SkyWard Recruitment Assignment

This repository contains my solution to the SkyWard Recruitment Assignment, focused on detecting crucial events during a rocket launch, flight, and landing based on sensor data, including pressure and acceleration. The implementation is written in C and is based on a Kalman filter to smooth the data and detect the events.

Logical Solution

Since the given set of data is composed by a series of raw measurements of the pressure and the acceleration of the rocket, the first step is to filter the data to remove the noise.

To reduce noise in the sensor data I've opted for a Kalman filter, which is an iterative algorithm that predicts and updates the true state of the system, making it ideal for smoothing sensor data and predicting future states of the rocket.

Application of the Kalman filter to the altitude datas

Having a filtered set of data, the next step is to detect the events. There where a lot of possible criteria to detect a certain event, but based also on papers founded on the internet and a some simulations with MATLAB, I've decided to use the following criterias:

Liftoff: when the rocket's acceleration exceeds a threshold relative to gravitational acceleration (g). Based only on accelerometer data
Apogee: when altitude begins to decrease. Based only on barometer data
Landing: when a peak of acceleration is detected, signaling the rocket's impact with the ground. Based only on accelerometer data

Resources

For a deeper dive into the Kalman filter and its mathematical foundation, consult the papers in the Papers folder.

Code implementation

The code is implemented in C, and it is composed by two main files:

grader.c: the entry file, which contains the main function and the functions to read the data from the file. It's also responsible for calling the event detection functions
state_updater.c: contains an init function to initialize the Kalman filter (matrices) and the update function, which is responsible for apply the filter to the current data and perform the event detection based on the criteria stated in the logical solution

Along with these two files, there is also a matrices.c file, which contains all the linear algebra functions needed to perform the Kalman filter, such as matrix multiplication, matrix inversion, and matrix addition...

Data structures

Most of the code uses a custom data structure called Matrix, which is a simple struct composed by a pointer to a 2D array of doubles and the dimensions of the matrix. This data structure is used to represent the matrices used in both the Kalman filter and the measured data.

typedef struct
{
    int rows;
    int cols;
    double **data;
} Matrix;

How to run

To run the code, simply run the following commands from the root directory:

gcc src/grader.c src/matrices.c src/state_updater.c -o OnBoard_Software.exe

./OnBoard_Software.exe

Results

By comparing the results of the code with the expected results from a simple visualization of the data, it is possible to see that the code is able to detect the events with a good accuracy.

However, it's possible that in some situation the algorithm fails to detect the events, especially the landing, due to the fact that the algorithm is based on a peak detection, which is not always reliable. A possible solution to this problem could be to have a dual criteria for the landing event, based on both the peak detection and the altitude or the velocity.

Have a nice coding day,

Tommaso 🐼