Preliminary Detailed Design
Team Vision for Preliminary Detailed Design Phase
- CAD model
- Estimated total structure mass
- Choice of material
- Internals sub-structure interface
- Deployable Structure
- CAD model
- Estimated mass
- Chose assumed solar panel
- Deployment Mechanism
- Build/Purchase Decisions
- Hot knife support
- Retaining wire routing
- Build/Purchase Decisions
- Begin simulation design
MSD I Deliverable Planning
Updated ER and HOQ
Internal PCB Volume and Shape
First and foremost, there is a given PCB standard for CubeSats, which will define their interiors to a great extent .This will drive interior volume space and require changes to that engineering requirement (ER 8).Metric Payload PCB Specification
Overhang on Sides
The initial overhang requirement was further clarified and we realized that we could actually extend outwards into the PPOD container more than expected, freeing up area on the sides. This helped make the engineering requirement make more sense and free up some engineering constraints.
Prototyping, Engineering Analysis, SimulationIterative activities to demonstrate feasibility, including assumptions you made in your analyses or simulations. Have you completed sufficient analysis to ensure that your design will satisfy requirements? Have you included all usage scenarios in your modeling?
Hot Knife Testing
In order to construct a working hot knife, a specific type and amount of NiChrome wire must be chosen. A material to be used for the restraining line must also be chosen. The testing in this section allowed us to make those decisions.
Hot Knife was chosen last phase due to its heritage, low cost, low infrastructure, and no moving parts.
What does the ideal hot knife look like?
In order to ensure that the hot knife mechanism can provide the required power to melt the restraining line without adding too much mass, testing was performed with multiple hot knife designs. In the hot knife design, NiChrome wire is coiled around a restraining line and heated until the line breaks. The number of times the NiChrome is coiled around the restraining line was varied in this test. The results of the testing are shown below.
Testing clearly showed that with each added coil, the extra resistance added outweighs the extra heat dumped into the restraining line and that the one coil setup requires the least energy to break the line. Given that the single coil also has the least mass, we will not make a design that requires multiple coils.
Electrical requirements dictate that the hot knife provide 2.5 ohms of resistance. This target, combined with the above results has lead us to use a thinner NiChrome wire. This decision will allow us to meet our electrical requirements while further lowering the mass of the system without compromising the ability of the hot knife to melt the restraining line.
How much will our design deform while in storage after integration? How will it react to waiting for launch?
Or design requires the deployable solar arrays be held secure by nothing but a single restraining line before deployment. There is potential for this line to stretch between when the CubeSat is assembled to when it finally leaves the PPOD in orbit. If the line stretches, it will create slack and allow the deployable solar panels some movement. If the line stretches too much, there will be enough slack for a deployable array to open partially and contact the PPOD inner wall. Any contact between the deployable array and the PPOD could jeopardize both our CubeSat and the other CubeSats in the PPOD. Our design must preclude this possibility.
To get a sense of magnitude for how much strain the restraining line will undergo, a rudimentary creep test was constructed. Two types of restraining line similar to the kind we expect to be used in the final design were tested. The lines had a 320g weight hung from their ends for a period of one week.
The initial and final lengths of a segment of each line was measured. From these lengths, a % strain was calculated.
Testing showed that the restraining line experienced a total strain of about 3.6%. With this nominal strain, the restraining line can only be 16.8cm long without allowing the deployable solar array to come dangerously close to the PPOD wall.
The information gained from this test effects our placement of the restraining line and directs us to both consider strain during our purchase of restraining line and continue to test restraining line strain in more realistic conditions.
What electronics and power requirements are necessary to drive the hot knife?
There are limited electronics available on the vehicle and very little power to work with. These systems working with the CubeSat design standard will have upwards of 2500 mAh available and a 3.3V at 5A and 5V at 4A rail, like the nanopower board underneath.
Ultimately, we want to maintain at least 2 amps on any line to allow avionics, communications, and other CubeSat components to function during the hot wire cutting process.
These metrics can be met with this piece of NiChrome wire and this material is easy to solder and attach to pre-existing electronics, as tested by actual soldering of the components. The needed transistor could be met with this transistor, which is designed to work with the given temperature range and power demand.
Drawings, Schematics, Flow Charts, Simulations
Preliminary Structure Designs
In order to allow ideas from each team member on the structure of the CubeSat to be realized, each member created their own preliminary CubeSat structure design. These designs were all evaluated against each other and the best elements from each of them were combined and added to to make our team's first overall design.
Preliminary Structure Design 1
In this design, four identical side walls slide directly into a slot in each rail. Two opposite walls are securely fastened to each rail so that when they deploy, the rails deploy as well. The top plate has a similar design to the side plates. This design does not include a bottom plate.
+ Walls and panels fastened to rails on their larger faces for added stability
+ Interior of rails machined out to facilitate fastening
+ Less structural support given to bottom face than any other face to save mass
- Rails unnecessarily deploy
- Bottom face does not have enough structural support
- Hinge fastening mechanism uncertain
- Non-deployable solar panels are given unnecessary backer plates which add much mass
Preliminary Structure Design 2
This design features a support plate opposite the main base panel to support the side solar panels. Rails are slotted to allow for mechanical interface with the solar panels. The solar panels act as the main structural support connecting the rails, and the payload is supported by the base plate and the bottom plate.
+ Rail connections with side panels provide good structural support
+ Backer panels for solar panels are eliminated to reduce mass
+ Design can be 3D printed or manufactured using sheet metal
- Small hinge does not supply enough support
- Solid rails are heavy
- Depends on adhesives for some joints
- Depends on solar panels for structural support
Preliminary Structure Design 3
This design featured the rails connecting to the thicker side plates that were used to extend and collapse the structure. The large top plate contained all the components to help contain the hinge without extra fasteners as well as providing a mechanical stop and mounting location for all components. Disregarding the connections between the rails and the plates, the entire system could be put together with 8 bolts.
+ Fully integrated hinge into 3d printed structure
+ Strong Frame Elements
+ Multiple Directions of Support and Connection
+ Reduces number of extra components like set screws, rivets, etc.
+ Could also be machined
- Exaggerated volume=Exaggerated Mass
- Difficult printing in some cases
- Little internal volume
- Assembly would be difficult
Preliminary Structure Design 4
The above design uses the exploded deployment style. The hinges are not detailed and are just mated at the rail midsection. The hinge rotation allows for the rails to be stopped by hitting aluminum and not relying solely on the hinge. The hot knife design would be incorporated into the cut out section of aluminum. This also had a mass estimation through solidworks of 368 g.
+Uses dove-tail to ensure rigidity.
+The hot knife is incorporated into the crossmember.
+Uses crossmember to create an aluminum wire frame.
+Bottom plate has 4 dove tails integrated in the base crossmembers creating a rigid base.
+All fasteners are the standard M3 CSSHCS.
+Mass from SW simulation is 360g.
-Does not have incorporated solar cells.
-No hinge design incorporated.
-Rails would be difficult to machine.
-Fasteners would need to be modified to fit.
Intermediate Structure Design
Selection choices and why
Our new design takes advantage of extra space in the PPOD. Before deployment, the solar panels, and deployment structure are located outside of the primary 100x100x100mm design space. By using extra exterior space between the rails as defined in the CubeSat Standard we were able to free up extra space on the inside for the payload. Before deployment, 5 faces of the cube are available to gather solar energy during the pre-deployment detumble stage.
The fully deployed structure triples the exposed surface area when aligned with solar radiation. By 3D printing the deployable structure behind the solar panels, we are able to reduce weight, and complexity by keeping our part count down.
The integrated hinge design involves 3D printing the hinge system directly into the base plate and deployable structure components. This makes for a more simple design and also incorporates built in end stops to locate the panels after deployment.
Since the aluminum of the CubeSat rails is one of the biggest mass contributors, we hollowed out the majority of the inside of the rails, leaving a flance to mount the stationary panels, and another flange to mount the base plate. This feature also increases the available interior volume for our payload.
To ensure that the deployable structure is held stationary during vibration, maximum edge contact with the rails was desired. This caused some concern for possible jamming of the deployable structure if it experienced significant thermal expansion. To reduce the chances of of failed deployment, the edges of the deployable structure and the rail flanges were chamfered.
To keep the hot knife coil away from the payload, the retaining wire was routed along the edge of the bottom panel through the use of 3D printed guide features. This also allows us to mount redundant hot knife coils. Lastly, routing the wire around the edge makes the wire tensioning process easier and more repeatable.
To keep the hot knife from melting into the structure, guide features were added to lift the retention wire above the surface. The hot knife will be mounted by compressing its extra leads beneath a screwed on plate.
All solar panels are mounted through the use of standard mounting hole spacing.
The torsional spring is retained by the hinge shaft. A feature was added to the base plate to transfer the spring force.
This shows the PPOD fitting into a PPOD with the extra available protrusion space.
Our design is made under the assumption that the solar panels being used will be from the GOMspace NanoPower P110 Series. This is merely a placeholder to design around and the design can be modified to fit other brands of panel. This brand was chosed due to it's optional magnetorquers and accessible CAD model.
How well does our design meet current Engineering Requirements?
Comsol and SimulationCOMSOL is a tool developed to solve PDE. For analyzing vibrations and transient solutions, it is great
VibrationHow does our design respond to the launch environment? A vibrational analysis was conducted through the use of COMSOL on the CubeSat design. The Eigen frequencies were determined to find the resonant nodes. These were then analyzed +- from these frequencies. In addition P16103 vibration specs were incorporated into this analysis.
Y-Direction LoadHere the load was switched to the Y direction due to the possibility of the CubeSat/PPOD being loaded either horizontal or vertically in the LV.
- Frequencies around 800 - 2000 Hz is where resonance
becomes a concern with a 2g load.
- At these frequencies the internal stresses will cause failure.
- The frequencies within that range are show the failure for certain sub-components.
- When passed 5% passed the resonant frequencies extrema the internal stresses fall off to non threatening values.
- The maximum frequency that would be experienced during P16103 vibration-load would be ~100Hz
- The y directional applying of the loads did not drastically change internal stress behavior, and showed similar characteristics to the z directional of applied load.
Z-Direction LoadBased on launch envelope g-loading, how does our model respond? Here a 6g load was applied to the entire model. This would mimic the force felt on the load during ascent.
Y-Direction LoadHere is a corresponding load to he Y-Direction with same loading as the All other Y-Direction loading Figures.
- The stationary loads of 6gs did not show deviation from the vibration-load as these had similar forces.
- Y direction of applied load has a slightly higher internal stresses but not more than 30%.
Mass BreakdownIn our systems level design phase, we made some estimates to budget available mass to each of the 3 main subsystems. At this stage in our design, we were able to greatly reduce the overall mass of our system despite a frame mass that was higher then expected. Our greatly reduced deployment mechanism mass was caused by integrating some of its features directly into frame and deployable frame parts.
|ER and Description||Minimum||Ideal||Current||Status?|
|1 Min Undeployed Area Time (cm2-orbit)||100||100||100||SATISFIED|
|2 Deployed Area Time (cm2-orbit)||150||300||300||SATISFIED|
|3 System Mass (grams)||420||300||~368||SATISFIED|
|4 CubeSat Clearance (mm)||1||1||>1||SATISFIED|
|5 Time from Command (s)||2<t<8||2<t<8||~ 7||SATISFIED|
|6 Operating Temperature (deg C)||(-40,40)||(0,20)||?||?|
|7 Available Interior (mm)||96 90 85||100 100 100||96 90 ?||?|
|8 Exterior Protrusion Space (mm)||6.5/face||6.5/face||?||?|
|9 Change in COM (mm)||50||>10||?||SATISFIED-Simulation|
|10 Constant Launch Acceleration (g)||6||8||?||SATISFIED-Simulation|
|11 Cost of Prototype ($USD)||500||400||100-500||SATISFIED|
|12 Time to Remove Blank (s)||8||6||?||?|
|13 Launch Vibration Test (Pass/fail)||Pass||Pass||SATISFIED-Simulation|
|14 Full Documentation||Pass||Pass||Pass||SATISFIED|
Bill of Material (BOM)
In order to ensure requirements are met, the deployment mechanism must go through two types of testing: creep testing on the restraining line and functional testing of the hot knife. Early in MSD II hot knife testing similar to tests already conducted will be run using the final restraining line and NiChrome wire chosen for the design. This will test our compliance with ER5 - Time from command to deploy. This system will be tested again later in the semester attached to the full CubeSat system so once again test ER5 as well as ER9 - change in center of mass. Early in MSD II, there will also be creep testing done under the most realistic temperature, positioning and loading requirements we can provide. This will check progress on ER8 - Available exterior extrusion space - and ensure that the CubeSat deployables will not contact the PPOD's walls.
To ensure that our design meets vibration requirements set forth by the CubeSat standard (Engineering Requirement E13), we will perform vibration testing in the spring. This testing will be performed using the device built by the P16103 senior design group. Our CubeSat will be mounted into their PPOD fixture, and vibrated based on prescribed vibration patterns generated by P16103.
High Altitude Balloon TestingAn opportunity has presented itself to fly a section of our payload on a high altitude balloon. This will help test our low pressure and thermal properties of launch and our operation in orbit.
We will send two deployable arrays, and of them, one will actually deploy while in flight above a 80,000 ft flight ceiling. This should replicate the actual launch outcomes. At this height, pressure will be 2% of what it is at the surface and operating at -50 degrees Celsius (-60 degrees Fahrenheit), but ambient heat should keep it slightly warmer and within the -40 to 40 degree operating range.
It will test ER 5 (time to deploy) and ER6 (operating temperature).
Design and Flowcharts
Risk Assessment and Major Questions
NylonIn our research of the proposed 3D printed material, we discovered that there is a potential for offgassing. The material we intend to use contains a considerable amount of nylon, for support of the carbon fiber. Nylon tends to absorb a large amount of moisture from the atmosphere, and this moisture can offgass when the nylon is exposed to a vacuum. This makes our original concept of a carbon fiber 3D printed frame significantly less attractive.
Nylon AlternativesTo aviod potential offgassing isuues associated with nylon containingp components, one option for our group is to replace the carbon fiber material with another more suitable option. Several possibilities exist as seen in the following table.
Epoxy CoatingsIn order to prevent offgassing from a largely nylon frame, a low-offgassing epoxy can be applied to the surface of the CubeSat. A variety of epoxys that pass NASA's offgassing requirements can be commercially purchased.
Updated Risk Assessment
Our risk list was updated to include the recently discovered risk of nylon off gassing.
Phase V Deliverables
- Structure/Deployable Structure
- Optimize Design based on Comsol feedback
- Reduce mass
- Maintain strength
- Design for manufacturing
- Make final material choice
- Optimize Design based on Comsol feedback
- Deployment Mechanism
- Build enhanced creep test fixture
- Discus thermal creep testing with Prof. Humphrey
- Retaining Wire
- Chose material
- Chose knot
- Finalize Simulations
- Plan ordering schedule
- Choose printing facility
MSD I Deliverable Planning
MSD II Plan
- Order Components
- Printing Filament
- Electronic Components
- Ask for Boilerplates
- Talk to previous co-ops for glass, polymers to use to simulate black box mass and solar panels
- Order relevant components
Spring Semester Phases
- Prototype and Characterization
- Machine Rails Paul
- Organize Printing, Starting to Print Rob
- Prepare Boilerplates Anthony
- Breadboard Electronics Tristan
- Begin Building/Printing
- Print Frame Elements Rob
- Assemble Frame Elements Anthony/Paul
- Implement Electronics/Hot Knife Tristan
- Begin First System Review and Characterization
- First pass at various tests Anthony/Tristan
- Validate final design implementation through simulation as well Rob/Paul
- Rebuild, Redesign, Repair
- Documentation and Closeout