(CNN) If it seems like Mars is a popular destination right now, that's for a reason: The chance to fly there only comes around every 26 months.
Four missions were planned to launch to Mars this summer, including three rovers, from multiple space agencies.
Two, including China's Tianwen-1 (which is carrying a rover) and United Arab Emirates' Hope Probe, launched last week and are now on their way to Mars. NASA's Perseverance rover is up next, scheduled to launch on July 30. And Europe's first planetary rover will have to wait a little longer to begin its journey to Mars.
The European Space Agency and Roscosmos, Russia's space agency, have postponed the launch of their ExoMars rover, partially due to concerns over the coronavirus, they announced in March. The agencies cited concerns over the coronavirus and spacecraft component readiness as reasons for the delay.
Further tests will ensure that the spacecraft's components are completed and ready. The rover was scheduled to launch in July 2020. Now, the joint-agency project teams are eyeing a new launch window between August and October 2022.
While the pandemic has posed challenges and caused delays to other missions, teams working on missions scheduled to land on Mars were motivated to get everything ready by the planned launch date.
For the Perseverance rover teams, which includes more 1,000 people, the pandemic hit at a crucial time.
"To make a mission like this be successful, it takes a lot of perseverance and a lot of brilliant hard work in the best of times," said Michael Watkins, director of NASA's Jet Propulsion Laboratory, during a conversation hosted by the Space Foundation last week. "And I don't think any of us anticipated this Covid pandemic right during the most busy time of the mission."
This is when mission teams were working during three different shifts a day, 24/7, to finish final assembly, conduct final testing of the clean flight hardware and make sure the mission was ready to go, Watkins said.
Although Perseverance teams had to shift to telework and completing mission work from home, there were still team members who had to work directly with the hardware. They wore masks and practiced social distancing.
"I really just cannot say enough about how incredible this team was," Watkins said. "They really knuckled down and completed this on schedule and we are ready to go. NASA really came together as a family and really it's just been a surprisingly smooth experience given all the troubles with Covid."
Earth is the third closest planet to the sun and Mars is the fourth, which influences the orbits of the planets around the sun as well as the number of days that equal a year on each planet.
For example, Earth is moving at a pretty fast clip of 67,000 miles per hour as it orbits the sun -- which creates our 365-day orbit. But Mars is farther from the sun, so it's slower and takes longer. A year on Mars is about 687 Earth days.
The planets aren't moving in perfect circular paths around the sun, either. Instead, they have elliptical, or more oval-shaped, orbits. And Mars' orbit is tugged on by massive gas giant Jupiter, which can change the orbit shape as well.
Mars and Earth are also slightly tilted in their orbits.
But every 26 months, Mars and Earth end up in a nice alignment on the same side of the sun and are closer together than usual. Launches to Mars are targeted at this time because any spacecraft leaving Earth will experience a shorter trip to Mars -- which means less resources such as fuel are needed as well.
Other factors, like the lift capability of the launch vehicle, the mass of the spacecraft and landing time, also help determine the launch window.
This biennial alignment provides a short window of opportunity. For Perseverance, the launch window is between July 30 and August 15.
Although NASA has successfully landed on Mars multiple times, including four rovers, it's a challenge that requires communication to be possible during landing. That's so that teams understand what happens during descent and landing.
Scheduling a specific launch window ensures that the spacecraft will land as NASA's orbiters at Mars will pass over the landing site, providing radio transmissions from the spacecraft.
NASA will attempt the first launch of Perseverance at 7:50 a.m. ET on July 30, with opportunities for launch occurring every five minutes during a two-hour window.
If the rover launches during the two-week window between July 30 and August 15, it will land on Mars on February 18, 2021. The Chinese and UAE Mars missions will also land on Mars in February 2021.
While Mars will make its closest approach to Earth in October, at only 38.6 million miles from Earth, the greatest distance between Earth and Mars can reach as many as 249 million miles, according to NASA.
If the rover doesn't launch during the two-week window, it will be placed in storage and the teams will have to wait two years for another launch opportunity.
Storage of the spacecraft and other factors of the delay would cost NASA $500 million and impact the long-term goals of NASA's Mars Exploration Program, according to NASA Administrator Jim Bridenstine.
"I hope people watch this mission and that they're inspired that we can strive and achieve even in the midst of challenging times," he said during a press conference in June.