How the Sun played a role in SpaDex success

On December 30, ISRO put two satellites — SDX01, the Chaser and SDX02, the Target — in a low-Earth circular orbit and later set them apart at a distance of around 20 km in space. The Chaser satellite was planned to approach the Target satellite following strategic reduction in the distance between them to 5 km, 1.5 km, 500 m, 225 m, 15 m, and 3 m, before the final docking Thursday.

Docking will be a crucial manoeuvre needed to be performed in future space missions like the Chandrayaan-4 or in establishing the Bharatiya Antariksha Station, where multiple components will need to be docked in space.

“Achieving precision for docking is very challenging, even under normal circumstances. During severe space weather, when the space environment is disturbed, the task becomes even more difficult,” said Dibyendu Nandi, solar physicist and former head, Center of Excellence in Space Sciences India (CESSI) at IISER, Kolkata.

For any space missions, the launch gets a go ahead when weather is favourable at the launching site, and if not, it is often deferred. Strong or gusty winds, lightning or electrically charged atmosphere, impending or progressing cyclones or storms are all deterrents.  “This is because enhanced high energy radiation or solar energetic particles associated with strong flares from the Sun can blind sensors and interfere with electronic control systems,” said Nandi.

“Magnetic storms from the sun, known as coronal mass ejections or very high speed solar wind streams, can disturb the space environment resulting in loss of communication and positional errors. If these occur when the docking is being attempted, a whole new set of uncertainties are introduced which are challenging to handle,” he said.

The peak phase of the solar activity cycle has more sunspots and is typically characterised by more hazardous space weather conditions. This makes any space manoeuvers unconducive, especially in the case of docking (or undocking) as it requires negligible relative velocity and precise alignment of their docking ports to prevent collision or damage.

Since the beginning of the ongoing solar cycle 25 in 2020, the current phase has been that of an extended period of strong solar activity. “But the days leading up to the SpaDeX docking were surprisingly different. There were fewer sunspots and other magnetic structures on the sun and the CESSI analysis found an unlikely development of stormy activity that could have disturbed the near-earth space environment. So, the Sun certainly cooperated in helping achieve this extraordinarily challenging task,” he said.

The SpaDeX demonstration underscores the need for investing more to make available improved space weather forecasts in near real-time, just as weather forecasts are vital on Earth to save lives and key infrastructure establishments from severe weather.

“So, it is useful to have space weather forecasts and near real-time assessment of space environmental conditions whenever a critical task is being planned in space during this solar maximum phase,” Nandi said.