Keep sense of orientation: facing a dead sensor

Keep sense of orientation: facing a dead sensor

As the season shifted to winter in Jezero Crater, conditions became increasingly harsh for Ingenuity, which was designed for a short flight test campaign during the much warmer Martian spring. Increased amounts of dust in the atmosphere, combined with lower daytime temperatures and shorter days, have impacted Ingenuity’s energy budget to the point that it is unable to warm itself throughout. Martian nights. In its new paradigm of winter operations, Ingenuity effectively shuts down overnight, letting its internal temperature drop to approximately minus 112 degrees Fahrenheit (minus 80 degrees Celsius) and letting the on-board electronics reset. This new way of operating poses risks to Ingenuity’s electronic components, many of which are not designed to survive the temperatures to which they are exposed at night. Additionally, extreme temperature cycles between day and night tend to cause stress that can lead to component failure.

During the last few sols on Mars, the Ingenuity team has been busy getting the helicopter back into service for flight, going through a series of activities that include pre-flight checks of sensors and actuators and a high-speed rotation of the rotor. These activities revealed that one of the helicopter’s navigation sensors, called the inclinometer, had ceased to function. A non-functioning navigation sensor sounds like a big deal — and it is — but it’s not necessarily the end of our flight to Mars.

Navigation sensors

As Ingenuity flies, the on-board flight control system closely tracks the helicopter’s current position, speed, and orientation. It does this using a suite of sensors consisting of:

  • an inertial measurement unit (IMU), which measures accelerations and angular velocities in three directions
  • a laser range finder, which measures distance on the ground
  • a navigation camera, which takes pictures of the ground below

The data from these sensors is processed by a set of algorithms implemented on Ingenuity’s navigation computer. For the algorithms to work properly, they must be initialized before takeoff with a roll and pitch attitude estimate from Ingenuity. This is where the inclinometer comes in.

The inclinometer consists of two accelerometers, the sole purpose of which is to measure gravity before rotation and take-off; the direction of sensed gravity is used to determine how Ingenuity is oriented relative to the downward direction. The inclinometer is not used during the flight itself, but without it we are forced to find a new way to initialize the navigation algorithms before takeoff.

Imitation of the inclinometer

Ingenuity’s sensor suite provides some redundancy when it comes to sensing ground attitude. The IMU contains accelerometers which, like the accelerometers in the inclinometer, can be used to estimate the initial attitude. Unlike the inclinometer, the IMU is not specifically designed to detect static orientation, so its initial attitude estimates will generally be somewhat less accurate. However, we believe that an initial attitude estimate based on the IMU will allow us to take off safely and thus provide an acceptable fallback that will allow Ingenuity to resume flight.

Taking advantage of this redundancy requires a patch to Ingenuity’s flight software. The patch inserts a small snippet of code into software running on Ingenuity’s flight computer, intercepting incoming garbage packets from the inclinometer and injecting replacement packets built from the data from the IMU. For the navigation algorithms, everything will look like before, the only difference being that the inclinometer packets received do not actually come from the inclinometer.

Anticipating that this situation could potentially occur, we prepared the required software patch before last year’s arrival on Mars and kept it on the shelf for this eventuality. So we are able to move quickly with the update, and the process of uplinking to Ingenuity is already underway.

Put back into service

If all goes well, over the next few months the team plans to finalize the uplink and patch application, which will be followed by go-live activities to ensure the new software works as expected. . Barring any further surprises, we expect Ingenuity to take flight for Flight 29 – a southwesterly repositioning move designed to keep us within communication range of Perseverance – in the near future.

Leave a Comment

Your email address will not be published. Required fields are marked *