1. Team 57 Heart of Steel Stanford Student Space Initiative, Rockets Team
Project Leads: Marie Johnson, Ian Gomez Faculty Advisor: Hai Wang Authors: Heart of Steel Team
The Project
Members: Marie Johnson, Ian Gomez, Thomas White, Rushal Rege, Logan Herrera, Christopher May, William Alvero-Koski, Ruqayya Toorawa, John Dean, Rebecca Wong, Derek Phillips, Saylor Brisson, James Kolano, Calvin Lin, Shi Tuck
Payload
Recovery
The year marks the inaugural entry of the Stanford Student Space Initiative (SSI) Rockets Team to IREC and the Spaceport America Cup. We are a core team of 14 undergraduates and 2 graduate students from Stanford University’s largest project-based student engineering group. For this year’s submission, we are competing in the 30,000 ft Commercial Off The Shelf (COTS) motor challenge and in the Space Dynamics Laboratory Payload Challenge. Throughout our project, we placed heavy emphasis on rigorous testing and maximizing as many Student Researched And Developed (SRAD) components as we could confidently produce. As a result, we have designed, developed, and built our own PocketQube payload and deployer, parachute and deployment bag, avionics suite including a SRAD altimeter, and custom composite body structures and motor retention system.
At every step of the way, we have dedicated specific efforts into documenting all the work that has been done, and we have included both a PDR and CDR into our design life-cycle. Between these incredibly helpful design reviews with professionals, professors, and members of the amateur rocketry community, and the various test launches that we have completed, our team has sought to instill a strong sense of professionalism and a high caliber of rigor into our work and design processes.
The recovery system has one goal: bring the rocket back to the ground slowly enough that it does not suffer any damage and can be relaunched. We do this through the use of a serial dual deployment system. This means both the main and the drogue parachutes are released from the same part of the airframe. In turn, we had to develop a system to keep the main parachute from deploying too early, which we did through the use of a retention shock cord and kevlar thread. The airframe separation is triggered through CO2 canisters and the main parachute is deployed at 1500 feet. We developed the main parachute and deployment bag in-house and tested the ejection processes extensively on the ground and in our test flights.
As submission to the 2017 Space Dynamics Laboratory Payload Challenge, the team will have two descending 2P (5cm x 5cm x 10cm) PocketQubes, which perform a ranging technique that will measure their respective relative positions to each other. Each PocketQube includes a custom avionics platform for sensor logging, communications, and recovery tracking. These will be deployed out of our custom CO2 deployer system which is loaded into our nose cone.
Avionics
The overarching design objectives of the avionics system are reliability and launch day symplicity. To achieve this, we use COTS components with long flight heritages integrated into a custom-designed, highly tested mechanical integration assembly. In addition, we designed a custom SRAD system to provide extra functionality and flexibility that could not be achieved with COTS modules. We looked to aerospace and automotive best practices for achieving system reliability. Our avionics bay has undergone shock and vibe testing to NASA Sounding Rocket specifications, giving us confidence in the robustness of the system.
The avionics on board our rocket serve 3 main functions:
1. Igniting charges that deploy parachutes (main and drogue) and payload
2. Logging and transmitting flight information to determine flight profile and apogee
3. Locating the rocket after it has landed
Carbon Dioxide Deployer System
Parachute
Cable cutter
Electronics
Carbon Dioxide Canister
Steel Ballast
Rocket Layout
Mechanical Layout
PAYLOAD
AVIONICS BAY
RECOVERY SYSTEM
MOTOR
Simulations
Structures
We completed our trajectory analyses in OpenRocket and RasAero, two free rocket modeling programs. OpenRocket is used to model precise layout, mass, and CG, but is less accurate with aerodynamics at supersonic speeds. Therefore, we use RasAero to model flight trajectory based on model input from OpenRocket and given flight conditions (altitude, launch angle, launch rail length, etc.).
There were three main uncertainties we tried to account for in our simulations: mass, weather, and surface finish. While we had an initial mass estimate based on CAD designs, most aerospace projects end up being times heavier than initial estimates. For this reason, we adopted a system of mass contingency and margin. We calculated “worst-case” maximum expected mass values to account for expected growth. We then used simulations to find the maximum possible mass that would still allow us to get us to 30,000 feet with the worst expected surface finish and weather conditions (Cast Iron, 44 mph wind, 75°F). Our design requirement was that the margin be at least 10% of the current mass estimate, guaranteeing that even with the worst possible scenario, we could account for unforeseeable growth.
Given our design requirements, we chose the Cesaroni N2900 is a reloadable 6-XL grain, 98mm diameter solid motor with average thrust of Ns, max thrust of N, total impulse of Ns, and a burn time of 6.14 seconds. With the N2900, the rocket is simulated to reach Mach 1.5 and approximately 30,000ft with 75lbs of loaded weight and worst case weather conditions. This gives us an additional 27% mass margin from our predicted mass of 59lbs. The expected flight profile under expected weather conditions is displayed to the below.
In order to build our rocket for this competition, we knew that we had to accomplish two goals: be structurally strong and light, and be radio transparent for our telemetry system. We were able to achieve this goal by doing a mixed carbon fiber - fiberglass layup for our forward airframe and constructing the rest of our fins, nose cone, aft airframe, and couplers out of carbon fiber. Our goal for this project was to create an entirely SRAD rocket body. This allowed us to showcase our strength in construction and a flexibility in design that would not have been possible if we had only used COTS components. The largest issues that we faced were the process of getting the cures to work correctly and how to get a nice surface finish. These were both important as they directly affected our altitude margin and our structural strength. After several iterations, we were able to demonstrate producing parts with enough reliability and uniform finish that we went ahead with constructing all the structural elements from our custom composites.
System Layout
Custom Altimeter - “Skybass”
The subscale rocket and its OpenRocket diagram
Aft airframe of our final rocket
Thank You To Our Generous Sponsors
Special Thanks To
Prof. Hai Wang, Prof. John Pauly, Prof. Simone D'Amico, Tina Dobleman, Eric Melville, Stewart Cobb, James Dougherty, Ian Johnson, Ben Kolland, Max Praglin