Earth Return Orbiter – the first round-trip to Mars

The Earth Return Orbiter (ERO) is a mission of firsts. The European orbiter would be:

• The first interplanetary spacecraft to make a full round-trip from Earth to Mars.
• The first spacecraft to rendezvous and capture an object in orbit around another planet.
• The biggest spacecraft to orbit the Red Planet.

ESA’s Earth Return Orbiter is one of three missions launched from Earth that would be part of the intricate Mars Sample Return campaign to bring martian rock, soil and atmospheric samples back to Earth.

In addition to the rendezvous and return mission, ERO would provide critical Mars-Earth communications coverage for the NASA’s Perseverance rover and the Sample Retrieval Lander to deliver the martian samples.

Just as the Apollo Moon samples have fuelled research for decades, the scientific community would have pristine samples from Mars to study for years to come. 

ERO’s round-trip to the Red Planet, as well as its rendezvous with an object launched from the martian surface, would pave the way for crewed missions to Mars.

Mission overview at a glance

The ERO mission has several mission phases foreseen with many technical firsts executed in synchrony with other elements of the Mars Sample Return campaign.

1. The European spacecraft would fly to Mars using the most powerful electric propulsion for an interplanetary mission.
2. The Earth Return Orbiter would capture a basketball-sized capsule launched from the surface of Mars filled with a set of samples previously collected by Perseverance.
3. European teams would orchestrate the catch in Mars orbit from 50 million km away with the help of ESA and NASA navigation teams.
4. The capsule would safely be sealed into NASA’s Earth Entry System to ensure that the precious samples reach Earth’s surface intact for maximum scientific return.
5. Three years after reaching Mars, ERO would spend two years changing its orbit to make its way back to Earth.
6. Three days away from Earth, ERO would release the reentry system and place it on a precision trajectory for landing at a precise location on our planet.
7. ERO performs a series of maneouvres to enter orbit around the Sun, never to return to Earth.
8. The martian samples would be transported to a specialised curation facility, to be analysed by top scientists and laboratories from around the world.

5 things to know

1. First round-trip mission to another planet. It would take ERO about two years to reach its operational orbit around Mars, a year to perform its Mars mission and another two years to leave Mars and return to Earth.
2. First spacecraft to capture a man-made object launched from another planet. ERO would demonstrate the first in-orbit rendezvous at Mars.
3. Biggest spacecraft to ever orbit Mars. The seven-tonne, seven-metre tall spacecraft would be equipped with 144 m² of solar arrays spanning nearly 40 metres – the largest ever built for interplanetary flight.
4. Powerful, hybrid propulsion. The electric propulsion system would be the most powerful flown for an interplanetary mission. While ERO would use chemical propulsion to enter Mars orbit, it would rely on solar electric propulsion for the cruise to and from Mars, and for placing itself in operational orbit.
5. Radiation monitor. ERO would measure the total radiation dose it receives throughout its flight. Results will help monitor the health of the spacecraft and provide information on how to protect human explorers in future trips to Mars. 

Quick facts

• Main job: Find and capture a sample capsule in Mars orbit and return it to Earth
• Launch date: No earlier than 2027
• Launch vehicle: Ariane 64
• Launch site: Kourou, French Guiana
• Arrival to Mars: 2029
• Arrival to Mars operational orbit: 2030, 325 km above Mars surface

Tech specs

• Wingspan: 38 m
• Height: 7.5 m
• Solar array surface area: 144 m²  
• Mass: 7 tonnes
• Propulsion system: hybrid – electric and chemical propulsion

About Mars Sample Return

Returning samples to Earth from Mars is expected to be the most complex robotic space flight campaign ever attempted. The NASA-ESA Mars Sample Return Campaign promises to revolutionise humanity’s understanding of Mars by bringing scientifically selected samples to Earth for study using the most sophisticated instruments around the world. The campaign would fulfill a solar system exploration goal, a high priority since the 1970s and in the last three National Academy of Sciences Planetary Decadal Surveys.

This strategic NASA and ESA partnership would be the first mission to return scientifically selected samples from another planet and the first launch from the surface of another planet. The samples collected by NASA’s Perseverance Mars rover during its exploration of an ancient lakebed are thought to present the best opportunity to reveal clues about the early evolution of Mars, including the potential for past life. By better understanding the history of Mars, we would improve our understanding of all rocky planets in the solar system, including Earth.