The mission was supposed to take off from NASA’s Kennedy Space Station in Florida at 5.30 India time on Wednesday. But during tests on Monday, a leak of liquid oxygen (LOx) from the Falcon 9 rocket was detected. SpaceX, the company that produces these rockets, had initially said that it would be able to fix the problem by Tuesday to enable a Wednesday launch. However, on Tuesday night, it was decided to put off the launch to allow for more time to carry out the repairs.
“Standing down from tomorrow’s (Wednesday’s) Falcon 9 launch of Ax-4 to the space station to allow additional time for SpaceX teams to repair the LOx leak identified during post static fire booster inspections. Once complete — and pending range availability — we will share a new launch date,” SpaceX said in a statement Wednesday morning (late Tuesday evening in the United States).
Till Wednesday evening, there was no update on a new launch date and time.
What exactly is the leak?
Liquid oxygen is a critical component in rocket propulsion as it allows the combustion of the main fuel, highly refined kerosene in this case. Oxygen attains liquid state at very low temperatures, well below -180 degree Celsius. The leak can happen either in the storage chamber of the rocket or in the pipelines that supply the LOx to the rocket’s engine. In the best case scenario, a leak reduces the amount of LOx available for enabling combustion of the main fuel. In the worst case, it could trigger a fire or an explosion.
“As part of launch vehicle preparation to validate the performance of booster stage of Falcon 9 launch vehicle, seven second of hot test was carried out on the launch pad (on Monday). It is understood that LOx leakage was detected in the propulsion bay during the test. Based on the discussion on this topic by ISRO team with the experts of Axiom and SpaceX it has been decided to correct the leak and carry out necessary validation test before clearing for the launch. Hence the launch of Axiom-4 slated for 11th June 2025 for sending first Indian Gaganyatri to ISS is postponed,” ISRO chairman V Narayanan, who is in the United States to witness the launch, said in a statement.
A reusable rocket
Falcon 9 is a partially reusable rocket. Its first stage (booster) returns to the Earth after separating from the mission it has launched, and can be reused after a refurbishment. This is the second trip for the booster being used in the rocket that will launch Ax-4 mission. It had earlier flown on a Starlink mission in April this year.
William Gerstenmaier, vice-president of build and flight reliability at SpaceX, had talked about this leak, and some other problems with the rocket, during a pre-launch press conference on Monday evening (Tuesday morning India time).
“We discovered a few things during the static fire that we had to go take a look at. We found a LOx leak that we had previously seen on this booster during its entry on its last mission and discovered that we had not fully repaired the booster during the refurbishment or we didn’t actually find a leak and didn’t get it corrected. We have now gone out to the launchpad. We are continuing to trouble shoot that. We should get that completed today (Tuesday) and we will have that back in configuration,” Gerstenmaier had said.
He had said the team was also working to make the rocket leak-proof.
“We are installing a purge that will essentially mitigate the leak if it still continues if we see it on the launch day. So, we will be fully ready to go fly,” he had said.
“We also discovered an engine 5 thrust vector control problem and we are going to change out the components associated with that. In fact, they are already changed out now and we will be complete with all work this evening and we will be ready to support a launch as early as tomorrow (Wednesday),” he had said.
There was no update on the problems from Axiom Space or SpaceX after Wednesday’s launch was put off.
How are launch windows of rockets decided?
The mission has another launch window on Thursday, June 12, but with no update forthcoming till Wednesday evening, it was unlikely that the launch would happen immediately.
“This shows the difficulty of getting ready. You can always be prepared, but during the testing, during the dry runs, during the activities with the crew to make sure we are really ready is tremendously important because we always learn something,” Gerstenmaier said on Monday.
At the same press conference, Dana Weigel, Manager, International Space Station Program, at NASA, said that there were many more windows of opportunity for the Axiom-4 mission to fly during June and then also in July.
“In terms of launch opportunities, we have these opportunities all the way through June 30th and then after a brief cut-out, we pick up again in the middle of July, in fact in the second week of July. So there are plenty of opportunities actually to fly the vehicle,” Weigel said.
Launch windows for rockets are calculated keeping in mind the movements of the celestial bodies involved, the most fuel-efficient path possible with both the starting and the landing points always in motion, and the weather.
Apart from Shukla, Axiom-4 is supposed to carry three astronauts, one each from Poland, Hungary and the United States, to the International Space Station, where they are scheduled to perform about 60 experiments, studies and outreach exercises. This is the first time that astronauts of India, Poland or Hungary are going to the International Space Station, a permanent space laboratory that orbits the Earth at a distance of 400 kilometres.
This photo provided by Axiom Space shows Shubhanshu Shukla from India, Peggy Whitson from the U.S., Slawosz Uznanski-Wisniewski from Poland and Tibor Kapu from Hungary. (Axiom Space via AP) 
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