Why space missions to Mars are linked these days

• In the space of two weeks, three space missions will be launched for March.
• This group shot is not surprising. The Mars launch window has just opened. This period when the Sun, the Earth and Mars are aligned, in this order, is optimal to join the red planet.
• Missing this window means waiting another 26 months. The fear of space agencies?

For the Al-Amal (Hope) mission, it's done. The UAE space probe left Earth early in the day on Monday, powered by a Japanese launcher, from the Tanegashima space center in southwest Japan. Direction the orbit of Mars that the probe should reach next February for a two-year mission (that is, a Martian year) which will aim to take a complete photograph of the Martian atmosphere.

Doha can therefore breathe: Hope, the first interplanetary mission led by an Arab country has successfully passed the delicate stage of takeoff. We will not have to wait very long to see a new space mission to the red planet appear on the launch pad. “Probably this Thursday with the Chinese mission Tianwen [Questions in heaven], specifies Olivier Sanguy, from the Cité de l'Espace in Toulouse. This is in any case the date mentioned by Chinese observers, even if it has not yet been formalized by the national space agency. Anyway, takeoff should be done by July 25. "

Three missions for March in two weeks

If the date is still dotted, the objectives of this space mission, the first Chinese to Mars, are well known. This will involve placing a probe in Martian orbit and then landing a rover [a probe capable of moving on a star] on the surface of the red planet to conduct analyzes. Like Hope, the arrival is expected for next February.

That's not all. NASA also has in its boxes a trip to Mars with Perseverance, another rover that the American space agency wants to place in the Jezero crater, the first stage of a large-scale mission which will seek, in the long term, to bring back samples of Martian rocks on Earth. This time, the launch will be from Cape Canaveral, Florida, and a priori on July 30, if there are no new reports.

To sum up, it's been three space missions to fly to Mars in a fortnight. This is not surprising: the launch window to Mars has just opened. For about three weeks, conditions will be optimal to reach the red planet.

"The idea is to take advantage of what is called opposition, when the Sun, the Earth and Mars are aligned exactly in this order," explains Olivier Sanguy. The Earth and Mars are found on the same side compared to the sun and the distance which separates the two planets is then the shortest. Finally, there are still 55 million kilometers to hike, or six to seven months of travel.

A shooting window every 26 months

"We could launch missions to Mars outside this shooting window," continues Olivier Sanguy. But it would then be necessary for the same mass of the probe or the rover, a much larger launcher and therefore embark more fuel. We would then face technological but also budgetary limits. We should also boost more speed, which in space is a double-edged sword. "Since there is no air to resist, the spacecraft does not lose its initial speed during the voyage," continues Oliver Sanguy. If it goes too fast, the risk is that it exceeds its objective and ends up going around in circles around the sun. So you have to be able to brake, which again potentially means, if the speed is too high, to consume fuel. "

This is why space agencies prefer to wait for these famous windows of fire. Even if they only occur every 26 months, insofar as the Earth and Mars do not rotate at the same speed around the sun. A revolution in 365 days for the first, in 668 * for the second. As you can imagine, these three weeks not to be missed must cause great stress within space agencies. In the past, some missions have already missed the mark. "Often, space agencies know this well in advance," says Oliver Sanguy. This is the case for example, quite recently, of ExoMars 2020, a Martian mission led by the European Space Agency (ESA) and Roscomos (Russian space agency) and which should have been launched, too, these days. . Due to technical problems and the Covid-19 crisis which affected the work of their teams, they announced that they could not be ready for this shooting window. "

Perseverance about to miss the start?

ExoMars 2020 has thus been renamed ExoMars 2022 and now plans to arrive on the red planet only in March 2023. A postponement that lengthens the bill? "Of course," says Oliver Sanguy. You cannot put a probe or a rover on a shelf to take it out until the next shooting window. Storing the device in accordance with all procedures already has a cost. Above all, even if the preparation was well advanced before the postponement, it will be necessary to requalify all the parts before the start, if only to make sure that everything is still working. These operations generate significant costs. After the postponement of Mars Insight [another Martian mission which took off in 2018 instead of 2016 as originally planned], NASA gathered its partners to find out whether or not to follow up on this mission. "

Due to processing delays in preparations to unite me with the rocket, my first launch attempt will be no earlier than July 30. @NASA and @ulalaunch are working to update the target launch date and have been able to expand the launch period until Aug. 15. https://t.co/cwfwy5cTY0 pic.twitter.com/XICMjwtx7h

Could Perseverance know such a disappointment? In any case, NASA is accumulating glitches in preparation for the launch of its rover. Delay in assembling the Atlas V launcher, contamination incident in an ultra-clean room and, recently, defect observed during a dress rehearsal, Futura Sciences list. The departure was initially scheduled for July 17, was first postponed to 20, then to 22, and now to 30. In parallel, Nasa teams have revised their calculations and are now talking about a shooting window around March which could extend until August 11 or see August 15. "But the longer we wait, the more the margins to deal with new errors or unforeseen events, such as bad weather, shrink," says Olivier Sanguy. And the conditions of arrival on Mars will be less optimal. "

* 668 Martian days (called soils) which correspond to the duration of 687 Earth days, specifies the Cité de l'Espace, because the Martian day is a little longer than the one we are used to: 24 hours ... and 40 minutes

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