Sounding Rocket

03/25/2020

Screenshot of lochlin's website code

Project Overview

I developed this sounding rocket in collaboration with a student team at the University of Alberta whose sole mission is to provide students with the opportunity to explore rocket engineering. I joined the team shortly after its inception and quickly became the lead designer of the rocket. The learning curve was a challenge. Rather, it was a challenge I was willing to accept.

Our objective was to develop a solid fuel rocket to reach an altitude of 3040 m, break the sound barrier, and cost less than $5000 to build.

Discussion

To successfully design a rocket capable of attaining an apogee of 3040 ± 10 m, is no easy feat. This was undoubtably a team effort. I will, to the best of my ability, describe how my team and I tackled this project and the role I played in bringing this project to completion. My discussion of the project will highlight the following key points:

Conceptual design

The key to a project of this scale is to divide it into smaller, more manageable sub problems. We must first describe what the solution looks like before we can identify the sub problems in the solution process. This is very similar to the way differential equations are solved in mathematics. We begin by understanding the general form of the solution and then work backwards to determine the steps required to arrive at our final solution. Now for a rocket, this means estimating the vehicle’s geometry, the approximate mass of each subsystem, their respective locations inside the rocket, and the expectations of the planned mission. Three concept designs were developed, based on the collective flight experience of the rocketry community, rules of thumb, and open source software. The best concept was then chosen based on a decision matrix that ranked each design on the following factors: mass, cost, and complexity.

With the general solution now known, our team then divided the subsystems of the rocket into sub problems. The most notable sub problems our team encountered during the detailed design phase of the project were as follows:

The trajectory problem

The ability to predict the trajectory of the rocket with accuracy and precision, is critical to mission success. Without reliable trajectory data, our team could not safely design the rocket’s structure or guarantee that our rocket would deliver the payload to its required altitude. To fully convey the magnitude of this problem, I will first provide some background information on trajectory prediction and then describe how our team was able to overcome this challenge.

With this understood, our next step was to figure out how implement this into a simulation. I studied the physics behind this problem until I had gathered enough information to at least comprehend the solution procedure required for such a simulation. The solution procedure for a 6 degree of freedom trajectory simulation is as follows:

  1. Initialize the rocket in a known position and orientation in time t = 0
  2. Compute the local wind velocity and other atmospheric conditions
  3. Compute the aerodynamic forces and moments affecting the rocket
  4. Compute the effects of the motor thrust and gravity on the rocket
  5. Compute the mass and moments of inertia of the rocket and from these the linear and angular accelerations of the rocket
  6. Numerically integrate the acceleration equations to obtain velocities, positions, and orientations during time step Δt
  7. Update current time to t = t + Δt
  8. Repeat steps 1-7 until the entire trajectory has been plotted (read: the rocket has landed)

Although we understood the simulation procedure, our team was ill-equipped at the time to implement such a thing into a full software package. Thankfully, we live in an age where open source software is in abundance. In 2009 Sampo Niskanen, an MSc. candidate attending Helsinki University of Technology, completed his MSc. thesis titled “Development of an Open Source model rocket simulation software”. What his work translated to, was a complete software package wherein a rocket could be designed, and its trajectory simulated, accounting for the aforementioned factors. The software Niskanen developed was aptly named OpenRocket and was immediately implemented into our design cycle. Upon discovery of this open source software, we studied Niskanen’s thesis which doubled as documentation describing how the software functioned. Once we completely understood the assumptions and limitations of the software, our team was finally able to compute the necessary parameters for further design work involving loads estimation and design optimization.

The load estimation problem

Coming soon!

Lessons learned

I figured out how to determine the structural loads on a rocket. How to predict the static stability of a rocket. I learned what the most appropriate materials and manufacturing methods were and relayed that to my team.

Future development

This rocket is only the beginning. A solid fuel rocket allowed my team to get comfortable with rocket vehicle design and the physics underlying rocket flight. I intend to guide my team through liquid fuel engine development in the very near future. The future of spaceflight depends on the design of more effiecient and more powerful engines. The sooner we can get students involved, the sooner they can make a huge impact in industry.