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PICTURE GALLERY

After months of simulations, flight controllers at European Space Operations Center, ESOC, in Darmstadt, Germany, conduct final phase of training in the runup to the ExoMars-2016 launch in March 2016. Click to enlarge. Credit: ESA

ESA's deep-space tracking facility in New Norcia, Australia. Click to enlarge. Credit: ESA

ESA'a ground station in Maspalomas, Canary Islands. Credit: ESA

An artist rendering of the separation between Briz-M stage and the ExoMars-2016 spacecraft. Click to enlarge. Credit: ESA

ExoMars-2016 begins deployment of its solar arrays after its separation from Briz-M upper stage. Click to enlarge. Credit: ESA

In the images by the Observatório Astronômico do Sertão de Itaparica team in Brazil, the spacecraft appeared as a bright object surrounded by at least six other fainter spots – elements of Briz-M stage – moving together in the sky. Many more smaller objects are not visible in this version of the photo. Later calculations indicated that the main object on the photo is actually Briz-M itself not ExoMars. Click to enlarge. Credit: ESA

Following its launch on the Russian Proton rocket on March 14, 2016, the ExoMars-2016 mission successfully embarked on a journey to the Red Planet at a speed of 33,001 kilometers per hour. However, ground observations showed that the Briz-M rocket stage disintegrated after successfully sending the probe on its path to Mars. A million-dollar question puzzling observers is when exactly the incident took place and how far apart the spacecraft had been at the time of a possible explosion.

Previous chapter: Launch of ExoMars-2016

The ground track during the launch of the ExoMars-2016 mission on March 14, 2016. Passive phases of the mission are shown in red and powered flight is marked with yellow. Moving eastward, the spacecraft made three progressively higher orbits around the Earth pushed by four firings of the Briz-M space tug at perigee (lowest points of the orbit). As the spacecraft entered its Mars-bound trajectory over Africa after the fourth maneuver and begins its movement away from Earth rather than around it, the planet's own eastward rotation caused the reversal of the probe's ground track over the Southern Hemisphere.

Spacecraft activation

During ExoMars-2016's entire ride on a Proton rocket and on its Briz-M space tug only Russian ground control stations were receiving telemetry from the mission. The European Space Operations Center, ESOC, in Darmstadt, Germany, had to wait for the separation of the TGO spacecraft from Briz-M on March 14, 2016, at 20:13:01 GMT (4:13 p.m. EDT, 23:13 Moscow Time).

Due to limitations on power consumption on the night side of the Earth, the main transmitter onboard the TGO was activated only one hour 15 minutes after the separation from Briz-M or 11 hours 57 minutes after liftoff.

The very first signal acquisition from the ExoMars by the European mission control was made via the Italian Space Agency's small X-band antenna in Malindi, Kenya, at 21:28:26 GMT (5:28 p.m. EDT) on March 14. At right time, the signal appeared on computer screens at ESOC.

First order of business was the deployment of solar panels scheduled to begin within a minute after the first radio contact with mission control. Moments later, ESOC confirmed that the panels started moving and few minutes later reported that they had been fully open.

Around an hour later, at 22:13 GMT, the spacecraft was scheduled to establish contact with ground control via ESA's 15-meter antenna in Maspalomas on the Canary Islands, and at 22:23 GMT also contact Malargue, Argentina, and then, at 23:24 GMT call a ground station in Kourou, French Guiana. The combined radio-measurements from all three sites allowed very accurate determination of the probe's actual trajectory. According to ESA's statement on March 23, the accuracy of the departure speed provided by Briz-M was within 1.5 meters per second.

By the end of its first day in space, the control over the ExoMars-2016 mission was transferred to Europe's Deep-Space Network, ESTRACK, with facilities in Malargue, Argentina, and in New Norcia, Australia, sporting 35-meter antenna dishes.

The deployment of the high-gain antenna onboard TGO was scheduled around 22:47 GMT, however its use was not expected until more than two weeks after launch, in order to prevent its powerful X-band signal from interfering with Deep-Space Network antennas on the ground at such a close distance from Earth. (The International Telecommunications Union, ITU, imposes limitations on the so-called power flux density and ExoMars' X-band communications system operating at 8,400-8,500 MHz fell within the restricted range.)

Based on the information from ExoMars during the first 24 hours in space, everything went well with the mission for the exception of some concerns about the overheating of the main engine on the TGO spacecraft. According to ESA, within hours after establishing a communication link, ground controllers noticed that the temperature of the main engine had started to rise more than expected. After consultations with engineers from Thales Alenia Space France, who built the TGO, flight controllers changed the attitude of the spacecraft by a few degrees to prevent the direct sunlight from heating the engine nozzle. It was enough to resolve the problem, ESA said.

Ground tracking reveals disintegration of Briz-M

Because the spacecraft began its trek into deep space over the western section of the Southern Hemisphere, what turned out to be the most critical tracking of ExoMars soon after its separation from the Briz-M space tug was mostly limited to South Africa and South America.

The Russian ground stations and tracking assets had no opportunity to follow this phase of the mission. Ground facilities in Brazil and Bolivia, which Russia could use, were reportedly out of commission at the time. Bad weather also prevented observations from Crimea, Northern Caucasus and Armenia.

Fortunately, observations made by Greg Roberts in Cape Town, South Africa, indicated that Briz-M had apparently initiated its post-separation maneuvers. Roberts began tracking the ExoMars mission at 21:37 GMT, which is around one hour 24 minutes after the separation of the ExoMars.

According to Roberts, when the Briz-M emerged over his northern horizon, it appeared unusually bright, at a magnitude of around +8.2 and seemingly had a misty glow, hinting some liquid or gas venting. The phenomenon could be caused by a disintegration of the space tug, but it also could be a result of a nominal pre-programmed command to vent propellant and pressurized gas.

Roberts tracked the mission continuously until 23:22 GMT, during which time, "it faded quite a good deal," as Roberts wrote in an e-mail to an editor of this web site. During the same period, the spacecraft climbed from around 26,000 kilometers to around 47,000 kilometers above the Earth's surface.

Here is how Roberts described his historic and rare "encounter":

"I observed two objects only - the much fainter ExoMars and the much brighter Briz rocket. I lost sight of ExoMars when it got too faint (fainter than about magnitude +12 or so) but continued to track the rocket till I lost it as it passed through my zenith -- I observed the part of the trajectory, where the mission first headed east then did a sharp turn to move westward and pass through elevation about 84 degrees." (see ground track map at the top of the page)

Above: Greg Roberts' image shows the bright Briz-M stage and much fainter ExoMars to the left.

As the ExoMars headed west across the Atlantic, just before midnight local time (near 03:00 GMT on March 15), a team led by Daniela Lazzaro, with Sergio Silva at the telescope at the Observatório Astronômico do Sertão de Itaparica, OASI, in Rio de Janeiro, Brazil, captured the most critical images of the mission. The photos showed an object, initially interpreted as ExoMars, surrounded by six large debris. Many smaller objects were also suspected in the vicinity. Later calculations showed that photos from Brazil captured Briz-M itself surrounded by debris, not the ExoMars spacecraft.

A sequence of images captured by the OASI observatory in Brazil.

Still, it was obvious that the Briz-M stage likely disintegrated after separating from the spacecraft. The question still remained when the disintegration of the upper stage had taken place and how far apart the two spacecraft had been at the time of the incident.

According to one Russian source, Briz-M was to complete its two post-separation maneuvers by 23:39:52 Moscow Time (20:39 GMT) or just 26 minutes after releasing the ExoMars. Interestingly, during a typical mission to the geostationary orbit, Briz-M's first post-separation maneuver takes place around two hours after payload release and the second firing happens around three and a half hours after the separation. Roskosmos had never publically released the exact timeline for Briz-M's operations during the ExoMars mission but said that all post-separation maneuvers and the Briz-M passivation precedures had gone as scheduled according to the telemetry transmissions, which had been discontinued soon afterwards.

Summary of ExoMars separation events on March 14-15, 2016 (GMT):

20:13:01: TGO separates from Briz-M stage;

20:39:52: Briz-M to complete its post-separation maneuvers, according to Russian sources (?);

21:29: ExoMars to establish contact with ground station in Malindi, Kenya;

21:37: Greg Roberts begins tracking Briz-M and ExoMars in Cape Town, South Africa;

~03:00 (March 15): An OASI observatory in Brazil images multiple debris around the Briz-M stage.

To be continued!

Next chapter: ExoMars-2016 mission

Read (and see) much more about the history of the Russian space program in a richly illustrated, large-format glossy edition:

Page author: Anatoly Zak; Last update: May 12, 2016

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