Mars may not be the kind of place to raise your kids, but chances are that one day [Elton John]s famous lyrics will be wrong about there being no one there to raise them. For now, however, we have probes, orbiters, and landers. Mars missions are going strong this year, with three nations about to launch their rockets towards the Red Planet: the United States sending their Perseverance rover, Chinas Tianwen-1 mission, and the United Arab Emirates sending their Hope orbiter.

As all of this is planned to happen still within the month of July, it almost gives the impression of a new era of wild space races where everyone tries to be first. Sure, some egos will certainly be boosted here, but the reason for this increased run within such a short time frame has a simple explanation: Mars will be right around the corner later this year relatively speaking providing an ideal opportunity to travel there right now.

In fact, this year is as good as it gets for quite a while. The next time the circumstances will be (almost) as favorable as this year is going to be in 2033, so its understandable that space agencies are eager to not miss out on this chance. Not that Mars missions couldnt be accomplished in the next 13 years after all, several endeavors are already in the wings for 2022, including the delayed Rosalind Franklin rover launch. Its just that the circumstances wont be as ideal.

But what exactly does that mean, and why is that? What makes July 2020 so special? And whats everyone doing up there anyway? Well, lets find out!

Even the simplest model of our solar system will show how Earth and Mars revolve differently around the sun, with distance and speed being the most obvious ones. Earth rotates in a distance of roughly 149,597,870.7 km 1 astronomical unit (AU) from the sun at an average speed of 29.78 km/s, while Mars does the same at ~1.523 times the distance and an average speed of 24 km/s. It takes Earth ~365 days to end up in a same spot again, and Mars ~668 amounts of its own definition of a day, i.e. sols, which is roughly the equivalent of 687 Earth days.

Throwing around all these numbers shows mainly one thing: Earth and Mars dont have much in common here, and as a result, they dont hang around much in each others proximity. Still, they do revolve around the same sun, and are therefore bound to meet on occasion. Okay, meet is a strong word with fatal results if taken too literally here, but rather have close encounters with each other. The accurate terminology would be that they are in opposition on occasion.

Every time the Sun, Earth, and another celestial object are aligned in a way that you could draw a straight line through them, theyre said to be either in conjunction, or in opposition, depending on which side of the sun that third object is. If the arrangement is in conjunction, the object in question has the furthest possible distance from Earth, usually having the Sun between them, while in opposition, its as close as its ever going to get in that specific moment of proximity. Mars is in opposition with Earth on average every 780 days: 2 years and 50 days. That means in theory, theres a great opportunity to travel to Mars every 780 days.

However, opposition as reference for a launch window isnt only about traveling the shortest possible way for resources reasons, but to do so in a perfect time frame to match the speed and trajectory of everyone involved, and make sure there is an actual chance of our rocket meeting our object of desire in this case Mars. Lets not forget that were dealing with giant objects moving with unimaginable speed through space here. They may be close to each other in a relative sense, but were still talking about millions of kilometers distance between them.

The thing is, we cant just launch a rocket along that imaginary line in the moment of opposition. Not only will it take months to reach there, the rocket also has to travel in an elliptical orbit that matches up between Earth and Mars. Doing so on the shortest possible distance simply has the highest chance for success. Launching too early, the rocket might have to wait unnecessarily long for Mars to catch up, wasting fuel and potentially running out of it altogether. Launching too late, and itll end up like Wile E. Coyote desperately chasing the Road Runner minus the rocks and cliffs.

As a result of all that, Mars missions happen indeed roughly every 2.x years, launching usually a few months before the opposition itself, and landing / entering orbit a few months after the opposition then.

Looking at the history of the last few oppositions and the launch dates of the missions at that time, it all adds up:

We can go back as far as October 1960 with this, when the Soviet Union (unsuccessfully) attempted the very first launch to hit the window in late December that year and of course 1965 when NASAs Mariner 4 performed the first successful flyby of Mars. While this shows a steady amount of launch windows over the years, it also shows that missing the opportunity will cause a definite delay until the next windows opens as it happened with the InSight mission in 2016, and the previously mentioned joint mission between ESA and Roscosmos this year.

There are two other things noticeable in the mission history excerpt above: Im quite vague about the dates, and the period between mission launches and opposition varies. Lets get into the date vagueness first by taking a look at the actual launch windows.

While there is a definite time we can attach to the opposition and the closest proximity, we dont have to be at a specific point at a very specific time here, but have a bit of tolerance hence launch window. The exact width and location of that window varies on different factors like the rocket and its trajectory, and is individually determined for each single mission.

For example, as shown above, there were two launches at different periods back in November 2013 for the April 2014 opposition. Indias Mars Orbiter Mission (MOM) had a window from October 28th to November 19th and was launched on November 5th, while the USs MAVEN had a window from November 18th to December 7th, and was launched straight away on its first possible launch date on November 18th.

Each day within the launch window has usually its own window of a very few hours for a rocket to launch in hopes to rendezvous with another object. Remember, everything is rotating and spinning in all sorts of directions in space, so depending where on Earth you launch from, you have to account for that as well.

Considering that a launch also depends on weather conditions, its a good thing that there is usually a ~3 weeks window for each mission, which explains my vagueness on the mission times earlier. But what about that shift between the launch frame and opposition time then? Well, nothing is going perfectly round up there in space.

In an ideal world, the planets would rotate in a perfect circle around the sun, having the same distance to it at any given time. In the real world, its all a bit off-center though, and eccentricity causes a variation of the distance over the (local definition of a) year. For example, the apsides of Earth, i.e. the closest and farthest points from the sun, differ around five million kilometers or five gigameters (Gm) within the year, This may sound like a lot, but at an average distance of ~150 Gm, its eccentricity is a low 0.0167. Its still enough to have spring and summer a few days longer than autumn and winter, and as someone living close to the Arctic Circle, I can certainly appreciate this.

Mars is, after Mercury, the most unbalanced planet in our solar system, with an eccentricity of 0.0934 that places its apsides at ~206.6 Gm and ~249.2 Gm respectively. Since the timing of opposition occurrences dont add up to either of the planets orbital period, their moment of closeness always happens at a different place within their orbit. As a result, the actual distance of each opposition varies, and with it, the time it takes to travel. However, it falls within a similar range every 15 to 17 years.

Currently, were in a good position where Mars and Earth are on the lower end with their distance during opposition at 62.07 Gm. However, its also not as good as during the 2018 windows 57.29 Gm, or the all-time low record in 2003 of 55.76 Gm not counting that one encounter back in 57,617 BC. However, seeing that the distance increases again, it is as close as it gets until 2033 and 2035 with their 63.28 Gm and 56.91 Gm respectively heres a list if you want to check more. Looking at those years, the every 15 to 17 years parts really adds up.

That list also shows that the Soviet Unions series of missions back in 1971 that resulted in the first lander on Mars, along with the United States Mariner 9 as first orbiter, all happened at a good time with a opposition distance of 56.20 Gm. Unlike the previous Mariner 4 mission in 1965 at almost double the distance of 100.00 Gm which makes its success on the other hand even more impressive. Comparing it with all the Mars missions, it might also explain why there were barely any launches between the two Vikings in 1975 and Pathfinder in 1996, with the Soviet Union once again using the best window back in 1988.

This also shows that even the worst case scenario wont stop Mars missions, so even though the conditions wont be as ideal as in 2018 or this year until 2033 which incidentally matches everyones current time frame for sending humans to Mars we definitely wont have to wait that long to see more rockets launched towards it.

But lets not rush off into the future, after all we have a whole series of launches just waiting to happen right now. So whats that all about then?

As mentioned in the beginning, three different countries will each launch their own independent mission this July. In the grand scheme of Mars missions, this is the first time we see this happening the same number of countries were involved in 2011, but Russia and China had a single, collaborative launch back then. This time, its actually three independent missions.

Some more fun facts about this years run to Mars. Assuming that all three missions succeed, it will be the first time an Arabic nation is on an interplanetary journey. Further assuming that Curiosity remains active, it will break the record of active rovers roaming Marss surface, and the first time a non-US rover is one of them. We can also expect to see the first drone footage from Mars!

While thats all great, its hardly all there is to it though. So what else can we expect from these missions?

First up in the schedule is the United Arab Emirates (UAE), which had to postpone their initial July 16 launch due to bad weather conditions in their launch site in Japan for three days. The good news is, their launch window had just opened on July 15th, and would have remained open until August 12th, so there wasnt too big time pressure yet. But there was no need for further delay, the weather conditions improved, and in the early Monday morning hours local time July 19th, 21:58:14 UTC their HII-A rocket successfully took off from the Tanegashima space center.

The mission will send their Hope probe into Marss orbit, where it will record everything about the atmosphere with the main objective to create the first complete picture of the Martian atmosphere. Their goal is to research the climate dynamics on Mars essentially creating the first full weather map of Mars and how the escaping hydrogen and oxygen play into that and why its escaping in the first place. The probe itself is equipped with three imaging instruments: an infrared spectrometer, an ultraviolet spectrometer, as well as a high resolution imager.

While the missions main focus is naturally on the research itself, the UAE takes this also as an opportunity to demonstrate their newly achieved position in space exploration, especially as a rather small nation. Aiming to inspire future Arab generations to pursue the field of space science, they want to establish themselves as beacon of progress in the region and show that nothing is impossible. Considering the achievements the Islamic world once contributed to humankind during its Golden Age, the UAEs hope is also to commemorate, if not revive, the regions importance within astronomy.

The second mission is Chinas Tianwen-1, scheduled to launch on 23. July. After the joint expedition with Russia in 2011, which unfortunately ended unsuccessfully as the rocket failed to leave low Earth orbit, China conducts their second-ever attempt to travel to Mars on their own and doesnt appear too eager to share much details about the mission itself or the instruments involved.

From what is known and speculated, Tianwen-1 is a full-blown, all-inclusive mission with orbiter, lander, and rover on board, unlike the previous mission which was just an orbiter. While parts of its objective will also look into Marss atmosphere, its assumed that the main focus lies on and below its surface. The main objectives seem to include creating a geological map, exploring soil characteristics, and finding water-ice pockets also in hopes to find evidence of past and possibly present life on Mars.

Finally, the third mission, the USs Mars 2020 mission, is expected to launch the Perseverance rover with its Ingenuity drone on July 30th the first day of the its launch window that closes on August 15th. And even though the US has made it to Mars numerous times before, an endeavor like this is hardly ever a routine operation, and theres just as much at stake as for the other two countries.

Continuing the work of the Mars Exploration Program, Perseverance will look for past life on Mars, specifically microbial life, by collecting soil and rock samples. The idea is that a future mission could either bring further equipment to Mars to analyze those samples, or bring them back to Earth, whichever seems more feasible at that time. [Dan Maloney] wrote about the details earlier this year, so if youre interested in it, go check it out.

There are certainly some exciting days ahead of us, followed by weeks and months of enduring until we will see the actual outcome of all the launches, as all three missions are expected to reach Mars in February 2021. What will come of it? Well just have to wait until next Spring to find out.

As for sending humans to Mars, theyve missed this window, so thats still at least a good decade ahead of us for now. And nothings going to change the orbital dynamics of the situation.

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Window In The Skies: Why Everyone Is Going To Mars This Month - Hackaday