Technical Sessions

Session XI: Advanced Technologies 3

Chair: Chuck Finley, Operationally Responsive Space Office

Thursday, August 13, 2009

8:30 a.m. Integrated After‐Market Solar Panel Antennas for Small Satellites

Timothy Turpin, Mahmoud Mahmoud, Reyhan Baktur – Utah State University; Cynthia Furse – University of Utah

ABSTRACT: The majority of surface area on a small satellite is taken up by solar panels for power. Integrating antennas with solar panels, would save a valuable amount of satellite surface area, and thus directly contribute to the size reduction and multi‐functionality of solar panel. Furthermore, such integration does not require deployed mechanism and therefore is cost‐friendly design.

Two types of integrations are presented in this paper. The first type is to place optically transparent antennas directly on top of after‐market solar cells. Meshed conductors with optical transparency higher than 90% are used to design antennas in this case. The second type is to utilize the area between solar cells on the solar panel to design slot antennas. The slot antennas are highly integrative and lie on the same plane with the solar cells without blocking solar energy.

The paper discusses both types of solar panel antennas that can be conveniently integrated with after‐market solar cells, providing a novel and cost‐friendly solution for small satellite system.

8:45 a.m. Multi‐Aperture Miniaturized Star Sensors, Modular Building Blocks for Small Satellite AOCS Systems

Jeroen Rotteveel, Anita Le Mair – Innovative Solutions In Space (ISIS)

ABSTRACT: Accurate attitude determination is an important enabler for micro‐ and nanosatellite missions. For remote sensing applications and formation flying missions, the attitude of the spacecraft must be known and controlled with a high accuracy. ISIS introduces a modular and scalable attitude determination system based on a multi‐aperture miniature star sensor. Based on a patented concept, the Multi‐Aperture Baffled Starsensor, the attitude sensor integrates several apertures into a single star tracker. The main advantage of this concept is that it eliminates the need for large baffles as there is a redundancy of independent apertures. Even when several apertures are obstructed, for instance by the Earth and the Sun simultaneously, the star tracker will still have apertures available with a ‘free’ field of view and will be able to determine star positions. The concept consists of a standalone sensor element for an attitude determination and control system and allows for integration, alignment, and calibration of the sensor on subsystem level rather than on spacecraft level. The system consists of an optical head that can include up to 9 miniature star cameras, and an electronics system that combines the star camera inputs and determines and outputs the spacecraft attitude vector.

9:00 a.m. Frequency Reconfiguration of a Small Array Enabled by Functionalized Dispersions of Colloidal Material

Sean Goldberger, Frank Drummond, Rachel Anderson, Joel Barrera, Amy Bolon, Stephen Davis, Jamie Edelen, Justin Marshall, Cameron Peters, David Umana, Gregory Huff – Texas A&M University

ABSTRACT: This paper will discuss the performance and adaptability of a microfluidic reconfiguration mechanism in a small array. Discussion will also include its ability to reduce system degradation resulting from complexity and physical limitations incurred from the close spatial proximity of bias/control systems on or near the antenna. Implementation of the microfluidic mechanism can reduce or mitigate the interactions between individual mechanisms within the aperture and increase the competitiveness of microfluidics over current state‐of‐the‐art. Research at Texas A&M University in conjunction with the Space Engineering Institute, has developed a novel frequency reconfiguration system for antennas using electromagnetically functionalized colloidal dispersions (EFCDs). These EFCDs are electrostatically‐stabilized dispersions of magnetodielectric colloidal nanoparticles in a low‐loss non‐aqueous fluid. As proof‐of‐concept a 1x2 array of linearly polarized microstrip patch antennas with parallel capillary structures is presented. Several theoretical considerations, models, simulated results, and measured results will be provided. The results include impedance data and radiation behavior as well as effects of the applied fields on the nanoparticles.

9:15 a.m. Rapid Development of Experimental LEON 3FT Controller Board

Sam Stratton, Dave Stevenson – Aeroflex; Michael Johnson – NASA Goddard Space Flight Center

ABSTRACT: The LEON 3FT Controller Board (LCB) is part of a NASA experiment and designed to provide control and monitoring capability of up to four commercial high performance DSP processor cards. The experiment is part of the Materials on the International Space Station Experiment (MISSE) program and is set to launch on the Space Shuttle in the November 2009 timeframe. The primary goal of this experiment is to assess in a space environment the effectiveness of radiation mitigation strategies on a commercial DSP processor.

At the heart of the LCB is the LEON 3FT microprocessor. The processor is the brains of the entire system, controlling which board gets powered on, as well as monitoring analog channels and watchdogs from each DSP board. These processes are facilitated by the use of a UT6325 RadTol Eclipse FPGA and a set of registers. The registers are memory mapped into the I/O space of the LEON 3FT. Memory resources on the LCB are in the form of 4MB of EDAC protected SRAM as well as 4MB of NVRAM. An RS‐485 interface is used for ground communication and can also be used for software uploads. The power circuits include an autonomous over‐current trip that is asserted when a DSP board exceeds the 2 amp load.

Communication between the LCB and the DSP cards is achieved by the implementation of an 8‐bit address/data bus and board select signals to indicate which of the four cards the LCB is accessing. Again, the LEON 3FT uses an FPGA register to initiate these transactions. An LVDS serial interface is also provided, though it is not being used for the current MISSE mission.

The rapid development from concept to flight delivery of the LCB posed some interesting and challenging requirements on the design team participants. The author will outline in more detail these challenges, as well as greater detail on the functionality and performance of the LCB.

9:30 a.m. Lithium‐Ion Technology: Balancing Increased System Capability with the Potential for Explosion

Jeremy Neubauer, Chris Pearson, Ka Lok Ng – ABSL Space Products

ABSTRACT: The push to increase the capability of satellites has driven significant increases in space battery performance over the past fifty years, progressing to the use of today’s state of the art technology: Lithium‐ion. To date Lithium‐ion batteries have flown on many missions and have demonstrated their tremendous potential to increase the capability of both large and small satellite technologies.

However, recent events in the consumer electronics industry have highlighted the risk of this technology when handled improperly, and several factors are currently combining that increase both the likelihood and hazard of a battery failure: the larger size of spacecraft batteries in general, the push for ever greater energy density, and the shrinking infusion period both for payload and platform technologies. This paper discusses the necessary precautions that must be made to ensure safe use of Lithium‐ion technology via the lessons learnt from a fifteen year Lithium‐ion space battery program at ABSL. This program has yielded more than fifty successful launches and the space qualification of five Lithium based COTS cell technologies without a single safety incident.

9:45 a.m.  Advanced Hardware‐In‐the‐Loop RF Testing Assures Communication System Mission Success

Steve Williams – RT Logic

ABSTRACT: Robust Radio Frequency (RF) Communication Systems (COMMS) are vital to the success of every satellite mission. But, most RF COMMS links are subject to a wide variety of signal impairments, many of which are particularly acute with small satellites. Powerful RF COMMS modeling and simulation techniques have emerged to assure the performance of these vital communications systems. Even greater assurance is possible when real‐world RF signals are directly generated by the same modeling and simulation systems, and are liberally used for component‐level and full‐system test.

For effective and full‐coverage flight COMMS and/or ground COMMS testing, RF Channel Simulators must augment traditional Test & Measurement gear such as signal generators, spectrum analyzers and oscilloscopes. RF Channel Simulators enhance flight COMMS and ground COMMS tests with signal and carrier Doppler effects, as well as range attenuation, range delay, Additive White Gaussian Noise (AWGN) and interference.

Inserted in the lab within Intermediate Frequency (IF) or RF signal paths, RF Channel Simulators create signal impairments that precisely match the RF path perturbations that will be experienced when the communications devices are actually deployed. Use of RF Channel Simulators increases mission confidence through deeper testing, minimizes design and test time, and reduces system over‐design that can occur when low‐fidelity simulations are employed.

10:00 a.m.Peak Power Tracking on a Nanosatellite Scale: The Design and Implementation of Digital Power Electronics on the SFL Generic Nanosa‐tellite Bus

Grant Bonin, Robert Zee – Space Flight Laboratory/University of Toronto; Doug Sinclair – Sinclair Interplanetary

ABSTRACT: This paper describes the design and implementation of an advanced high‐performance nanosatellite power system, with an emphasis on its battery management and peak power tracking (PPT) capabilities. This power system has been developed for the University of Toronto Institute for Aerospace Studies’ Space Flight Laboratory (UTIAS/SFL) Generic Nanosatellite Bus (GNB), which has enabled a wide variety of new space applications on a small scale. The GNB has a 20cm cubical form factor with no deployed solar arrays, making it inherently power‐limited. Consequently, the need to accommodate relatively high powered payloads for multi‐year missions has dictated the need for maximum utilization of solar power, and with maximum efficiency. To accomplish this, the GNB power system implements an unconventional parallel‐regulated Direct Energy Transfer (DET) architecture with PPT functionality using a single bi‐directional digital switch‐mode power converter per battery, which also permits multiple redundant batteries as required. The trade space between different power system architectures is explored for missions of this class, and a parallel‐regulated DET bus is shown to be the regulated topology of highest efficiency, advantageous when the range of solar array and bus voltages for a spacecraft are closely matched. The primary regulation device—referred to as a Battery Charge/Discharge Regulator (BCDR)—is described, and the advantages of its design are discussed. Finally, a new variant on conventional peak power tracking—referred to as Peak Current Tracking (PCT)—is discussed. The PCT algorithm is implemented using spacecraft BCDRs, and works to maximize battery charge current as well as to minimize battery discharge current. PCT operates during both sunlight and eclipse, and interrogates the entire system to determine the optimal voltage for battery charge management, which is an emergent property of the technique. PCT is shown to reduce battery depth‐of‐discharge by almost 20% compared to systems with fixed system voltages. The GNB power system design represents a significant advance over what has previously been implemented on a nanospacecraft scale, further enabling advanced missions on a power‐limited platform.

10:15 a.m.FPGA‐Based MSK DS‐SS Modulator for Digital Satellite Communications

Ahmed Maghawry Ibrahim – National Authority for Remote Sensing & Space Science (NARSS); Esam Eldiwany – Electronics Research Institute (ERI)

ABSTRACT: Minimum shift keying (MSK) modulation fits in satellite communications links due to its superior performance in providing low sidelobe spectral energy and reduced sidelobe regrowth. This paper investigates design, implementation and testing of MSK modulator on FPGA. Direct sequence spread spectrum (DS‐SS) modulation is also considered because it provides low power spectral density and allows accurate ranging of the satellite. Direct digital synthesis (DDS) is employed to generate the modulated signal. A novel technique for digital implementation of type II MSK modulator is shown. The MSK modulator is designed and simulated using VHDL language and then implemented on Xilinx XtremeDSP Development Kit Pro (which contains Xilinx FPGA XC2VP30‐4FF1152 and Analog Devices AD9772A digital to analog converters (DAC)). Evaluation of the implemented modulator is done by comparing the resultant MSK modulation spectrum and the modulated waveform to the theoretical ones, which showed good performance.

Alternate  MEMS in Space – A New Technology Advancing from Flight Experiment to Proven COTS Product

Andrew Carrel – Surrey Satellite Technology Ltd./Surrey Space Centre; Paul Alderton – Atlantic Inertial Systems

ABSTRACT: Over the past 25 years, SSTL has shown that Small Satellites are an effective alternative to larger missions. To remain competitive, however, these spacecraft need to fit more and better functionality into the same low mass, low volume envelopes that allow them to be launched at low cost. Micro‐electrical‐mechanical systems (MEMS) is an advanced technology that addresses this need and an area that is presently developing rapidly.

Atlantic Inertial Systems’ RRS01 MEMS rate sensor was developed for terrestrial applications but has since been found to be suitable for space flight. This compact, light‐weight unit has already been shown to be very robust in military applications and has a long lifetime owing to the design of resonating silicon ring at the heart of the sensor. Silicon‐wafer mass production techniques are employed, bringing all the benefits of production repeatability as well as low cost and a short lead time.

SSTL has developed an inertial sensor module, incorporating this technology that will fly on 5 missions over the next few years. This product builds on the results from 3 previous missions where SSTL has flown MEMS rate sensors, including the RRS01. NigeriaSat‐2 uses this inertial sensor to supplement star tracker measurements in attitude estimation, while de‐tumbling and Sun‐acquisition is the application on the Kanopus platforms.

This paper describes the RRS01 MEMS rate sensor and its use in SSTL’s inertial sensor module. Results will be presented from flight experimentation and environmental testing that has been undertaken by SSTL to qualify this technology for use on its customers’ satellite platforms as well as its own. The application of this MEMS technology to various missions is also discussed.

Alternate  A Common Ground Experiment Testbed for Synthetic Mission Demonstration of Small Satellites

Xiaoqian Chen, Wen Yao, Yiyong Huang, Yong Zhao – National University of Defense Technology

ABSTRACT: This paper introduces the development of a ground experiment testbed for synthetic mission demonstration of small satellites in National University of Defense Technology (NUDT). This testbed consists of five parts: test platform, small satellite simulator, monitoring and control system, data collecting and simulation system, and displaying system. It can simulate small satellite motion with two or three degree of freedom by means of smooth granite platform and air bearing system, and support hardware‐in‐the‐loop simulation. This experiment testbed has been applied to several multi‐satellite mission demonstration projects, including the formation flying of three small satellites, the rendezvous and docking of two small satellites, the on‐orbit refueling demonstration, etc. The experiment processes as well as the results of these experiments are given in this paper.