Integral’s “Apollo 13” Moment: Three Hours To Rescue Spacecraft From “Death” - SciTechDaily

The task of Integral, ESA’s International Gamma-Ray Astrophysics Laboratory, is to gather the most energetic radiation that comes from space.

On September 22, around midday, ESA’s Integral spacecraft went into emergency Safe Mode.

As a result of the spacecraft turning, data were only reaching ground control patchily and the batteries were quickly discharging.

The task of Integral, ESA’s International Gamma-Ray Astrophysics Laboratory, is to detect and gather the most energetic radiation that comes from space.

The Integral Flight Control Team, together with Flight Dynamics and Ground Station Teams at ESA’s ESOC mission control, teams at ESAC and Airbus Defence & Space, set to work?

Three hours to save Integral – what happened.

“Based on a discussion with our colleagues in the Flight Control Team, it looks like that the anomaly was triggered by charged particles trapped in the radiation belts around Earth.”.

Integral uses ‘reaction wheels’ – wheels that store energy as they spin – to subtly control the direction the spacecraft points in without the need of thrusters.

Suddenly, one of these reaction wheels stopped and, because of the law of conservation of energy, that turning force previously in the wheel had to go somewhere else – the entire spacecraft.

The Integral Flight Control Team set to work rescuing the mission.

The reaction wheel was reactivated by teams on the ground, but the spacecraft kept spinning at an average rate of about 17 degrees per minute (roughly one rotation every 21 minutes), as well as wobbling unpredictably about its axes.

This may not sound like much, but the spacecraft was rotating at five times its maximum when under control.

With support from industry experts, the team at ESOC analyzed the state of the reaction wheels, coming up with a series of commands to change their speed and brake the spinning satellite.

“Most of the Control Team were working from home at this point – I was following operations from the train.

– and worked until four in the morning to get the spacecraft fully stable, back into position and facing the Sun to recharge its batteries.”.

Unfortunately, a few hours later as the team reconvened to discuss the next steps, the spacecraft once again started to rotate, its reaction wheels again turning at high speed.

The reason for this is still not completely understood but is thought to be associated with a ‘star tracker occultation’ or ‘blinding’ which wasn’t handled correctly by the satellite’s control systems – effectively when Earth gets in the way of the spacecraft’s view of the stars, which it uses to orient itself.

The team repeated the previous days steps to stabilize the spacecraft and return to a Sun pointing position, this time without getting in the way of the star trackers.

“We are also back to ‘target of opportunity’ observations, which means that Integral is again reacting quickly to study unexpected explosive events in the Universe,” says Erik Kuulkers, ESA’s Project Scientist for Integral.

It’s not the first time this almost 20-year-old mission gave the control team at ESA’s ESOC Operations Centre a scare.

With the mode now disabled, the Control Team are working on a new automatic rescue sequence that should mimic many of the operations carried out after this anomaly, only much faster.

When the propulsion system failed, the team realized they would have to learn to maneuver the four-tonne satellite using its highly sensitive reaction wheels alone, to dump energy at regular periods and counteract forces on the spacecraft, including the gentle shove from the Sun’s light.

“Thanks to our quick-witted team and the help of experts from across industry, Integral lives on

October 17, 2021

October 17, 2021