Story so far: Veteran American astronauts Sunita Williams and Barry (Butch) Wilmore, are still docked with the International Space Station (ISS) since June 6 after facing delays, space debris threats, helium leaks and technical glitches on the Starliner spacecraft on which they travelled.

The U.S Space Agency — National Aeronautics and Space Administration (NASA) — held a ‘space-to-earth’ news conference with the two astronauts on July 10 to receive an update on their mission’s progress. Both astronauts said they ‘felt confident’ that they could return to Earth on Starliner itself.

Also read | How Boeing can bring NASA’s Sunita Williams, Barry Wilmore back to Earth

“I have a real good feeling in my heart that this spacecraft will bring us home, no problem,” said Ms. Williams, while Mr. Wilmore said, “That mantra you’ve heard, failure is not an option.” He added that both crew members were staying on the ISS to test the spacecraft

NASA along with the space capsule’s manufacturer Boeing is evaluating Starliner’s propulsion system and the five small helium leaks in the service module. The team is conducting ground tests on identical thrusters at New Mexico’s White Sands Missile Range while another investigation is underway at NASA’s Marshall Space Flight Center in Alabama to determine why the propulsion system’s seal failed, leading to helium leaks.

The continued delay in Ms. Williams and Mr. Wilmore’s safe return, which was initially scheduled to begin on June 18, has piqued concerns across the world, including India. Apart from Ms. Williams and Mr. Wilmore, NASA astronauts Michael Barratt, Matt Dominick, Tracy C. Dyson, Jeanette Epps and Russian Cosmonauts Nikolai Chub, Alexander Grebenkin, and Oleg Kononenko are aboard the ISS.

Here’s a look at the attempted launches, what went wrong, and current efforts for the crew’s safe return

Starliner’s attempted launches and success

Sunita Williams, 58, is the pilot of NASA’s Crew Flight Test mission aboard Boeing’s Starliner space capsule. The mission is a joint venture between NASA and American private space players to open up commercial travel to low-Earth orbits and the ISS to more people for scientific and commercial purposes.

United Launch Alliance, a joint venture by Boeing and Lockheed Martin manufactured the Atlas V rocket which transported the astronauts via Boeing’s space capsule Starliner to the ISS. With this, NASA will have a second space capsule option (apart from SpaceX’s Crew Dragon), which has a crew module which can house up to seven astronauts and a non-reusable service module which houses the equipment and systems (air, temperature controls, water supply etc) needed for a stay in space.

The first crewed test flight of Starliner with the above-mentioned astronauts was scheduled for May 6 for a week-long stay at the ISS. However, the flight was scrapped less than two hours before the launch after an issue was detected in an oxygen relief valve of the rocket’s second stage. All launch activities were suspended and the flight was postponed to May 17.

A helium leak was detected in a thruster in Starliner’s service module, further postponing the launch to June 1. On that day, the ground launch sequencer, the computer which launches the rocket, triggered an automatic hold stopping the countdown clock three minutes fifty seconds before the launch.

On June 5, Starliner was finally launched successfully from NASA’s Space Launch Complex-41 at Cape Canaveral Space Force Station in Florida and the two astronauts docked with the forward-facing port of the ISS. During their week long stay, the astronauts were tasked with verifying if Starliner was performing as intended by conducting tests on the various control systems and manoeuvring the thrusters. Prior to take-off, a small helium leak was noticed in the space capsule’s propulsion system but not deemed serious.

What went wrong?

En-route to the ISS, four more small helium leaks sprung up. Both NASA and Boeing officials reviewed flight data to find out the cause of the leaks. On June 6, NASA’s Commercial Crew Program manager Steve Stich admitted that similar thruster issues were revealed during the spacecraft’s uncrewed test flight in 2022, adding, “thought we had fixed that problem,” at a press conference.

The undocking and return journey of Starliner, which was scheduled for June 18, was postponed to June 22, then June 25 and later to July 2.

Mr. Stich opined that thruster issues may have been caused overheating when fuel was burned during the space capsule’s rendezvous with the ISS. According to CNN, the Starliner’s service module has 28 reaction control thrusters, of which five have failed during flight. Four were brought back online eventually.

The Starliner, which had its first uncrewed Orbital test flight in 2019, faced a software glitch, leaving the space capsule in the wrong orbit before it returned to ground without docking with the ISS. In 2022, the space capsule successfully conducted its first uncrewed test flight when it docked with the ISS and then undocked four days later to return to Earth. This flight too faced issues with the thrusters.

What is causing the delay?

Apart from technical issues, the crew also faced a debris collision threat on June 28. The US Space Command alerted the six astronauts onboard the ISS to execute ‘safe haven’ procedures i.e. crew members board the spacecraft they arrived in, in case an emergency departure is needed. This was necessitated after a defunct Russian satellite (RESURS-P1) broke into more than 100 pieces of debris in an orbit near the ISS. Ms. Williams and Mr. Wilmore were forced to board the Starliner to take shelter for an hour before they resumed their activities on the ISS.

On July 2, NASA said that the spacecraft was in good shape to remain docked to the ISS for over 45 days (its upper limit), giving the ground teams of NASA and Boeing time to conduct simulations and tests on the thrusters. Analysis is also underway to determine why several helium leaks have arisen in the capsule, said NASA. Currently, NASA has not set any end date to the mission, making the extension indefinite.

How will the crew return?

In the July 10 press conference, NASA has said, that if absolutely necessary, Starliner would be capable of returning to Earth – acting as an escape pod. Moreover, NASA also has the option of ferrying Mr. Wilmore and Ms. Williams to Earth aboard Crew Dragon. The SpaceX spaceship transported four astronauts to the ISS in March and is capable of fitting more people in case of an emergency. However, such an option has would be a last resort in case Starliner is deemed non-functional.

But NASA has reiterated its confidence in the Starliner to return the duo, dropping the option of using the Crew Dragon.

Washington:

A pair of US astronauts stuck waiting to leave the International Space Station said Wednesday they were confident that the problem-plagued Boeing Starliner they rode up on would soon bring them home, even as significant uncertainties remain.

Butch Wilmore and Sunita Williams blasted off on June 5 aboard the brand new spaceship that NASA is hoping to certify to ferry crews to-and-from the orbital outpost.

They docked the following day for what was meant to be roughly a week-long stay, but their return was pushed back because of thruster malfunctions and helium leaks that came to light during the journey.

No date has been set for the return, but NASA officials said Wednesday they were eying “late July.”

Asked during a live press call from the station whether they still had faith in the Starliner team and the spaceship, mission commander Wilmore replied: “We’re absolutely confident.”

“I have a real good feeling in my heart that the spacecraft will bring us home, no problem,” added Sunita Williams.

She said they were continuing to enjoy their time aboard the ISS, performing tasks like changing out the pump on a machine that processes urine back into drinking water, and carrying out science experiments such as gene sequencing in the microgravity environment.

They have also tested Starliner as a “safe haven” vehicle in case of problems aboard the ISS and checked out how its life support performs when four people are inside.

Lingering uncertainty

Before Wilmore and Williams can come home, however, engineering teams need to run more simulations of similar thrusters and helium seals on the ground, to better understand the root causes of some of the technical issues Starliner experienced — and modify the way it will fly down, if necessary.

It was known there was one helium leak affecting the spaceship before the launch, but more leaks emerged during the flight. Helium, while non-combustible, provides pressure to the propulsion system.

What’s more, some of Starliner’s thrusters that provide fine maneuvering initially failed to kick in during its approach to the station, delaying docking.

Engineers are not sure why the craft’s computer “deselected” these thrusters, though they were able to restart all but one of them.

In a subsequent press call, Boeing executive Mark Nappi told reporters that the “working theory” for the thruster malfunction was overheating due to excessive firing.

Theories on the cause of the helium leaks ranged from debris entering the propulsion system to Boeing possibly installing seals that were undersized for the task.

NASA and Boeing insist Starliner could fly home in case of an emergency, particularly since the problems affected only certain thrusters that control orientation.

They have no concerns over any of the more powerful thrusters responsible for the “deorbit burn” that will bring the spaceship back.

But much remains unclear — including whether the orientation control thrusters that malfunctioned have become degraded, which would make it necessary to rely on other thrusters during descent, NASA official Steve Stich said.

He insisted that NASA wasn’t yet considering bringing Williams and Wilmore back on a SpaceX Crew Dragon, in what would amount to a major humiliation for the aerospace giant Boeing, whose reputation has taken a hit in recent years over the safety crisis affecting its commercial jets.

“The prime option today is to return Butch and Suni on Starliner,” said Stich, while conceding that a return flight on a SpaceX spaceship can’t be ruled out.

In 2014, both SpaceX and Boeing were awarded multibillion-dollar contracts by NASA to develop crewed spaceships after the retirement of the Space Shuttle program. SpaceX carried out a successful crewed test in 2020 and has flown dozens of people since.

(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)