First Pictures: Views of Mars from NASA’s Mars Observer – July 27, 1993

Having enthusiastically followed NASA’s Viking mission to Mars as a teenager during the late-1970s, the lack of any new NASA missions to Mars during the 1980s was a frustrating disappointment (see “The Future That Never Came: Planetary Missions of the 1980s”). Needless to say, the announcement of NASA’s new Mars Observer mission, originally slated for launch on the Space Shuttle in 1990, was exciting news for not only myself but, for a growing community of Mars enthusiasts as well.

Mars Observer shown being prepared for launch. (NASA)

Mars Observer was the first in NASA’s then-new Planetary Observer series of missions that adapted existing spacecraft and instruments for planetary missions with the goal to keep costs low in a time of tight federal budgets. To this end, Mars Observer employed a modified General Electric’s three-axis stabilized Satcom K communication satellite bus as well as subsystems adapted from other satellite programs including military and civilian polar orbiting meteorological satellites. Mars Observer’s mission was to perform a wide range of investigations of Mars from a circular 378-kilometer orbit during a nominal one Martian year primary mission using an extensive suite of state-of-the-art remote sensing instruments.

A diagram showing the major components of the Mars Observer. Click on image to enlarge. (NASA/JPL)

By far, the one instrument carried by Mars Observer which excited me the most was the 21-kilogram Mars Observer Camera (MOC) built by Malin Space Science Systems, Inc. with Michael C. Malin as the Principal Investigator. The MOC actually consisted of a pair of camera systems integrated into a single package. Both cameras employed one-dimensional CCD arrays which operated in a pushbroom mode which relies on the motion of the spacecraft as it orbited Mars to build up a two-dimensional image one pixel column at a time. The wide-angle camera on MOC used a pair 3,456-pixel CCD arrays each employing an 11.3 mm focal length, f/6.5 lens to yield a 140° wide field of view. The nominal image scale of this camera system ranged from 280 meters/pixel at nadir to two kilometers/pixel at the limb. One of these cameras was fitted with a red filter while the other used a blue filter. With proper processing, the data from these cameras could generate wide-area color images of Mars which would be used to monitor global weather conditions daily on Mars.

Diagram of the Mars Observer Camera (MOC). Click on image to enlarge. (NASA/JPL)

The much more exciting (and larger!) camera was the narrow angle system which used a 2,048-pixel CCD array fitted with a 3.5-meter focal length, f/10 telescope. With a very narrow 0.4° field of view, the image scale of this camera was an astounding 1.4 meters/pixel at nadir – over an order of magnitude finer than the best orbital imagery acquired by the Viking orbiters. This camera was fitted with a spectral filter which spanned from 500 nanometers wavelength in the green part of the visible spectrum to 900 nanometers in the near-infrared to maximize the visibility of surface features. The very high-resolution images returned by MOC promised to revolutionize our understanding of the geology of Mars.

The launch of Mars Observer on September 25, 1992 using a Commercial Titan III/TOS rocket. (NASA)

As a result of the Space Shuttle Challenger accident in January 1986, the launch vehicle for the 1,018-kilogram Mars Observer spacecraft was eventually switched to the expendable Commercial Titan III/TOS with a resulting two-year launch delay. Mars Observer finally lifted off on September 25, 1992 and was sent on its way to Mars – the first NASA mission to that planet in 17 years. During Mars Observer’s 11-month cruise to the Red Planet, engineers checked out the spacecraft’s various systems and instruments including the MOC. By slowly rotating the spacecraft, the linear CCD camera arrays would scan across a target to produce a two-dimensional image which could be used to assess the health and performance of the MOC. One of the targets used during a routine to adjust the focus of the camera was the planet Jupiter which was observed at 00:52:47 UT on April 14, 1993. Although somewhat blurred, the image not only showed the banded disk of this giant planet familiar to amateur astronomers, but two of its large moons, Europa and Ganymede. During June and July, MOC acquired several hundred star images as the camera’s focus control heaters were being calibrated including an image of the two bright, Sun-like stars at the heart of the nearby Alpha Centauri system acquired at 23:59:38 UT on June 18 (see the Alpha Centauri page).

This is a test image of the planet Jupiter acquired by MOC at 00:52:47 UT on April 14, 1993 as part of a camera test during its 11-month cruise to Mars. (MSSS)

This is an enlarged closeup from a 2048×1024 pixel star field image showing the pair of Sun-like stars at the heart of the nearby Alpha Centauri system acquired by MOC at 23:59:38 UT on June 18, 1993. (MSSS)

When Mars Observer was still about a month away from orbit insertion, MOC was slewed to acquire some distant images of the Red Planet as a further check of the cameras’ performance. At 03:52:41 UT and again at 04:52:41 UT on July 27, 1993, MOC acquired a pair of narrow angle images of Mars at a range of 5.8 million kilometers. With an image scale of 21.5 kilometers/pixel, the disk of Mars was about 315 pixels across. At this range and resolution, only albedo features are visible including the bright, 2000-kilometer across impact basin known as Hellas towards the bottom of Mars’ disk as well as the dark volcanic feature called Syrtis Major Planum to its north. MOC’s wide angle camera also secured a test image but Mars was just an unresolved red dot. NASA officially released the first MOC Mars image on August 6.

This is a closeup of an MOC image of Mars taken at 03:52:41 UT on July 27, 1993 as Mars Observer was 5.8 million kilometers away and still a month out from orbit insertion. (MSSS)

This is a closeup of an MOC image of Mars taken at 04:52:41 UT on July 27, 1993. (MSSS)

This is an enlargement of a color image of Mars acquired by MOC’s wide angle cameras on July 27, 1993. Mars is just an unresolved red dot at this range. (MSSS)

On August 21, 1993, Mars Observer’s propulsion system was finally pressurized in preparation for orbit insertion 68 hours later. Because of concerns about the effect the mechanical shock caused by detonating the pyrotechnics used to open the valves would have on the radio electronics in a powered state, the decision was made to shut down Mars Observer’s transmitter during this vital operation. Unfortunately, Mars Observer was not heard from as scheduled 14 minutes after pressurization and all attempts to regain contact failed. There would be no close up images of Mars from the MOC.

A schematic of the Mars Observer propulsion system with the location of the probable nitrogen tetroxide leak indicated. Click on image to enlarge. (NASA/JPL)

Investigators never determined a definitive cause for the loss of Mars Observer because of a lack of telemetry during the pressurization of the propulsion system. Although there are many possible causes, the consensus seems to be that Mars Observer was lost as a result of a fatal failure of the propulsion system which, since it was borrowed from an Earth-orbiting satellite, was never designed to delay pressurization after months in space. The best guess is that a small amount of nitrogen tetroxide oxidizer leaked past a check valve during the long cruise to Mars and came into contact with the hydrazine fuel during pressurization, causing a rupture in the system’s plumbing. Mars Observer would have gone into an unrecoverable tumble as a result of venting propellants from broken propellant lines. This loss—which showed the weakness of the philosophy of adapting Earth-orbiting spacecraft to planetary missions—along with Mars Observer cost overruns, essentially killed the Planetary Observer program and set the stage for the “faster, better, cheaper” Discovery program (see “A Brief History of Planetary Orbit Insertion Failures”).

This image shows Nanedi Vallis which cuts through the cratered plains in the Xanthe Terra region of Mars. It was acquired at about 06:00 UT on January 9, 1998 by the Mars Orbiter Camera (MOC) during the 87th orbit of the Mars Global Surveyor spacecraft. The picture covers an area 9.8 by 18.5 kilometers and features as small as 12 meters can be seen. Click on image to enlarge. (MSSS/NASA)

In the meantime, a flight spare of the MOC (now redesignated the “Mars Orbiter Camera”) was eventually flown on NASA’s Mars Global Surveyor which reached Mars on September 11, 1997. During its nine years of operation, the MOC returned 240,000 images which helped to revolutionize our understanding of the Red Planet.

Related Reading

“A Brief History of Planetary Orbit Insertion Failures”, Drew Ex Machina, February 13, 2020 [Post]

“The Future That Never Came: Planetary Missions of the 1980s”, Drew Ex Machina, November 27, 2014 [Post]

General References

Paolo Ulivi with David M. Harland, Robotic Exploration of the Solar System Part 2: Hiatus and Renewal 1983–1996, Springer-Praxis, 2009

America’s Return to Mars – Mars Observer Press Kit, NASA 92-142, September 1992