NASA ceased communication with its Martian rovers on Saturday, November 11, and will not resume until November 25.
If you’re an amateur astronomer, you’ll know it’s been impossible to see Mars for a while as it edges closer to the Sun from our perspective. Even while we cannot see it, however, radio waves have made their way to the red planet and back, allowing a stream of new discoveries, such as the recent confirmation Mars was once a planet of rivers.
Nevertheless, there is a limit, and we have reached the point where signals passing between the two worlds would suffer enough interference from the solar corona that it’s been judged best to shut things down.
These events, known as solar conjunctions, happen every 25 months or so. Curiosity has been through five great silences previously, before celebrating its 4,000th day of operation last week. Perseverance has been out of contact once, less than eight months after it first arrived on Mars, which we can all agree is too young for a rover to be unsupervised for two weeks. At least it had Ingenuity for company.
NASA has taken different approaches to dealing with the interference created by conjunctions in the past, depending on the type of craft that has been isolated. In some cases, it has been considered a priority to keep communication lines open, despite the loss of clarity. In others, shutdowns have been judged best.
The exact timing also varies. Earth’s orbit is very close to circular, but Mars travels a more elliptical path, which means it moves a fair bit faster when it is closest to the Sun than when furthest away. Consequently, the period of obstruction can last longer when Mars is crawling through the most distant part of its orbit.
Data collected during these periods is stored for transmission once the alignment is better. While out of sight, the rovers will stay still, and Ingenuity will certainly not be making any flights. Observations will continue, but will be restricted to those – such as weather measurements – that can be done safely on autopilot.
As the video below notes, having a message from Mars get a little bit garbled isn’t a huge problem – we’ve got a lot of capacity to reassess communication until we think we’ve got it right. It would be much worse if an outgoing message got so distorted a rover thought we were telling it to drive over a nearby cliff.
Consequently, “Prior to solar conjunction, engineers send two weeks' worth of instructions and wait,” NASA’s website reads.
“Our mission teams have spent months preparing to-do lists for all our Mars spacecraft,” said NASA’s Roy Gladden in a statement. “We’ll still be able to hear from them and check their states of health over the next few weeks.”
Orbiters face fewer dangers, so they can continue operating as normal, merely saving their data for sending home afterward.
Just to make sure mission control doesn’t get too anxious, the rovers will send updates through this period (aside from two days in the middle) just to confirm all is well. For a team that went through “seven minutes of terror” while waiting for the rovers to land safely, two weeks without verification would be just too much.