How do spacecraft on the other side of the Sun keep working?

What happens to robotic spacecraft when the Sun gets between the Earth and them?

Astronomers eagerly wait for when the planets in Solar System beyond the Earth line up with us. This is when we’re closest to the planet and an ideal placement for both visual observations and photography.

This is called “opposition” and simply means when planets are opposite each other during their respective orbits.

Illustration of how a planet is position during opposition.  (Not to scale!)

At the moment – November 2023 – Jupiter and Saturn are not lot long past their opposition and are not also large and bright in the night sky, but also visible throughout most of the night.

There are also periods when the Earth and planets are on the opposite side of the Sun. When this happens the planet disappears behind the Sun and can’t be observed from Earth. We simply have to wait a few weeks until we can see it again.

A NASA illustration of how the Sun blocks the view of Mars from Earth. This happens about once every two years. 

In 2023 things are a little different! We now have several robotic space craft on the surface of Mars and in orbit around it. When Mars “disappears” behind the Sun during what’s called a Mars solar conjunction, how are these spacecraft controlled from Earth?

It’s also not just when the Sun’s disk blocks the view physically with Mars. The Sun also emits hot, ionized gas from its corona. This extend extends far into space and is visible during a total Solar Eclipse. The Sun’s corona will interfere with any radio signals to and from Mars. It’s clearly not a good idea to be sending delicate spacecraft command or trying to receive via radio results from their research.

This happens on the 11th to the 25th of November this year.

Does this mean that Mar orbiters and spacecraft sit idly by and twiddle their antennae for a couple of weeks every two years? Sort of….

NASA NASA’s Perseverance and Curiosity rovers will be on a two-week interplanetary working holiday They won’t move around and will stay in one location and will spend the time gathering data on changes on surface conditions, weather and radiation during this time. Once back in communication with Earth, the data collected will be transmitted back to NASA and they’ll be able accept commands to move again.

The Perseverance rover sent back this selfie from its parking spot on the Martian surface for the next two weeks. Image via NASA

The Mars helicopter, Ingenuity, will remain grounded as well. While the many flights carried out on Mars by this tiny helicopter have been under its own control and not via real-time from Earth, it’s going to be kept safe and on the surface. The colour cameras aboard Ingenuity will continue to record the Martian surface.

The Mars Reconnaissance Orbiter and the Odyssey orbiter will continue imaging of Mars from orbit and transmit their findings once a clear line of communication with Earth is available.

The break in communications with Mars is a regular happening and something NASA is well prepared for.

“Our mission teams have spent months preparing to-do lists for all our Mars spacecraft,” said Roy Gladden, manager of the Mars Relay Network at NASA’s Jet Propulsion Laboratory in Southern California. “We’ll still be able to hear from them and check their states of health over the next few weeks.”

While the spacecraft on and around Mars might be ok with some down time, it’s going to be interesting to see how such blackouts are handled when humans finally get around to landing on the surface!

For astronomers who are interested in seeing Mars at its best, it will next be at opposition in January 2025.


Earl White


13th November 2023


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