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Focus...The Power Of The Picosatellite

Over the past several years, CubeSats have evolved from excellent hands-on teaching tools in the university domain into high performance, high reliability picosatellites with increasing interest from the Department of Defense (DoD) space community for experimental and operational applications. The vision for future CubeSat mission types range from technology demonstration missions to augmenting larger satellites to performing stand-alone operational missions, with dedicated payloads. Comtech AeroAstro, Inc. (CAA) and the Space Dynamics Laboratory (SDL) have teamed together to develop a high-performance CubeSat design that is able to meet the requirements of these more stringent mission types.

In response to this growing interest from DoD, commercial and university organizations, CAA, drawing on lessons learned from development and test of the Standard Interface Vehicle (SIV) microsatellite bus for the DoD Space Test Program, has developed the Coral picosatellite spacecraft bus design.

This development was performed in conjunction with SDL at Utah State University, drawing on their PEARLsoft flight software solution and CubeSat experience. The goal was to design a robust, flexible and reconfigurable CubeSat bus with sufficient performance and design margins to meet the increased performance requirements of pointing, power and volume. In addition to the three primary design objectives, the Coral bus design incorporates the following points to ensure reliability and mission success.

i. High-performance components

ii. Standardized and non-proprietary interfaces

iii. Proven software architectures

iv. Support for a large majority of mission and payload types

v. Standard quality processes and procedures

vi. Spacecraft experience

CAA has targeted these areas to increase the performance over current capabilities and rigor in traditional CubeSat designs. The combination of these enhancements has resulted in a CubeSat design targeted for a wide variety of missions, beyond just demonstration, to include operational missions.
CAA’s/SDL’s technical approach features a commoditized Coral bus, USING a high-performance PCI-104 architecture (commercial, non-proprietary architecture) which offers a flexible, modular and standardized payload interface that meets or exceeds the majority of published Government and civil requirements. The Coral bus is a standard 3U design that meets all of the requirements of a CubeSat spacecraft. Additionally, the Coral bus is compatible with the Cal-Poly P-POD launcher and can, therefore, be launched on any launch vehicle designed to carry CubeSats into orbit.

To meet the stringent Coral requirements, the team performed an industry-wide search of component suppliers/vendors in all subsystem disciplines to establish a technical baseline that met the required design criteria. CAA assessed current and emerging technologies in all areas to increase subsystem performance while maintaining self imposed stringent schedules. The technical baseline includes a significant number of innovations that provide the customer greater utility for mission and payload flexibility.

Simple, standard payload interface (mechanical, electrical and flight software)

High bandwidth PCI-104 architecture capable of 1 Gbps data rates

High precision ADCS design, including sun sensors for safe hold mode operations

High performance EPS subsystem design providing 45 watts of peak power

Low risk, modular, existing flight software design easily tailored for custom payload flight software integration

High data rate/link margin, ultra-high frequency radio/antenna system with AES-256 bit encryption

High performance central processing unit board based on LEON III processor operating up to 66 MHz

Payload accommodations that allow all volume above the spacecraft bus to be dedicated to the payload (except where the solar arrays stow)

Passive thermal control of the bus and payload

SM_January3 Coral’s internal bus and payload electronics communicate over a high bandwidth PCI-104 bus interface. The PCI-104 offers excellent bandwidth performance while conforming to the Coral form factor (3U-CubeSat). The Coral design permits a dedicated payload interface card volume located on the Coral bus side to maintain a flexible, seamless protocol (RS-422, 1553, SpaceWire). The design uses a dedicated fifth row, or Row E, on the PCI-104 bus to provide substantial power and general purpose input/output to the payload.

SDL’s PEARLsoft flight software provides the core C&DH software components required to operate the Coral bus and payload elements. Key components include a system monitor, communications handler, network manager, code update handler, command handler, ADCS controller and resolver, telemetry processor and payload manager. The flight software uses a multi-threaded architecture providing excellent design modularity that allows a high level of reuse and adaptability to meet a broad range of mission requirements. Separate threads for communications, attitude control and payload management allows for ease of modification, upgrade, or reconfiguration without extensive retest or recode.

The Coral bus is designed to be manufactured, assembled, integrated and tested in a production/assembly line environment. Missions that require multiple busses can be greatly benefited by this approach. The structure, at 10 percent mass fraction to the overall Coral bus mass, consists of Aluminum 6061-T6 panels (sides and bottom) that have cutouts for ease of electrical integration between the PCI-104 avionics boards and peripheral components (star tracker, reaction wheel, torque rods, etc.).

The Coral design meets the 25-year de-orbit requirements (NASA Safety Standard 1740.14 and DoD Instruction 3100.12, Sec 6.4) without the use of a dedicated de-orbit mechanism. Per Satellite Tool Kit (STK) modeling, the Coral bus is predicted to de-orbit in 21.4 years based on using a conservative drag coefficient of 2.0 and a space vehicle mass of 3.83 kg.

The CAA/SDL team offers the Coral bus implementing a technical approach that provides users with maximum payload flexibility. Comtech AeroAstro has optimized several key areas, pointing, power and volume within the system design and addressed critical areas lacking in the current CubeSat arena. These features allow our Coral design to accommodate the stringent pointing/slew requirements of electro-optical, or space situational awareness missions, and accommodate missions requiring higher payload power such as communications or SAR with no changes to the bus design. Mission and payload reconfiguration is simple, rapid and reliable with minimum logistics footprint, reducing overall program cost.

For more information, see us at www.aeroastro.com, or email us at info@aeroastro.com.