A European-Russian effort to land on Mars has been hit by another parachute failure, during a drop test in Sweden.
It's the second test mishap involving the parachutes, so with launch under a year away, the Exomars project cannot afford another failure.
It means the next test is critical if the mission is to avoid a delay to its targeted launch date of July 2020.
The plan is to send a Russian surface platform and a European rover down to the Martian surface.
The European Space Agency's (Esa) Rosalind Franklin rover will collect samples of soil with a drill and analyse them for the presence of organic material. This could provide clues to the presence of past or even current life on Mars.
The rover and the Russian Kazachok lander will be encapsulated in a carrier module during their six-minute journey down to the surface.
During a high-altitude test on 5 August in Kiruna, Sweden, a test mass designed to represent the combined lander and rover was dropped from a stratospheric helium balloon at the height of 29km.
Engineers were testing the largest of two main parachutes, measuring 35m in diameter, designed to slow the vehicle to a speed required to land safely on Mars. The European Space Agency says it's the largest ever to fly on a Mars mission.
However, the test article crashed into the ground at high speed. Preliminary analysis shows that the initial steps in the parachute's deployment were carried out correctly. However, specialists spotted radial tears in the canopy of the parachute prior to its inflation.
As result, the test module descended under the drag of the pilot chute alone.
The same tearing problem was seen on a previous test at the Swedish Space Corporation's Esrange site, on 28 May. The balloon drop test was designed to test the deployment of the two main parachutes and the pilot chutes designed to extract them from bags on the descent module.
Changes were made to the design of the parachutes and bags following that test, but they evidently didn't solve the problem.
"The test took place eight days ago so, as you can imagine, the analysis is still running. We have to have a good understanding of the root cause because we have only one more chance to fix this issue," said Nico Dettmann, human and robotic exploration development projects group leader at Esa.
"We have two remaining test windows. One is in November, the other is in February next year. If those tests are okay then we are on for a flight in July. However, if one of them was to fail, we would not take the risk. Our mission success is the first priority."
He told BBC News: "But at the moment we are confident we will be able to find a fix and implement it in time."
If Exomars misses its launch window in 2020, the next opportunity to fly the mission will arrive in 2022, when Mars and Earth make another close approach.
But Nico Dettmann emphasised that there was more involved in such a decision than favourable planetary alignment. "This doesn't happen automatically. There are a number of programmatic questions to be clarified with the main stakeholders.
"The main stakeholders are not only our Russian partners, but also our member states. If we have to defer it will obviously cost some more money. This is something which is not yet under discussion because we are still optimistic that we can make the 2020 launch."
A low-altitude test conducted in March 2018, in which a test mass was dropped from a helicopter, had been successful.
The Rosalind Franklin rover is in its final stages of completion at Airbus' facility in Stevenage, UK. Engineers have been running through the end tasks of assembly and expect to get the six-wheeled vehicle out the door before August is up.
Roscosmos' Kazachok landing platform (the name translates as "little Cossack"), will carry a suite of instruments developed in countries including Belgium, Spain and Finland - in addition to Russian-built experiments. It is also nearing completion.
As it currently stands, the mission should launch on a Russian Proton rocket from the Baikonur Cosmodrome in Kazakhstan in July next year.
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