Team Vision for System-Level Design Phase
- Select a concept for engine design.
- Perform research and feasibility analysis to support concept selection.
- Define a high-level system design for the selected concept leading to material/equipment selection and preliminary modeling or analysis.
Concept 1 - ResistojetPropellant is stored in a high-pressure vessel and released with a binary solenoid valve. The propellant is convectively heated by a finned resistive heating element and exhausted out a conical nozzle.
- Safer (no HV risk, lower temperatures)
- Simple electrical design
- Lesser performance potential
- Difficult mechanical design of heating element
Concept 2 - ArcjetPropellant is stored in a high-pressure vessel and released with a binary solenoid valve. An electric arc is created across an cathode placed in the engine chamber and the nozzle throat, which serves as an anode. The propellant gas is heated as it flows through the electric arc and is exhausted out a conical nozzle.
- Greater performance potential
- Simple mechanical design
- Increased safety risks (HV, higher temperatures)
- Difficult electrical design of arc generator
Feasibility: Prototyping, Analysis, Simulation
*If judged to be suitable based on HT calculations.
Note: This is not total project cost. As material cost was a driving selection factor, the critical material purchases are shown here. Things not included that may need to be purchased include sensors, test stand material, microcontroller, electronic components, and a power supply.
- Altitude chamber
- Owned by RIT and available for student use
- Typically run at ~0.6atm for the ETA's testing, capable of going lower (testing needed to see min pressure)
- Not often used by other groups
- Allowed to install electrical pass-throughs if none exist (fan currently present)
- Test Stand
- Test stand will be required to fit within chamber
- Test stand will likely require mechanism to increase measured force, e.g. a lever
- Thruster Design Utility (TDU) is a lightweight, easy to use, and open source utility that computes engine performance parameters, including thrust, specific impulse, and the pressure, temperatures and flow rate at the exit of the nozzle. TDU is fast and flexible, allowing for quick and iterative analysis of compressible flow through a converging-diverging nozzle for different nozzle geometries or propellants without a complete fluid flow model. Currently TDU is a Matlab script with most outputs verified with NASA reported values. We intend to expand the utility to include a GUI and heat transfer models. Theory, mathematical derivations and analysis are discussed at https://stemn.com/projects/thruster-design-tool/. Visit https://github.com/runphilrun/TDU for the latest build and issue tracking.
- Nozzle analysis and design is in its early stages. Boundary conditions are not yet fully understood, nor the best method of converging to a solution. Some data from the pressure chamber will be useful in this regard. In the model below, the heat is transferred to the gas using convection instead of by direct arcing contact, however the convection coefficient is set up to imitate the amount of power that would be transferred in the real scenario. The example shown below calculates a predicted thrust of 1.8N, which is higher than expected. More work will be done on this in phase 3 to try and match values with research.
- Inlet flow: 15mg/s
- Environmental pressure: 1% atm
- Heat transferred: 800W
For a first-draft design of our nozzle please click here.
- Performance increases as molecular weight decreases
- Breakdown voltage will be significant driver in selection (Paschen's Law)
- Using flight proven propellants as baseline, excluding toxic compounds like Hydrazine (N2H4) and Ammonia (NH3)
- Common & inert gases like Argon (Ar), Nitrogen (N2), and Helium (He) have decent performance and low safety risks
- More investigation required to down select
Concept Screening Pugh Chart
Weighted Concept Selection Matrix
Test Stand System
Designs and Flowcharts
Olin College: Comparable Arcjet Prototype
- This project is the most applicable example that the group has found in terms of budget, construction, and design intention.
- The project was not successful due to the lack of
vacuum testing environment, compromise in material
selection for the anode (nozzle), and inadequate power
- We hope to use an altitude chamber to allow for the most realistic testing conditions in addition to the mitigation of some complications due to material properties, such as the oxidation and deterioration of tungsten, and extra power needed to create an arc at atmospheric pressure.
- The power supply used in this experiment was a simple welding supply with no control system. We plan to customize a power supply solution that allows us to create the conditions necessary to generate the arc as well as sustain it.
- The anode we are planning to manufacture will be made of pure tungsten or an alloy that does not have decreased electrical conductivity at high temperature, which we believe is a contributing factor to the issues seen in the Olin College example.
Design Review Materials
- Concept Selection Meeting Agenda
- Concept Selection Meeting Minutes
- EDGE Checklist as of 28Sept16
- Design Review 2 Notes
- Design Review 2 Powerpoint
Plans for next phase
- David Yin 3-Week Plan
- Phil Linden 3-Week Plan
- Matt Giuffre 3-Week Plan
- Dylan Bruce 3-Week Plan
- Anthony Higgins 3-Week Plan
- James Gandek 3-Week Plan