ITEM OF THE WEEK
MARS RECONNAISSANCE ORBITER
Originally appeared March 1, 2026
Twenty years ago this month (March 10, 2005), the Mars Reconnaissance Orbiter was safely inserted into Mars orbit. It’s been phenomenally successful; all of its instruments are still in full operation, and it is an important relay link in the present Mars “Internet,” helping to signals from other Mars probes back to Earth 24/7/365. Its detailed images of the martian surface helped guide the successful landing of Phoenix, InSight, Curiosity, and Perseverance. MRO’s instruments have returned over 500 terabits of data to Earth. Its HiRise pictures are available on-line, and the public can even suggest photo targets for acquisition via the HiWish outreach program.
Ominous Beginning
Mars exploration using robotic spacecraft is inherently difficult. While Mars has always been an attractive target, the first six attempts in the early 1960s ended in abject failure. Rocketry was still in its infancy, and six of those failures were rocket-related; the spacecraft did not live long enough to fail on their own. NASA began to hit its stride in the mid-60s, with Mariners 4, 6, and 7, losing only Mariners 3 and 8 to rocket failure. (Mariner 1 was a launch failure, and Mariners 2 and 5 were launched toward Venus. Mariner 2 was a full success, flying by Venus ten years to the day before the final footprint (for now) was made by Apollo 17’s Gene Cernan.)
The early Mars Mariners made it to the Red Planet, but the instruments they carried ware very primitive by the standards that would follow in the coming decades. In 1964, there were still a large number of people, including a few scientists, who were expecting to see canals and other artifacts of an inhabited Mars. Mariners 4, 6, and 7 could send back relatively few images as they flew by Mars, and as (bad) luck would have it, all three of them imaged areas of Mars that strongly resembled the Moon, a heavily-crated dead world.
Orbital mechanics dictates that launches to Mars need to occur in relatively-short windows about two years apart. Mariner 4 was in the 1964 launch window; Mariners 6 and7 were in the 1969 launch window (NASA was rather busy with crewed missions in the mid-60s!). That would all change in 1971, but not right away.
The Russians have always had terrible luck with Mars. They did manage to make the first (crash) landing on Mars with Mars 2, on November 27, 1971. NASA launched two Mariners toward Mars in May, 1971. Mariner 8 suffered a launch failure (the very last for NASA’s planetary exploration program); Mariner 9 changed everything.
NASA’s Batting Average Improves
Rocket and spacecraft technology advanced rapidly during the 1970’s. The first launch window of the decade was in 1971. The Russians launched four spacecraft, two were orbiters and two were fly-bys that would drop a lander with rover. There effort was almost a total failure. The primary reason was that Mars was suffering from a global dust storm that obscured the planet’s surface for many weeks. The Russian orbiters had pre-programming photo sequences that could not be altered, and what few images they could return showed a featureless dusty atmosphere. Mariner 9 could orbit and wait. And when the dust cleared, Mars’ surface was revealed in all its glory!
As NASA scientists watched patiently, the first things to appear from the murk were four dark spots (waggishly referred to as Carl’s Marks – Sagan was on the imaging team). Closer examination showed that each had a large summit crater, indicating that they were the tops of gigantic volcanoes (the largest in the entire Solar System). Subsequent imaging as the dust cleared showed the largest canyon system in the Solar System (named “Mariner Valley” in Mariner 9’s honor), what looked to be stream channels, streaks that appeared to change with time, and some areas that were heavily-cratered (as imaged by the earlier Mariners).
The next launch window was in 1973. NASA had been too busy with Apollo to mount an effort, and the four Russian attempts had very limited success.
The Russians took a breather for the 1975 launch window, but NASA hit a pair of homers with Vikings 1 and 2, both spacecraft having an orbital and lander component, all successful. Data poured in; what a great way to celebrate our Nation’s Bicentennial! [See the article in the Of Special Interest section above.]
Ominous Interlude
NASA had a lot going on in the late 1970s and the 1980s; the Space Shuttle, Voyager, and other programs had their attention (and budget money). The Russians tried an ambitious pair of missions for the 1988 launch window, each with an orbiter, and a lander for the martian moon, Phobos. Both failed abjectly, then national politics took Russia out of the Space business for a while.
NASA suffered one of its worst defeats at Mars during the 1992 launch window. Budgetary constraints allowed NASA a single launch, so there was great impetus for making it a “flagship” mission, one heavily-laden with objectives and instruments. The Mars Observer spacecraft was approaching Mars but all contact was lost when it pressurized its thruster system for orbital insertion. The spacecraft had had a troubled development history, originally planned to be launched from the Space Shuttle, but forced to downsize after the Challenger disaster; other missions were prioritized higher for when the Shuttle flights resumed. Budget constraints forced the cancellation of two other planned instruments. Things looked really bleak.
A Respite
NASA bounced back sooner that expected for the 1996 launch window. Two less-complex spacecraft were planned, Mars Global Surveyor, an orbiter, and Mars Pathfinder, a lander that would use a novel landing style – wrapping the landing craft in air bags and letting it impact the surface. Pathfinder would carry a small rover, Sojourner, and would be NASA’s first mission with an Internet outreach component. Both missions were an outstanding success. MGS outlived its planned lifetime by a wide margin, and Sojourner, and its scientist’s penchant for naming the rocks it visited after cartoon characters, attracted two billion website visits, forcing NASA to use the first-ever mirror sites to handle the load!
More Woes
NASA tried to maximize the value of its Mars exploration while minimizing its cost at the 1998/9 launch window with the Mars Climate Orbiter and Mars Polar Lander missions. “Faster, Better, Cheaper” turned out to be “Faster, Cheaper, Failure.” What happened to these two missions nauseates me to the point I cannot/will not describe them further.
Back on the Horse
The new millennium dawned with an unbroken string of successes for NASA Mars exploration. My ASU colleague, Phil Christensen, won NASA’s approval for an innovative Mars orbiter called Mars Odyssey, launched in 2001, with a name commemorating the wonderful film, 2001: A Space Odyssey! It is still in operation today, far, far longer than its design lifetime.
My undergraduate colleague at Cornell, Steve Squyres, scored big-time as the Principal Investigator for the Mars Exploration Rovers, Spirit and Opportunity, launched in the 2003 window. They, too, had lifetimes far greater than expected. [If your car performed as well against its warranty as did the two MERs, you would have enjoyed two-million miles of maintenance-free rides with no stops at a gas station!]
ESA had joined the party at this point, with its Mars Express mission launching a few days before the MERs. Its orbital component was fully successful and is still in operation today. It’s lander, Beagle II, crashed on landing, a total failure.
The Hero of Our Story and Beyond
The next NASA Mars mission was the Mars Reconnaissance Orbiter, launched on August 12, 2005. More on it below. But first, let me round out the list.
NASA’s 2007 Phoenix mission, a replacement for the Mars Polar Lander, was a complete success, but is now defunct.
The India Space program had a success with its 2013 Mangalyaan orbiter. So did NASA with its MAVEN orbiter. MAVEN lasted for 23 years, far beyond its planned lifetime; contact was lost with it last December (see the Solar System News section below).
NASA’s 2018 InSight spacecraft landed successfully. Its on-board seismometer has revealed much about Mars’ internal structure, and the lander lasted longer than its design lifetime, but is now defunct.
Three spacecraft, all very successful, were launched in the 2020 launch window: the United Arab Emirates’ Hope orbiter; China’s Tianwen-1 orbiter, lander, and rover; and NASA’s outstanding Perseverance rover and the Ingenuity helicopter. Percy is still going strong, having climbed out of Jezero Crater; Ingenuity was planned only as a test-of-concept, but it proved so valuable and successful that it was used as a scout for Percy for many flights.
Now, Let’s Go Back to the Mars Reconnaissance Orbiter!
Establishment of the Mars Exploration Program
The failure of the Mars Observer mission in 2004 triggered several changes in NASA operations. A Naval Research Laboratory investigation board, independent from NASA, found that the loss of the spacecraft was due to a communications failure caused by the tumbling of the spacecraft due to a leak in its thruster system. “A NASA investigation board further suggested that too much reliance may have been placed on spacecraft hardware that had been designed for fundamentally different operations than required of the Mars Observer mission.” “A NASA investigation board further suggested that too much reliance may have been placed on spacecraft hardware that had been designed for fundamentally different operations than required of the Mars Observer mission.” “Following the failure of Mars Observer, NASA undertook several organizational reforms, implementing new policies to avoid over-reliance on heritage spacecraft systems and revising project management protocol.” Quotes from here.
“ Furthermore, the Mars Exploration Program was established in 1993 to provide a long-term, comprehensive program for the exploration of Mars, with goals focused on identifying the location of water, and preparing for crewed missions to Mars.” Quote from here.
The Mars Reconnaissance Orbiter mission was built around the recommendations above.
“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 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.” Quote from: https://science.nasa.gov/mission/mars-reconnaissance-orbiter.
Mission Profile
Insertion directly into the best orbit for its planned observations would require a lot of fuel, with its attendant weight. Mission planners decided to use Mars for an assist. After a seven-month transit to the vicinity of Mars, MRO’s main motor was used to insert the spacecraft into an elliptical orbit, with its closest approach dipping into Mars’ rarified upper atmosphere, aerodynamically slowing the spacecraft further. The aerobraking process took six months. Then its scientific mission began in earnest. The goals: determine the history of water on the surface of Mars, conduct reconnaissance to assist the landing of subsequent missions, and to act as a radio relay for other spacecraft at Mars.
MRO Instruments
The MRO carried six different yet complementary instruments to meet mission objectives. In addition, it carried a suite of “Engineering” instruments that would provide additional information about the near-Mars environment.
HiRISE
Arguably the most important single MRO instrument was the High Resolution Imaging Experiment, aka “HiRISE,” a visible and near-infrared camera capable of resolving surface features as small as one meter. HiRISE has been extraordinarily successful; it recently returned its 100,000th image to Earth! HiRISE images have been used to create 3-D renditions of the surface, scout landing areas for subsequent missions, create virtual fly-over videos, and more. There is even a mechanism, the HiWish program, for the general public to request that a specific feature be imaged by HiRISE!
Context Camera (CTX)
HiRISE images that can see very small objects on Mars cover such a small area that it becomes difficult to see the “bigger picture” of the area. The CTX makes observations concurrently with HiRISE to give a broader context of the more detailed focus. CTX produces visible light images with 6 meter/pixel resolution for image swaths almost 20 miles across.
Mars Color Imagers (MARCI)
Detailed examination of the martian surface is only one of MRO’s primary objectives. Attaining a broader understanding of martian weather and atmospheric processes is important, too, and that is the job of MARCI. It’s a lower-resolution imager (~1 mile/pixel) with seven filters, five in visible light and two in ultraviolet, enabling it to see variations in ozone, dust, and CO2, data that not only enables study of Mars weather, but also monitor seasonal changes in Mars’ polar caps.
Mars Climate Sounder
The MCS complements MARCI by producing local atmospheric profiles. It looks at the martian horizon in both visible and IR to make vertical profiles of temperature, water vapor, and dust that allows scientist to prepare daily 3-D weather global-scale weather maps, just like meteorologists do for Earth to better understand climate and predict weather on Earth.
Compact Reconnaissance Imaging Spectrometer (CRISM)
HiRISE images reveal surface features and structures in great detail, but are less useful in the determination of the composition of such features. That’s where CRISM comes in. It has a slightly-lower spatial resolution, but it has enormous spectral resolution, able to distinguish small nuances in visible and IR “colors,” of great value in knowing the chemistry of the surface materials, including those that formed in the presence of water.
Shallow Radar (SHARAD)
HiRISE looks for stream channels and other features indicative of past water flow on the surface (among other things). But there is little or no liquid water on the surface of Mars today. However, there may be water or water ice buried beneath the surface, and it’s SHARAD’s job to find it. Water, liquid or solid, strongly reflects radar waves; changes in the radar return from an area is examined to indicate the presence of buried water. SHARAD’s radar is powerful enough to penetrate the first few hundred feet of the Mars subsurface, even deeper under some conditions.
“Engineering Instruments”
Not all of the instruments on MRO are used (directly) to examine Mars. Some are needed to facilitate the operation and navigation of the spacecraft. But valuable data about Mars can be derived from them as well.
Sensitive Accelerometers
The long period of aerobraking once MRO first entered the martian atmosphere had a big advantage for science in addition to putting MRO in the desired final orbit. MRO carried a suite of very sensitive accelerometers that could detect changes in spacecraft speed, which in turn could be used to assess the atmospheric density at MRO’s altitude. Mars’ thin atmosphere is affected seasonally by CO2 ice being added to, or sublimated from, Mars’ seasonal polar caps, and since the aerobraking process took months, density data changes at specific altitudes helped determine seasonal variations in amount of atmosphere, winds, and more.
Gravity Field Investigation Package
The telecommunication system on MRO produces a signal of a very precise wavelength. Changes in MRO’s speed produce minute Doppler shifts in the signals received at Earth, allowing the determination of subsurface structure to depths of several hundred kilometers. Changes in the shifts observed from polar regions also allow mapping frozen CO2 deposits and their seasonal changes, augmenting the results from the accelerometers.
Mission Support Instruments
Optical Navigation: Spacecraft have carried some form of an optical navigation system since the early days of Solar System exploration; that’s how spacecraft like Voyager and New Horizons could be guided to hit locations only a few miles across when they were a billion miles or more from Earth. MRO carried an optical navigation camera that allowed mission managers to navigate MRO very precisely. Optical navigation has been used since the days of Mariner missions, with increasing levels of precision as the equipment enabling the navigation measurements improved.
Radio Relays: Spacecraft usually communicate with Earth using radio signals in the microwave part of the spectrum called “X-band,” which typically operates in a frequency rang3 of 8-12 Gigahertz, corresponding to a wavelength of 2.5 to 3.75 cm. MRO was fitted with a robust X-band radio, since it was designed not only to send a LOT of its own data from Mars to Earth, but also serve to relay signals to Earth from other spacecraft in the vicinity of Mars.
In addition to its powerful X-band radio, MRO carried an experimental Ka-band radio, which operates with a frequency of 27-49 GHz (corresponding to a wavelength on the order of 1 cm). Ka band radio’s shorter wavelength allows it to transmit at four-times the data rate of an X-band system, and it also consumes significantly less power to do so.
REFERENCES
MRO: https://science.nasa.gov/mission/mars-reconnaissance-orbiter
MRO: https://science.nasa.gov/mission/mars-reconnaissance-orbiter/science
MRO: https://www.jpl.nasa.gov/missions/mars-reconnaissance-orbiter-mro
MRO: https://www.planetary.org/space-missions/mars-reconnaissance-orbiter
Wikipedia: https://en.wikipedia.org/wiki/Mars_Reconnaissance_Orbiter
MRO Image Gallery: https://science.nasa.gov/mars/resources
MRO Images from NASA Photojournal: https://science.nasa.gov/photojournal/search
Mars Orbital Data Explorer: https://ode.rsl.wustl.edu/mars
HiRISE: https://hirise.lpl.arizona.edu/index.php
Context Camera: https://www.msss.com/all_projects/mro-ctx.php
MARCI: https://www.msss.com/all_projects/mro-marci.php
CRISM: http://crism.jhuapl.edu
Mars Climate Sounder: https://arcnav.psi.edu/urn:nasa:pds:context:instrument:mcs.mro
SHARAD : https://www.asi.it/en/planets-stars-universe/solar-system-and-beyond/mars-reconnaissance-orbiter-mro