India’s space agency called off the launch of its Chandrayaan-2 spacecraft about an hour before its scheduled 2.51am lift-off on Monday, citing a “technical snag” and promising a future launch date for the country’s first intended lunar lander.

“A technical snag was observed in (the) launch vehicle system at 1 hour before the launch,” the Indian Space Research Organisation said through a spokesperson and a tweet shortly after 2.15am on Monday.

“As a measure of abundant precaution, (the) Chandrayaan2 launch has been called off for today.”

Isro said a revised launch date would be “announced later”. The agency’s Twitter handle, which had been active through Sunday with updates in preparation for the launch, had no additional details about the snag on Monday.

The countdown appeared to have stopped at 56 minutes and 24 seconds before lift-off when the Geosynchronous Satellite Launch Vehicle Mark III, Isro’s most powerful rocket to date and designed to ferry Chandrayaan-2 into space, was undergoing pre-launch checks and scrutiny.

During these checks, teams of engineers at the Sriharikota launch pad would have been tracking the multiple lines of data and information streaming in from various parts of the launch vehicle — typically, pressure and temperature readings from sensors embedded throughout the rocket.

Space technology analysts say that while launch holds may be disappointing, especially ahead of a high-profile mission, they are not unknown in the high-risk space business and can help prevent more embarrassing and more dramatic post-launch failures.

In December 2018, the launch of a United Launch Alliance “Delta IV Heavy rocket” from Vandenberg Air Force Base in California, US, was put on hold 7.5 seconds before lift-off, Aviation Week, an aerospace industry journal reported.

“The abort was the first unplanned shutdown during a terminal count of a Delta IV Heavy which has flown 10 times since its debut in 2004, the journal said.

The Delta IV Heavy rocket successfully launched its payload in January 2019.

In September 2017, the launch of an Ariane 5 rocket of the European Space Agency, carrying two commercial satellites, was aborted only seconds before lift-off from the ESA spaceport in French Guiana.

News agency IANS quoted an unnamed Isro official as saying the technical snag had been noticed while the cryogenic fuel — liquid oxygen and liquid hydrogen at extremely low temperatures — was being loaded into the GSLV Mark III’s cryogenic stage.

“We have to approach the vehicle to assess the problem. First, we have to empty the fuel loaded in the rocket. Then the rocket will be taken back for investigation,” the IANS report quoted the official as saying. “This process will take 10 days. After that we can decide on the launch schedule.”

From Isro’s tweets on Sunday, it appears that everything was going to plan until the engineers began loading the cryogenic stage with liquid oxygen and then with liquid hydrogen.

Late on Sunday night, Isro had tweeted: “Filling of liquid oxygen in cryogenic stage… completed and filling of liquid hydrogen is in progress.”

About an hour and 15 minutes later, Isro tweeted: “Filling of liquid hydrogen in cryogenic state… completed.”

At 1.30am, Isro tweeted that the live webcast of the launch would begin at 2.30am. The next message announced the technical snag.