Fuel leak delays Indian astronaut's launch: The science behind using liquid oxygen

India Today

12-06-2025

The launch of the Axiom-4 mission, which was set to carry a crew of four astronauts, including India's Group Captain Shubhanshu Shukla, to the International Space Station (ISS) was delayed hours before launch on June 10, 2025.The mission was earlier delayed by a day due to bad weather at the Kennedy Space Center in Florida. Now, a new technical issue has caused a further delay -- a leak of liquid oxygen (LOX) has been found in the launch system.advertisementEngineers discovered the leak during a routine seven-second 'hot fire' test of the Falcon 9 rocket's booster stage, about 12 hours prior to the launch time.
These tests simulate launch conditions by briefly igniting the rocket's engines to check for performance and structural integrity. During the test, a leak was detected in the propulsion bay, an area that houses critical fuel and engine components. As a precaution, SpaceX, the company which owns and operates Falcon 9, has paused the launch to repair the issue and conduct additional tests before setting a new launch date.WHAT DOES LOX DO IN ROCKETS?To understand what went wrong, it is important to know the role of LOX in rocket launches. Rockets need two main components to create the thrust needed to escape Earth's gravity: a fuel and an oxidizer.advertisementThe fuel provides the energy, while the oxidizer enables it to burn. On Earth, oxygen from the atmosphere acts as the oxidizer in everyday combustion.But in space or even higher altitudes, where there is less or no air, rockets must carry their own source of oxygen.That is where LOX comes in.LOX acts as the oxidizer and is combined with fuels like kerosene, liquid hydrogen, or methane in the rocket's engine. When ignited, the fuel and LOX burn together at very high temperatures and pressure, creating the powerful thrust that pushes the rocket into space. Without LOX, the fuel alone wouldn't burn in the vacuum of space.LOX must be kept at an extremely cold temperature, around -183 degrees Celsius, to stay in liquid form. This makes it very sensitive and dangerous to handle.Even a small leak can cause frost to form on critical parts or lead to dangerous pressure buildup. If LOX comes into contact with fuel or other materials, it can catch fire or even explode. Because of these risks, handling LOX requires very strict safety measures.RISKS OF USING LOXLOX is used in many of the world's most powerful rockets. NASA's Saturn V, SpaceX's Falcon 9, the European Ariane series, and India's GSLV all rely on LOX as oxidizer for their missions.advertisementHowever, the dangers of LOX leakage are not just theoretical. There have been several accidents in the past caused by problems with oxidizers.
Gp Capt Shubhanshu Shukla ahead of launch with Ax-4 crew. (Photo: Axiom)
One major example is from the early Soviet space program.On July 3, 1969, the USSR's N1 rocket exploded just 23 seconds after launch. This rocket was built to compete with NASA's Saturn V and send cosmonauts to the Moon, and was powered by a combination of kerosene (RP-1) as fuel and liquid oxygen (LOX) as the oxidizer.A fault in one of the engines caused the rocket to lose thrust and fall back onto the launch pad. Upon impact, the tanks ruptured, and the two substances mixed uncontrollably. This triggered a massive explosion. At the time, it was the largest non-nuclear explosion in history.A more recent and widely known incident occurred on January 28, 1986, when NASA's Space Shuttle Challenger disintegrated just 73 seconds after liftoff, claiming the lives of all seven astronauts on board. While the immediate cause of the disaster was a failed rubber O-ring seal on the right solid rocket booster, LOX still played a critical role in the sequence of events that followed. The faulty seal allowed hot gases to escape and strike the shuttle's external fuel tank, which housed two cryogenic propellants: liquid hydrogen (LH2) in the lower section and LOX in the upper section. The escaping flame weakened the tank's structural integrity until it ruptured.advertisementOnce the LOX and hydrogen were mixed outside the tank, they ignited in a massive fireball that engulfed and destroyed the orbiter. The Challenger tragedy shocked the world and led to a suspension of NASA's shuttle program for nearly three years.A related incident of oxygen leakage threatening catastrophic failure happened in 1970 during the famous Apollo 13 mission. This was meant to be NASA's third Moon landing, but it turned into a gripping fight for survival. Apollo 13, soaring more than 300,000 kilometers from Earth, suffered an explosion in one of its oxygen tanks (though this gaseous oxygen) — the lifeline of the spacecraft. In an instant, systems collapsed, and three astronauts were left stranded in space. advertisementWhat followed was nothing short of extraordinary. Engineers on Earth and the astronauts aboard worked around the clock,improvising solutions with limited resources. Using the lunar module as a lifeboat, they pulled off a miraculous return.While delays may seem frustrating, they are a small price to pay when human lives are at stake.In space, even a minor flaw can spiral into a disaster. By postponing the Axiom-4 launch to address the LOX leak, SpaceX and Axiom are prioritising safety over speed. A delay today prevents a catastrophe tomorrow.Once the repairs and rechecks are complete, a new date will be set, and when liftoff comes, it will still fulfil the hopes of a nation proud to see one of its own reaching for the stars. And of course, this is just the beginning for India's manned space mission.(This is an authored article by Srijan Pal Singh. He is an author and an IIM Ahmedabad graduate, who was the Advisor for Policy and Technology to Dr. APJ Abdul Kalam, 11th President of India.)Tune InTrending Reel