What is Solar Beta that extended astronaut Shubhanshu Shukla's stay in space?

As part of the Axiom-4 mission crew, India's Group Captain Shubhanshu Shukla flew to space on June 25thand docked with the International Space Station on June 26th. The crew was to spend up to 14 days aboard the orbiting lab, which is 420 km above the Earth. If the Axiom-4 crew were to return after their two-week mission, they should've been back on Earth by July 10thor so. However, their return journey is now scheduled to commence at 4:30 pm Indian time, Monday, 14thJuly, and they are to splash down off the American coast at 3 pm Indian time, Tuesday. Why did the Axiom-4 crew spend a handful of extra days aboard the space station?

High Solar Beta

While announcing that the Axiom-4 mission (Crew Dragon spacecraft) is targeting to undock around 14thJuly, NASA's Commercial Crew Program Manager had said that the undocking and return would be done after the high solar beta period. In simple terms, solar beta is the angle between the Sun and the orbit of a spacecraft (like the Axiom-4 Crew Dragon).

In the case of a high solar beta angle, the sun is above or below the spacecraft, and the craft is exposed to a constant period of sunlight. During ideal conditions, the spacecraft frequently alternates between sunlight and Earth's shadow. Having high solar beta conditions would mean that the craft is continuously illuminated by the sun for days or even weeks, depending on the orbit.

How high solar beta and continuous Sunlight exposure affect spacecraft

In space, while being exposed to sunlight, the spacecraft's external temperature can get as high as 120-150 degrees Celsius. While the outside is burning at up to 150 degrees Celsius, theinside of the craft maintains a temperature of 20-30 degrees Celsius for the comfort of astronauts and for maintaining an ideal working temperature for electronics.

In space, while the craft is in Earth's shadow, the external temperature of the craft can dip to minus 150-170 degrees Celsius. The temperature inside the craft must be maintained at a temperature of 20-30 degrees Celsius for the comfort of astronauts and for maintaining an ideal working temperature for electronics.

For a spacecraft, long-term sunlight exposure and long-term exposure to Earth's shadow are both potentially harmful. When there is continuous sunlight exposure, there is a risk of overheating in some of the external components of the craft, such as the solar panels, radiators. These components and their functioning become less effective during excessive heating caused by prolonged sunlight exposure. Overall, the heat management becomes challenging when there is prolonged sunlight exposure. While sunlight exposure is helpful to generate solar power and charge the batteries, it could also potentially overload the systems, affect batteries and related electronics. This is why space agencies avoid certain types of missions and activities during high solar beta periods.

High Solar beta was mentioned even before Axiom-4 launch

Owing to a variety of reasons, the launch of Axiom-4 was postponed at least seven times, over a four-week period between May and June. Amid these repeated postponements, Dana Weigel, Manager, International Space Station Programme, NASA, had said that the Axiom-4 Crew Dragon had a launch window until 30thJune. If the launch does not take place by June 30th, it can be done after the High Solar Beta period ends in the second week of July, she had said.

Typically, every rocket launch mission has a launch window/launch opportunity- an ideal period of a few days or weeks within which the launch can take place. On each of these specific days within the launch window, there are a few minutes when the rocket can blast off to space. All of these launch times are precisely planned down to the second, based on various technical parameters. Which is why many rocket launch missions happen at odd hours, and no two missions (even of the same type) follow the same launch time.

In the case of Axiom-4, NASA has been clear that they will not carry out either the launch or the return during the high solar beta period, owing to the possible technical challenges caused by overheating of the spacecraft, due to excessive sunlight exposure. This is standard practice for all missions.