The first flight of Nasa's Mars helicopter, Ingenuity, was delayed so engineers could update the software on the tiny rotorcraft.
The $85 million technology demonstration involves the first controlled, powered flight on another planet.
A high-speed spin test of the rotors last week ended earlier than planned.
Engineers have now identified the issue and are updating the software, with a new flight date to be confirmed.
The landmark flight was initially planned for Monday.
“Over the weekend, the team considered and tested multiple potential solutions to this issue, concluding that minor modification and reinstallation of Ingenuity’s flight control software is the most robust path forward,” Nasa said.
“This software update will modify the process by which the two flight controllers boot up, allowing the hardware and software to safely transition to the flight state.
“Modifications to the flight software are being independently reviewed and validated today and tomorrow in testbeds at [the] Jet Propulsion Laboratory.”
The 1.8-kilogram chopper is healthy and critical functions, such as power, communications and thermal control, are stable.
Ingenuity has survived several key milestones so far, including the 'drop-off' from the Perseverance rover's belly.
The rotorcraft has also survived freezing Martian nights, when temperatures drop to as low as minus 130 degrees Celsius.
Its six lithium-ion batteries keep the heater running for several hours, before needing to recharge through the onboard solar panels.
“It is not unexpected for a technology demonstration like this to encounter challenges that need to be worked in real time,” said Nasa.
“The high-risk, high-reward approach we have taken to the first powered, controlled flight on another planet allows us to push the performance envelope in ways we could not with a mission designed to last for years such as Perseverance.”
Ingenuity aims to measure the engineering capabilities of Nasa and pave the way for more advanced, science-focused missions in the future.
'Perseverance' rover's first drive on Mars - in pictures
