Spaceflight Honeycomb Panel
Testing Structure for Depressurization Analysis
Spring 2024 MAE 156B Senior Project
University of California San Diego
Sponsored by ATA Engineering, Inc.
Embedded Files
Honeycomb panels are used frequently in aerospace due to their versatile nature and high strength to weight ratio. However, their construction allows for pockets of air that expand and burst when rapid depressurized during flight out of our atmosphere .
The honeycomb walls can be perforated to allow flow between cells, and traditional methods of analysis evaluate the theoretical porous resistance coefficients of these panels, which are untested and computationally expensive. Our project seeks to bridge the gap by experimentally measuring the characteristics of the airflow and calculating these coefficients.
Design Solution
Design Solution
Video of Final Design
Narrated procedure of device operation for honeycomb sample testing.
Final Setup
Final Setup
The testing device for spaceflight honeycomb panel depressurization analysis flows air linearly through a sample of the vented honeycomb paneling. Fluid parameters of the airflow are measured both before and after the sample to understand the effect of varying airflow rates on honeycomb panel venting.
The pressure drop across the honeycomb paneling is correlated to the air mass flow rate to calculate the porous resistance coefficient of any given sample.
Hardware
Hardware
Filter
Inlet Chamber
Variable Mounting Device
Outlet Chamber
Needle Valve
Vacuum Reservoir
Vacuum Pump
Sensors
Sensors
Temperature Sensor
Differential Pressure Sensor
Absolute Pressure Sensor
Mass Flow Sensor
Project Background
Project Background
ATA Engineering, Inc. is a San Diego based consulting company specializing in testing and analysis of engineering systems. They work on a wide range of systems including satellites, robots, roller coasters, and more. ATA Engineering deals heavily with aerospace systems and hardware.
What are Honeycomb Panels
What are Honeycomb Panels
Honeycomb panels are made of very light, thin metal. The shape of the honeycomb cell gives it a high strength to weight ratio.
This makes the honeycomb panel a great candidate for use in aerospace applications, as weight is one of the most important factors when building spacecraft.
The heavier something is, the more energy it takes to send it into space.
Image of manufactured honeycomb panels. Image credit.
Practical use case
Practical use case
In order to visualize these honeycomb panels better and their functionality, the figure to the left shows a satellite with a solar array setup.
These solar panels are used to power the satellite and allow it to function thousands of miles above Earth’s surface.
Satellite in space with solar arrays on left and right sides with multiple solar panels attached to each. Image credit.
Inside the array
Inside the array
The figure below shows the exploded view of a solar panel found on satellites.
The honeycomb panel, colored yellow and gray, has cutouts used to fit around electronic parts and create a barrier between those components and the solar panel itself.
Graphic image of spaceflight honeycomb panel exploded to show face sheets, adhesive, and honeycomb core. Image credit.
The effect of space
The effect of space
When the honeycomb panels are created, crimped pieces of metal are glued together to create a honeycomb cell. A face sheet is then glued to the top and bottom of these cells to create an airtight pocket.
When these honeycomb panels are sent into space, they experience a rapid depressurization as the ambient pressure surrounding the honeycomb panel goes from 14.7 psi on Earth’s surface to 0 psi in space.
Ambient air pressure decreases as one travels from Earth’s surface to space.
On Earth’s surface, the air molecules are being pushed down, but as elevation increases, the pressure on these air molecules lessens and they are able to spread more easily.
If you have ever brought a bag of chips up a mountain and they have expanded the bag, or even popped, this is the same concept.
Exploded view of single solar panel found on satellite showing how the honeycomb panel (yellow) is used to add structural support to solar panel. Image credit.
When the honeycomb panels are launched into space with this trapped air, the air wants to escape.
When the honeycomb panels are launched into space with this trapped air, the air wants to escape.
And just like the bag of chips has the possibility of popping, the same can, and has, happened to spaceflight honeycomb panels. When the panels make it all the way to space, the pressure within them becomes so great that the walls of the panel can burst outward, causing a variety of failures. Some examples of failure modes are graphically shown below.
When these failures occur, there is a high chance that the solar panels or other surrounding structures could be badly damaged.
There have been many instances of a spaceflight honeycomb panel failing due to rapid depressurization. One unfortunate, true story showcases this failure. Andrew LePage explains the Mariner-Mars project failure, which was developed in the early 1960s [DREW EX MACHINA]. It was a spacecraft that was meant to reach Mars for scientific exploration. After many successful simulated launches, the spacecraft was launched into space. However, shortly after, the team noticed that the solar panels used to power the spacecraft were not opening. They realized that the shroud used to initiate the solar panel opening was not functioning.
It was later found that the shroud used a fiberglass honeycomb core, which had separated and broken due to the pressure differential between the ambient pressure in space and the pressure inside the honeycomb cells. A huge sum of money was lost, as this spacecraft lost power only a couple of days later, missed Mars, and continued its journey deep into space.
This was a devastating loss for the company, and could have been avoided.
Mistakes, such as the one on the Mariner-Mars spacecraft, have paved the way for innovative solutions to these honeycomb panel failures. As of now, the industry solution for this issue is to create vent holes in the side of the honeycomb walls to create a forced path for air to flow safely from the inside of the honeycomb cells to the ambient air.
The method for creating these vent holes vary, but the method used by the manufacturers of the samples provided by ATA utilizes extremely small needles to poke holes in the sheet metal that will then be crimped and glued into whole honeycomb panels. The holes can vary in size, however some standard sizing as mentioned by ATA includes 0.001 inches in diameter to 0.005 inches in diameter. Often, multiple holes are poked into each honeycomb cell wall to generate the desired depressurization rate.
Possible failure modes that could occur between honeycomb cell interfaces. Adhesion failure, when the glue holding two pieces of metal fails, is pictured above.
Possible failure modes that could occur between honeycomb-to-face-sheet interfaces. Buckling failure, when internal pressures get too high and air causes the metal to buckle, is pictured above.
Optimization of these vent holes are essential.
Optimization of these vent holes are essential.
Creating a hole that is too large could cause a significant decrease in the structural integrity of the honeycomb panel. Conversely, creating a hole that is too small could result in structural failures as pressure is put on the cell walls due to the air not being able to leave at a high enough rate.
ATA Engineering has used analytical and numerical techniques to attempt to optimize the size and placement of these vent holes. However they have not been able to validate their theoretical values experimentally, as they do not have the apparatus necessary to accurately measure the flow conditions through these honeycomb panels. This is where our team comes in. We have been tasked with creating a testing apparatus that can accommodate a wide range of honeycomb panel sizes and obtain steady state flow measurements that will be put into calculations to find porous resistance coefficients. Resulting coefficient values can be seen below.
Objective
Objective
Our goals
Our goals
We're looking to combine theory with empirical data while reducing assumptions and computational expense of current CFD models used to obtain flow characteristics of honeycomb panels.
Design and fabricate a test apparatus for applying differential pressure across test samples of honeycomb panel, ensuring unidirectional flow with no leaks through the panel sides
Design and integrate a method to apply differential pressure across honeycomb panel samples of a range of sizes
3" to 9" Long
3" to 6" Wide
0.4" to 2" Thick
Theoretical calculation of air flow through perforated honeycomb panel core to aid in sizing of flow devices and measurement sensors
Select and integrate pressure transducers and flow measurement sensors
Measure flow through samples of a honeycomb panel provided by ATA, in the two principle directions at a suitable range of flow rates
Compute honeycomb sample porous resistance coefficients based on test data within +- 10%
Use error analysis to demonstrate that first system requirement has been met
Apparatus must be easily transportable in a cargo van, either in one piece or disassembled. Must require 2 or less people to lift
Operable by one engineer
Stretch Goals:
Stretch Goals:
Develop non-destructive method of sealing honeycomb sample edges
Develop an inspection method to measure perforation size and quantity (per cell wall)
Develop an inspection method that is non-destructive of the sample
Create user procedure documentation to ensure that any engineer who needs to operate this apparatus has the knowledge to confidently run and repeat their necessary tests.
Test Results
Test Results
Pressure Drop vs Mass Flow Rate
Pressure Drop vs Mass Flow Rate
Experimental pressure drop vs mass flow rate of air using four different flow rates (1, 2, 3, 3.5 LPM). Steady state values were used from each test and then a line was best fit to the data to compare with the theoretical curve.
Experimental Porous Resistance Coefficients
Experimental Porous Resistance Coefficients
Using the measured pressure drops and volumetric flow rates, we can use the theoretical equation to solve for the PRC at each flow rate. There was an error of 12.7% between the theoretical coefficient and the averaged PRCs.
Sealing Capability
Sealing Capability
To maintain an airtight seal and accommodate multiple sizes of honeycomb panel samples, each clamping direction was isolated and actuated by bolts that clamp the variable mounting device walls to the honeycomb paneling. Additionally, the thickness adjustability is continuous and fully variable, but the width of the paneling is discretized by switching out wall sizing.
Due to chamber size constraints, the final ranges of honeycomb paneling are:
3-7" Width and Length, in 1" increments
0.4"-2.1" Variable Thickness
Two examples of the discrete width control can be seen below.
6" Sample Width
6" Sample Width
4" Sample Width
4" Sample Width
Note: The 4" walls do not yet have the foam gasket attached in this image, but the final product includes gasket material on all mounting device walls.
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