Nasa’s Ingenuity helicopter managed to land safely on the Martian surface after a navigation timing error sent it on a wild sixth flight. The Jet Propulsion Laboratory (JPL) on Thursday said that approximately 54 seconds into the flight, a glitch occurred in the pipeline of the images that were being delivered by the navigational camera mounted on the experimental helicopter, resulting in unexpected motion. But the helicopter stopped oscillating in the final moments of the flight, levelled its attitude and touched down at the speed of design.
The National Aeronautics and Space Administration shared a sequence of images, taken by the navigation camera aboard the Ingenuity Mars helicopter, that depicted the last 29 seconds of the rotorcraft’s sixth flight.
Håvard Grip, the chief pilot of Ingenuity Mars Helicopter at JPL, later explained the in-flight anomaly. In a blog post, Grip said that during a flight, Ingenuity keeps track of its motion using an onboard inertial measurement unit (IMU), which measures the helicopter’s accelerations and rotational rates. The helicopter’s position, velocity, and attitude are estimated by integrating the information gathered over time.
However, the navigation system doesn’t rely on the IMU alone since the errors would accumulate over time, and the helicopter would eventually lose its way. In order to maintain better accuracy, Ingenuity’s downward-looking navigation camera takes 30 pictures a second of the Martian surface and immediately feeds them into the helicopter’s navigation system.
Every time the navigation system receives an image, it examines the timestamp to determine when the image was taken. The navigation algorithm then makes a prediction about what the camera should have been seeing at that particular point in time and at where those features actually appear in the image.
“The navigation algorithm uses the difference between the predicted and actual locations of these features to correct its estimates of position, velocity, and attitude,” wrote Grip.
The glitch in the pipeline of images caused a single image to be lost, which resulted in all later navigation images being delivered with inaccurate timestamps. The navigation algorithm started performing a correction based on the navigation image and operated on the basis of incorrect information about when the image was taken.
“The resulting inconsistencies significantly degraded the information used to fly the helicopter, leading to estimates being constantly ‘corrected’ to account for phantom errors. Large oscillations ensued,” the chief pilot added.
Despite the anomaly, a built-in system to provide an extra margin for stability “came to the rescue” and Ingenuity landed safely on the surface within approximately 16 feet of the intended touch down location, said Grip.
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