Last week, the European Space Agency (ESA) and its Russian partners celebrated a historic launch as the long-awaited ExoMars spacecraft headed off to the Red Planet to search for potential signs of life. The 4.3-ton dual spacecraft, including the Trace Gas Orbiter which will stay in orbit as well as the lander named Schiaparelli,blasted off on March 14 from the Baikonur Cosmodrome in Kazakhstan on a Russian Proton rocket.

After the launch reached the initial parking orbit around the Earth, the Proton's fourth stage (known as Briz-M, Russian for "breeze") acted as a space tug, boosting the space probe on a path to Mars with four engine firings. What happened next was a close call that could have ended the mission catastrophically. And ExoMars still isn't out of the woods.

The resulting "graveyard" trajectory would ensure that the "blind and deaf" space tug, now drifting through interplanetary space, would not come anywhere near Mars.

Shortly after the separation between ExoMars and the spent Briz-M, the probe called home, and the ground control center in Darmstadt, Germany, confirmed the mission was on a path to Mars. However, astronomers tracking the flight soon spotted a cloud of debris accompanying ExoMars in space. As many as six large pieces of space junk appeared on the photos taken by the OASI observatory in Brazil.

ExoMars sighting ESA

This was strange. For one thing, the Briz-M was supposed to separate cleanly in one large piece without producing any additional fragments. Secondly, and more importantly, after the separation the space tug was programmed to fire twice to propel itself to a safe disposal orbit as far away from its former cargo as possible. The resulting "graveyard" trajectory would ensure that the "blind and deaf" space tug, now drifting through interplanetary space, would not come anywhere near Mars, where it could contaminate the planet's pristine environment with Earth's bugs. (Unlike Mars landers, rocket stages are not sterilized in accordance with strict international standards.)

According to sources in the Russian space industry, the first of Briz-M's two collision-avoidance maneuvers was to last around 12 seconds. Once it was a safe distance from ExoMars, the rocket stage would fire again, this time for around 1.5 minutes, until the engine consumed all the remaining explosive propellant aboard. Upon completion of the second maneuver, valves would open to vent the high-pressure gas used to force propellant into the engines.

That's what's supposed to happen. The initial info available to Russian tracking experts after the launch of ExoMars indicated that Briz-M had worked as planned. But the latest tracking photos indicate that something happened before the spacecraft had had a chance to go into its graveyard orbit. The situation is complicated by the fact that Russia had no tracking means in the Western section of the Southern hemisphere, over which Briz-M was suppose to perform its maneuvers. The Russian Academy of Sciences previously had agreements to use tracking telescopes in Australia and Bolivia, but both facilities were apparently out of commission at the time of the ExoMars launch.

ExoMars separation Anatoly Zak

And history includes a few examples of the Briz-M's going wrong after launch. A Briz-M thatdelivered a secret military satellite into orbit on December 13 then exploded on January 16. It continues to sporadically eject gas from its damaged tanks, tracking experts say. A careful analysis of visible debris from that disaster suggests that one of the high-pressure tanks on the stage was sheered off. The most likely explanation for that is the failure to vent its gas and propellants into space. Sunlight could have heated up contents, triggering an explosion.

What is especially worrying about the latest accident is that Briz-M apparently exploded after just 10.5 hours in space, when its ExoMars cargo was still in the vicinity. The good news is that ExoMars appears to be undamaged by whatever happened to its space tug, but the mission is not out of the woods yet.

Briz-M cutaway Anatoly Zak

On March 17, ground control completed the early activation of the spacecraft with only most critical systems running. This week, European engineers are scheduled to begin the commissioning various service systems on board the probe. Four sensitive scientific instruments, which are the main reason for the flight, are not expected to be fully online until April. Only then can mission officials could breath a sigh of relief and declare the spacecraft ready to explore the Red Planet.

In the meantime, Briz-M, or whatever is left of it, continues its aimless trek into deep space, carrying its mystery with it.

Anatoly Zak is the publisher ofRussianSpaceWeb.com and the author ofRussia in Space: the Past Explained, the Future Explored

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