CubeSat Deorbit Devices
Old Dominion University
Project Design & Management I
ME 434W
December 10, 2010
Dr. Robert Ash
Lindsey Andrews
Jake Tynis
Joshua Laub
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Abstract:
The integration of electronic devices and subsystems within a satellite bus is not a trivial issue in the
design of a spacecraft. The benefit of this research is immediately apparent, expanding experiment
opportunities using low-cost access to space utilizing the CubeSat platform. However, once orbit
has been achieved, a CubeSat's lifetime is finite and can be on the order of decades. This research
has shown that an effective deorbit device can be deployed to shorten the lifetime of a CubeSat.
This technology is becoming more valuable as the total number of CubeSats in orbit increases. The
future safety of the earth orbit environment with regards to orbital debris depends on the ability to
safely deorbit nanosatellites.
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Table of Contents
List of Figures ................................................................................................................................................................... 4
Introduction ......................................................................................................................................................................... 5
I. Literature Review ........................................................................................................................................................ 5
II. Rationale ..................................................................................................................................................................... 6
III. Project Objective ..................................................................................................................................................... 8
IV. Benefits...................................................................................................................................................................... 8
Proposed Approach............................................................................................................................................................ 8
Organization ...................................................................................................................................................................... 10
Cost Consideration ........................................................................................................................................................... 10
Summary............................................................................................................................................................................. 11
Appendix ............................................................................................................................................................................ 12
I. Works Cited ............................................................................................................................................................... 12
II. Secondary Material.................................................................................................................................................. 12
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List of Figures
Figure 1: Six CubeSats and their respective P-POD launcher (California Polytechnic).......................................... 5
Figure 2: COTS CubeSat Structure (Pumpkin, Inc.) ..................................................................................................... 6
Figure 3: Predicted lifetime of a 1U CubeSat without deorbit module (Lokcu)....................................................... 8
Figure 4: Predicted lifetime of a 1U CubeSat with deorbit module (Lokcu)............................................................. 9
Figure 5: Deorbit Pillow Construction (Lokcu) ............................................................................................................. 9
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Introduction
I. Literature Review
Low cost access to space has been an area of concern since the early days of
spaceflight. Over the decades, advances in technology have allowed space structures and
avionics to decrease in size. The CubeSat architecture takes advantage of both of these
advances.
The CubeSat design standard is a collaborative project between California
Polytechnic and State University and Stanford University. A standard CubeSat is a 10
centimeter cube with a total mass of less than 1 kilogram. The premise behind CubeSat is
to be a secondary payload to a host launch system. In other words, if there is an extra mass
allotment on a launch, CubeSats have the opportunity to be deployed. CubeSats are
deployed using the Poly-Picosatellite Orbital Deployer, P-POD, as seen in Figure 1: Six
CubeSats and their respective P-POD launcher, also developed by California Polytechnic
and State University (California Polytechnic).
Figure 1: Six CubeSats and their respective P-POD launcher (California Polytechnic)
As stated previously, the standard size for a CubeSat is a 10 cm cube (referred to as
1U). This can actually be increased to a maximum size of 10 cm by 10 cm by 30 cm and 3
kilograms (3U). Obviously this is a larger, more expensive endeavor than a standard 1U
CubeSat; however it is a possibility.
The design challenges of CubeSats are very apparent: small size. The small size and
mass requirements seriously constrict the payload. The only volume and mass remaining
for the experiment is after essential systems have been integrated in the bus. There must be
an electrical power system, telemetry, data handling, thermal control, and various other
systems that must be incorporated prior to the experiment.
There are certain companies who specialize in commercial off the shelf (COTS)
CubeSat subassemblies, as seen in Figure 2: COTS CubeSat Structure. These kits greatly
aide in the development time and budgeting of a spacecraft. The main idea behind
CubeSats is to keep cost and development time to a minimum.
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Figure 2: COTS CubeSat Structure (Pumpkin, Inc.)
The launching of artificial satellites into earth orbit has produced some unintended
side effects. Every satellite which is put into orbit has a finite useful lifetime; at some point
they will no longer function and then become debris. As the total number of orbiting
satellites and debris increase, attention must be focused on minimizing their orbital lifetime.
There are currently over two million kilograms of space debris in orbit around the earth (R.
Janovsky). Orbital debris can be characterized by three distinct groups. The first group is
comprised of accidental or intentional break-ups. The second major category is the intentional
release of objects from launch vehicles and spacecraft during deployment. The third and
increasingly more common cause of debris is the in-orbit collision of space debris (Office for
Outer Space Affairs). These three separate categories may result in objects that have
lifetimes on the order of decades.
The United Nations Office for Outer Space Affairs has prescribed a series of
guidelines which are designed to mitigate orbital debris. The guidelines are as follows:
1.
2.
3.
4.
5.
6.
Limit debris released during normal operations
Minimize the potential for break-ups during operational phases
Limit the probability of accidental collision in orbit
Avoid intentional destruction and other harmful activities
Minimize potential for post-mission break-ups resulting from stored energy
Limit the long-term presence of spacecraft and launch vehicle orbital stages
in the low-Earth orbit (LEO) region after the end of their lifetime (Office for
Outer Space Affairs)
These new mandates, specifically guideline six, require that launch vehicles and their
payloads must have a timely return to earth at the conclusion of their mission. Additionally,
the Inter-Agency Space Debris Coordination Committee (IADC) along with NASA and the
International Standards Organization (ISO) put a limit on orbital lifetimes for Low Earth
Orbit (LEO) of 25 years (IADC).
II. Rationale
The current topic of development is CubeSat deorbiting. Designs for deorbit
mechanisms can range from long tethers to inflatable assemblies. The current level of
deorbit mechanism research provides many new areas to explore. As electronics size and
power requirements have decreased, small electromechanical devices have also miniaturized.
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The method chosen to best suit a CubeSat deorbit device is one that increases
surface area, producing drag. This design relies on creating a drag force to slow the orbital
velocity of the spacecraft (R. Janovsky). It can be shown that as the orbital velocity
decreases, the orbital altitude must also decrease. The drag force is a function of the density
at the respective altitude. Atmospheric density increases exponentially towards the earth’s
surface; therefore drag is higher at lower altitudes.
In spacecraft design a single term, ballistic coefficient, can be used to describe the
𝑀
drag efficiency. Ballistic coefficient is defined as 𝐵𝐶 = 𝐶 ∗𝐴 where M is the mass, CD is the
𝐷
drag coefficient, and A is the frontal area (D.C. Maessen). In this case, a lower ballistic
coefficient will have a larger surface area and be a better deorbit mechanism. A 1U CubeSat,
with a mass of 1 kg, cross sectional area of 0.01 m2, and a CD of 2, will have a ballistic
coefficient of 50.
The method for increasing the surface area of the spacecraft requires some sort of
deployable mechanism. The two main ways to increase the surface area of a spacecraft are
to deploy a rigid structure/array or an inflation device. Both of these methods require some
sort of activation technique and movement.
The deployable array technique would be similar to deploying additional solar panels.
The sides of the spacecraft would fold outwards to increase the total surface area. This
technique requires a significant level of sophistication and will not be discussed further.
The second method for increasing surface area is to inflate a generic volume of some
sort. From a drag perspective, the shape is irrelevant as long as the critical surface area for
producing the required lifetime is achieved. An inflatable must use some sort of gas to
inflate a closed thin walled volume. The volume must be able to be packed sufficiently small
and the gas must also be stored compactly. The material for the thin walled volume is also
of importance since it must remain in space for extended periods of time. Puncture
resistance is also a consideration, whether micrometeoroid impacts are a concern or not
(D.C. Maessen).
If an inflatable device is used, one possible modification is the addition of a
conductive ring inside the material. The ring would allow a current to flow, which would
interact with the Earth’s magnetic field according to the equation F = I*L x B. This
interaction could be beneficial in various ways. First, if the ring is perpendicular to the
magnetic field lines, then the ring experiences a torque, which could be used to orient the
CubeSat. Second, if the ring is parallel to the magnetic field, by applying the correct
direction of current (clockwise versus counterclockwise), the interaction causes the ring to
expand. This expansion could be useful. For example, if the inflatable device experienced a
leak, the expansion would help keep the material from collapsing in on itself, making it easier
for the gas to inflate the structure.
Although a conductive ring would be useful, it adds complexities to the deorbiting
device. One would need to ensure that dissipated heat from the ring does not degrade the
adhesive in the inflatable structure. The folding and packaging of the material would need to
be slightly altered. Also, the CubeSat would need to store more power, in order to supply
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the current of the ring. Lastly, and most importantly, a detailed computer program would be
necessary to predict the magnetic field of the Earth at the exact position of the CubeSat.
The purpose of the computer program is to ensure that the magnetic forces are pointed in
the correct direction, according to the right-hand rule. Due to these complexities, a
conductive ring will only be considered if a standard inflatable structure does not suffice.
III. Project Objective
The objective of this design project is to construct a CubeSat deorbit device. Using
applicable research sources, a best practice design for an inflatable deorbit device will be
constructed and demonstrated. The device shall be a payload for a 1U CubeSat, meeting all
of the standards under the CubeSat heading.
IV. Benefits
The benefits of constructing this device are proof of concept. The first concept to
be proved is that this payload can meet the constraints of a CubeSat payload (size, mass,
etc.). The second benefit is the development of a low cost, reliable method to deorbit a
CubeSat. The removal of high altitude CubeSats will reduce a significant source of space
debris.
Proposed Approach
The approach chosen to create this CubeSat deorbit device is that of an inflatable balloon or
pillow. This design offers a less complicated option to a fixed folding array design. Depicted in
Figure 3: Predicted lifetime of a 1U CubeSat without deorbit module . It can be seen in the figure that
the predicted lifetime is well in excess of 400 years. Depicted in Figure 4 is the predicted lifetime of
a 1U CubeSat with an arbitrary, increased surface area deorbit device. The deorbit device
successfully removed the satellite from orbit within the prescribed 25 year life span.
Figure 3: Predicted lifetime of a 1U CubeSat without deorbit module (Lokcu)
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Figure 4: Predicted lifetime of a 1U CubeSat with deorbit module (Lokcu)
The actual shape of the inflatable structure is dictated by the complexity of constructing the
volume. It is for this reason that a pillow shape, as shown in Figure 5, will be used. The pillow
design need only be sealed along the edges, and thus lends itself to a simpler design. Material
selection of the pillow is critical. In the harsh low earth orbit regime, radiation and atomic oxygen
are the primary concerns (Lokcu). The material chosen to survive this environment is a polyimide
film known as Kapton®. Kapton is a product of the DuPont Company and has a proven track
record for long term space applications (DuPont).
The inflation of this balloon must be done with a reliable gas source. There are two main
options in this area. The first is a cool gas generator, and the second is a stored refrigerant. Several
companies specialize in developing space qualified cool gas generators for various applications.
One company specifically, Bradford Engineering, has developed a 2 gram cool gas generator. This
is a perfectly viable method to inflate a small deorbit mechanism for a CubeSat (Bradford
Engineering). For the refrigerant option, a simple pressure vessel containing the fluid would be
sufficient (Lokcu).
Figure 5: Deorbit Pillow Construction (Lokcu)
The actual triggering of the deorbit device can be accomplished either by an onboard timer
or with ground based signaling. The actual activation will be processed through the main bus of
the CubeSat and should require a minimal fraction of the total CubeSat’s available power (~5%).
The housing for the deorbit device will be constructed of the 6061-T6 aluminum alloy, per NASA
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and California Polytechnic guidelines. This alloy is common to the entire CubeSat and P-Pod
launcher, and offers the best density option for design integration and weight minimization.
Organization
The organization and scheduling of this project is to fit within a two semester time frame.
All work for the project will be shared equally, dependent upon each team members' strengths.
The planned completion of this project is early April 2011 with allowances for extensions. The
bulk of the scheduling is comprised of design and manufacturing. Procurement of materials should
be minimal due to the simplicity in the design approach. The work breakdown structure of the
project currently consists of ten tasks:
1. Problem Definition – Define the task to be accomplished including constraints such as final
product volume and mass, and project scope.
2. Budget/Cost Analysis – Determine an estimate for the amount of capital necessary to develop
and test the prototype.
3. Finalization of Approach – Based on the background research and project scope, decide on the
method of deorbiting, be it an inflatable or rigid structure.
4. Software Development – Write software and code that will allow the mechanism to perform its
intended function.
5. Materials Sourcing – Obtain all of the materials necessary to construct and demonstrate the
prototype deorbiting system.
6. BUS Interfacing – Integrate the prototype hardware and software with the command and
control computer of the CubeSat.
7. Structural Design/Packaging – Finalize and construct the housing for the deorbiting device.
8. Integration – Integrate the hardware, software, and controllers into the CubeSat payload.
9. Testing
10. Report and Summary
Care has been taken to allow for leeway in the scheduling, so that any difficulties encountered
during a particular phase in the work breakdown structure will not cause the project to exceed the
firm deadline of the end of the Spring 2011 semester. Prototype testing is slated to begin in early
February of 2011. A Gantt chart has been developed of the project timeline, and is attached in the
Secondary Material section of the Appendix.
Cost Consideration
The costing of this project is supplemental currently. The primary purchasable components
are 606-T6 aluminum, Kapton®, adhesive, inflation gas, and the CubeSat development kit. The
Kapton® film has been acquired by donation, and is valued at approximately $200/lb. This saves a
considerable cost in the overall project. An additional donation of the CubeSat kit mitigates that
cost, which is currently $5,000.
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Of the many available adhesives Elastosil S36® (which is similar to an RTV silicone) was
chosen with regards to its low out-gassing and previous use in spaceflight qualified applications.
Elastosil® is produced by Wacker Chemie AG (Wacker Chemie AG) and is available from various
suppliers within the U.S. for around $18 per tube.
As mentioned previously the use of COTs technology allows for the cost of CubeSat
development to be kept to a minimum. This is especially true of the electronics. Controllers similar
to those utilized in recreational robotics can be integrated into the CubeSat, providing a cost
effective solution for running software. Controllers are available from many sources with single unit
costs averaging around $200 (RobotShop).
6061-T6 aluminum can be purchased in a variety of shapes and sizes. Price varies depending
on the amount of shaping and forming required (cold/hot working) and surface finish. Aluminum
naturally forms an oxide coating when exposed to the Earth environment, so no further surfacing is
required to prevent corrosion or per NASA regulations. Raw material is available from industrial
suppliers at a cost of approximately $0.10/cm3 (McMaster Carr). As the volume of the deorbiting
device is restricted to a maximum of 150 cm3 (Lokcu), the total raw material cost for the aluminum
in a single device is capped at $15.
Labor is estimated to be the largest contribution to cost during prototype development. Such
tasks as milling, machining, or circuit board printing/construction will incur labor costs. Labor rates
vary depending upon the location and task to be performed. Additional costs include miscellaneous
wiring and electronics, as well as assembly hardware and tools. These costs should be around $120.
The total cost for a single deorbiting unit, not including the cost of the Kapton® or labor, is
estimated to be $350.
Summary
Controlled deorbiting of retired satellites is of major importance in the coming years. As
space access becomes easier, a reliable means of deorbiting is essential. This project provides a testbed for such a device. The pillow design adopted here provides an easily assembled and inflatable
structure to increase the surface area of the CubeSat. The compactness, reliability, and low cost of
this device lends itself greatly to CubeSat integration
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Appendix
I. Works Cited
Bradford Engineering. "Sold Propellant Cool Gas Generator." 2006. <http://www.bradfordspace.com/pdf/be_datasheet_spcgg_sep2006.pdf>.
California Polytechnic, State University. "CubeSat Design Specification Rev.12."
D.C. Maessen, E.D. van Breukelen, B.T.C. Zandbergen, O.K. Bergsma. "Development of a Generic
Inflatable De-Orbit Device for CubeSats." (n.d.).
DuPont. "Summary of Properties for Kapton Polymide Films."
<http://www2.dupont.com/Kapton/en_US/assets/downloads/pdf/summaryofprop.pdf>.
IADC. "Space Debris Mitigation Guidelines." Standard. 2007.
Lokcu, Eser. "Design Considerations for CubeSat Inflatable Deorbit Devices in Low Earth Orbit." Old
Dominion University (2010).
McMaster Carr. 27 November 2010 <http://www.mcmaster.com/#aluminum/=a2cdo0>.
Office for Outer Space Affairs. "Space Debris Mitigation Guidelines of the Committee on the Peaceful Uses
of Outer Space." Vienna: United Nations, 2010.
Pumpkin, Inc. CubeSat Kit. 2008. <http://www.cubesatkit.com/>.
R. Janovsky, M. Kassebom, H. Lubberstedt, O. Romberg. END-OF-LIFE DE-ORBITING Strategies for
Satellites. Bremen: OHB System AG, 2002.
RobotShop. 30 November 2010 <http://www.robotshop.com/>.
Wacker Chemie AG. 1 December 2010 <http://www.wacker.com/cms/en/productsmarkets/trademarks/elastosil/elastosil.jsp>.
II. Secondary Material
Project Gantt Chart:
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