It’s a busy February for Mars, with three sins from three separate countries arriving at the Red Planet in just nine days. But this Mars party did not happen by chance – it has to do with the mechanics of the Earth and the orbits of Mars.
The United Arab Emirates’ first interplanetary mission, the Hope probe, orbits Mars on Tuesday (February 9) The Live Science sister site Space.com reported. China’s first interplanetary mission, Tianwen-1, will enter its own orbit around Mars on Wednesday (February 10). The Chinese probe contains both a track and a lander with a rover on board expects to try to land on the surface in May. And on February 18, NASA’s first descendant vehicle will reach Mars and sink directly through its atmosphere. If all goes according to plan, the vehicle will shake off its outer shell and use rockets to stop the descent at the last minute. Then it will soar above the surface to lower the rhino-sized, nuclear-powered, $ 2.7 billion endurance capability through skycrane to the dirt.
All of these robots that arrive at exactly the same time are not accidental, said Jonathan McDowell, an astrophysicist and space expert from Harvard University.
March and Earth is like ‘runners on a circular track’, he said. ‘And the really fast runner [Earth] the runner often walks only on the outside [Mars]. So sometimes they are right next to each other and sometimes on either side of the track. ‘This Earth-Mars cycle, which means the Earth is completely decaying, takes about two years to complete.
It will take a huge rocket, tons of fuel and much more time to reach Mars from Earth, while the planets are far apart, McDowell told WordsSideKick. However, it is also not the most efficient way to get to Mars, while the planets are the closest – on average 62.1 million kilometers (62.1 million kilometers) apart.
There is an earlier point in the two-year cycle of the planets where the journey takes less time and requires less fuel. At that point, which occurs once during the two-year cycle, the Earth is a little behind Mars, but it is still moving faster than its neighbor. With this positioning, the spacecraft could enter a so-called “Hohmann transfer orbit”, named after the German engineer Walter Hohmann, who worked out the underlying mathematics in 1925.
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This is how it works:
No rocket carries enough fuel to burn between Earth and Mars, a distance between ten and hundreds of millions of kilometers.
This means that any interplanetary adventure begins with a short, intense period of acceleration, followed by a long stretch of coast. The task of the rocket engines during the first period of acceleration is to place the spacecraft in orbit around the sun which will cross with Mars as soon as possible. The most efficient path between the planets is therefore the solar orbit that intersects with Mars, which can be reached with the least fuel expenditure, and the orbit becomes available once every two years.
But space agencies do not have to nail down exactly that day. As long as they are launched during a window of a few weeks around the date, they can place their spacecraft on the orbit of Hohmann. Stay longer than a few weeks, and the journey starts to get harder very quickly.
The Hope track launched on 23 July 2020, Tianwen-1 on 23 July and Perseverance on 30 July. The gaps between the arrival of the spacecraft do not exactly match their launch dates due to slight differences in their rocket technology, trajectories through space and destinations, McDowell said. (It takes a different angle, for example, to plunge directly into the planet’s atmosphere than to enter a high orbit as Hope did.)
McDowell pointed out that this is not the first time that the orbit in Mars is so fast. The Soviet Union launched four spacecraft to Mars in 1973, although one could not reach the orbit and none of the other three worked as expected upon arrival. Two Soviet spacecraft and one American spacecraft were launched to Mars in 1971, and all had at least partially successful missions. (Both countries planned additional probes that year, but the U.S. Mariner 8 probe failed during launch and the Soviet Cosmos 419 never escaped a low-Earth orbit.)
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What is different, McDowell said this year, is the large variety of spacecraft that reach Mars, and the fact that there are already several additional probes active across the planet. NASA has three orbits orbiting Mars, the European Space Agency (ESA) has one of its own and one orbit that is a joint project with the Russian Roscosmos, and the Indian Space Research Organization also has an active orbit. NASA’s Curiosity Rover and InSight Lander are also still active on the Martian surface.
Despite the relatively tight situation, McDowell said he doubts whether any of the sins will even come tens of thousands of miles apart, even if neither country has checked their paths with each other beforehand.
“Space is huge,” he said.
Originally published on Live Science.