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Rocket Stabilization - Northeastern University Capstone Project

Problem - 

Space.

Less than a century ago it took teams of experts, engineers and scientists, coming together to send a rocket to space. Fast forward to the present and just three years since its inception, Northeastern University's chapter of AIAA (American Institute of Aeronautics and Astronautics), or as the student body commonly calls them, the space club, is attempting to send a rocket to space. This is an enormously challenging project which includes innovation and updates to several subsystems. Four other mechanical engineers and I worked on one of these systems for our senior capstone project. We attempted to increase the attainable altitude of the AIAA's rocketry through advanced stabilization techniques in the hope that it would:

  • Increase altitude through a more vertical flight path with the thrust of the rocket always acting in the correct direction.

  • Increase altitude through the ability to reduce the size of fins on the rocket. Fins are used as a form of passive stabilization but the add extra drag reducing attainable altitude.

  • Increase rocket recoverability by making sure it only goes vertical, not off to a random direction that could land the rocket in a tree.

Process - 

This project started with a research phase. The team researched other solutions before settling on an active stabilization scheme. The active stabilization allows the rocket to constantly monitor itself and correct back to vertical. A passive stabilization model, such as spinning the rocket or adding a gyroscope, increases resistance to change in direction. However, if the direction is changed the rocket cannot force itself back to vertical. Our final design included:

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  • Radial gas jets to create a torque about the CG of the rocket and maintain rocket verticality
     

  • Solenoids to control the gas jets
     

  • A compressed air tank and regulator to bring the operating pressure to 80 psi
     

  • An Arduino to monitor rocket angle and control the solenoids
     

  • The rocket was 7 ft tall, 4 in diameter, 18 lbs, and expected to reach an altitude of 7000 feet

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To successfully create, test, and launch the rocket the work was divided up. I was part of the controls team and worked on:

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  • Electronics development, integration, and testing. Electronics shown below.
     

  • Arduino controls code (team lead)
     

  • Data analysis code (Python)

Gas Jet System and Electronics
Final Design Concept
How the System Works

Solution - 

One of the central components to this project was the ability of the rocket to accurately measure angle. This was achieved through the use of a 3 axis accelerometer, 3 axis gyroscopic sensor (measures angular velocity), and a kalman filter. The process for measuring angle is as follows:

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  • Take acceleration and angular velocity data at time T1.
     

  • Use an arcsin function to relate acceleration in the X and Y axes (Z axis is vertical) to gravity and determine angle.
     

  • Using the angle and angular velocity data, make a prediction for where the rocket will be at a time T2.
     

  • Once the rocket has reached time T2 take another measurement and compare the predicted and measured values.
     

  • Using the comparison, the filter makes an estimate on where the rocket is.
     

The chart at the right shows the noise reduction effects of the filter, as well as its ability to prevent large spikes from affecting the data.

Rocket Lab Testing

To test the system in the lab, a test stand was created that rotated about the X and Y axes with low friction. A variety of test were performed pushing the rocket to a certain angle and watching it respond with the system on vs off. The test setup and the lab results are shown below. The results show that the rocket responded and settled more rapidly when the system was on than when it was off.

The ultimate test for the team was launching the rocket and watching it respond. The launch day had ideal conditions with high sustained winds and about 20 other rockets being launched. Our rocket was the only rocket with an active stabilization system in it. It was also the only rocket to fly straight that day. See comparison below.

Similar Rocket w/o Active Stabilization
Capstone Rocket

What I learned - 

  • Arduino and electronics prototyping, development, and integration

  • Signal processing and filtering

  • Data analysis algorithm development

  • Collaborative report writing and presenting

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