CubeSat Concept and Deployer Services

The CubeSat program is a first attempt towards a picosatellite standard development. CubeSat is the name given to a cube-shaped picosatellite design of 10 cm side length (a cube of 10 cm x 10 cm x 10 cm with a total mass budget limit of 1 kg).

The CubeSat concept and program started in 1999 at SSDL (Space Systems Development Laboratory) of Stanford University under the leadership of Robert J. Twiggs. \[Note: The CubeSat concept was initially presented and proposed by R. J. Twiggs at the USSS (University Space Systems Symposium), Kauai Beach Hotel, Kauai, Hawaii, Nov. 6-8, 1999\].

The idea was to meet an educational need to define a meaningful satellite mission that could be developed within a timeframe of a year or two, be of very-low cost, and be of very low mass for reduced launch costs. - It turns out that picosatellites offer very promising scenarios to demonstrate new small-scale space technologies and mission concepts (testbed capability for low-power and low-mass devices such as MEMS). CubeSats, combined with new sensor, communications, and networking capabilities, may be able to carry out formation flight demonstrations in support of multi-point observations. - In the meantime, Stanford University and California Polytechnic State University in San Luis Obispo, CA (referred to as CalPoly) have combined efforts to develop a means of launching small standard picosatellites called CubeSats. ^{1) 2) 3) 4) 5)}

Figure 1: View of the CP1 (CalPoly-1) CubeSat (image credit: CalPoly)

The overall objective of the CubeSat program is to provide an effective framework (including specifications and guidelines) for the design, construction and launch of picosatellites. Defining a standard bus, developing standard hardware components using commercial off-the-shelf (COTS) components and a standard spacecraft frame will simplify the development of picosatellites. The CubeSat development will provide a standard spacecraft frame, a spacecraft controller, radio transceiver, attitude determination and control, solar cells, batteries, and an interface for a payload. The intend is to free the developer from repetitive spacecraft designs; thus, he should be able to concentrate on the payload. Nonetheless, a big challenge remains in the integration and packaging of all the subsystems into a very limited volume of available space.

Note: At the start of the 21st century, the picosatellite subsystem of "power" is still rather underdeveloped. Thus, tiny power budgets in the order of 100 mW of continuous power from solar cells limit the operational capabilities of any picosatellite mission.

P-POD (Poly-Picosatellite Orbital Deployer):

The CubeSat launch concept selected permits the launch of multiple secondary payloads which may be stacked into a launcher tube, called P-POD (Poly-Picosatellite Orbital Deployer), developed by CalPoly. P-POD is a standard deployment system that ensures all CubeSat developers conform to common physical requirements. The P-POD plays a critical role as the interface between the launch vehicle and CubeSats. It utilizes a tubular design and can hold up to 34 cm x 10 cm x 10 cm of deployable hardware space.

Figure 2: Illustration of the P-POD structure of the MK I model (image credit: CalPoly)

The standard P-POD holds up to three CubeSats, it is designed to be attached to many different launch vehicles. The double P-POD holds up to six CubeSats, it uses a common wall to save weight. In a nominal mission sequence, the CubeSats are ejected from the piggy-back P-PODs after reaching orbital altitude. Once safely away each CubeSat will activate itself and begin its mission. ^{6) 7) 8) 9)}

The key features of the common standard are:

• The common form factor is, 10 cm x 10 cm x 10 cm, and maximum mass of 1 kg. The common form factor and weight of the CubeSats is necessary to ensure that they are properly integrated into the CubeSat deployer.

• Spring plungers between the CubeSats. They provide the initial separation between the CubeSats after deployment.

• Deployment switches. These ensure that all CubeSats are inactive during launch and pre-launch activities.

Multiple Cubesats can be joined together to form a satellite with increased volume and mass constraints.

Table 1: Variations on the CubeSat standard regarding size and mass

Simplicity and reliability are the cornerstones of the CubeSat standard. The standard provides universities with structural, dimensional, and operational guidelines.

Launch opportunities are planned for at least once per year. With the demonstration of low cost picosatellites, and the development of Stanford University's CubeSat program, a new testbed for technology and science demonstrations is gaining acceptance. CubeSat spacecraft, having a mass of about 1 kg, are appropriately suited for test and qualification of microelectronics and MEMS technologies.

CubeSat launch services (arrangements with a launch vehicle provider, coordination, payload integration and test, etc.) are provided commercially by OSSS (One Stop Satellite Solutions) of Ogden, UT for the participants of the CubeSat program. OSSS also provides MPA (Multiple Payload Adapter) for multiple P-POD installation and deployment services. Note: MPA deploys P-PODs while P-POD deploys CubeSats.

Figure 3: Illustration of the P-POD structure of the MK III model (image credit: CalPoly)

Figure 4: Illustration of the double P-POD design (image credit: CalPoly)

Table 2: Overview of standard CubeSat requirements ¹⁰⁾

Background: During the 1990s, satellite and payload development projects have become the program of choice for challenging (multi-year) training courses in quite a few engineering departments at universities throughout the world. The intent is always to enrich the student training program, to stimulate interest in a problem-solving multi-disciplinary technical environment, to be imaginative and resourceful, and to take some risks – with ample and essential help from mentors and partners (industry, institutional, or otherwise).

Cooperation on many levels and active participation/publication within the international space science community are important ingredients in the overall objectives of research and development. In some instances, project-sharing among engineering departments of several universities is being practiced in order to handle the demanding and complex project goals in a certain time frame. In general, a good amount of enthusiasm and lots of volunteer work by all parties involved are needed to bring such low-cost program activities to maturity - an invaluable amount of professionalism is gained for all students in such programs. ^{11) 12) 13) 14) 15)}

The CubeSat program itself has been created to provide in particular colleges and universities the opportunity to develop and launch small satellites at very low cost -making their launch and operation affordable. As of 2004, the CubeSat initiative is in fact becoming a global collaborative effort. It represents an ideal platform to demonstrate new technologies and concepts. In this context, experimental failure is a basic element of university life, and from the university's perspective, a failed spacecraft is not necessarily a failed mission.

Other deployer designs for pico and nanosatellites:

Next to the P-POD design of CalPoly, there exist other POD designs. The University of Tokyo (Japan) developed T-POD (Tokyo Picosatellite Orbital Deployer) in collaboration with UTIAS/SFL (University of Toronto, Institute for Aerospace Studies / Space Flight Laboratory) of Toronto, Canada. ¹⁶⁾

Note: The other POD developments are not regarded as a competition to P-POD (Poly-Picosatellite Orbital Deployer) of CalPoly; rather, they are considered a complementary element in case of need being offered by a potential launch opportunity.

T-POD (Tokyo Picosatellite Orbital Deployer):

• The first T-POD was flown in 2003 (Rockot launch vehicle on June 30, 2003 from Plesetsk, Russia), using the original design of Tokyo University. The T-POD was used to eject the XI-V CubeSat of the University of Tokyo from the Rockot launch vehicle in a multiple CubeSat launch (6 picosatellites).

• The SSETI Express mission of ESA, launched October 27, 2005, deployed three CubeSat passengers (i.e., picosatellites): UWE-1 (Universität Würzburg Experimentalsatellit-1), Würzburg, Germany; XI-V (X-factor Investigator-V) of the University of Tokyo, Tokyo, Japan; and NCube-2 (Norwegian CubeSat-2) from Norway. The deployment of the CubeSats used the T-POD system; however, this time around it was provided by UTIAS/SFL, based on the T-POD design of the University of Tokyo.

Figure 5: Illustration of the T-POD and the CubeSats (image credit: TU Wien)

CSS (CUTE Separation System)

The Tokyo Institute of Technology (TITech), Tokyo, Japan designed and developed its own deployment system, referred to as CSS (CUTE Separation System), and launched its CubeSats or nanosatellites with this system.

• CSS was flown for the first time to deploy the CUTE-1 (Cubical Tokyo Tech Engineering Satellite) CubeSat. The launch was on June 30, 2003 on a Rockot launch vehicle of ELS (Eurockot Launch Services) from Plesetsk, Russia; the flight involved a multiple payloads, among them also six CubeSats.

• TITech conducted a separate test flight of the modified CSS to demonstrate its behavior. This mission is referred to as: TSD (TITech Separation system Demonstration) which took place on July 10, 2005 as a secondary payload to the Astro-E2 (Suzaku) spacecraft of JAXA/ISAS (Japan Aerospace Exploration Agency/Institute of Space and Astronautical Science), Tokyo.

• An improved version of CSS was used to deploy CUTE-1.7+APD (Cubical Tokyo Tech Engineering Satellite-1.7+ Avalanche Photodiode), a double-cube of TITech. The launch took place on Feb. 21, 2006, on the M-5 launch vehicle of JAXA as a sub-payload to the 3rd launch stage. The primary payload on this flight is the Astro-F (Akari) spacecraft of JAXA/ISAS. The launch site was the Uchinoura Space Center (USC) at Uchinoura on Kagoshima Island, Japan.

• The third CSS flight deployed CUTE-1.7+APD-2 of TITech. The multiple payload launch (10 spacecraft) on the PSVL-C9 flight of ISRO took place on April 28, 2008 from SDSC (Satish Dhawan Space Centre), Sriharikota, India. The primary payload on this multi-satellite flight was CartoSat-2A.

Figure 6: Illustration of the separation system for CUTE-1.7+APD-2 (image credit: TITech)

X-POD (eXperimental Push Out Deployer):

X-POD, also referred to as XPOD, is a custom designed separation system that was developed at the University of Toronto Institute for Aerospace Studies/Space Flight Laboratory (UTIAS/SFL). The XPOD system can be tailored to suit small satellites of different sizes ranging from a single CubeSat to larger nanosatellites of arbitrary dimensions.

The objective of the XPOD design/development at UTIAS/SFL is to provide a GNB (Generic Nanosatellite Bus) for the CanX (Canadian Advanced Nanospace eXperiment) series (as well as for other nanosatellite designs) and to deploy these nanosatellites from a launch system reliably and effectively. The XPOD separation system interfaces the GNB spacecraft to the launch vehicle. A typical rectangular spacecraft is accommodated within the XPOD on its four parallel edges. This allows for optimal use of exterior surface and simplifies the spacecraft structural requirements. The XPOD ejection units are basically tubes that have a spring at the base. With an activation signal, a spring-loaded door is released, and the base spring pushes a nanosatellite out into orbit (in the deployment sequence, two sides of the XPOD are completely open once the door has been unclasped). ^{17) 18)}

While accommodating a variety of form factors, the design of the XPOD imposes certain constraints on all nanosatellites using it as an ejection medium, namely the minimization of components that are mounted to the exterior shell that would (with specific expectations for pre-deployed units) interfere with the case. Each nanosatellite bus must be able to slide out of the deployer without any damage. This leads to a contact rail-based design where most nanosatellite components must be on the spacecraft's interior.

The main features of the XPOD development system are: ^{19) 20) 21)}

• Scalable design for spacecraft of arbitrary dimensions up to 5 kg; one XPOD per spacecraft

• Up to triple-cube units may be flown

• Closing mechanism:

- In-house design

- Implemented features to minimize the risk of jamming

• Redundant firing system

• Door and pusher plate sensors

• High performance materials

• Capable of full S/C deployment test in a 1 g environment.

Figure 7: Illustration of the XPOD system (image credit: UTIAS/SFL)

The first XPOD of UTIAS/SFL, formerly known as T-POD II, passed its vibration and thermal vacuum qualification in 2006.

• A 10-satellite launch on the ISRO PSLV-C9 took place on April 28, 2008 from SDSC (Satish Dhawan Space Centre), Sriharikota, India. The primary payload on the flight was CartoSat-2A, a military version of the CartoSat-2 imaging mission of ISRO. In addition, ISRO launched its own microsatellite, IMS-1 (Indian Microsatellite-1), of 83 kg.

Furthermore, the shared launch included eight secondary payloads with the following CubeSats or nanosatellites. Six XPOD units were provided by UTIAS/SFL to deploy all smallsats - except the CUTE-1.7+APD-2 (3.5 kg) double cube of TITech which used its own CSS deployment system(Figure 6).

- CanX-2 of UTIAS/SFL, Toronto, Canada (triple cube)

- CUTE-1.7+APD-2 (3.5 kg) CubeSat of the Tokyo Institute of Technology (double cube)

- AAUSat-2 of Aalborg University, Denmark

- COMPASS-1, University of Applied Sciences, Aachen, Germany

- Delfi-C3 of the Technical University of Delft, The Netherlands (triple cube)

- SEEDS-2 of Nihon University, Japan

- CanX-6 UTIAS/SFL, Toronto, Canada

- Rubin-8-AIS an experimental space technology mission of OHB-System, Bremen, Germany.

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