Solar Orbiter prepared for ‘worst-case scenario’

The ESA/NASA Photo voltaic Orbiter is approaching the closest level to the sun in its present orbit. It is a vital time for the mission’s science actions, and the mission management workforce at ESA is continually making ready for any attainable issues the spacecraft may face because it swoops previous our energetic and unpredictable star.

Mission management to Photo voltaic Orbiter. Are available Photo voltaic Orbiter…

“It is our worst-case scenario,” says flight controller Daniel Lakey. “If Photo voltaic Orbiter have been to expertise some main subject on board, after which we have been unable to reestablish communications.”

Photo voltaic Orbiter’s shut method to the sun (“perihelion”) is a interval of peak scientific exercise.

It requires flight management groups and flight dynamics consultants at ESA’s ESOC mission management middle to hold out a collection of extremely complicated operations.

If one thing goes improper throughout these actions, the spacecraft may auto-reset itself into “safe mode.”

In protected mode, the spacecraft’s software program restarts and solely its most simple capabilities are reactivated. Groups on Earth then work out what triggered the protected mode, remedy the problem, and restart extra superior programs like scientific devices.

A protected mode throughout perihelion could be notably unhealthy due to the extreme affect on science operations throughout this busy interval.

Photo voltaic Orbiter additionally has much less energy out there throughout perihelion as the extreme warmth requires it to tilt its solar arrays away from the sun with a view to keep away from injury.

The spacecraft should be recovered as shortly as attainable earlier than science is misplaced, or worse, it runs out of energy.

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“The sun is so vibrant that even a fundamental sun sensor is sufficient to make it possible for Photo voltaic Orbiter all the time is aware of the place the sun is and may all the time level its warmth protect in direction of it. This sensor prompts throughout protected mode and retains the spacecraft’s inner programs protected from the radiation emanating from our star,” says Lakey.

“So, we all know that Photo voltaic Orbiter will all the time level its ‘entrance’ in direction of the sun. However to work out which means ‘up’ it’s, we depend on star trackers.”

The highest precedence for a spacecraft in protected mode is to level its communication antenna in direction of Earth and reestablish contact as quickly as attainable.

The star trackers change on routinely throughout protected mode and the spacecraft makes use of them to acknowledge sure patterns of stars. It may then decide its orientation, and wherein course it ought to level its antenna to speak with Earth.

“But when the star trackers fail to lock on to the proper stars, or the restoration sequence is interrupted earlier than they are often switched on, Photo voltaic Orbiter has no means of understanding the place Earth is.”

Spinning into management

To make the state of affairs much more difficult, in protected mode, Photo voltaic Orbiter can solely use its back-up communication antenna.

The back-up antenna can transfer “up and down” in a single axis, however not “left and proper” within the different. This prevents plenty of potential issues, but it surely additionally means the entire spacecraft should rotate with a view to level the antenna in sure instructions.

The answer is “strobing”—if Photo voltaic Orbiter ever finds itself in protected mode and unable to find Earth, it’ll start to roll round one axis whereas protecting its warmth protect pointed safely on the sun.

“In strobing mode, Photo voltaic Orbiter emits a sign with a particular ‘tone’—a beacon within the darkness of space,” says Lakey.

“Ultimately, this sign will sweep throughout Earth. As quickly as we detect it at one in every of our ground stations, we will assess the state of affairs, work out what prompted the protected mode and perform our drawback fixing and restoration operations.”

That is the speculation, anyway. Throughout Photo voltaic Orbiter’s 4 years in space, it has by no means needed to depend on a strobing restoration—and it has by no means been examined in flight.

Till now.

The groups at ESOC used a latest interval of low communication delay with Photo voltaic Orbiter to check whether or not they’re able to deal with an actual strobing restoration.

“We started to spin Photo voltaic Orbiter round and see if we may detect the beacon from the back-up, antenna,” says Lakey. “We preloaded instructions to return to regular operations in case we did not detect it, so there was by no means any danger to the spacecraft.”

The restoration exams have been a hit. The groups confirmed that they may detect Photo voltaic Orbiter’s emergency beacon and determine the standing of the spacecraft within the occasion of a protected mode with malfunctioning star trackers.

These are the primary very important steps in regaining management of the spacecraft and demonstrated the workforce’s readiness for this important however unlikely state of affairs.

“We additionally efficiently examined our potential to speak with the satellite in notably difficult conditions, reminiscent of when its personal warmth protect partially obscures the antenna’s view of Earth.”

This is only one of a whole bunch of potential points that our groups dream up and plan for each day. ESA’s missions are distinctive one-of-a-kind spacecraft: They could face issues that no different spacecraft ever has.

There are few related examples to study from, and few established procedures to observe. It is important to check our spacecraft restoration operations in space and for the groups on Earth to observe them once they have a very good alternative.

“We’ll by no means cease occupied with new challenges that our missions may face,” says Lakey. “Or about how we’d overcome them.”