CubeSat De-Orbit Device
Status Report #2
03/27/2011
Air Brake
Kim Scheider Juan Parducci
Todd Estep
During the last few weeks the CubeSat Air Brake team has worked countless hours in
order to restore functionality to the physics department vacuum chamber. When permission was
granted to use the vacuum chamber, an entire overhaul of the chamber took place. All existing
components on the chamber plate were removed, disassembled and subjected to an ultrasonic
cleaner. The components consisted of various gaskets all of which were inspected and replaced
with new high-vacuum gaskets. The bell jar, itself, was thoroughly cleaned. After complete reassembly of the individual components, all of the surfaces mating with the chamber plate were
coated with a monolayer of Apiezon high vacuum grease.
Shortly after, the first leak test was performed and a thermocouple leak source was
repaired, resulting in a low pressure of 78 Torr . The turbo pump being utilized for testing has the
capability to easily reduce a sealed vacuum chamber's pressure to 10^-5 Torr. The minimal drop
in pressure from the atmospheric level of 760 Torr to 78 Torr was clearly indicative of a leak in
the system. A methodical approach to locating the leak was devised. All of the components
involved in providing a seal to the vacuum chamber were tested for leaks. Initially, it was
thought that the leaks were located in the plastic hose that was being used and in the electrical
feed through ceramic plugs. The hose was replaced with a metallic one and the electrical feed
through ceramic plugs were replaced with bolts and o-rings. A few more vacuum tests were
conducted and the same problem persisted.
Finally, the team decided to utilize the human auditory sense in order to detect other
possible leaks. In conclusion, it was determined a couple of knicks in the glass bell jar a few
millimeters deep were responsible for the apparent leak. The rubber gasket lip overlapping the
glass knicks made the leakage source initially difficult to detect. After improvised sealing
techniques were used, a new record low pressure of 4 Torr was recorded.
The bell-jar has been subjected to a restorative process in which custom fitting gaskets
were molded into the crevices. Later this week when the gasket molds have cured, the excess
will be sanded down and another vacuum test will be conducted.
Two different simulations using Satellite Tool Kit have been performed in order to better
understand heating requirements for a CubeSat in Low Earth Orbit and the drag coefficients
required in order to de-orbit a CubeSat in less than 25 years. The result of these simulations has
been posted on the team website.
-Nitinol
Using STK it was determined that the temperatures that a CubeSat will reach in orbit due
to solar heating will be sufficient to activate the material's shape memory effect. The Nitinol is
being trained in preparation for welding, which will be carried out by the ODU Machine Shop.
Structure Team Status Report II
Nathan Schwinn
Greg Lemmer
During the past few weeks, the structure team has made progress toward completion of
the computer model. Dimensions for the launcher skeleton were finalized and the information
was used to start generating a computer model so that stress and vibrational analysis could be
completed. The modeling was performed using the program PATRAN which serves as the
visualization for the analysis software NASTRAN. Once the initial model was built, there was
some difficulty in completing the inertial loading (pulling g’s effect of the booster rocket)
analysis as the mesh was incorrectly defined for the solid elements. Once the corrections were
made to the finite elements, boundary conditions and loading were defined, and the model was
analyzed using NASTRAN. The first trial indicated errors in the connectivity of the nodes in the
model which resulted in asymmetric stress distribution and deflection. Despite efforts to fix the
connectivity, the first model had to be scrapped entirely and work began on the new model
immediately. Since the construction of the new model, initial stress and vibrational analysis has
been successfully completed.
In addition to the fine tuning of the computer model, the design of the overall structure
has been continually fine-tuned in Autodesk Inventor. The overall mass of the launcher skeleton
has been reduced by the removal of sections from the side and back plates and the addition of
bolt holes indicates sites for joining the plates into the single structure.
The spring design has been completed and a quote was requested from a manufacturer in
Kentucky who has the capabilities of producing custom compression springs. Because the spring
that deploys the satellite from the launcher does not fall into the category of a mass producible
component, the price was higher than previously expected. The Prices for the Aluminum 7075
alloy that make up the sides of the launcher have also been investigated from a couple sources.
The cost of obtaining enough material to fabricate the launcher skeleton is roughly the same cost
to manufacture the spring. However, it was discovered that the raw aluminum may be able to be
machined for a relatively low cost, if not for free, by a local machine shop.
Current obstacles include verifying the vibrational analysis is correct and fine tuning the
design to meet the requirements of the RockeSat-X program. A more pressing problem consists
of obtaining the funds to purchase materials. After acquiring the necessary funds, the parts can
be ordered and the challenge would then be to receive the material in enough time before the
semester’s end so that construction can begin.
CubeFlow Hardware/Software
Dylan Blackshear Trevor McCarthy
Since the last mid-term update, the CubeFlow Hardware/Software Team has continued to
learn more about the CubeFlow Hardware/Software system. The team has been using the Utah
State Space Dynamics Laboratory (an online laboratory resource, provided by Utah State
University) as a means of easily establishing the coding for devices, interfaces, variables, and
commands. This generated code is then imported into the AVR Studio, where it is built and
compiled. Finally, the signal is flashed onto a micro-controller via the Atmel FLIP Software
(which is embedded in AVR Studio). Using this technique, the team has successfully established
live temperature sensing and LED-on command capabilities between the laptop computer and the
on-board micro-controller as of mid-February.
Since then the team has been tasked with establishing the additional sensory devices,
interfaces, and commands, to be used during concept testing of the Air-Brake. The team has
considered multiple options for sensing and testing the Air-Brake’s inflation performance.
Among these include a wire break detection, a wire stretch detection by voltmeter across a
resistor, and finally an internal ultrasonic range-finder to measure the Air-Brake’s internal
diameter. The most difficult thing about each of these techniques is that none of them directly
measure the Air-Brake’s internal volume, which is ultimately what needs to be understood.
Using these techniques, only the Air-Brake’s longitudinal diameter can be measured, and
therefore, the team must rely on the assumption that the Air-Brake will inflate to form a perfect
geometric shape, to make conclusions about its’ internal volume. The CubeFlow Team is
currently working with the Air-Brake Team to consider other volume measuring techniques that
rely on fewer assumptions.
As well as the measurement devices, and their interfaces, the CubeFlow Team must also
establish the commands to be given to the on-board micro-controller, via the laptop computer, to
be used during testing. The first and primary command that the team is working to establish is a
hatch release command, so that the Air-Brake will be contained until ready for inflation, and
unrestricted during deployment.
While the team did prove successful in using the Space Dynamics Lab’s code generation
capabilities to establish a sensory device (temperature sensor) and command (LED-on), the
online lab’s database is quite limited in the allowable devices and commands for which the
coding can be generated. This means that in order for the team to connect a foreign device to one
of the micro-controller’s input/output pins, they must bypass the Space Dynamics Lab’s coding
generator, and directly create the C-code in the AVR Studio. Unfortunately, since the team is not
comprised of any computer engineering majors, they must collaborate with others who have a
better understanding of C-style computational coding techniques. They have been in contact with
a computer engineering graduate (Joshua Birch), as well as a Dr. Dimitri Popescu of ODU’s
electrical and communications department. The team will be meeting with Dr. Popescu later this
week to discuss the problems they are having in using the input/output pins to integrate foreign
sensory devices with the micro-controllers, as well as in the C-coding used to define the
interfaces, variables, and commands to be used with the devices.