How do Mars rovers send their data to Earth?

In a nutshell

A rover such as Perseverance can talk to Earth directly, but only slowly. So it saves its pictures and measurements and sends them by UHF radio to orbiters that fly over it several times a day, at up to two million bits per second. The orbiter stores the data and later beams it to Earth with its own, much larger dish.

Commands go the other way, usually directly: each Martian morning the rover receives its instructions from Earth through its high-gain antenna. Since 2004 every image taken on the Martian surface has come home through this relay system, called the Mars Relay Network.

Why a rover does not simply call home

The distance between Earth and Mars keeps changing as both planets go round the Sun. At its smallest it is about 54.6 million kilometres, which radio waves cross in about 3 minutes. At its largest it is about 400.2 million kilometres, or about 22.4 minutes of travel at the speed of light. Over such distances a radio signal spreads out and grows extremely faint.

A rover has little room and little power for a big antenna. Perseverance does carry an X-band high-gain antenna, a hexagonal paddle that can be turned towards Earth, but NASA describes its ability to send data back as limited. And there is a simpler problem: Mars rotates, so for about 12 hours a day the rover is on the side of the planet facing away from Earth and has no line of sight to us at all.

How the relay works

The solution is to use spacecraft in orbit around Mars as relay stations. An orbiter passes above the rover at a time predicted in advance; this is called a pass or overflight. For a few minutes the two are close – a few hundred kilometres apart rather than tens of millions – and the rover can send its data quickly through a small antenna.

On Perseverance that antenna is a short cylinder at the back of the rover, about the shape of a paint can, working on UHF radio frequencies. According to NASA, 99.9% of Perseverance’s science data goes through it to passing orbiters. Rovers talk to orbiters at data rates of up to 2 megabits per second.

The orbiter stores what it receives. When it can see Earth, it sends the data home through its own dish antenna – on the Mars Reconnaissance Orbiter, a dish 3 metres across – to the 34- and 70-metre antennas of the Deep Space Network in California, Spain and Australia. The three complexes are spaced about 120 degrees apart around the globe, so one of them can always see Mars. Orbiters return rover data to scientists on Earth about a dozen times a week.

The orbiters that carry the traffic

The relay network is an international fleet. NASA’s Mars Odyssey has been in orbit since 2001 and the Mars Reconnaissance Orbiter since 2006. The European Space Agency contributes the ExoMars Trace Gas Orbiter, at Mars since 2016, and Mars Express, at Mars since 2003, which serves as a backup. The orbiters have to share: they use the same frequencies, so every session between an orbiter and a lander must be carefully scheduled. The Mars Reconnaissance Orbiter and Curiosity carry radios of a design called Electra, which can adjust the data rate automatically as the distance to the rover changes during a pass.

The Trace Gas Orbiter now carries the most data. Between February and May 2026 it relayed on average about 2,228 megabits per day, the Mars Reconnaissance Orbiter about 851 and Mars Odyssey about 107 (NASA figures, status as of 3 November 2026). The rovers the network serves are NASA’s Curiosity and Perseverance.

The fleet is ageing and can shrink. NASA’s MAVEN orbiter, which had relayed on average almost 900 megabits a day, was last heard from on 6 December 2025. A review board concluded in February 2026 that it could no longer carry out its science and relay mission, and NASA declared the mission over on 3 June 2026. The other orbiters took over its relay work.

The other direction: instructions for the day

Commands are a much smaller volume of data than pictures, so they can travel directly. Perseverance’s high-gain antenna is routinely used to receive commands each morning on Mars. Because of the delay of several minutes or more, nobody drives a rover with a joystick: the team plans the next day’s work on Earth, sends it up in one batch and lets the rover carry it out on its own. How spacecraft cope with the delay is explained in How a Mission Flies.

Relay at the most critical moment

The relay network matters most during landing. When Perseverance landed in Jezero Crater on 18 February 2021, the final two minutes of its descent were mostly beyond the Martian horizon as seen from Earth, so the rover could not report directly. The Mars Reconnaissance Orbiter received its entry, descent and landing data in real time and passed it on immediately. Even so, the news took 11 minutes and 22 seconds to reach Earth, so the landing was already over when engineers heard it had happened. MAVEN recorded the whole landing and sent its recording home several hours later. The landing itself is described on the Mars page.

Twenty years of relayed pictures

The system grew out of experience. Spirit and Opportunity, which landed in 2004, were the first rovers whose science data was routinely sent home through orbiters, and NASA states that every image seen from the surface of Mars since 2004 has passed through the relay network. New orbiters were tested on arrival: on 6 November 2014 MAVEN relayed 550 megabits from Curiosity in its first trial with real Mars data.

The robots themselves were mostly built and flown from Pasadena, at NASA’s Jet Propulsion Laboratory – an institution with a history older than NASA, told in Is JPL part of NASA?.

Sources

Sources checked on: 3 November 2026