energy storage capacity of 50 ampere hours (180 kC). The full range of the batteries cannot be used due to voltage constraints on the spacecraft, but allows the operators to extend the battery life—a valuable capability, given that battery drain is one of the most common causes of long-term satellite failure. Planners anticipate that only 40% of the batteries' capacities will be required during the lifetime of the spacecraft.[97]

Electronic systems

[edit]

MRO's main computer is a 133 MHz, 10.4 million transistor, 32-bit, RAD750 processor, a radiation-hardened version of a PowerPC 750 or G3 processor with a purpose-built motherboard.[99] The operating system software is VxWorks and has extensive fault protection protocols and monitoring.[100]

Data is stored in a 160 Gbit (20 GB) flash memory module consisting of over 700 memory chips, each with a 256 Mbit capacity. This memory capacity is not actually that large considering the amount of data to be acquired; for example, a single image from the HiRISE camera can be as large as 28 Gb.[100]

Telecommunications system

[edit]
MRO High Gain Antenna installation
MRO views Earth and the Moon roughly to scale from Mars orbit.

When it was launched, the Telecom Subsystem on MRO was the best digital communication system sent into deep space, and for the first time used capacity-approaching turbo-codes. It was more powerful than any previous deep space mission, and is able to transmit data more than ten times faster than previous Mars missions.[101] Along with the Electra communications package, the system consists of a very large (3 m (9.8 ft)) High Gain Antenna, which is used to transmit data to the Deep Space Network on Earth via X-band frequencies at 8.41 GHz. It also demonstrates the use of the Ka band at 32 GHz for higher data rates.[102] Maximum transmission speed from Mars can be as high as 6 Mbit/s, but averages between 0.5 and 4 Mbit/s.[101] The spacecraft carries two 100-watt X-band Travelling Wave Tube Amplifiers (TWTA) (one of which is a backup), one 35-watt Ka-band amplifier, and two Small Deep Space Transponders (SDSTs).[103][104]

Two smaller low-gain antennas are also present for lower-rate communication during emergencies and special events. These antennas do not have focusing dishes and can transmit and receive from any direction. They are an important backup system to ensure that MRO can always be reached, even if its main antenna is pointed away from the Earth.[105][106]

The Ka band subsystem was used to show how such a system could be used by spacecraft in the future. Due to lack of spectrum at 8.41 GHz X-band, future high-rate deep space missions will use 32 GHz Ka-band. NASA Deep Space Network (DSN) implemented Ka-band receiving capabilities at all three of its complexes (Goldstone, Canberra and Madrid) over its 34-m beam-waveguide (BWG) antenna subnet.[102] Ka-band tests were also planned during the science phase, but during aerobraking a switch failed, limiting the X-band high gain antenna to a single amplifier.[107] If this amplifier fails all high-speed X-band communications will be lost. The Ka downlink is the only remaining backup for this functionality, and since the Ka-band capability of one of the SDST transponders has already failed,[108] (and the other might have the same problem) JPL decided to halt all Ka-band demonstrations and hold the remaining capability in reserve.[109]

By November 2013, the MRO had passed 200 terabits in the amount of science data returned. The data returned by the mission is more than three times the total data returned via NASA's Deep Space Network for all the other missions managed by NASA's Jet Propulsion Laboratory over the past 10 years.[110]

High-resolution image of Victoria crater from HiRISE on October 3, 2006. The rover Opportunity can be seen at roughly the "ten o'clock" position along the rim of the crater.

Propulsion and attitude control

[edit]

The spacecraft uses a 1,175 L (258 imp gal; 310 US gal) fuel tank filled with 1,187 kg (2,617 lb) of hydrazine monopropellant. Fuel pressure is regulated by adding pressurized helium gas from an external tank. Seventy percent of the propellant was used for orbital insertion,[111] and it has enough propellant to keep functioning into the 2030s.[112]

MRO has 20 rocket engine thrusters on board. Six large thrusters each produce 170 N (38 lbf) of thrust for a total of 1,020 N (230 lbf) meant mainly for orbital insertion. These thrusters were originally designed for the Mars Surveyor 2001 Lander. Six medium thrusters each produce 22 N (4.9 lbf) of thrust for trajectory correction maneuvers and attitude control during orbit insertion. Finally, eight small thrusters each produce 0.9 N (0.20 lbf) of thrust for attitude control during normal operations.[111]

Four reaction wheels are also used for precise attitude control during activities requiring a highly stable platform, such as high-resolution imaging, in which even small motions can cause blurring of the image. Each wheel is used for one axis of motion. The fourth wheel is a backup in case one of the other three wheels fails. Each wheel weighs 10 kg (22 lb) and can be spun as fast as 100 Hz or 6,000 rpm.[111][113]

In order to determine the spacecraft's orbit and facilitate maneuvers, 16 Sun sensors – eight primaries and eight backups – are placed around the spacecraft to calibrate solar direction relative to the orbiter's frame. Two star trackers, digital cameras used to map the position of catalogued stars, provide NASA with full, three-axis knowledge of the spacecraft orientation and attitude. A primary and backup Miniature Inertial Measurement Unit (MIMU), provided by Honeywell, measures changes to the spacecraft attitude as well as any non-gravitationally induced changes to its linear velocity. Each MIMU is a combination of three accelerometers and three ring-laser gyroscopes. These systems are all critically important to MRO, as it must be able to point its camera to a very high precision in order to take the high-quality pictures that the mission requires. It has also been specifically designed to minimize any vibrations on the spacecraft, so as to allow its instruments to take images without any distortions caused by vibrations.[114][115][116]

Cost

[edit]
MRO development and prime mission costs, by fiscal year

The total cost of the MRO through the end of its prime mission was $716.6 million. Of this amount, $416.6 million was spent on spacecraft development, approximately $90 million for its launch, and $210 million for 5 years of mission operations. Since 2011, MRO's annual operations costs are, on average, $31 million per year, when adjusted for inflation.[117] The MRO's science budget has, like other long term missions, been declining, leading to reduced science activity.[8]: 44 

Discoveries

[edit]
See also: Evidence of water on Mars found by Mars Reconnaissance Orbiter

Ice

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Water ice excavated by an impact crater that formed between January and September 2008. The ice was identified spectroscopically using CRISM.

An article in the journal Science in September 2009,[118] reported that some new craters on Mars have excavated relatively pure water ice. After being exposed, the ice gradually fades as it sublimates away. These new craters were found and dated by the CTX camera, and the identification of the ice was confirmed using CRISM. The ice was found in a five locations, three of which were in the Cebrenia quadrangle. These locations are 55°34′N 150°37′E / 55.57°N 150.62°E / 55.57; 150.62; 43°17′N 176°54′E / 43.28°N 176.9°E / 43.28; 176.9; and 45°00′N 164°30′E / 45°N 164.5°E / 45; 164.5. Two others are in the Diacria quadrangle: 46°42′N 176°48′E / 46.7°N 176.8°E / 46.7; 176.8 and 46°20′N 176°54′E / 46.33°N 176.9°E / 46.33; 176.9.[119][120]

Radar results from SHARAD suggested that features termed lobate debris aprons (LDAs) contain large amounts of water ice. Of interest from the days of the Viking Orbiters, these LDA are aprons of material surrounding cliffs. They have a convex topography and a gentle slope; this suggests flow away from the steep source cliff. In addition, lobate debris aprons can show surface lineations just as rock glaciers on the Earth.[121] SHARAD has provided strong evidence that the LDAs in Hellas Planitia are glaciers that are covered with a thin layer of debris (i.e. rocks and dust); a strong reflection from the top and base of LDAs was observed, suggesting that pure water ice makes up the bulk of the formation (between the two reflections).[122] Based on the experiments of the Phoenix lander and the studies of the Mars Odyssey from orbit, water ice is known to exist just under the surface of Mars in the far north and south (high latitudes).[123][124]

Chloride deposits and aqueous minerals

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Chloride deposits in Terra Sirenum

Using data from Mars Global Surveyor, Mars Odyssey, and the MRO, scientists have found widespread deposits of chloride minerals. Evidence suggests that the deposits were formed from the evaporation of mineral enriched waters. The research suggests that lakes may have been scattered over large areas of the Martian surface. Usually, chlorides are the last minerals to come out of solution. Carbonates, sulfates, and silica should precipitate out ahead of them. Sulfates and silica have been found by the Mars rovers on the surface. Places with chloride minerals may have once held various life forms. Furthermore, such areas could preserve traces of ancient life.[125]

In 2009, a group of scientists from the CRISM team reported on nine to ten different classes of minerals formed in the presence of water. Different types of clays (also called phyllosilicates) were found in many locations. The phyllosilicates identified included aluminum smectite, iron/magnesium smectite, kaolinite, prehnite, and chlorite. Rocks containing carbonate were found around the Isidis basin. Carbonates belong to one class in which life could have developed. Areas around Valles Marineris were found to contain hydrated silica and hydrated sulfates. The researchers identified hydrated sulfates and ferric minerals in Terra Meridiani and in Valles Marineris. Other minerals found on Mars were jarosite, alunite, hematite, opal, and gypsum. Two to five of the mineral classes were formed with the right pH and sufficient water to permit life to grow.[126]

Recurring slope lineae

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Images from HiRISE showing the appearance of dark marks on the floor of Valles Marineris. Images taken at various times in the year.
See also: Seasonal flows on warm Martian slopes

On August 4, 2011 (sol 2125), NASA announced that MRO had detected dark streaks on slopes, known as recurring slope lineae caused by what appeared to be flowing salty water on the surface or subsurface of Mars.[127] On September 28, 2015, this finding was confirmed at a special NASA news conference.[128][129] In 2017, however, further research suggested that the dark streaks were created by grains of sand and dust slipping down slopes, and not water darkening the ground.[130]

See also

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Notes

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References

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Further reading

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Mars Reconnaissance Orbiter

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The Mars Reconnaissance Orbiter (MRO) is a spacecraft designed to investigate the geology and climate of Mars, search for evidence of past water on its surface, and support future missions by relaying communications and identifying landing sites. Launched on August 12, 2005, from Air Force Station in aboard an rocket, MRO successfully entered Martian orbit on March 10, 2006, after a seven-month journey. As of November 2025, the mission remains active after nearly 20 years, making it the third longest-operating Mars orbiter and continuing to deliver unprecedented on the planet's dynamic environment. MRO's primary science objectives focus on characterizing Mars' current and its seasonal variations, mapping the distribution of water-related minerals and landforms, and probing for signs of ancient aqueous or hydrothermal activity to assess potential . The operates in a polar, at an altitude of about 255–320 kilometers (158–199 miles), allowing it to scan the planet daily while conserving fuel through maneuvers during its early mission phase. It also serves as a critical data relay for surface missions, transmitting over 1.8 terabits of data from rovers and landers like , Perseverance, and back to , functioning as a cornerstone of NASA's "." The orbiter carried six primary science instruments to achieve its goals: the High Resolution Imaging Experiment (HiRISE) for detailed surface imaging at resolutions down to 25 centimeters per pixel; the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM), which operated until 2023, to detect minerals indicative of water; the Context Camera (CTX) for broader contextual imagery; the Mars Climate Sounder (MCS) to profile atmospheric temperature, dust, and water vapor; the Mars Color Imager (MARCI) for global color and weather monitoring; and the Shallow Radar (SHARAD) to penetrate the surface up to 1 kilometer deep in search of subsurface ice or water. These tools, complemented by engineering instruments like the Electra radio for relay communications, enable comprehensive observations across visible, , and spectra. Among MRO's notable achievements, it has revealed recurring slope lineae—seasonal dark streaks caused by wind-driven dust avalanches—and vast mid-latitude ice deposits, reshaping understandings of Mars' hydrological history over billions of years. The mission has documented dynamic surface processes, including avalanches, dust devils, and "spider" formations from sublimating carbon dioxide ice, while tracking global dust storms that influence climate and mission operations. By providing high-fidelity imagery for landing site certification—such as for the Phoenix lander in 2008 and Perseverance rover in 2021—MRO has directly enabled safer exploration and sample return planning, with its extended operations yielding ongoing discoveries about Mars' evolving atmosphere and geology.

Development and Planning

Mission Objectives

The primary scientific objectives of the Mars Reconnaissance Orbiter (MRO) mission encompassed characterizing Mars' present climate, including seasonal and yearly variations, as well as monitoring global atmospheric dynamics and weather patterns on a daily basis. The mission also focused on investigating the planet's complex terrain to identify landforms associated with , searching for sites evidencing past or present or hydrothermal activity, and probing the subsurface for geological layering, , and ice deposits, including the internal structure of polar ice caps. Additionally, a central goal was to advance understanding of role in Mars' geological and climatic history by identifying of long-term surface persistence, analyzing water-formed minerals, and detecting ancient shorelines, lakebeds, or layered deposits indicative of flowing . Engineering objectives emphasized demonstrating advanced technologies for sustained Mars exploration, including large deployable solar arrays to power high-performance operations and high--rate communication systems capable of transmitting over 10 times more than prior missions, enabling detailed observations and future mission support. MRO was tasked with identifying and characterizing safe landing sites for upcoming robotic missions, such as the , by providing reconnaissance on surface hazards and resources. It also served as a critical relay node for surface landers, facilitating the return of scientific from Mars' surface to . Specific targets included high-priority sites for potential future human or robotic landings, as well as recurring surface phenomena like storms and seasonal slope flows to study dynamic processes. Quantitatively, the mission aimed for complete global coverage of Mars at 6 meters per resolution to provide contextual mapping, while achieving ultra-high-resolution imaging better than 1 meter per —specifically around 0.3 meters per —for approximately 1% of the surface to enable detailed analysis of key sites. These goals supported daily monitoring of atmospheric , , and distributions to track evolution.

Pre-Launch Design and Cost

The Mars Reconnaissance Orbiter (MRO) was selected in October 2000 as a key element of NASA's Mars Exploration Program, aimed at advancing understanding of the planet's geology, climate, and potential for past life. The mission's development was managed by NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California, with Lockheed Martin Space Systems in Denver, Colorado, serving as the prime contractor responsible for spacecraft assembly and integration. This collaboration leveraged lessons from prior missions to design a robust orbiter capable of long-term operations in Mars orbit. Key design features emphasized reliability and high-performance data handling, drawing heritage from the mission, including proven techniques for orbit insertion and adjustment. A notable advancement was the incorporation of both X-band and Ka-band radio systems, enabling high-rate data transmission from Mars to at speeds up to 6 megabits per second, far exceeding previous Mars orbiters to support detailed scientific observations. The spacecraft's structure incorporated a 3-meter high-gain antenna and large solar arrays spanning 13.6 meters, designed to generate approximately 2,000 watts of power while withstanding the rigors of interplanetary travel. The total development cost for MRO reached approximately $720 million in 2005 dollars, encompassing fabrication, science instruments, and ground systems, with an additional $90 million allocated specifically for the launch vehicle; ongoing operations costs were budgeted separately at around $180 million for the primary mission phase. Timeline milestones included the program's formal announcement in late 2000, completion of assembly at facilities in early 2005, and subsequent delivery to for integration with the launch vehicle. Pre-launch testing focused on critical environmental factors, such as thermal vacuum chamber simulations to verify control systems under simulated conditions and assessments to ensure electronics hardness against cosmic rays. A primary engineering challenge during design was balancing the power demands of high-resolution imaging and spectroscopy—driven by mission objectives for detailed surface mapping—with the limitations of solar power generation in Mars' variable orbital environment, where dust storms and distance from the Sun could reduce output by up to 40%. Engineers addressed this by optimizing instrument duty cycles and incorporating efficient battery storage, allowing the orbiter to prioritize data collection during peak power windows without compromising overall mission longevity.

Launch and Orbital Operations

Launch Sequence

The Mars Reconnaissance Orbiter (MRO) was launched on August 12, 2005, at 7:43 a.m. EDT (11:43 UTC) from Launch Complex 41 at Air Force Station, , aboard an 401 rocket consisting of a single Atlas booster stage powered by an engine and a upper stage with an engine. The 57.4-meter-tall, 333,000 kg vehicle provided the necessary performance for trans-Mars injection without solid rocket boosters, achieving precise trajectory delivery within 1σ bounds of less than 20 m in position and 0.7 mm/s in velocity at separation. Liftoff occurred at T+0 with booster ignition, followed by booster engine cutoff (BECO) at T+4 minutes, when the vehicle reached an altitude of approximately 101 km and a downrange distance of 300 km. At T+4 minutes 10 seconds, the Centaur separated from the booster and ignited for its first burn, which concluded at T+13 minutes after a coast phase. The Centaur then performed a second burn from T+33 to T+55 minutes, lasting 5 minutes 29 seconds, to inject the spacecraft onto its interplanetary trajectory. Spacecraft separation from the Centaur occurred approximately 1 hour after launch. Post-separation performance included an achieved of 11.6 km/s and a hyperbolic excess of 2.9 km/s directed toward Mars, establishing the baseline cruise over the subsequent 210 days to Mars arrival. Immediately after separation, the solar arrays deployed on Earth's night side and fully extended within 20-30 minutes upon illumination, spanning 13.6 meters to generate operational power. Four deep correction maneuvers were planned and executed successfully using the spacecraft's 170-newton thrusters, with the first occurring 15 days after launch to refine the path. Minor transient issues, including heater faults, arose during early flight but were resolved without mission impact.

Mars Orbital Insertion and Early Maneuvers

The Mars Reconnaissance Orbiter arrived at Mars on March 10, 2006, executing a critical Mars insertion (MOI) burn with its six main engines lasting approximately 27 minutes and delivering a delta-v of 1,015 m/s. This maneuver consumed roughly 70% of the spacecraft's total propellant load of 1,149 kg of . The burn captured the spacecraft into a highly elliptical with a periapsis altitude of 430 km, an apoapsis of approximately 45,000 km, and an orbital period of 35 hours. Following MOI, the spacecraft initiated on March 30, 2006, to gradually lower and circularize the while conserving . Over the subsequent six months, MRO completed 445 atmospheric drag passes, systematically reducing the apoapsis from 45,000 km to about 320 km by August 30, 2006. During peak drag passes, atmospheric friction generated heating up to 750°C on exposed surfaces, which was closely monitored using onboard temperature sensors to ensure structural integrity. To fine-tune the orbit during and after , the spacecraft performed a series of propulsive maneuvers using its intermediate and main thrusters, including six main engine burns that provided a total delta-v of 400 m/s and achieved a near-circular science orbit at 255–320 km altitude. These adjustments included corridor control at apoapsis to manage periapsis depth and a final walkoff phase to establish the sun-synchronous configuration. Early operations commenced immediately after MOI, with systematic checkout of the six scientific instruments to verify functionality and calibrate performance. The first science data, including test images from the High Resolution Imaging Science Experiment (HiRISE) and Context Camera (CTX), were acquired and returned in late March 2006, followed by broader instrument activations in April. By September 2006, following the completion of aerobraking and propulsive adjustments, the spacecraft reached its primary science orbit, enabling full-scale observations.

Spacecraft Design

Structural and Power Systems

The Mars Reconnaissance Orbiter's spacecraft bus is constructed primarily from titanium, carbon composites, and aluminum honeycomb materials, providing structural integrity, lightweight design, and thermal isolation for long-duration operations in Mars orbit. This framework supports the integration of scientific instruments, propulsion systems, and other subsystems while withstanding launch accelerations exceeding 5 g. The overall spacecraft measures 6.5 meters in height, including the 3-meter-diameter high-gain antenna, and spans 13.6 meters in width with deployed solar arrays. At launch, the total mass was 2,180 kg, comprising a dry mass of 1,031 kg for the bus and instruments (including 139 kg for the science payload) and 1,149 kg for propellant and pressurant. The power subsystem relies on two deployable solar arrays, each approximately 10 m² in area and populated with 3,744 solar cells that convert over 26% of incident to , yielding up to 2,000 of power at Mars' distance from the Sun. These arrays, gimbaled for optimal orientation, total about 20 m² and are critical for sustaining operations during the primary mission and extensions. Power is regulated and distributed via a nominal 28 V DC bus to all subsystems and instruments. For periods of or peak demand, two nickel-hydrogen batteries, each with a 50 Ah capacity (equivalent to 1,600 Wh), supply backup energy, typically utilizing around 40% to preserve longevity. Thermal control systems maintain component temperatures within safe limits using a combination of radiators for heat rejection, specialized surface coatings to manage absorption and emission, blankets for passive protection, and electrically activated heaters for critical electronics. These measures ensure operational ranges suitable for the varying thermal environment of Mars orbit, including extreme conditions during phases. The solar arrays are specifically engineered to endure temperatures approaching 200°C without degradation during atmospheric passes. To support a mission lifetime exceeding 10 years, the incorporates radiation-hardened electronics, including the RAD 750 processor, to mitigate effects from cosmic rays and solar particles in Mars' space environment. The robust composite structure also provides inherent shielding against impacts, enhancing overall durability for extended orbital operations.

Propulsion, Attitude Control, and Telecommunications

The propulsion subsystem of the Mars Reconnaissance Orbiter (MRO) utilizes a monopropellant system pressurized by , with a total usable load of approximately 1,149 kilograms at launch. This configuration enables a total delta-v capability of about 1,400 m/s, sufficient for major maneuvers such as Mars and ongoing maintenance. The system includes six 170-newton main thrusters for primary changes, including the insertion burn that reduced the spacecraft's by roughly 1,000 m/s over 27 minutes, six 22-newton thrusters for trajectory corrections and adjustments, and eight 0.9-newton thrusters for fine attitude control during propulsion events. Attitude control is achieved primarily through a set of four reaction wheels—three orthogonal wheels each providing 100 N·m·s of storage and a fourth skew-mounted for redundancy—allowing precise three-axis stabilization without frequent propellant use. These wheels maintain the spacecraft's orientation for science observations and , with the small thrusters serving as backups for desaturation and recovery from disturbances. Attitude determination relies on two star trackers for high-accuracy pointing, an incorporating gyroscopes and accelerometers for dynamic rate sensing, and 16 sun sensors for coarse acquisition and safe-mode operations, collectively enabling pointing knowledge accuracy of 0.035 mrad and stability of approximately 2.4 μrad during high-stability imaging modes. The subsystem supports high-volume data return and functions using a 3-meter high-gain antenna with a gain of 28 dB at X-band, complemented by two low-gain antennas for backup and emergency communications. Primary communications occur via X-band at 8.4 GHz downlink, with a 100-watt enabling data rates from 2 to 6 Mbps during science operations, while the Ka-band system at 32 GHz, powered by a 35-watt , achieves up to 6 Mbps to for demonstration purposes. For proximity operations, a UHF subsystem using the Electra at around 400 MHz data to and from surface assets like rovers and landers at rates up to 256 kbps return and 2 Mbps forward, facilitating over 5 gigabits per day in support of missions such as Phoenix and . Operational use of these systems includes annual station-keeping maneuvers to maintain the , typically consuming 20 to 30 m/s of delta-v per year to counter atmospheric drag and gravitational perturbations, executed via the 22-newton thrusters. automates safe-mode entry using the low-gain antennas and reaction wheels to preserve and ensure recovery, with thruster backups available for desaturation. The Ka-band demonstration, initiated during cruise and continued in , tests higher bandwidth for future deep space networks, achieving link margins suitable for operational use despite atmospheric variability on .

Scientific Instruments

High-Resolution Imaging Systems

The High-Resolution Imaging Systems on the Mars Reconnaissance Orbiter (MRO) consist of two complementary cameras: the (HiRISE) and the Context Camera (CTX). These instruments enable detailed visible-light imaging of the Martian surface, supporting the mission's objectives by providing high-fidelity data for geological analysis and site characterization. HiRISE, developed by the , features a 0.5-meter primary mirror with a 12-meter effective , achieving a of approximately 0.25 to 1.3 meters per from MRO's nominal orbital altitude of 255-320 kilometers. Its focal plane incorporates 14 (CCD) detectors, each 2048 wide and 128 high for time-delay integration (TDI), covering a swath width of about 6 kilometers. The central six CCDs employ red, blue-green, and near-infrared filters (wavelengths 400-1000 nanometers), enabling color imaging over a 1-1.3 kilometer wide strip within the panchromatic swath, which aids in distinguishing surface materials. HiRISE stores data in the spacecraft's solid-state recorder with a capacity of 36 gigabytes, allowing for large image files up to 20,000 by 40,000 . CTX, provided by Malin Space Science Systems, uses a 350-millimeter f/3.25 catadioptric Schmidt telescope with a 5.7-degree field of view, delivering panchromatic images (500-800 nanometers) at 6 meters per resolution and a 30-kilometer swath width from the same orbital range. Its 5056-pixel linear CCD array supports grayscale imaging up to 160 kilometers in length, with a 256-megabyte DRAM buffer for data handling. CTX operates simultaneously with to capture broader contextual views overlapping high-resolution targets. In operations, employs nadir-pointing pushbroom scanning, with the spacecraft's slew capability enabling the acquisition of stereo image pairs at convergence angles of 15-30 degrees for deriving 3D , targeting about 1000 such pairs during the primary mission. As of 2025, the RED4 CCD has been non-functional since July 2023, resulting in a gap in the central red channel of images, though the instrument remains operational overall. CTX routinely images for global coverage, contributing to cumulative mosaics that have imaged over 99.5% of Mars' surface as of 2024, with an output of hundreds of images and thousands of CTX strips annually. Calibration for both instruments involved pre-launch ground tests, including radiometric and flat-field measurements, followed by in-flight adjustments using stellar observations and surface targets to refine sensitivity and correct for degradation, ensuring radiometric accuracy within 5% for CTX and high signal-to-noise ratios exceeding 100:1 for . These systems uniquely support color-based material discrimination and stereo-derived digital elevation models with vertical precision better than 25 centimeters per pixel, enhancing surface process studies without relying on spectroscopic data.

Spectroscopic and Mapping Instruments

The Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) was a hyperspectral imager designed to identify compositions on the Martian surface, particularly hydrated minerals and ices, by analyzing reflected light across a broad spectrum. It operated in the visible to near-infrared range from 0.362 to 3.92 micrometers with a of 6.55 nanometers per channel, enabling detection of absorption features indicative of water-altered materials such as phyllosilicates and sulfates. At its nominal orbital altitude of 300 kilometers, CRISM achieved a of 18 meters per in targeted observations, covering swaths approximately 10 kilometers wide. Data acquisition ended in May 2022 following the failure of its last , though its extensive dataset continues to support mineralogical analyses. CRISM supported multiple observation modes to balance resolution and coverage. In targeted mode, it acquired full-resolution data over small areas of interest, such as potential landing sites or geological features, with hyperspectral coverage at 18 meters per . Mapping mode provided coarser global context at 200 meters per using 72 selected wavelengths, while a ride-along mode at 100 meters per allowed integration with other instruments during high-priority observations. The Mars Color Imager (MARCI) consists of two cameras for broad-scale surface and atmospheric mapping: the medium-angle MC11 for visible-light imaging and the wide-angle MC12 for and visible observations. MC11 uses five filters from 425 to 725 nanometers to produce color images at resolutions of about 1 kilometer per pixel, while MC12 employs two filters (260 and 320 nanometers) plus one visible (425 nanometers) for wider coverage up to 6-10 kilometers per pixel. These enable daily global mosaics that track surface color variations, polar cap dynamics, and atmospheric phenomena like dust storms. MARCI's operational modes include routine nadir-pointed imaging for global maps and limb-scanning sequences with MC12 to measure distribution via absorption. Data products from both instruments include spectral libraries derived from CRISM for precise identification and atmospheric opacity maps from MARCI to quantify loading and its effects on surface . CRISM and MARCI were co-pointed with the (HiRISE) to provide compositional context for detailed topographic imagery, facilitating correlated analyses of distributions relative to surface features.

Subsurface and Atmospheric Sensors

The Shallow Radar (SHARAD) is a subsurface sounding operating at a central frequency of 20 MHz with a 10 MHz bandwidth, enabling detection of interfaces between layers of different properties in the Martian subsurface. It achieves a vertical resolution of approximately 15 meters in and horizontal resolutions ranging from 300 to 1000 meters, allowing it to penetrate up to 1 kilometer in depth under low-loss materials like polar deposits. SHARAD has been instrumental in identifying layered structures and buried craters, such as those beneath the north polar layered deposits, by transmitting frequency-modulated pulses and analyzing the returned echoes for reflections from subsurface features. SHARAD operations include the use of off-nadir beams, which facilitate three-dimensional by combining data from multiple orbital passes to construct radargrams that reveal volumetric structures in regions like Planum Boreum. This approach has enabled the mapping of extensive ice sheets and sediment layers within the polar caps, confirming the presence of multiple ancient ice deposits buried under current formations. As of 2025, SHARAD continues operations with enhanced off-nadir pointing up to 120 degrees using large spacecraft rolls. Calibration of SHARAD data involves cross-verification with ground truth from the Phoenix lander, where radar reflections at the landing site were attributed to deep ground ice layers consistent with in-situ measurements of near-surface ice. The Mars Climate Sounder (MCS) is an infrared radiometer designed to measure vertical profiles of , dust opacity, and content through limb-sounding observations. It employs nine spectral channels—five in the mid-infrared (12–45 μm), three in the far-infrared (7–11 μm), and one broadband visible channel (0.3–3.0 μm)—providing a vertical resolution of approximately 5 kilometers from the surface up to 80 kilometers altitude. MCS scans the Martian horizon continuously during orbital passes, capturing thermal emissions to derive profiles of key atmospheric constituents, with particular sensitivity to dust and condensates that influence radiative balance. In its occultation-like limb-staring mode, MCS performs pressure sounding by integrating profiles under assumptions, enabling detailed monitoring of atmospheric density variations. This capability has supported the tracking of thermal tides, revealing diurnal oscillations in the middle atmosphere (35–80 km) driven by solar heating and dust loading, with amplitudes up to 20–30 K in the during southern summer. Calibration efforts for MCS include cross-verification against Phoenix lander meteorological data, which confirmed the accuracy of derived profiles near the surface during the lander's 2008 operations in the northern plains. As of 2025, MCS remains operational despite some anomalies. Together, SHARAD and MCS provide complementary insights into subsurface volatiles and atmospheric dynamics, contributing to global models of Mars' volatile cycle without direct overlap in surface compositional mapping.

Mission Timeline and Operations

Primary Mission Phase

The primary mission phase of the Mars Reconnaissance Orbiter (MRO) began in November 2006, following the completion of to establish its science orbit, and lasted two Earth years until November 2008, encompassing one full Mars year of operations in a sun-synchronous, near-polar . This phase focused on achieving the mission's core scientific goals, including high-resolution mapping of the surface, monitoring of atmospheric and dynamics, and probing for subsurface and minerals, while also demonstrating relay capabilities for surface missions. Key activities during this period involved the full activation and systematic operation of the spacecraft's instruments, enabling comprehensive across multiple wavelengths. Aerobraking concluded successfully in August 2006, transitioning MRO into its primary science orbit with an altitude of about 255–320 km. The orbiter conducted relay demonstrations, notably supporting the Phoenix lander after its May 2008 arrival by relaying over 100 GB of data in the initial weeks and imaging the landing site to confirm safe terrain. Instruments such as , CTX, and CRISM were deployed for targeted observations, capturing daily global context images and detailed spectral scans. MRO returned approximately 26 terabits (Tb) of scientific data during the primary phase, including over 9,000 images that provided sub-meter resolution views covering about 0.65% of Mars's surface area (non-overlapping equivalent), highlighting features like craters, dunes, and layered deposits. This data volume supported detailed analyses of geological processes and atmospheric variations, with alone contributing 8 terapixels of imagery. Significant milestones included ongoing support for the Spirit and Opportunity rovers via high-resolution imaging of their traverses and efficient data relay sessions, enhancing their longevity and scientific output. In 2008, MRO's observations aided the Phoenix mission by identifying bright, salty soil exposures suggestive of water , paving the way for the lander's direct confirmation of subsurface deposits. These efforts marked MRO's role as a vital asset in Mars exploration infrastructure. The phase faced challenges from the intense global dust storm of late 2007, which elevated atmospheric opacity across the planet, obscured surface views, and required operational adjustments to prioritize safe spacecraft health while minimizing science disruptions. Instruments like the Mars Climate Sounder continued monitoring the storm's evolution, providing critical data on its global impacts despite reduced imaging opportunities.

Extended Mission Phases and Current Status

Following the primary mission phase (November 2006–November 2008) and Extended Science Phase (November 2008–December 2010) that focused on targeted imaging of surface composition, polar caps, and subsurface ice while supporting the site selection, the Mars Reconnaissance Orbiter (MRO) entered its first extended mission (EM-1) from December 2010 to September 2012, focusing on characterizing seasonal processes, surface changes, and the diversity of surface units to support future missions. This was followed by the second extended mission (EM-2; 2012–2014), which emphasized monitoring recurring slope lineae and other dynamic features, alongside continued relay support for surface assets. The third (EM-3; 2014–2016) and fourth (EM-4; 2016–2018) extended missions shifted toward higher-priority targeted observations, including detailed mapping of potential sites and studies of atmospheric cycles, while optimizing operations to conserve . The fifth extended mission (EM-5) ran from 2018 to 2022, incorporating adaptations such as reduced relay duties to prioritize data return amid instrument constraints, notably the failure of CRISM's last in 2017, which degraded its capabilities and led to the instrument's retirement in 2023 while preserving limited visible/near-infrared functions until then. The sixth extended mission (EM-6), approved in 2022 and spanning fiscal years 2022–2025, continued investigations into Mars' surface evolution, ices, active , and , with over 40 peer-reviewed papers published by the team during this period. As of November 2025, MRO has operated for over 19 years in Mars orbit, completing more than 100,000 orbits and returning more than 500 terabits (over 60 terabytes) of science data, with all remaining instruments—HiRISE, CTX, SHARAD, MARCI, and MCS—fully operational. The spacecraft retains approximately 80% of its initial propellant reserves, sufficient for continued operations beyond 2029, though solar array degradation has reduced power output to around 1,500 watts from an original peak of over 2,000 watts. Operations include ongoing monitoring of the Perseverance rover and Ingenuity helicopter in Jezero Crater, with recent high-resolution imaging campaigns targeting recurring slope lineae and impact sites, alongside pauses during the 2023 solar conjunction to mitigate communication risks. In June 2025, approved the seventh extended mission (EM-7; fiscal years 2026–2029), rated excellent for scientific merit, which will emphasize early Mars via sedimentary deposits, modern surface changes like migration, and enhanced subsurface mapping using new 120-degree spacecraft rolls to boost SHARAD signal strength by up to 10 times. Post-2030, mission planners anticipate controlled deorbiting to minimize orbital risks, ensuring safe end-of-life disposal.

Scientific Discoveries

Evidence of Water and Ice

The Mars Reconnaissance Orbiter's Shallow (SHARAD) instrument provided the first definitive evidence of extensive buried glaciers in the southern mid-latitudes of Mars, revealing strong subsurface reflectors consistent with thick layers of water ice covered by a thin mantle of and debris. These features, known as lobate debris aprons, exhibit radar properties indicating compositions of more than 90% pure water ice, with the ice layers extending up to several kilometers in width and at least 100 meters in thickness. Observations from demonstrated that these ice deposits are widespread across the region between 40°S and 55°S, supporting the interpretation of past glacial activity during periods of higher obliquity in Mars' climate history. Further SHARAD mapping in , a vast northern plain, identified massive subsurface ice sheets buried under 10 to 20 meters of soil, with the total volume of water ice equivalent to that of —approximately 2,900 cubic miles. These deposits, detected through radar echoes showing low typical of nearly pure ice, span an area larger than and suggest a significant reservoir for potential future resource utilization. The purity of the ice in these mid-latitude regions exceeds 99% in some exposed scarps, as confirmed by complementary orbital and landed observations. At the polar regions, the High Resolution Imaging Science Experiment (HiRISE) and Mars Climate Sounder (MCS) on MRO imaged and profiled the layered structure of the permanent caps, revealing alternating layers of (CO2) and water , with the residual caps primarily composed of water beneath a seasonal CO2 frost cover. MCS thermal data indicated that the south polar layered deposits contain at least 90% water by volume, while HiRISE captured the dynamic retreat of the seasonal caps through sublimation, with surface features like pits and scarps expanding at rates of 1 to 3 meters per year during spring warming. These observations highlight the caps as the largest known reservoirs of surface water on Mars, preserving records of ancient climatic cycles. MRO's HiRISE also documented recurring slope lineae (RSL), first systematically observed in 2011 as seasonal dark streaks forming on steep, equator-facing slopes at mid-latitudes, particularly during warmer months when surface temperatures exceed 250 . These linear features, typically 0.5 to 5 meters wide and extending up to 100 meters in length, appear at over 200 sites and incrementally elongate downslope, fading in cooler seasons; as of 2025, their characteristics are most consistent with dry granular processes, such as avalanches of fine dust sliding down slopes. MRO supported the 2008 Phoenix lander mission by relaying data from the surface and providing pre- and post-landing images that validated the excavation of subsurface water at the northern plains site. Phoenix's robotic arm uncovered a hard layer of nearly pure water just 5 to 18 centimeters below the surface, which sublimated rapidly upon exposure, confirming predictions from orbital surveys; imagery before landing identified polygonal terrain indicative of ice-rich soil, and follow-up images post-mission documented the site's seasonal frost patterns and ice table stability.

Mineralogical and Geological Features

The Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) aboard the (MRO) has revealed diverse aqueous mineral deposits on the Martian surface, providing key insights into the planet's geological history. In particular, CRISM identified chloride-bearing salts in the Terra Sirenum region in 2008, appearing as light-toned, fractured deposits underlying or interbedded with phyllosilicates. These chlorides, likely evaporites formed from ancient brines, suggest the presence of evaporating lakes or upwelling in a wetter environment during the Hesperian period. While specific compositions such as magnesium or variants have been inferred in related hydrated salt contexts, the Terra Sirenum findings highlight enrichment as evidence of prolonged activity. CRISM data further documented phyllosilicates and sulfates across ancient terrains, indicating episodic aqueous alteration. Smectite clays, a type of phyllosilicate, dominate Noachian-aged highlands, formed through low-temperature water-rock interactions that imply neutral to alkaline conditions conducive to . In Valles Marineris, CRISM observations from 2007 to 2010 mapped layered exposures of iron-magnesium and sulfates, such as , within canyon walls up to 7 kilometers thick, signaling a transition from early wet phases to acidic, evaporative environments. These minerals, often interbedded, reflect a complex history of and in standing bodies of water. Complementing spectroscopic findings, the High Resolution Imaging Science Experiment (HiRISE) enabled detailed geological mapping through , resolving features at sub-meter scales. HiRISE stereo pairs have delineated impact craters, tectonic fault lines, and volcanic lava flows, revealing structural evolution across Mars' hemispheres. Over the mission's duration, HiRISE has identified more than 1,000 new small impact craters by comparing repeated images, refining models of recent bombardment rates. High-resolution views also captured ancient river channels and deltas in craters like Jezero and during the , showcasing meandering patterns and fan deposits that attest to fluvial transport and deposition in paleolakes. Crater counting using and CRISM contextual data has dated these features, establishing a timeline for Mars' watery past. Accumulations of impact craters on phyllosilicate-rich terrains and deltaic sediments indicate ages of 3 to 4 billion years, aligning with the Noachian-Hesperian boundary when liquid water was widespread. This underscores the antiquity of mineralogical signatures, linking them to a period of intense geological activity before the planet's aridification.

Dynamic Surface Processes and Climate Insights

The () on the Mars Reconnaissance Orbiter has provided detailed observations of active slope processes, revealing ongoing geological activity driven by seasonal and seismic forces. In Ganges Chasma, a major canyon within , images acquired since 2007 have documented recurring dry avalanches, where loose material cascades down steep walls, often initiated by the sublimation of seasonal frost that destabilizes slopes. These events produce dark streaks and debris flows extending hundreds of meters, indicating dry granular flow without liquid involvement, and highlight the role of thermal contrasts in mobilizing surface material. Additionally, has captured boulder tracks suggestive of marsquake-induced falls, with linear paths formed by rolling or bouncing rocks over distances up to several hundred meters, as seen in repeated imaging of faulted terrains like Cerberus Fossae; these tracks, fresh and unweathered, imply seismic events within the past 10,000–100,000 years. Dust devils and larger storms represent key monitored by multiple MRO instruments, illustrating the planet's volatile surface-atmosphere interactions. The Mars Color Imager (MARCI) and Mars Climate Sounder (MCS) have tracked global dust storms, including the intense event that encircled the planet for months, raising atmospheric dust opacity to levels that blocked sunlight and ended the Opportunity rover's operations by depleting . complements these wide-scale views with sub-meter resolution images (approximately 0.25 m/pixel) of individual dust devils, capturing their swirling paths as dark tracks etched into dusty surfaces, sometimes kilometers long, which reveal wind speeds exceeding 50 m/s and preferential activity in low-albedo regions during summer afternoons. MCS observations have yielded critical insights into Mars' atmospheric dynamics and cycles, profiling vertical structures that link surface processes to weather patterns. The instrument detects clouds forming at altitudes of 10–40 km, particularly in the aphelion season, where they influence radiative balance by and ; these clouds correlate with dust lifting mechanisms, as convective plumes raise fine particles into the atmosphere, enhancing initiation. MCS data also map the seasonal and sublimation of CO2, driving polar energy budgets and global pressure variations of up to 25%, while revealing enhancements rather than depletion during winter polar nights due to reduced in darkness. In the polar regions, MCS limb-sounding measurements show strong temperature inversions within vortices, with ground-level temperatures dropping below 150 and overlying warmer layers up to 20 higher, fostering wave patterns like baroclinic instabilities that propagate dust and trace gases equatorward. As of 2025, over 10 Mars years of operation (since 2006), MRO's combined datasets from MARCI, MCS, and have enabled analysis of long-term climate trends, particularly in dust cycle variability. Column dust opacity has fluctuated between 0.1 and 0.5 in non- periods, with decadal increases linked to regional frequency, potentially indicating a subtle cooling trend as higher dust loads enhance atmospheric thermal emission to space; this is evidenced by multiyear MCS profiles showing polar cap advances and reduced summer abundances by up to 20% in recent years. These observations underscore the interconnectedness of surface , atmospheric , and climatic feedback, providing a baseline for modeling future environmental changes.

Role in Broader Mars Exploration

Support for Landers and Rovers

The Mars Reconnaissance Orbiter (MRO) plays a critical role in supporting Mars surface missions through its ultra-high frequency (UHF) relay system, which enables efficient data transfer from landers and rovers to Earth. Launched in 2005, MRO's telecommunications hardware facilitates proximity-1 relay communications, allowing it to act as a high-bandwidth intermediary for surface assets that lack direct line-of-sight to Earth's Deep Space Network. This capability has been essential for missions including the Phoenix lander in 2008, the Opportunity rover from 2006 until its end in 2018, the Curiosity rover since 2012, and the Perseverance rover since 2021. MRO's relay operations involve scheduled overflights, typically providing 2–4 passes per Martian day depending on orbital geometry, with contact durations varying to optimize volume. MRO has conducted thousands of sessions for surface missions, enabling the return of substantial volumes that would otherwise be limited by direct-to-Earth links. For instance, during the Phoenix mission, MRO served as a primary orbiter, coordinating atmospheric measurements while transferring and back to . Similarly, MRO has relayed critical updates from and Perseverance, including during high-demand periods, contributing to over 90% of from Mars surface vehicles being handled via orbital relays like MRO. As of November 2025, MRO continues to from active rovers, having transmitted over 1.8 terabits from surface missions since 2006. In addition to relay functions, MRO's High Resolution Imaging Science Experiment (HiRISE) provides vital imaging support for landing site selection, hazard avoidance, and mission monitoring. Prior to Curiosity's 2012 landing, HiRISE captured detailed images of candidate sites in Gale Crater to certify safe terrain and assess geological features. For Perseverance's 2021 touchdown in Jezero Crater, MRO imagery helped evaluate delta deposits and potential hazards, while post-landing HiRISE maps have tracked the rover's traverse paths through 2025 as of November 2025, identifying obstacles and science targets. These images, at resolutions up to 25 cm per pixel, enable real-time operational adjustments and extend surface mission longevity by informing route planning. MRO has demonstrated its value in dynamic scenarios, such as the 2018 global dust storm, where it detected the event's onset and relayed Curiosity's atmospheric observations, allowing the rover to continue science amid reduced visibility. During Perseverance's Ingenuity helicopter operations in 2023, HiRISE imaged flight paths and the helicopter's position, supporting navigation and performance analysis for the 50th flight and beyond. Challenges include synchronizing overflights—intervals ranging from 2 to 26 hours based on relative positions—and prioritizing relay loads during concurrent mission demands, which require precise scheduling to maximize data return without interfering with MRO's science observations. Overall, MRO's support has enabled more than 90% of rover data throughput, significantly extending operational lifespans by reducing reliance on lower-rate direct communications.

Contributions to Future Missions

The High Resolution Imaging Science Experiment (HiRISE) and Context Camera (CTX) on the Mars Reconnaissance Orbiter (MRO) have been instrumental in certifying landing sites for subsequent missions by delivering detailed imagery for terrain assessment and hazard avoidance. For NASA's InSight lander, which touched down in Elysium Planitia in 2018, CTX images enabled rapid mapping of smooth terrains, while HiRISE provided sub-meter resolution views to confirm the site's safety, including slopes generally below 1% and minimal rock hazards. Similarly, HiRISE-derived digital terrain models at 50 cm/pixel resolution validated Jezero Crater as the landing site for the Perseverance rover in 2021, verifying low-relief areas with slopes under 1% and identifying safe ellipses free of major obstacles. MRO's extensive dataset, archived in the publicly accessible Planetary Data System (PDS), underpins planning for international missions, including the European Space Agency's ExoMars Rosalind Franklin rover, scheduled for a 2028 launch and landing in Oxia Planum, where orbital imagery informs geological context and site suitability. This repository also supports NASA's Mars Sample Return campaign by supplying high-fidelity maps for trajectory design, sample collection strategy, and risk assessment in Jezero Crater. Technological advancements pioneered by MRO have established benchmarks for future orbiters, such as its Ka-band telecommunications demonstration, which achieved record data rates and informed efficient communication architectures for missions like in 2014. MRO's onboard software for image targeting and fault recovery has provided heritage to later spacecraft, enhancing operational efficiency in resource-constrained environments. Additionally, HiRISE's 25-30 cm/ resolution has become the gold standard for surface reconnaissance, influencing instrument designs on subsequent Mars orbiters. Looking ahead to 2025 and beyond, MRO continues to contribute through data relay capabilities and long-term monitoring, serving as a technological analog for outer solar system missions like to Titan and providing environmental insights relevant to Mars analog studies for NASA's . The mission's legacy endures in its scientific output, with datasets enabling over 3,000 peer-reviewed publications to date and fostering training for the next generation of planetary scientists through educational programs and tools.

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