5101: Why Mars is having its busiest two weeks in 47 years


Mars and Earth lined up neatly last summer, and three separate space agencies seized their opportunity.

Left: An illustration shows the United Arab Emirates orbiter “Hope.” Center: An illustration shows the skycrane lowering NASA’s rover Perserverance to the Martian surface. Right: A still shows a Chinese Long March 5 rocket hefting Tianwen-1 into space.
(Image: © United Arab Emirates, NASA/JPL, China News Service)

It’s a busy February for Mars, with three probes from three separate countries arriving at the Red Planet over the course of just nine days. But this Martian party didn’t happen by coincidence — it has to do with the mechanics of both Earth and Mars’  orbits.

The United Arab Emirates’ first interplanetary mission, the Hope probe, achieved Mars orbit Tuesday (Feb. 9), as Live Science sister site Space.com reported. China’s first interplanetary mission, Tianwen-1, is scheduled to enter its own Martian orbit Wednesday (Feb. 10). The Chinese probe includes both an orbiter and a lander with a rover onboard, which is expected to try to land on the surface in May. And on Feb. 18, NASA’s first-of-its-kind descent vehicle will reach Mars and plunge directly through its atmosphere. If all goes according to plan, the vehicle will shed its outer shell and use rockets to stop its descent at the last moment. Then it will hover above the surface to lower the rhinoceros-sized, nuclear-powered, $2.7 billion Perseverance rover to the dirt via skycrane.

All these robots showing up at almost the exact same time is no coincidence, said Jonathan McDowell, a Harvard University astrophysicist and spaceflight expert.

Mars and Earth are like “runners on a circular racetrack,” he said. “And the really fast runner [Earth] regularly laps the runner just on the outside [Mars]. So sometimes they’re right next to each other, and sometimes they’re on opposite sides of the track.” This Earth-Mars cycle, meaning Earth completely laps Mars, takes about two years to complete.

It would take an enormous rocket, tons of fuel and much more time to reach Mars from Earth while the planets are far away from each other, McDowell told Live Science. But launching while the planets are at their absolute closest — when they are 38.6 million miles (62.1 million kilometers) apart on average —  isn’t the most efficient way to get to Mars either.

There’s an earlier point in the planets’ two-year cycle where the journey takes less time and requires less fuel. At that point, which occurs once during the two-year cycle, Earth is a bit behind Mars but continues to move faster than its neighbor. This positioning allows the spacecraft to enter a so-called “Hohmann transfer orbit,” named after German engineer Walter Hohmann, who worked out the underlying mathematics in 1925.

An animation shows the path NASA’s InSight lander took from Earth to Mars, an example of a Hohmann transfer orbit. (Image credit: Phoenix7777 – Own work Data source: HORIZONS System, JPL, NASA/Wikimedia Commons/CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/))

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Here’s how that works:

No rocket carries enough fuel to burn all the way between Earth and Mars, a distance that ranges between tens and hundreds of millions of miles.

That means any interplanetary adventure begins with a brief, intense period of acceleration, followed by a long stretch of coasting. The job of the rocket engines during that initial period of acceleration is to put the spacecraft into an orbit around the sun that will intersect with Mars as soon as possible. The most efficient path between the planets is therefore the solar orbit intersecting with Mars that can be reached with the least expenditure of fuel, and that orbit becomes available once every two years.

But space agencies don’t have to nail that day exactly. As long as they launch during a window of a couple weeks around the date,they can place their spacecraft on Hohmann transfer orbits. Tarry longer than a couple weeks, however, and the trip starts getting much more difficult very quickly.

The Hope orbiter launched July 19, 2020, Tianwen-1 on July 23 and Perseverance on July 30. The gaps between the spacecrafts’ arrivals don’t exactly line up with their launch dates due to minor differences in their rocket technology, trajectories through space and destinations, McDowell said. (It takes a different angle of approach, for example, to plunge directly into the planet’s atmosphere than it does to enter a high orbit as Hope has done.)

It’s not the first time Martian orbital space has been this crowded, McDowell pointed out. The Soviet Union launched four spacecraft to Mars in 1973, though one failed to attain orbit and none of the other three worked as intended upon arrival. Two Soviet spacecraft and one American spacecraft launched to Mars in 1971, and all had at least partially successful missions. (Both nations planned additional probes that year, but the American Mariner 8 probe failed during launch and the Soviet Kosmos 419 never escaped low-Earth orbit.)

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What’s different this year, McDowell said, is the sheer diversity of spacecraft reaching Mars, and the fact that several additional probes are already active around the planet. NASA has three orbiters active in Martian orbit, the European Space Agency (ESA) has one of its own and one orbiter that’s a joint project with the Russian Roscosmos, and the Indian Space Research Organization has an active orbiter as well. NASA’s Curiosity rover and InSight lander are also still active on the Martian surface.

Despite that relatively crowded situation, McDowell said he doubts any of the probes will even come within tens of thousands of miles of each other, even if none of the countries had checked their trajectories with each other in advance.

“Space is big,” he said.

Originally published on Live Science.
By Rafi Letzter – Staff Writer

5099: The UAE reaches Mars for the first time with its Hope probe


The UAE joins a small group of space players to reach Mars

UAE’s Hope probe sits in a clean room before launch.

A probe from the United Arab Emirates successfully reached Mars on Tuesday, earning the country a spot in a small group of spacefaring powers that have sent spacecraft to study the fourth planet from the Sun. The UAE hopes the mission will yield key discoveries on Martian weather patterns and catalyze a new science and technology sector as it looks to wean its economy from oil dependence.

“Mission accomplished,” UAE’s vice president Mohammed bin Rashid Al Maktoum tweeted as mission control in Dubai celebrated confirmation of the Hope spacecraft’s orbital insertion around Mars at 11:14AM ET.

The SUV-sized Hope probe carried out an intricate and fully automatic maneuver called a Mars Orbit Insertion (MOI) on time at 10:30AM ET, mission engineers said. This maneuver slams the brakes on the spacecraft’s final leg of its journey, slowing Hope’s cruising speed of 75,000 mph down to 11,000 mph by firing all six of its Delta-V thrusters for 27 minutes. The deceleration allowed Hope to get swept up in a “capture orbit” around Mars, officially crossing the finish line in its seven-month journey.

“MOI was the most critical and dangerous part of our journey to Mars, exposing the Hope probe to stresses and pressures it has never before faced,” the mission’s project director, Omran Sharaf, said. “With this enormous milestone achieved, we are now preparing to transition to our science orbit and commence science data gathering.”

Manual, real-time control of the spacecraft is impossible, so Hope has been programmed to carry out these orbital dances on its own. Mission control didn’t have confirmation of a successful MOI burn until 11:14AM ET because of a 22-minute roundtrip communications delay through NASA’s Deep Space Network.

Emirates Mars Mission managers cheer upon confirmation of Hope’s successful insertion into Mars’ orbit. Video: Emirates Mars Mission

For mission managers, Hope’s arrival at Mars was a nerve-racking climax in the UAE’s first mission to deep space. The spacecraft traveled 300 million miles after launching from Japan’s Tanegashima Space Center last July, as Earth and Mars aligned in their orbits around the Sun. It’s also the first of three Mars spacecraft visiting the planet this month, with a Chinese spacecraft arriving tomorrow and NASA’s Perseverance rover following next week.

With a successful injection into Mars’ orbit, the spacecraft is on track to spend two years capturing global snapshots of the planet to better understand its atmosphere and weather changes. The spacecraft will carry out a few more maneuvers until April to ease into a closer orbit around Mars that offers “unprecedented local and seasonal time coverage of the Martian atmosphere,” the mission’s science lead Hessa Al Matroushi said. Hope will orbit Mars every 55 hours and capture a complete snapshot every nine days.

UAE officials and program engineers saw the program as a symbolic achievement for the country as it became the first Arab nation to launch a mission to Mars. With Hope reaching Mars, the UAE’s cabinet is aiming to inspire a new science and technology sector as the Gulf State looks to wean its economy from oil dependence. The probe’s arrival marked “a historical moment and a great extraordinary achievement for the Emirati and Arab space sector,” Abu Dhabi mayor Hamdan bin Zayed Al Nahyan tweeted, as translated from Arabic by Twitter’s translation service.

The timing of the Hope mission was crucial. UAE launched the probe in a narrow, roughly two-month window last summer when Earth and Mars aligned at their closest point around the Sun. Such alignment only happens once every two years, and mission managers wanted to celebrate UAE’s 50th anniversary this December with the country’s first Mars mission. Under pressure from UAE’s Prime Minister Mohammed bin Rashid Al Maktoum, the timeline was “very, very strict,” Sharaf told The Verge last year.

“Your bold endeavor to explore the Red Planet will inspire many others to reach for the stars. We hope to join you at Mars soon with” Mars Perseverance, Thomas Zurbuchen, NASA’s associate administrator for the agency’s science mission directorate, tweeted.

The Verge