And Then Silence: 25 Years Since the Rise and Fall of Mars Observer

“Range Safety Command Destruct System has been armed…fuel valves are now being opened…”

It was Friday, 25 September 1992—a quarter-century ago—as NASA counted down the final moments on Earth of its first voyage to the Red Planet in almost two decades. Mounted atop the final Commercial Titan III booster on Space Launch Complex (SLC)-40 at Cape Canaveral Air Force Station, Fla., the 2,200-pound (1,000 kg) Mars Observer would follow in the footsteps of Mariner 9 and the twin Viking missions to become only the fourth U.S. spacecraft to successfully enter orbit around the Red Planet. It was destined to spend at least one Martian “year”, equivalent to 687 Earth-days, performing a comprehensive survey of the surface, atmosphere, climate and magnetic field. In the words of Project Manager David Evans of NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, Calif., Mars Observer would reveal far more about the planet than all previous missions combined. “We want to put together a global portrait of Mars as it exists today,” he said before launch, “and, with that information, we can begin to understand the history of Mars.”

Alas, in a sad quirk of fate, Mars Observer never got the chance to complete its ambitious mission of exploration. In circumstances which remain imperfectly understood, it vanished like a blip from a radar screen, only days before it was due to enter Martian orbit.

The origin of the mission dated back to the early 1980s, with a projected launch aboard the shuttle in the 1990 timeframe. Tragically, the loss of Challenger caused such plans to slip further to the right and NASA’s March 1988 manifest—published just months before shuttle Discovery returned the fleet to regular flight operations—listed Mars Observer as a “call-up” payload on STS-64, then targeted for 14 September 1992. However, the spacecraft and its powerful Transfer Orbit Stage (TOS) were later transferred onto the expendable Commercial Titan III, which completed three missions between January and June 1990. After a two-year hiatus, and extensive upgrades totaling $425 million to the SLC-40 infrastructure at the Cape, the Commercial Titan III would loft Mars Observer on its final voyage.

“T-minus-four, three, two, one…and liftoff of the Titan III rocket,” came the call from the launch announcer at 1:05 p.m. EST, “with the Mars Observer and America’s return to the Red Planet!” Powering the Commercial Titan III uphill for the first 116 seconds were a pair of side-mounted solid-fueled rocket motors, producing a combined propulsive yield of 1.4 million pounds (635,000 kg). The solids pushed the stack through maximum aerodynamic pressure and at 108 seconds the Titan’s core stage engine ignited, adding 548,000 pounds (248,560 kg) of thrust. A few seconds thereafter, the solids were expended and jettisoned. All told, the core burned for 2.5 minutes, before the second stage took over, delivering the Mars Observer/TOS combo into orbit.

Weighing 24,000 pounds (10,890 kg), the spacecraft and its booster was one of the largest ever destined for a journey to Mars. The solid-fueled TOS was being used for the first time on this mission. Thirty-one minutes after leaving the Cape, its engine fired for 2.5 minutes to attain a maximum velocity of 25,575 mph (41,160 km/h), before separating from Mars Observer. Over the course of the next hour or so, the spacecraft began to unfold like a mechanical insect from a cocoon. First came its gigantic solar array, then its high-gain communications antenna, followed by its gamma-ray spectrometer, magnetometer, attitude-control system and low-gain transmitter.

The stage was set for Mars. Or so it seemed.

After an 11-month cruise, the spacecraft was targeted to enter orbit around the Red Planet in the penultimate week of August 1993. Plans called for it to be captured into a highly-elliptical orbit, which would be gradually shaped over four months into a near-circular path, at an altitude of 234 miles (377 km). Inclined 93 degrees to the Martian equator, its orbit would sweep close to the planet’s poles. Mapping would commence in January 1994, with the spacecraft bringing a sophisticated suite of imaging and remote-sensing equipment to bear on an alien world. Its Mars Observer Camera (MOC) had already returned several tantalizing, far-off shots of the planet, whilst other instruments—a laser altimeter for topography, thermal emission spectrometer, infrared radiometer and gamma-ray spectrometer for surface and atmospheric analysis, together with magnetometer and radio-science hardware—would be put to work examining the Red Planet.

For 687 Earth-days, from January 1994 through the end of 1995, it would have surveyed the ochre-hued world. “Once the primary task is completed,” noted NASA’s Mars Observer press kit, “the mission may be extended, if the spacecraft and instruments are still in good condition and if there is enough fuel to control the spacecraft’s attitude and orientation.” The status of Mars Observer seemed good as spring burned into summer 1993. It acquired a pair of images of its planetary destination in late July and there seemed no doubt that the United States was heading for another spectacular success to add to the tally it had accrued with the Mariner 9 orbiter and the two Viking landers.

Then, late on 20 August, the entire mission figuratively and literally unraveled and fell to pieces. Contact with Mars Observer was abruptly lost, for no obvious reason, and repeated attempts to communicate with the spacecraft proved fruitless. It was never heard from again. Five months later, in January 1994, an investigation panel from the Naval Research Laboratory (NRL) concluded that the most likely cause of the spacecraft’s disappearance was a ruptured fuel pressurization tank in its main propulsion system. Hypergolic monomethyl hydrazine may have leaked past valves during the 11-month journey to Mars and inadvertently mixed with nitrogen tetroxide. The leaking fuel may have induced an extremely high spin-rate and likely damaged critical components aboard Mars Observer itself.

It was a sad and untimely end for a promising spacecraft, as well as providing yet another gremlin to the reservoir of “cursed” missions to Mars. Yet 25 years later, Mars Observer’s legacy lives on, in that many of its instruments and their descendents have seen actual service on more fortunate missions. The Mars Global Surveyor, for example, carried an upgraded version of the Mars Observer Camera; unlike its ill-fated predecessor, which acquired just three images, the second one returned no fewer than 243,668. And then, of course, there is the launch pad. For the Cape went on to host not one, but two, Mars-bound missions—the Mars Reconnaissance Orbiter (MRO) and the Curiosity rover—which continue to return a wealth of scientific data to this very day.

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