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1 of 93rd Responsive Space Conference 2005

CUBESATS AS RESPONSIVE SATELLITES

Armen ToorianMechanical Systems Lead, Graduate Student

[email protected](805) 756 - 5087

Emily BlundellGraduate Student


Dr. Jordi Puig SuariAerospace Engineering Department Chair


Aerospace Engineering DepartmentCalifornia Polytechnic State University

San Luis Obispo, CA 93407

Robert TwiggsDirector Space Systems Development Laboratory


Stanford UniversityStanford, CA 94305

ABSTRACT

California Polytechnic State University, incoordination with Stanford University, hasdeveloped the CubeSat standard to provideinexpensive and timely access to space for smallpayloads. These picosatellites, built mostly byuniversities, are 10 centimeter cubes with a massof 1 kilogram. Of the 40 or so participatinguniversities and private firms, more than 60% ofCubeSat developers reside in the United States.Our goal is to make launching these satelliteseasy and cost effective by coordinating launchesand providing a reliable deployment system.This paper will discuss Cal Poly’s role in theCubeSat program, and the characteristics of theproject which create practical, reliable, and cost-effective launch opportunities.

TABLE OF CONTENTS

1 Introduction ................................................... 12 The Deployment System (P-POD)............. 23 The CubeSat Standard .................................. 44 Launching CubeSats...................................... 55 The Results..................................................... 76 Conclusion...................................................... 77 Acknowledgment........................................... 88 References ...................................................... 8

1 INTRODUCTION

The CubeSat Program is a collaborative effortbetween California Polytechnic State University,San Luis Obispo (Cal Poly) and the SpaceSystems Development Laboratory (SSDL) atStanford University. The objective of theCubeSat Program is to provide a standardplatform for the design and launch of a newclass of picosatellites - CubeSats.1

The CubeSat Program is designed so that spacemissions can be completed in two years or less(the average collegiate lifetime of a graduatestudent). This accelerated schedule allowsstudents to be involved in the complete lifecycle of a mission. Specifically,

• Mission and requirements planning• Design, analysis, & testing• Fabrication, assembly, & quality control• System level testing• Integration and launch• Ground based satellite operations

A unique feature of the CubeSat Program is theuse of a standard deployment system. Throughthe Poly Picosatellite Orbital Deployer, or P-POD, standardization is used to reduce missioncost and accelerate development time. CalPoly’s current roles are to maintain the CubeSatStandard, coordinates launch opportunities, andcontinue to develop and fly the P-POD. Thisframework allows universities and organizationsworldwide to develop and launch CubeSats

"Copyright © 2005 by Armen Toorian. Published byAIAA 3rd Responsive Space Conference 2005 withpermission."

AIAA-RS3 2005-3001


without directly interfacing with launchproviders (LP).

2 THE DEPLOYMENT SYSTEM (P-POD)

Additional hardware, such as a deploymentsystem, usually only increases complexity. ForCubeSats, however, addition of this hardware iscritical to mission success.

Figure 2-1: P-POD with door open.

2.1 ObjectivesThe functions of the P-POD are to protect thelaunch vehicle (LV) and primary payload, toprovide a safe and reliable deployment systemfor the CubeSats, and to maintain flexibility incompatible LV options.

2.1.1 Protect Primary Payloads and the LVLow cost missions usually imply high risk.Therefore, it is imperative that the P-PODminimize risk to the LV and primary payload.

The P-POD must maintain its own structuralintegrity and offset any failures that CubeSatsmay have during launch. Encapsulation ofCubeSats within the P-POD, mechanically andelectrically isolates CubeSats from the rest of theLV, reducing risk of damage due to

• Accidental activation of electronics• Debris produced by structural damage• Prematurely deployed antennas/booms

2.1.2 Protect CubeSatsAssuring the safety of the CubeSats is animportant but secondary objective of the P-POD. The P-POD should still provide a safeenvironment for the CubeSats during launch,and maintain a high level of reliability. Also, theP-POD should not introduce large spin rates tothe CubeSats during deployment.

The P-POD also serves as a storage binbetween integration and launch, protectingCubeSats from hazardous environmental factorssuch as dust, ESD, and damage due tomishandling or good-intentioned “last minutetuning” by engineers.2 Once integrated,CubeSats may charge batteries and undergodiagnostics through an access port, but willotherwise remain in a dormant mode until beingdeployed in space.

Figure 2-2: P-POD Access ports.

2.1.3 Provide LV FlexibilityPublished secondary payload envelopes played alarge role in defining the P-POD’s size andshape. As a result, the P-POD is compatiblewith a wide variety domestic and foreign LV.

Table 2-1: Some compatible launch vehicles.Delta II3 PegasusDelta IV – SAM TaurusDelta IV – ESPA4 Falcon IAtlas V – ESPA4 Rockot (Russian)Space Shuttle Dnepr5 (Russian)


Though the small size of the P-POD allows formany interface possibilities, launch providers(some Russian LP excluded) are not willing tosqueeze secondary payloads wherever they canfind extra room. Therefore, only the mostconservative secondary payload envelopes wereconsidered viable options.

2.2 P-POD DesignThe P-POD’s design is extremely simple, andpurposefully so. It is an aluminum box with aspring, a door, and a mechanism to open thatdoor. CubeSats are stacked inside the P-PODand constrained by a set of hard anodized,teflon-impregnated rails. These rails provide alow-friction surface for the CubeSats to slideagainst during deployment.

The P-POD’s only task is to open the door (atthe right time) and push CubeSats out. Thephilosophy of simplicity was adopted very earlyon because the P-POD has to do its taskextremely well. After all, the owners of a newlydisintegrated $90million mega-satellite probablywill not be very accepting of their loss due to asecondary payload failure (even if the studentsdo learn a valuable lesson).

2.2.1 ModularityThe P-POD can hold a number of differentCubeSat configurations, totaling a length of340.5mm (the length of three standard sizedCubeSats). Double (227.0mm long), and triple(340.5mm long) CubeSats can also be integratedwithout modification to the P-POD.

Figure 2-3: CubeSat configurations.

2.2.2 SimplicityDue to its simplicity, working on the P-POD isa painful exercise in restraint for anundergraduate engineering student. However,less time spent designing, means more timespent testing.

Minimizing the number of mechanisms allowsthose mechanisms to be designed carefully, andparts to be chosen meticulously. Furthermore,reducing the number of mission criticalcomponents, affords those components a largerportion of the budget. The P-POD has threesuch mechanisms.

2.2.3 Critical ComponentsThe Starsys Qwknut 3k is used to release the P-POD door. It is a non-pyrotechnic bolt releasesystem6 with redundant electric circuitry (noelectronic components). It is very reliable, andas a result, more expensive than the cost ofevery other P-POD component combined.

Figure 2-4: Starsys Qwknut 3k.

The Qwknut 3k was chosen over less expensive,or student-designed, components to offsetconcerns about the P-POD’s reliability andlimited flight heritage. In addition, the Qwknutis user resettable, which allowed us to performdeployment tests to our hearts’ content.

Two torsion springs are used to open the doorof the P-POD. These springs provide enoughtorque to quickly move the door out of theCubeSats’ path. The design allows positivemating of the door and release mechanism toreduce stress. Appropriate geometry andlubrication are used to prevent binding of thedoor.


Figure 2-5: Torsion spring for opening door.

An internal compression spring and plateassembly ejects the CubeSats from the P-POD.There is no direct contact between the CubeSatsand the spring; only the plate guides theCubeSats throughout the length of the P-POD.The spring is customized based on the requiredejection parameters for a given mission. TheDnepr 04-05 mission requires CubeSats to beclear of the P-POD within one second ofreceiving a deployment signal, but limits theirvelocity to 2 m/s relative to the upper stage.5

Figure 2-6: P-POD main compression spring.

3 THE CUBESAT STANDARD

A broad objective of the CubeSat Program is tolearn which attributes of a spacecraft can bestandardized, and which cannot. The CubeSatDesign Specification7 is defined based on somepractical requirements, the dimensions of the P-POD, and a number of safety issues.

3.1.1 General SpecificationsEven the most basic spacecraft will need acomputer, some kind of power generation andstorage system, a communication system, andpayload. A CubeSat is a cube-shaped spacecraft,measuring 10 cm per side, with a mass of up to1kg. It is based on the following considerations.

• The market offers a number of solarcells about 30 x 70 mm. CubeSats

should be able to body mount at leasttwo solar cells per face to generateenough voltage to support commonmicrocontrollers (3 to 5 volts).

• A wide variety of cylindrical andprismatic cell batteries of variouschemistries are available in compatiblesizes.

• Most CubeSats will use amateur radiofrequencies (around 437 MHz) and lowgain antennas. The CubeSat mustgenerate and store enough power forperiodic transmissions from low earthorbit (LEO).

• 1 kg is a convenient number in terms ofdefining cost. Many universities canafford to launch a 1 kg spacecraft. Thenumber of willing and able participantsdrops dramatically with even a slightincrease in mass.

Figure 3-1: Excerpt from CubeSat Specification.

3.1.2 Specifications Due to the P-PODLikewise, some standards were set based on theshape and size of the P-POD.

• The center of mass of a CubeSat mustbe within 2 cm of its geometric centerto minimize spin rates produced duringdeployment.

• The location of access ports on the P-POD determines areas on the CubeSatsthat can be used for diagnostic portsand remove before flight (RBF) pins.

• CubeSat rails should be smooth, flat,and hard anodized to prevent cold


welding due to the launch environmentand minimize friction while deploying.

• Thermal expansion of the CubeSatshould be similar to that of aluminum7075-T73 (P-POD material).

• Tolerances in the specification arebased on P-POD materials, dimensionsand tolerances.

3.1.3 Specifications Due to SafetyA major benefit of the P-POD is that it allowsCubeSat developers to take risks withoutendangering the LV or primary payload. Anumber of safety features are required on allCubeSats to minimize risk to other CubeSats.

• Incorporated separation springs ensuretimely separation between CubeSats.

• At least one deployment switch mustphysically disable the electronic systemsof the spacecraft while depressed (wheninside the P-POD).

• A delay of several minutes must beimplemented before deployment oractivation of any antennas, booms, ortransmitters.

• A RBF pin is required to keep theCubeSats inactive during integration.

Finally, the most important aspect of theCubeSat Specification Document is itsmaintenance by an objective third party. Thisdetachment is essential to successfully enforcingthe standard and meeting launch providerrequirements.

4 LAUNCHING CUBESATS

In the CubeSat Program, everything isconsidered a component of a larger system.Understanding the interactions between thesesystems is crucial to flying secondary payloads.

4.1 Testing PhilosophyA “test as you fly” approach is used throughoutthe CubeSat Program. Integrated tests areperformed to identify any problems caused byunknown interactions between specificCubeSats, and between those CubeSats and theP-POD.

The P-POD itself is designed to withstand veryharsh environmental conditions. However, in

the event of a failure of one or more CubeSats,the P-POD must protect the primary payloadand launch vehicle. Therefore, even flight P-PODs are tested above and beyond LPrequirements.

Design level testing, following any modificationor addition to the P-POD, is much morestringent. Since dynamic loading due tovibration is the biggest concern, multiple P-POD engineering models have been successfullytested to random vibration levels of 14.1 Grmsfor 10 minutes per axis, compared to 1 minuteper axis required by NASA GEVS8

documentation. P-PODs are also designed tooperate between -45°C and +65°C.

0.001

0.010

0.100

1.000

10 100 1000 10000

Frequency (Hz)

ASD

(g^2

/Hz)

Dnepr

Shuttle

Pegasus

Delta II

Envelope

Figure 4-1: Various random vibration profiles.

CubeSat developers can choose to design andtest to elevated environmental conditions aswell. This qualifies a developer’s CubeSat forany launch opportunity with equivalent, or morelenient, requirements. CubeSat developers areurged to think of their spacecraft as onecomponent in a larger family of systems. Thequality of their work can have tremendousimpact on other CubeSats as well as the successof the mission.

4.2 Advantages of RepetitionOnce the P-POD and interface have been flightproven, minimal work is required forsubsequent launches on the same LV. Thisstrategy eliminates a large portion of missionspecific design, analysis, and testing.


Figure 4-2: Integrated P-PODs (Dnepr mission).

As the CubeSat Program evolves, it is feasible todevelop a catalog of prequalified P-POD/LVinterfaces. The large number of developersworldwide creates the necessity for frequentlaunches. This means flight heritage can beestablished quickly, since every mission providesmore experience with the same system, andmost missions require multiple P-PODs.Additionally, P-POD components can beordered in large quantities, and therefore, withquantity discounts. Eventually, the early stagesof a CubeSat mission might be:

1. Assemble a group of nearly completedCubeSats

2. Conduct a survey of near-term launchopportunities

3. Choose a preexisting P-POD/LVinterface

4. Begin negotiating secondary payloadaccommodations with the LP

4.3 Multiplexing SpacecraftWithout sacrificing robustness, the P-POD hasbeen carefully optimized for mass. One emptyP-POD for the Dnepr 04-05 mission has a massof 2.5 kg, and carries a 3 kg payload.

If a P-POD was designed for one CubeSat, itsmass would roughly be 1.75 kg. Combiningmultiple CubeSats into one P-POD increasesrisk for CubeSats, but decreases the total massof the deployment system by over 50%. Also,each developer is now only paying for one thirdof a very expensive release mechanism.

Figure 4-3: Group of 6 CubeSats and 2 P-PODs.

Due to cost and the large number of developerslooking for access to space, it became apparentthat three CubeSats per mission would not beefficient. However, with a dozen or soparticipants, total mission launch costs of half amillion dollars become manageable foruniversity projects. Launch costs to thedeveloper include

• Cost to launch 1 kg of CubeSat• Cost to launch 1/3 mass of the P-POD• P-POD and LV interface development,

manufacturing, and testing• Licensing and administrative costs

4.4 Building Block ApproachAt one point, the P-POD endured many designiterations to increase capacity to more thanthree CubeSats. The result was, instead, tomount multiple P-PODs in small clusters. Thisway, groups of CubeSats can easily be added toor removed from a mission as necessary. Risk isalso mitigated in this way, since a malfunction ofone P-POD does not mean a failure for theentire mission.

Figure 4-4: Interface for SAM and ESPA.


Additional hardware is required to group P-PODs in this way. Usually, this additionalhardware is also the interface between the LVand P-PODs. Available secondary payloadenvelopes and mass requirements determine thenumber of P-PODs per cluster.

Sometimes one cluster of P-PODs does notprovide the required capability. In this case,multiple clusters can be mounted to the launchvehicle. The final package – composed ofCubeSats, P-PODs, and P-POD clusters – isthen delivered to the launch provider. The goalis to make intermediary systems transparent tothe LP so that the delivered hardware can betreated as a single, non-separating payload.

Figure 4-5: Delta II secondary accommodations.

5 THE RESULTS

In June 2003, a Rockot launch vehicle (LV)launched one commercial and 5 universityCubeSats into orbit from Plesetsk, Russia. Asecond CubeSat launch, scheduled for thesummer of 2005, will place 14 CubeSats intoorbit using a Dnepr LV and five P-PODs.Concurrently, a third launch is planned toaccommodate six P-PODs in December 2005.After only three missions, there will be morethan 30 CubeSats in low earth orbit. Based oncurrent capabilities, the CubeSat community caneasily sustain one or more launches per year,with multiple P-PODs on every mission.

Around 600 students currently participate inCubeSat projects worldwide. As a result, thereis a large community of developers working tosolve similar problems. Students can learn from

others’ past experiences and pose questions inan open forum.

Since few S-class parts fit into a 10 cm cube,CubeSats use a wide variety of COTScomponents, due to their size, cost, and shortlead times. Consequently, a number of “adhoc” standards are emerging within the CubeSatcommunity. Laptop and cellular phone partsare very popular, and many developers chooseto use COTS components that have shownsuccess and reliability on other CubeSatmissions (Pic™ processors, Lithium Polymerbatteries, etc.)

Additionally, CubeSat developers are likely tohave internal standards. Often, developers useidentical or similar components and systems onmultiple missions. A number of developersdesign their spacecraft bus generic enough tosupport a wide variety of payloads.

By participating in a launch coordinated by CalPoly, developers can focus on design anddevelopment rather than interfacing with thelaunch provider. The level of handholdingrequired between LPs and universities with littleor no space experience, greatly increasesintegration time and costs.

To alleviate these issues, Cal Poly acts as alaunch coordinator, working with developers tosolve problems without stealing precious timefrom the launch provider. As a result, the LPinteracts with one organization and one piece ofhardware. The process is fairly transparent toboth the CubeSat developers and the launchprovider.

6 CONCLUSION

With a single launch of two P-PODs and sixCubeSats (three of which were successful), thequantity of CubeSat launches and operationalsuccesses is small.

Even with such small numbers, some claim thatCubeSats have already proven themselves asdisruptive technology9. In the six year history ofthe CubeSat Program, a standard has beendefined, has gained widespread recognition, andhas been adopted by over 40 organizations


worldwide. Through standardization, launchcosts have been reduced, and mission life cyclehas been accelerated to acceptable levels foruniversity projects.

With some experience behind us, and someopportunities quickly approaching, the CubeSatProgram is in a position to offer low cost access,to space to a large customer base at regularintervals. Because of its low cost, rapid missionlife cycles, and flexibility10, the CubeSat Programhas shown significant success as a responsivespace program.

7 ACKNOWLEDGMENT

Dr. Jordi Puig-Suari, who continually guides, encourages,and provides insight. His work to secure funding for andestablish facilities to research, design, construct, test, andoperate CubeSats at Cal Poly has been fundamental to thesuccess of the project.

Our “coordinator in chief”, Simon D. Lee for answeringheaps of emails organizing meetings, dealing with ITAR,making those phone calls, and always taking one for theteam.

Our late night pal, Wenschel Lan who worked on the DeltaII P-POD adapter design concept. She also produced fourvery “trendy” mass models for our upcoming Dnepr 04-05launch, which are currently spending some much neededvacation time in the Ukraine. We love to keep a plaque ofall her achievements.

Roland Coelho, for his time and effort in keeping up ourthermal vacuum chamber in order to perform necessaryqualification testing. As well as agreeing that someanalogies just don’t make sense.

The PolySat team, for putting up with the CubeSatstandards and CubeSat team members.

Bob Twiggs, for his guidance and advice. Also thank youto all participating universities helping to make the CubeSatProgram a success.

Special thanks to Raytheon, the Solar Turbines & BentlyNevada Vibrations Lab, Cal Poly Mechanical EngineeringDepartment, Northrop Grumman, Agilant Technologies,Boeing, Cal Poly Aerospace Engineering Department,California Space Authority, Lockheed Martin, and theAMSAT community.

The Multidisciplinary Space Technologies Laboratory forproviding all of us a place to work and sleep.

8 REFERENCES

1 Schaffner, J, “The Electronic System Design, Analysis,Integration, and Construction of the Cal Poly StateUniversity CP1 CubeSat” 16th AIAA/USU on SmallSatellites Conference, Logan, UT, October 2002, pp. 1-2

2 Fleeter, R., “The Logic of Microspace,” Microcosm, ElSegundo, CA, 2000, pp. 146.

3 Boeing Company Launch Services, “Delta LaunchVehicle Secondary Payload Planner’s Guid for NASAMission” <http://www.boeing.com/defense-space/space/delta/docs/DELTA II PPG 2000.PDF>

4 DOD Space Test Program, “Secondary Payload Planner’sGuid for Use on the EELV Secondary Payload Adapter,”Version 1, June 2001.<http://cadigweb.ew.usna.edu/~midstardownloads/structures/ESPA Payload Planners Guid.pdf>

5 International Space Company Kosmotras, “InterfaceControl Document of EgyptSat-1, SaudiSat-3,SaudiComsSat, AKC-1, AKC02, containers P-POD withCubeSat spacecraft and SS-18 Intercontinenal BallisticMissile (modified as the Dnepr Launch Vehicle),” Dnepr-2004-2.3.6061.103, November 2004.

6 Starsys Research Corp., “Operation Manual, Qwknut,”Gen 1, January 2005.<http://starsys.com/catalog/pdf/src_33.pdf>

7 CubeSat Program, “CubeSat Design Specification,”<http://cubesat.calpoly.edu/_new/documents/cubesat_spec.pdf>

8Milne, J.S., Garvin, J., Baumann, R., “GeneralEnvironmental Verification Specification for STS & ELVPayloads, Subsystems, and Components,” NASA GoddardSpace Flight Center, GEVS-SE Rev A, Greenbelt, MD,June 1996.

9 Swartwout, M., “University-Class Satellites: FromMarginal Utility to ‘Disruptive’ Research Platforms”, 18thAnnual AIAA/USU Conference on Small Satellites Conference,Logan, UT, August 2004.

10 Correll, Randall, “Responsive Space Transforming U.S.Space Capabilities,” Washington Roundtable on Science &Public Policy, George C. Marshall Institute, Washington,D.C. November 2004, pp. 2-5


AUTHOR INFORMATION

Armen Toorian is a graduate student in the AerospaceEngineering Department at CalPoly, San Luis Obispo. He isenrolled in a blended program and expects to graduate with both hisB.S. degree in Mechanical Engineering and M.S. degree in AerospaceEngineering in June 2006. His thesis work includes thedevelopment and testing of the Poly Picosatellite Orbital Deployer(P-POD) for launching on a Dnepr rocket.

Emily Blundell is a graduate student in the AerospaceEngineering Department at CalPoly, San Luis Obispo. She isenrolled in a blended program and expects to graduate with both herB.S. and M.S. degrees in Aerospace Engineering in December2005. Her thesis work includes the design and analysis ofinterfaces between the P-POD and a number of domestic launchvehicles such as the Delta IV and Atlas V.

Jordi Puig-Suari received B.S., M.S., and Ph.D. Degrees inAeronautics and Astronautics from Purdue University. In 1993 hewas a visiting assistant professor in the Department ofAeronautics and Astronautics at Purdue University. From1994 to 1998, he was an Assistant Professor in theMechanical and Aerospace Engineering at Arizona StateUniversity. In 1998, Dr. Puig-Suari joined the AerospaceEngineering Department at CalPoly, San Luis Obispo as anAssociated Professor where he is charged with leading thedevelopment of the astronautics program. Currently he acts asDepartment Chair and adviser to the CubeSat Program. Hisresearch interests include spacecraft design, low-cost space systems,vehicle dynamics and control, and tethered satellites.

Robert Twiggs is a consulting Professor in Aeronautics andAstronautics Department. He established the Space SystemsDevelopment Laboratory (SSDL) in January 1994 at StanfordUniversity with both formal classes and laboratory classes forthe development of microsatellites. The laboratory had its firstmicrosatellite OPAL launched in Jon January 26, 2000. The secondmicrosatellite SAPPHIRE will be launched August 31, 2001 onan Athena from Kodiak, Alaska. There are three othermicrosatellites under development for a shuttle launch in 2003. TheStanford group is now developing a picosatellite called CubeSat. This1 kg 10cm cube will provide students in many universities with a low-cost, quick-to-launch project that will give them and other spaceexperimenter’s easy access to space. The first launches of theseCubeSats is scheduled for May 2001on the Russian DneprELV. Professor Twiggs received a BSEE degree from University ofIdaho and an MSEE degree from Stanford University.

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