How is spaceflight safety ensured?

A SpaceX capsule carrying NASA astronauts Sunita Williams, Butch Wilmore, and Nick Hague, and Russian cosmonaut Alexander Gorbunov splashes down in the Gulf of Mexico, off the coast of Florida, U.S., on March 18.
| Photo Credit: NASA

The recent safe return of NASA astronauts Sunita Williams and Barry Wilmore after a nine-month stay onboard the International Space Station (ISS) underscored the importance of following safety protocols. While these protocols were hidden from view, they allowed NASA to make sure that the astronauts were not harmed physically or mentally in the course of their unpredictable Starliner test mission. The Indian Space Research Organisation (ISRO) is currently putting similar protocols in place as it prepares for its maiden human spaceflight mission, Gaganyaan. In this endeavour, its scientists and engineers are drawing from both the latest in research and incidents and accidents of the past.

Human spaceflight has three key phases: launch, orbit, and reentry. Let’s explore safety protocols in each phase.

Before and during launch

On the launchpad: In 1967, three members of NASA’s Apollo-1 crew met with tragedy when the crew capsule they were testing on a launchpad in Florida — even before the rocket took off — caught fire, killing all of them. Should a similar incident recur today, the crew will need to flee the area quickly. Thus, ISRO has installed ziplines and a fireproof bubble lift at its second launch pad at SHAR in Sriharikota.

After ignition until orbital insertion: A human-rated launch vehicle includes an emergency exit device, like the back door of a bus, to be activated in case a life-threatening incident occurs after the rocket has lifted off. In contrast to the Launch Vehicle Mark-3 (LVM3), ISRO’s medium-lift launch vehicle that lifts satellites, the human-rated version will feature a tower-like structure on top.

The crew module is fastened to this tower-like structure. In case of a launch vehicle malfunction, the crew module and its escape mechanism will first disengage from the main rocket, then, the escape tower’s solid fuel engines — designed to ignite quickly — will produce a tremendous amount of thrust in a short period of time, propelling the space capsule upwards and away from the rocket.

This is the Crew Escape System. On the human-rated LVM3, it is tractor-type, meaning a powerful engine will pull the crew module away from harm. The SpaceX Crew Dragon capsule utilises a pusher-type system where the system is located beneath the crew module and pushes it away from the main rocket.

During launch: The crew escape mechanism operates in three modes depending on the altitude obtained during the emergency. ISRO’s Crew Escape System has two types of motors: the Low-altitude Escape Motor (LEM), which can generate enough thrust to propel the crew module away from the launch vehicle during the initial phase of the flight, and the High-altitude Escape Motor (HEM), which will kick in at high altitude to provide enough pull to yank the crew module quickly to a safe distance from the rocket.

Pad abort: This is when the emergency escape has to take place moments after ignition. Both the HEM and LEM motors of the Crew Escape System are activated to rapidly transport the whole crew escape assembly and capsule to a safe distance in the shortest amount of time. In low-altitude abort scenarios, both motors are triggered; however, now, the crew module will splash down at a designated spot in the sea. In normal conditions, the Crew Escape System is effectively dead weight. Therefore the LEM — which is the pencil-like element of the tower — is jettisoned at a specific height to reduce weight while the HEM remains attached to the crew module.

The Soyuz T-10 rocket caught fire on the launchpad just before liftoff in 1983. The crew could evacuate safely thanks to the Crew Escape System. Similarly, one minute into the Blue Origin New Shepard flight NS-23 on September 12, 2022, a launch engine failed and the launch escape device worked as intended, allowing the capsule to detach and land safely.

Entering and staying in orbit

ISRO’s Gaganyaan crew capsule, which will transport humans, consists of a pair of interconnected modules. The crew module serves as the living quarters for the crew and passengers if any while the service module carries the fuel, engines, control systems, etc.

By the time the capsule gets close to its intended orbit, all components of the crew escape systems will have been released into space. In this case, the capsule’s onboard propulsion system, in the service module, will launch the crew module onto a sub-orbital trajectory if emergency evacuation is required.

In the event of an emergency after the spacecraft is in orbit, the service module’s propulsion system and the crew module’s thrusters will together attempt to reenter the earth’s atmosphere, towards the ground.

At the ISS

Gaganyaan isn’t expected to dock with any space station, but its crew will nonetheless be familiarised with the established procedures for docking.

After docking, the first step is to keep the capsule docked as a ‘lifeboat’ in the event of an emergency aboard the station. When the capsule that carried Williams and Wilmore to the ISS malfunctioned, NASA launched another with two vacant seats and docked it to the ISS during their mission. There were two capsules at any time — one SpaceX Crew Dragon and one Russian Soyuz — with passenger capacity to fly them back.

The space station is also to have a ‘safe refuge’ space where its occupants could go to escape any danger, such as a fire, collision with space debris, or higher doses of radiation released in a solar flare. This area can be airlocked and kept apart from the rest of the module.

Returning to the earth

The most challenging part of spaceflight is reentry. Orbiting the earth is like riding a bicycle: in order to keep from falling down, you need to keep moving forward. Any capsule not firing its thrusters in orbit will slowly be pulled back by gravity and atmospheric drag. When reentry is desirable, the capsule will fire its thrusters accordingly to begin its descent, controlling its speed while also trying to ensure it lands in a particular region on the ground.

Once reentry has begun, atmospheric friction will heat the capsule’s outer heat shield to up to 1,800º C. The crew in the crew module will be protected by the shield. Once the capsule has descended to a particular altitude, the crew will slow its descent using retrograde thrusters and deploy parachutes.

The Gaganyaan crew capsule will decelerate throughout reentry using a 10-parachute system. Its apex cover separation parachutes will deploy when it is 15.3 km from the ground and travelling at 276 m/s, After that, a pilot chute will deploy drogue parachutes, stabilising and decelerating the capsule to 70 m/s up to a height of 3 km. Then pilot parachutes will deploy and open the three primary canopies, reducing the drop speed to 10-12 m/s. The parachute will be disconnected once the capsule has splashed down using a pyrotechnic release mechanism.

T.V. Venkateswaran is a science communicator and visiting faculty member at the Indian Institute of Science Education and Research, Mohali.