ExoMars-2016: A difficult road to Baikonur
In 2015, the orbiter and the lander for the ExoMars-2016 project entered the final stretch on the road to the launch pad. Preparations generally went well, but last-minute problems kept cropping up one after another until they finally forced a delay to the launch of the mission from January 7, 2016, until March 14 of the same year.
Thales Alenia Space engineer works on the protective shell of Schiaparelli lander at the company's Cannes facility in France on Sept. 14, 2015. Credit: ESA
Final assembly and testing
At the start of 2015, key activities to prepare the Trace Gas Orbiter, TGO, for the ExoMars-2016 mission centered in Cannes, France, at a facility of the project's prime contractor, Thales Alenia Space. The same company's division in Turin, Italy, had continued working on the Schiaparelli lander before its shipment to Cannes in March for integration with the orbiter. Both spacecraft were in the process of assembly, integration and testing, collectively known in the industry as AIT. The most important trials for both spacecraft would be electro-magnetic compatibility tests for onboard electronics, mechanical vibration tests on a special shaker and thermal tests in a vacuum chamber. Engineers were also racing to complete the software for the mission.
The testing of the orbiter prototype started in January, as did the trials of the lander prototype at the end of the following month. Engineers also tested the deployment of a large antenna dish and of a pair of solar panels on the orbiter.
The project's mission control center in Darmstadt, Germany, was also preparing for the mission. In particular, controllers tested space-to-ground communications between the spacecraft and mission control, including the capability to send crucial maneuvering commands to the spacecraft.
One potential spoiler for the schedule popped up in the spring, when bad weather damaged a balloon which was to be used for drop tests of the parachute system for the Schiaparelli lander. Concerned that the next available test window from September to December was too late for launch in January, ESA urgently arranged testing of the parachute inside a wind tunnel at NASA's Ames research center in California. At the end of July, the parachute went through the tests with flying colors and balloon drop tests were then cancelled.
Engineers were also able to take Schiaparelli's critical landing radar, known as Radar Doppler Altimeter, RDA, on a helicopter ride near Rome, Italy, for a series of tests. Helicopter flights followed tests of the same radar suspended from a crane. The lander's touchdown engines were also test-fired.
Also, Moscow-based GKNPTs Khrunichev, the developer of the Proton rocket, which would be used to launch ExoMars missions, sent an adapter to test interfaces between the spacecraft and the Briz-M upper stage. The structure was also used to conduct a separation test on May 25 to measure the shock, which would be experienced by the spacecraft during the split from its space tug more than 5,000 kilometers away from Earth.
During the first quarter of the year, electromagnetic tests were completed on the flight version of the TGO orbiter after which it was integrated with the Schiaparelli lander for the first time for vibration and acoustic testing in April.
However due to delays during the final assembly, the vacuum testing of the flight-worthy orbiter started on August 9 instead of the planned date of June 10, ultimately leaving its team only three days in reserve by the end of the summer.
On August 26, European and Russian officials began the so-called Qualification and Acceptance Review, QAR, which had to confirm that all the hardware was ready for launch before it was to be shipped to Baikonur then planned for October 21. At the time, the dual spacecraft was undergoing its final tests in Cannes.
ESA was also able to strike a deal with NASA to get support from the US agency's deep-space communications antennas and one of its orbiters near Mars during the risky descent of the Schiaparelli lander onto the surface of the Red Planet. In addition, a Russian ground station with a 64-meter deep-space antenna was also being upgraded to include it into the European space tracking network, ESTRACK, so it could receive scientific data from the TGO orbiter. As a test, the antenna was used to communicate with ESA's Mars Express orbiter currently operating around the Red Planet.
Problems with payloads
All four scientific instruments to be installed on the TGO spacecraft gave last-minute stress to their engineers, who had to postpone their delivery for installation on the orbiter.
During the final mechanical testing of the TGO only the Russian-built FREND neutron detector was present on the spacecraft in its flight configuration, while the other three instruments were represented by test versions.
But even FREND was not trouble free. It arrived at Cannes from Moscow in February, and within a month, it was integrated with the orbiter. However during tests, one of four neutron detectors within the instrument began showing noise in its signal. Moreover, tests at the Space Research Institute, IKI, in Moscow discovered that other detectors of this type also misbehaved in a similar way. Engineers took the faulty detector offline during vacuum tests, hoping that the problem would not spread. Back in Moscow, IKI scientists rushed to complete a backup model, so it could be ready to fly instead of the original if necessary.
In the end, three out of four flight instruments for the orbiter were in place for its crucial vacuum tests in Cannes. The missing one was the high-resolution camera, known as CaSSIS, which stands for Colour and Stereo Surface Imaging System.
Because it was the last component of the ExoMars-2016 project to receive funding, the development of the complex camera was lagging behind the work on all other instruments.
To save time, plans were made to ship the flight version of the CaSSIS from the University of Bern, Switzerland, directly to Baikonur for the final assembly on the spacecraft at the launch site. For the trip to Kazakhstan, the TGO spacecraft was equipped with a prototype model of CaSSIS, while the three other instruments -- NOMAD, ACS and FREND -- were in place.
Obviously, assembly outside of the spacecraft's main development home in Cannes, France, could jeopardize the hyper-sensitive device. Still, mission managers were ready to take this risk, but by August, a new issue arose that wiped out all the time reserve and put the launch in question.
HEPA filter problem
In the second quarter of 2015, engineers rolled the Schiaparelli lander into a vacuum chamber. According to ESA, during these tests the outer shell of Schiaparelli would reach temperatures ranging between -100 degrees to +30 degrees in vacuum conditions to ensure the spacecraft could survive in space and on Mars. In addition, the test was to verify the thermal model of the lander.
However as engineers began pumping out air out of the vacuum chamber with the Schiaparelli lander inside, it was discovered that the so-called high-efficiency particulate air filter, HEPA, installed on the spacecraft was not allowing air to go through fast enough. The test had to be halted and the chamber reopened. To complete the tests, a prototype of the filter was installed on the module. Still, further testing revealed that the flight model would have to be redesigned. As with other late items, engineer could re-install the device at the last minute in Baikonur to make up the schedule. However yet another problem came up.
Pressure sensor problem
Sometimes in 2015, the Netherlands-based developer MOOG-Bradford discovered that the new welding equipment that the company had started using in 2012 was leaving cracks in seal welds. The company was manufacturing pressure sensors, known as "transducers," which were installed in propulsion systems on various European spacecraft including the Schiaparelli lander. According to ESA, the sensors were not part of the control loop necessary for landing, but would rather have gathered ancillary data for monitoring the system.
In any case, all sensors of this type fell under suspicion including a pair installed on the lander. Potentially, a high-pressure leak in a sensor could lead to a catastrophic failure. ExoMars engineers faced the difficult choice of replacing the transducer with a different one, trying to repair it in place, removing the sensor altogether or taking a considerable risk and flying without any repairs. The problem was exacerbated by the fact that there was no way to check the welds on the already assembled spacecraft.
It was ultimately decided to cut off the suspected components and replace them. However, as a result, the planned delivery of the ExoMars hardware to Baikonur on October 21 or its launch during the first 21-day window opening on January 7, 2016, would no longer be possible.
Fortunately, the ExoMars-2016 mission still had the second and final launch window available in 2016, which would be open from March 14 to March 25.
On September 18, ESA announced the delay of the mission and the schedule change was officially endorsed at the September 24 meeting of the joint steering board of ESA and the Russian space agency, Roskosmos. Inevitably, the price tag for the overall mission had increased somewhat.
Traveling to Baikonur
After a series of joint functional and acoustic tests, the Schiaparelli lander and the TGO orbiter were split again and between December 11 and December 17 packed into separate transport containers at Cannes, France, for departure to the Turin-Caselle airport, Italy, from where they would make the flight to Baikonur via Moscow.
The Schiaparelli and the TGO were loaded on a pair of An-124 Ruslan aircraft, which delivered them to Baikonur's Yubileiny airport, on December 22 and December 23 local time, respectively. The third An-124 flight was used to deliver various clean-room equipment for the spacecraft processing.
Known milestones in the ExoMars-2016 mission during 2015:
Jan. 15: Testing starts on the prototype of the TGO orbiter.
February: A flight version of the FREND instrument arrives from Russia. (The instrument later has to be replaced with a backup version).
Feb. 27: Testing starts on the prototype of the Schiaparelli lander.
March 4: ESA commits to the Jan. 7, 2016, launch date for the ExoMars-2016 mission. (The schedule remains official until around September).
March: The Schiaparelli lander ships from Turin, Italy, to Cannes, France, for integration with the TGO. The Russian-built FREND instrument is installed on the TGO orbiter.
Beginning of April: Functional tests of the FREND instrument within the TGO orbiter.
April: The TGO/Schiaparelli stack undergoes vibration testing at Cannes, France.
April 29-30: The Critical Design Review, CDR, for the Proton rocket system intended to launch ExoMars-2016 is held at NPO Lavochkin near Moscow. (The event was previously postponed from January and from the end of March 2015).
May 25: Separation tests between the spacecraft and the payload adapter of the Briz-M stage take place. (These tests were previously planned for March and in June 2015.)
June 9: The thermal and vacuum testing starts on the Schiaparelli lander flight model. (Postponed from May 28).
July: Mission controllers complete Operations Readiness Test, ORT-2.
July 17: ESA and Roskosmos officials participating in the ExoMars project meet in Moscow.
July 24, 25: Parachute tests for the EDM lander are conducted at NASA's Ames research center.
August 2: Thermal and vacuum testing of the flight version of the TGO orbiter starts. (Postponed from June 10).
August 26: The Qualification and Acceptance Review, QAR, begins.
Sept. 18: ESA publicly confirms a delay of the ExoMars-2016 launch from the January to March 2016 window.
Sept. 24: A meeting of the joint steering board of ESA and the Russian space agency, Roskosmos, approves the ExoMars-2016 launch delay from Jan. 7 to March 14, 2016.
Nov. 25: The flight version of the TGO and Schiaparelli lander integrated for final tests. (Postponed from June 11, Aug. 27 and Sept. 25).
Dec. 11: The Schiaparelli lander is placed into a transport container for the trip to Baikonur, Kazakhstan.
Dec. 17: The TGO orbiter is loaded into a Spacebus 4000 container for the trip from Cannes, France, to Turin, Italy, and to Baikonur.
Dec. 20: Schiaparelli leaves Turin.
Dec. 22: Schiaparelli arrives at Baikonur. The TGO leaves Turin.
Dec. 23: The TGO arrives at Baikonur.
Dec. 25: The Schiaparelli lander and the TGO orbiter are unloaded from their transport containers at Facility 92A-50 in Baikonur.
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The Trace Gas Orbiter inside the Compact Antenna Test Range, CATR, at the Cannes, France, facility of Thales Alenia Space is undergoing electromagnetic compatibility tests to demonstrate that all the spacecraft's systems will operate without interfering with one another, and that they are sufficiently immune from external electromagnetic radiation. Click to enlarge. Credit: Thales Alenia Space
The Trace Gas Orbiter, TGO, and the Schiaparelli lander undergo vibration testing in a clean room at Thales Alenia Space in Cannes, France, on April 24, 2015 . Click to enlarge. Credit: Thales Alenia / ESA
The ExoMars 2016 spacecraft during acoustic noise tests at the Thales Alenia Space premises in Cannes, France at the beginning of May 2015. Click to enlarge. Credit: ESA
Testing of the solar panel deployment on the TGO spacecraft on May 29, 2015. Click to enlarge. Credit: ESA
The flight model of the Schiaparelli is loaded into the ESP70 Thermal Vacuum Chamber at the Thales Alenia Space on June 8. In June and July, Schiaparelli was subject to thermal vacuum and thermal balance tests. Click to enlarge. Credit: ESA
On July 20, the Trace Gas Orbiter is moved to the ESP500 Thermal Vacuum Chamber at the Thales Alenia Space premises in Cannes, France, prior to the start of thermal tests. Click to enlarge. Credit: ESA
Schiaparelli, also known as the ExoMars Entry, descent and landing Demonstrator Module is seen here being installed at the top of the Trace Gas Orbiter, at Thales Alenia Space, in Cannes, France, for final integrated tests. Click to enlarge. Credit: ESA
ExoMars-2016 arrives at Baikonur at the end of December 2015. Click to enlarge. Credit: ESA
The Schiaparelli lander is loaded on a railway trailer by the Yubileiny runway for a trip to Site 92A-50, shortly after its landing in Baikonur on an An-124 aircraft on Dec. 22, 2015. Click to enlarge. Credit: ESA
The Schiaparelli lander is unloaded from its transport container at Facility 92A-50 in Baikonur on Dec. 25, 2015. Click to enlarge. Credit: ESA