Why has the Axiom-4 mission been delayed? | Explained

This photo provided by Axiom Space shows Axiom-4 crew members (L-R) Shubhanshu Shukla, Peggy Whitson, Sławosz Uznański-Wiśniewski, and Tibor Kapu.
| Photo Credit: AP

The story so far: On June 10, Axiom Space announced that the launch of its Axiom-4 mission to the International Space Station (ISS) would be postponed indefinitely. The mission crew included India’s astronaut-designate Shubhanshu Shukla, who — if the rocket had lifted off as planned — would have become the first Indian in earth orbit after 40 years and the first Indian onboard the ISS.

What is the Axiom-4 mission?

The Axiom-4 mission is the fourth mission planned by US-based spaceflight company Axiom Space to the ISS. It consists of a crew of four people — Peggy Whitson, Shubhanshu Shukla, Sławosz Uznański-Wiśniewski, and Tibor Kapu — plus cargo.

To facilitate the mission, NASA had contracted Axiom, which in turn had contracted the Falcon 9 rocket and the Dragon crew capsule for the mission from SpaceX. The mission is commercial in nature and isn’t part of the regular resupply missions NASA undertakes to the ISS.

Following an announcement to strengthen India-US ties in 2023, the Indian Space Research Organisation (ISRO) spent more than Rs 500 crore for Mr. Shukla to fly on the mission. Mr. Shukla is one of the four astronaut-designates for ISRO’s forthcoming Gaganyaan human spaceflight mission. His compatriot Prasanth Nair is part of the Axiom-4 backup crew.

Why was the launch called off?

Ahead of Thursday’s flight, SpaceX had tested one of the rocket’s engines as a matter of procedure and discovered it was leaking liquid oxygen (LOX). LOX is cryogenic, meaning it needs to be stored at an extremely low temperature. If it is exposed to warmer conditions, the oxygen will turn into gas and not be usable as fuel.

Falcon 9 engines combust a mix of rocket-grade kerosene and LOX to generate thrust, so a LOX leak is a serious issue. The Axiom-4 mission had first been scheduled for liftoff on May 29 but had to be postponed four times. The delays were a result of a combination of unfavourable conditions related to the weather and the launch vehicle.

Then on June 12, NASA also said it and Russia’s Roscosmos were tracking an anomalous pressure reading on an ISS service module after recent maintenance.

“The postponement of Axiom Mission 4 provides additional time for NASA and Roscosmos to evaluate the situation and determine whether any additional troubleshooting is necessary,” NASA had said in a statement.

Why was no new date announced?

Since a LOX leak is a serious issue, SpaceX needed to find the precise source of the leak and why the underlying component(s) failed. How much time this would have taken was unclear. There are also particular launch ‘windows’ when a launch can deliver the crew to the ISS with minimal fuel and energy use, including the amount of time the crew capsule will be exposed to sunlight.

But because the ISS is so close to the earth, launch windows appear more frequently than those for the moon or Mars. NASA has already indicated there are more opportunities through June and July.

Other factors that affect the suitability of a launch window include time on the launch pad for liftoff and access to free docking ports on the ISS. The US’s NASA, Russia’s Roscosmos, and (less often) some other space agencies also send missions to the ISS and need to plan when and for how long their capsules are docked.

At noon on June 14, it was announced that Axiom would reattempt the launch on June 19.

How hard is it to fix a LOX leak?

When it leaks, LOX flashes to an invisible vapour almost instantly and can be blown away by winds or fans nearby. Detecting it often entails time-consuming, labour-intensive work.

Many joints in the components associated with storing and pumping LOX are insulated with foam or are located in nooks, meaning many regular leak-detecting methods can’t physically reach them. Materials contract at cryogenic temperatures (around 90 K), so a hole may appear closed at ambient temperature but open at cryogenic temperatures.

So once a hole has been fixed, engineers may need to repeat tests at both warm and cold conditions or test with liquid nitrogen to mimic operating conditions. Testing with LOX itself can be hazardous.

Fortunately experts have been working with cryogenic engines for long enough to know which tools to use and which processes to follow once the leak has been identified. They include visual inspection, bubble tests, helium signature tests, flow-meter tests, ultrasonic microphones, and thermal imaging.