The first flight of NASA’s Ingenuity Mars helicopter was delayed again after running into a glitch in the rotorcraft’s flight control software during tests last week. The mini helicopter remains grounded on the surface of Mars’ Jezero Crater while it waits for engineers to tweak, test, and reinstall the software. NASA said it will come up with a new date next week for the inaugural flight test.

Ingenuity, the four-pound helicopter that arrived on Mars on February 18th with its parent rover, Perseverance, is nine days into a monthlong test window that began when its four little legs touched the Martian surface for the first time on April 4th. The helicopter has been going through a series of tests and checkouts before flying, which includes surviving its first frigid night on Mars, unlocking its twin carbon fiber blades, and doing a few stationary rotor spin tests.

The first slow-speed rotor spin at 50 rpm went well early last week, while NASA was working toward a debut flight on Sunday night. But engineers ran into a problem on Friday night when they went for the high-speed rotor test: Ingenuity’s “watchdog” software detected a bug and prevented the craft from performing the test. Ingenuity was healthy, it just couldn’t do the high-speed rotor spin.

Over the weekend, engineers at NASA’s Jet Propulsion Laboratory decided “that minor modification and reinstallation of Ingenuity’s flight control software is the most robust path forward,” NASA said in a Monday night blog post. Altering the software means independent engineers will have to review and test the changes before installing it back onto Ingenuity’s computer, a process that could take all week to complete.

Photo: NASA / JPL

NASA said “our best estimate of a targeted flight date is fluid right now, but we are working toward achieving these milestones and will set a flight date next week.” Engineers will come up with a new date for the high-speed test and its first flight after they send the new software through Perseverance’s communications hub and boot it to Ingenuity.

In the meantime, NASA said Perseverance will continue doing science and prepare for a test of MOXIE, an onboard instrument that will try to produce oxygen from Mars’ carbon dioxide atmosphere. The rover’s primary mission is to search for signs of ancient life and leave pods of soil samples on the surface for a future mission to retrieve and send back to Earth.

For Ingenuity’s flight test, Perseverance will watch from a football field’s distance away using two onboard cameras. The rover also serves as a communications hub; its onboard Mars Base Station will relay signals from Ingenuity to satellites orbiting Mars, which will beam those signals back to Earth.

Ingenuity is expected to carry out at least five flight tests within its 31-day test window (or 30 Mars days). For its debut flight test, the craft will ascend 10 feet above the surface and hover in place, pivot, then descend for a landing, lasting about 40 seconds altogether. Subsequent tests are expected to fly higher and travel short distances, but the exact flight details will be determined by how well the craft nails its first flight.

Ingenuity will need to exert immense power to achieve lift in Mars’ thin atmosphere. If it can do so, it’ll mark the first powered flight on another world, a historic achievement NASA is calling a “Wright brother’s moment” that could expand interplanetary mobility to where traditional wheeled rovers can’t travel.

Ingenuity’s carbon fiber rotor blades will spin roughly 2,400 rpm during flight. For the high-speed spin test beforehand, the blades will spin at 2,537 rpm (while tilted in a certain position so it doesn’t accidentally lift off). As engineers tweak the craft’s software, the clock is ticking. NASA officials have said Ingenuity’s monthlong flight test window can’t be extended if the helicopter runs into more issues before flying.

“The is primarily a science mission for the Perseverance rover, and it needs to get on with that primary mission,” Hårvard Grip, Ingenuity’s chief pilot, told The Verge on Saturday night. “So that’s why there’s a time limit for the helicopter.”