Technical Sessions

Session XI: Mission Enabling Technologies 2

Chair: Paul Graven, Microcosm, Inc.

Thursday, August 12, 2010

8:15 a.m. Switchable Antenna Polarization using Surface-Integrated Fluidic Loading Mechanisms

Sean Goldberger, Frank Drummond, Joel Barerra, Stephen Davis, Jamie Edelen, Michelle Geppert, YaShavaun Judie, Quinn Manley, Cameron Peters, Samantha Smith, Gregory Huff – Texas A&M University

ABSTRACT: Multipath wireless communication can increase system-level demands on antenna radiation behavior, impedance matching, and bandwidth requirements. Research with the Space Engineering Institute at Texas A&M University has developed a novel antenna polarization reconfiguration system using nanoparticle dispersions. Potential applications encompass space and military missions operating in harsh physical and electromagnetic surroundings, multiple input and output (MIMO) systems, and cognitive radios. This paper will discuss the design, fabrication, and reconfigurable performance of a single crossed-dipole microstrip antenna with pressure-driven and electrokinetic manipulation of nanoparticle dispersions. Appropriately positioned gaps, on the crossed dipole, manage the frequency and antenna polarization diversity. Analytical, simulated, and measured impedance, VSWR, and radiation behavior results will be provided for an S-band design. These results are extended to consider the dielectrophoretic effects on the dispersion from a low-frequency applied bias (up to 1 MHz) to change nanoparticle dispersions from random homogeneous to quasi-ordered anisotropic dispersions changing the gap loading.

8:30 a.m. The First In-Space Demonstration of a Green Propulsion System

K. Anflo, B. Crowe, M. Persson – ECAPS

ABSTRACT: This paper describes the first in-space demonstration of a “Green” propulsion system on the PRISMA main satellite. The PRISMA mission is a unique opportunity to demonstrate the High Performance Green Propulsion (HPGP) system in space, and thus take a significant step to towards its use in future space applications. The PRISMA mission objective is to perform autonomous rendezvous and formation flying (Main and Target Satellite) including homing and proximity operations. The PRISMA satellites were launched on Dnepr from Yazny in June 2010. The HPGP system is used both for providing the required delta-v for the PRISMA main satellite manoeuvres and as an experiment with the objective to demonstrate performance in space. Delta-v is nominally generated in an autonomous and combined operation of the HPGP and Hydrazine propulsion systems while the performance measurements are performed with one propulsion system at the time. PRISMA is an international technology demonstration program with Swedish Space Corporation as the Prime Contractor and major contributions from DLR, CNES and the Technical University of Copenhagen.

8:45 a.m.Proposed Encoding/Decoding Algorithm to Recover Satellite Uncompleted Received Frames

Alaa Eldin Hassan – National Authority for Remote sensing and Space Science (NARSS); C. Schlegel, Dmitry Truhachev – University of Alberta; M. Shokair, Atef Abou Elazm – Menoufiay University

ABSTRACT: In some cases, a communication session between a satellite and a ground station can be interrupted during the frame reception. Despite the fact that strong FEC (Forward Error Correction) codes such as turbo codes are used to protect frames from errors they are unable to recover the data in the case when the received frame is incomplete. As a result, incomplete frames are lost even if they contain critical mission data. In this paper, we propose a modification to turbo encoding and decoding algorithms which provides an ability to recover incompletely received data frames. The proposed modification causes a negligible rate loss and only a slight increase in encoder and decoder complexity. The proposed algorithm is based on segmentation of the information frame into sub-frames and calculation and insertion of terminations bits after each sub-frame during the encoding process. The inserted termination bits help the ground station decoder to recover the incomplete frames. This modification can be used in any turbo coding/decoding system since it can be realized as a slight adjustment to the maximum a posteriori probability (MAP) decoding algorithm (standard turbo decoder) and hence it does not require any additional hardware. The proposed algorithm has been tested on Consultative Committee for Space Data Systems (CCSDS) turbo codes of rates 1/2 and 1/3 with information frame length of 1784 bits. For incomplete frames which are 1700 bits long the modified decoder provides a 20dB performance gain over the standard turbo encoding/decoding algorithm.

9:00 a.m. Fully Integrated Solar Panel Slot Antennas for Small Satellites

Mahmoud Mahmoud, Reyhan Baktur – Utah State University; Robert Burt – Space Dynamics Laboratory

ABSTRACT: This paper presents two prototypes of integrated solar panel antennas that can potentially replace the current deployed wire type antennas used in small satellites. The antenna design is based on cavity backed slot antennas that do not require additional satellite surface area to mount the antenna or any cost for deployment. Because the antenna design is independent from solar cells, one can choose any after-market solar cells without custom fabrication. The first prototype is a circularly polarized slot antenna that is integrated on top of a printed circuit board (PCB). The PCB is a common solar panel material in small satellite industry, and the solar cells are then inter-connected on the top most layer of the PCB. The second prototype is a linearly polarized two-element array. Both the antenna and solar cell functionalities were rigorously tested and we achieved outstanding performance from both antennas and solar cells.

9:30 a.m.Optical Networking for Aerospace Systems Provisioned Through Plug-and-Play Avionics

Keith Avery, Nathaniel Francis, James Lyke – Air Force Research Laboratory; Patrick Collier – SAIC

ABSTRACT: A high performance extension of the space plug-and-play avionics (SPA) technology is described based on the addition of optical fiber interconnection. This optical SPA (“SPA-O”), due to the bandwidth potential, provides the possibility of moving unprecedented amounts of data and rendering super-computing systems rapidly in orbital platforms. By exploiting the ideas of SPA, the optical properties of SPA-O components can be added to electronic datasheets embedded within the component so that the system-at-large can discover these components and exploit them in dynamically provisionable optical networks formed on demand.

9:45 a.m. Attitude Manoeuvring Under Dynamic Path and Time Constraints for Formation Flying                    Nanosatellites

B. Johnston-Lemke, R. E. Zee – Space Flight Laboratory/University of Toronto

ABSTRACT: Large angle attitude manoeuvres are often subjected to dynamic and celestial path constraints such as maintaining ground link communication, GPS lock, or Sun avoidance while tracking various primary targets in real time. Considered in this paper is an onboard approach to maximizing the signal lock with GPS satellites with a restricted antenna field of view while tracking primary attitude targets. The proposed time optimal attitude controller does not require a priori knowledge of the target(s) and avoids the time and computational requirements of typical avoidance and random search techniques. Included in this paper are the attitude requirements to maintain GPS lock as derived from ground based and on orbit experiments as well as the proposed controller and the results of numerical simulations. This controller has been developed for the Canadian Advanced Nanosatellite eXperiment (CanX) 4 and 5 satellites currently under development at the University of Toronto’s Space Flight Laboratory. CanX-4 and CanX-5 are identical satellites that will be launched together and will make use of differential GPS measurements and a cold gas propulsion system to demonstrate autonomous sub-meter control formation flying based on differential GPS measurements.

10:00 a.m.A Self-Scrubber for FPGA-based Systems

G. Alonzo Vera , Xiaoyin Yao – Micro-RDC; Keith Avery – Air Force Research Laboratory/Space Vehicles Directorate

ABSTRACT: Scrubbing is generally used in conjunction with triple modular redundancy (TMR) to increase the reliability of FPGA systems in space borne applications. We present in this paper a scrubber solution labeled Femto, currently being developed at Micro-RDC. Femto is a RISC, 8-bit, 9-instruction microcontroller specifically designed for scrubbing memories. The self-scrubber based on Femto occupies < 600 slices and operates at 100 MHz. It has the capacity to calculate a CRC codebook of up to 1024 words on the fly and to use it to detect errors. Femto can be configured to perform blind scrubbing or readback-detect-correct type of operations. It also supports frame-based scrubbing, which allows a user to develop custom scrubbing techniques that better adapts to a specific system's requirements.

10:15 a.m.A Control Moment Gyro for Dynamic Attitude Control of Small Satellites

Craig Clark, Kevin Worrall – Clyde Space Ltd; Emre Yavuzoğlu – Turkish Aerospace Industries, Inc. (TAI)

ABSTRACT: Control Moment Gyroscopes (CMGs) are not often considered for use on small satellites and, as a result few small satellite missions have implemented CMGs as on-board actuators. There are many reasons for this, but mainly this is due the complexity of the mechanical and control system needed to implement an effective CMG, and also because off-the-shelf CMG systems are generally made for the larger satellite market. CMGs offer many advantages over reaction wheel systems. When used on a small satellite, a CMG based control system can provide the ability to perform very fast slew maneuvers, making CMGs very attractive to high resolution small satellite imaging missions.

The CMG described in this paper incorporates two motors; a Brushless DC Motor (BLDC) and a Stepper Motor. The BLDC provides an efficient means of driving the inertia disk to store the angular momentum, whilst the stepper motor provides precision gimbal control. In order to keep mass and power consumption low, both motors are controlled from a single FPGA. The FPGA runs all associated commutation, speed and position control for both motors and also provides the command and telemetry interface to the rest of the spacecraft. The resulting system is a compact, power efficient design that is ideal for small satellites.