All 2007 Content

Modular Shielded Solar Panels Made using Low Cost Lamination Process

Theodore Stern — Thu, 16 Aug 2007 11:00:00 PDT

A modular, laminated solar panel approach has been demonstrated which uses high efficiency cells and allows application to a variety of smallsat footprints without customizing each application. The module design includes a contiguous integral shield which protects the solar cells more effectively from a variety of space environments, and also provides electromagnetic cleanliness to protect sensitive instruments from solar array generated EMI. The laminated approach also provides significant cost reduction by incorporating self-tooling and reducing the number of steps and processes needed to assemble a solar panel from individual cells. Modularity leads to standardization, which allows process controls and inherently improved reliability. A number of alternative cell and module sizing approaches were considered to meet the needs of smallsats which often have small and discontinuous surface areas available for solar cell strings. The modular laminated solar panel provides a means of obtaining reliable, efficient panels for smallsats at an acceptable cost.

Wide Coverage Antennas

Jan Zackrisson — Wed, 15 Aug 2007 14:45:00 PDT

Small satellites require small and lightweight antennas for telemetry and command function as well as for downlinking of data. We have during the last thirty years developed a large suite of wide coverage antennas. The basic radiator designs used are quadrifilar helices, waveguides, horns and patch excited cups (PEC) depending on frequency range, coverage requirements and application. The antenna designs range from L-band up to Ka-band frequencies. Typical coverages for the antennas are from low gain hemispherical, isoflux, fill-in, toroidal to medium gain, global and semiglobal coverage antennas. The paper gives a brief overview of the antenna family and a selection of recently developed and interesting antennas is presented more in detail. L-band antennas have been developed for satellite-born GPS receivers and for earth observation satellite downlinks. Two recently developed GPS antennas are presented together with a complementary LNA. One is a helix antenna, an antenna type of which we have a hughe experience, the other a PEC antenna. Several PEC antennas have been designed through the years. This radiator type can be used either as a complementary fill-in antenna or as a free-standing medium-gain antenna for telemetry and command. Three S-band antenna developments are presented. An X-band helix antenna has been developed for downlinking of data from LEO satellites. This antenna has an isoflux coverage. It is a compact and light-weight design. The X-band helix antenna and some ongoing and future developments are presented.

Spaceborne Fiber-Optic Data Bus: A Small Satellite Perspective

Dustin Rider et al. — Thu, 16 Aug 2007 12:00:00 PDT

Small-satellite system developers are poised to benefit from yet another technology that was developed with large satellites in mind: standards-based, broadband, on-board payload data networks. Large and small remote-sensing satellite payloads are continuing to advance to higher data rates thereby significantly increasing the demands on on-board networks. The networked satellite payloads include combinations of components commonly found on small satellites: sensors, processors, formatters, storage devices (recorders), broadband downlinks and payload controllers. An effective data-handling network for either type of satellite must support real-time data, must be fault tolerant and must be able to withstand the rigorous conditions of launch as well as the space environment. The Space-borne Fiber Optic Data Bus (SFODB) is the next generation in on-board data-handling networks. Designed specifically to support real-time broadband payload data with precise deterministic latency, it will do for high-speed payloads and small satellites what SAE 1553 has done for on-board command and telemetry systems. That is, SFODB will significantly reduce the cost and time of payload development, integration and testing through interface standardization. The SFODB network is also highly reliable, fault tolerant, and capable of withstanding the rigors of launch and space. SFODB achieves this operational and environmental performance while providing the small size, light weight, and low power necessary for small-satellite applications. SFODB utilizes fiber-optic components for subsystem interconnect, eliminating the need for cable-to-cable and box-to-box EMI mitigation. This paper will describe the SFODB architecture and its benefits for small satellites; the current set of flight transmitters, receivers and protocol ASICs that have been developed; the Development & Evaluation System; and planned component developments by DoD, NASA, and industry organizations.

Probe Bus Avionics Unit Development and Validation

Bob Kraeuter et al. — Thu, 16 Aug 2007 11:45:00 PDT

The THEMIS project, a NASA MIDEX program managed by the University of California at Berkeley, was launched in February 2007 and was the first NASA mission to launch five science satellites simultaneously. The low power requirements and tight volume constraints of the mission were the major drivers with the design of the Bus Avionics Unit. The Bus Avionics Unit performs the functions of a primary Bus computer, Communication I/O interface, and Power Control Electronics for the satellite. It consists of five modules, consumes less than 6.4 watts, and weighs only 2.8 kg. This optimized design was a major enabler for this mission due to its compact design and low power consumption.

Deployable Reflectors for Small Satellites

Rory Barrett et al. — Thu, 16 Aug 2007 11:30:00 PDT

A key limitation for future Small Satellite communications and radar missions will be available antenna reflector aperture. Two types of reflectors are dominant for satellite RF systems today, rigid, single-piece reflectors and deployable mesh reflectors. Single-piece reflectors are limited to the aperture that fits inside a launch vehicle without packaging the reflective surface. Mesh reflectors have become the workhorse of the deployable reflector market, however these reflectors are expensive because they require complex mechanisms and have substantial labor cost for fabrication. The recurring cost for a 4m mesh reflector of sufficient surface precision for a radar mission is on the order $10M. This historically high cost for deployable reflectors will limit small satellites to missions and performance that can be achieved with the relatively small aperture of a single-piece reflector unless a low-cost deployable reflector can be developed. This paper will discuss a deployable solid surface reflector that can be packaged into small, low-cost launch vehicles, such as the Taurus and Falcon 1e, while also minimizing cost with a simple, low-part-count design. This technology is being developed by Composite Technology Development (CTD) using TEMBO® Elastic Memory Composites (EMC).

Autonomous Distributed LQR/APF Control Algorithm for Multiple Small Spacecraft during Simultaneous Close Proximity Operations

Shawn McCamish et al. — Thu, 16 Aug 2007 11:15:00 PDT

An autonomous distributed LQR/APF control algorithm for multiple small spacecraft during simultaneous close proximity operations has been developed. This research contributes to the control of multiple small spacecraft for emerging operation, which may include inspection, assembly, or servicing. A control algorithm is proposed which combines the control effort efficiency of the Linear Quadratic Regulator (LQR) and the robust collision avoidance capability of the Artificial Potential Function (APF) methods. The LQR control effort serves as the attractive force toward goal positions, while APF-based repulsive functions provide collision avoidance for both fixed and moving obstacles. Refinement of both the APF and LQR control algorithms to small spacecraft applications offered insight and enhancement of the resulting control algorithm. Comprehensive performance evaluation of the multiple small spacecraft LQR/APF control algorithm is conducted for simultaneous close proximity maneuvers, such as convergence, rally, rendezvous, and docking maneuvers. These simulations show the developed LQR/APF control algorithm to be both robust and efficient based on the primary metrics of maneuver duration and required vΔ. Promising simulation results are presented for simultaneous multiple small spacecraft gathering, rendezvous, and docking maneuvers.

A Simple Multi-Mission Flight Control Software for CubeSAT

Warren Soh — Thu, 16 Aug 2007 11:00:00 PDT

One of the challenges to date for operational spacecrafts is to satisfy high attitude pointing accuracy missions using picosatellites. This is due to the limitations of putting a capable spacecraft attitude control subsystem into an extremely small volume. To overcome this design constraint, Micro Electrical Mechanical subsystem (MEMS) for attitude sensors and actuators are used. However MEMS are still limited in accuracy and performance compared to conventional sensors and actuators. Given these hardware limitations, the trade off is to increase the software capabilities of the Flight Control Software (FCS) without compromising on a simple architecture concept. Astronautic Technology Sdn. Bhd. (ATSB)™ is currently developing a 10x10x30cm3 CubeSat capable of meeting missions requiring spinning or full three axis stabilization. The Attitude Determination and Control (ADCS) suite consist of a MEMS 3-axis magnetometer, three 1-axis gyroscopes, coarse sun sensing capabilities, magnetic torque coils, a pitch actuator and the well known 8051 microprocessor housing the FCS. The 8051 communicates with the master MSP430 onboard computer via a Serial Peripheral Interface (SPI). An alpha version of the FCS was developed and tested on an 8051 board. The FCS was compiled using a commercial Integrated Development Environment (IDE) and loaded directly onto the 64KB on-chip flash. The software consist of a single axis Spin control law for regulating the spin rate on any predefined axis using only magnetic torque coils. A single axis Proportional Derivative (PD) control law was also developed to manage 3-axis slew maneuvers using a mini reaction wheel and magnetic torque coils. The 8051 board was linked via RS232 to a test PC running the full spacecraft orbit and attitude simulation in real-time, i.e. Hardware-in-the-Loop (HIL). The FCS was able to detumble the CubeSat, bring it to the designed pitch spin axis, achieve 3-axis stabilization and perform 3-axis maneuvers. This simple setup allows the FCS to be designed, debugged and performance tested quickly. The FCS has been validated to meet CubeSat’s current spinning and limited 3-axis pointing mission requirements.

Linux and the Spacecraft Flight Software Environment

Edward Birrane et al. — Thu, 16 Aug 2007 10:45:00 PDT

Flight software development must evolve as the operational characteristics of spacecraft evolve. Flight development typically makes use of a monolithic architecture comprised of custom-built, tightly coupled software. This dense coupling precludes the development agility desired by small spacecraft software efforts. Specifically, mission requirements are becoming aligned with re-use centered, highly decoupled, distributed architectures otherwise popular in desktop and web development. To meet the engineering challenge of matching the needs of these missions, the software environment must be modernized and the software architecture decoupled. The use of Linux in a flight environment promises to fill this need while significantly lowering the barrier of entry for new developers, especially in the university setting. To assess this promise, a team of flight software researchers at The Johns Hopkins University Applied Physics Laboratory (JHU/APL) have completed a study of the impact of real-time Linux in a real-world embedded environment. This study assessed the impacts of Linux on the spacecraft software development environment and explored the new types of software architectures enabled by that environment. At the end of the study, the team reached conclusions regarding the value of pursuing Linux in a flight environment.

The Use of Carrier Grade Linux in Space

Kevin Scharpf et al. — Thu, 16 Aug 2007 10:30:00 PDT

The telecommunications industry is embracing Linux as a means of providing high-availability, high-reliability systems. Realizing that proprietary systems have tremendous development and support costs, the push for commercial-off-the-shelf solutions that provide greater than 5-Nines reliability (no more than 5 minutes of downtime/ year) is a major industry focus. The carrier grade efforts encapsulate an entire ecosystem of hardware standards for interconnection, monitoring and control as well as the software to support it. This paper examines the current state of the art in carrier grade Linux software solutions, such as those put forth by standards organizations like the Linux Foundation and the Service Availability Forum, and identify those standards and approaches that have applicability in satellite systems.

Model-Based Anomaly Management for Small Spacecraft Missions

Christopher Kitts et al. — Thu, 16 Aug 2007 10:15:00 PDT

Space missions produce value through the production of mission data products and services. In doing so, however, significant resources are expended in order to maintain system health and to manage anomalies as they occur. These tasks are costly in terms of the expertise, personnel, and time required to detect, diagnose and resolve problems. Our recent work in model-based reasoning (MBR) techniques has demonstrated the applicability of this technology to the small satellite domain. MBR uses fundamental design knowledge of a system in order to compute reasoning conjectures relating to the existence of symptoms, diagnosis estimates, and resolution control actions. In doing so, it provides a systematic and efficient framework for automated reasoning, which in turn can dramatically accelerate the analysis of anomalies with significantly improved results. In this paper, we describe the MBR approach to anomaly management and review our theoretical and algorithmic contributions to this field. We outline our software toolboxes that implement these algorithms, and we highlight the tools that are being developed to apply this software to real space systems. Finally, we review results of using this reasoning system for several small satellite missions, ranging from the student-built Sapphire microsatellite to the NASA GeneSat-1 spacecraft.