Buddy J. Walls

Constellations, clusters, and communication technology: Expanding small satellite access to space

The trend toward small-sized spacecraft continues in government applications and is even increasing in commercial space endeavors that are funded by venture capital. Small spacecraft, including nanosatellites, microsatellites, and small satellites (smallsats), are an attractive alternative to traditional, larger spacecraft due to reduced development costs, decreased launch costs, and increased launch opportunities. A significant disadvantage, however, of a small spacecraft is its reduced or limited capabilities. The physical size of the small spacecraft reduces the size of the payload and/or the number of payloads that it can host, its propulsion capabilities, and its power. Small spacecraft are most commonly used in low Earth orbit, limiting the number of observation opportunities for a particular area of the Earth or space and the number of ground station downlink opportunities for stored data. These constraints affect the complexity and types of applications that small spacecraft can serve. Using multiple spacecraft that work together can overcome many of these limitations and expand the utility of small spacecraft. Two concepts for cooperative groups of spacecraft are constellations and clusters. A key technical challenge for small spacecraft, constellations, and clusters is communication of data. Communication challenges exist for accommodating varying numbers of users, serving high user densities in a given geographical area, and providing a consistent quality of service for different types of applications (e.g., Internet access, voice communication, machine-to-machine). This paper explores concepts for emerging communication technologies for space-ground and inter-satellite communication, while citing examples of existing and new constellation and cluster concepts. Several aspects of the communication systems are examined in terms of frequency bands, data rates, multiple access methods, and accommodation on spacecraft.

Avionics of the Cyclone Global Navigation Satellite System (CYGNSS) microsat constellation

The Cyclone Global Navigation Satellite System (CYGNSS), which was recently selected as the Earth Venture-2 investigation by NASAs Earth Science System Pathfinder (ESSP) Program, measures the ocean surface wind field with unprecedented temporal resolution and spatial coverage, under all precipitating conditions, and over the full dynamic range of wind speeds experienced in a tropical cyclone (TC). The CYGNSS flight segment consists of 8 microsatellite-class observatories, which represent SwRIs first spacecraft bus design, installed on a Deployment Module for launch. They are identical in design but provide their own individual contribution to the CYGNSS science data set. Subsystems include the Attitude Determination and Control System (ADCS), the Communication and Data Subsystem (CDS), the Electrical Power Supply (EPS), and the Structure, Mechanisms, and Thermal Subsystem (SMT). This paper will present an overview of the mission and the avionics, including the ADCS, CDS, and EPS, in detail. Specifically, we will detail how off-the-shelf components can be utilized to do ADCS and will highlight how SwRIs existing avionics solutions will be adapted to meet the requirements and cost constraints of microsat applications. Avionics electronics provided by SwRI include a command and data handling computer, a transceiver radio, a low voltage power supply (LVPS), and a peak power tracker (PPT).

A non-broadcast address resolution protocol for SpaceWire networks

SpaceWire is a switched network designed for space environments. To support the Internet protocol (IP) and other high level network protocols, SpaceWire requires a method for mapping the physical interface addresses to global network protocol addresses. Standard address resolution protocol (ARP) cannot be used because SpaceWire does not have a broadcast mechanism. This paper describes a non-broadcast SpaceWire ARP (SW-ARP) that supports any higher network protocol, including IPv4, IPv6, and the CCSDS SCPS-NP address family. Our protocol includes forward and reverses ARP mappings, and is applicable to all devices that conform to the SpaceWire standard specification. SW-ARP can be implemented in node software drivers and requires no changes to the interface hardware, SpaceWire routing switches, or the SpaceWire standard specification

CYGNSS command and data subsystem and electrical power subsystem phase A and B developments

The Cyclone Global Navigation Satellite System (CYGNSS), which was selected as the Earth Venture-2 investigation by NASAs Earth Science System Pathfinder (ESSP) Program, measures the ocean surface wind field with unprecedented temporal resolution and spatial coverage, under all precipitating conditions, and over the full dynamic range of wind speeds experienced in a tropical cyclone (TC). The CYGNSS flight segment consists of 8 microsatellite-class observatories, which represent SwRIs first spacecraft bus design, installed on a Deployment Module for launch. The microsatellites (microsats) are identical in design but provide their own individual contribution to the CYGNSS science data set. Within the first year of the CYGNSS program (Phase A and B), the design has been analyzed, vetted, and reviewed which culminated in a succession of updates and design improvements. This paper will discuss relevant updates to the electrical systems of the microsat, specifically the command and data subsystem (CDS) and the electrical power subsystem (EPS). For the CDS, more detailed analysis of the communication link and maturation of the transceiver module design are presented. The link budget was reviewed by the team and verified via simulation. The transceiver module has moved to a dedicated box consisting of a radio frequency (RF) board and a digital signal processing (DSP) board. For the EPS, a detailed power analysis of the mission has led to an update in the solar array configuration. The details of the power analysis, which is performed in STK and Matlab, are presented.

A hybrid PCI/VME architecture for space

Southwest Research Institute has developed a hybrid space system architecture incorporating both the VME and PCI buses. The combined architecture allows the incorporation of heritage space qualified VME modules with new high performance PCI modules, reducing development cost and providing risk mitigation at the system level. The core of the hybrid architecture is the SwRI PCI to VME Bridge (PVB), a high performance interface between the two buses. The PVB was initially prototyped using standard commercial FPGA technology, then subsequently migrated to radiation tolerant implementation, with the ultimate goal of a radiation hardened ASIC in Q4-2001.

Enabling fractionated spacecraft communications using F6WICS

Southwest Research Institute® (SwRI®) has designed a wireless transceiver to provide inter-satellite communications as part of the Defense Advanced Research Projects Agency (DARPA) System F6 program. System F6 (Future, Fast, Flexible, Fractionated, Free-Flying Spacecraft United by Information Exchange) seeks to demonstrate the feasibility and benefits of a satellite architecture wherein the functionality of a traditional “monolithic” spacecraft is delivered by a cluster of wirelessly-interconnected modules capable of sharing their resources and utilizing resources found elsewhere in the cluster. SwRIs System F6 Wireless Inter-module Communication System (F6WICS) provides the data link and physical layers of the network stack that are specifically designed to meet the needs of fractionated space missions. F6WICS provides deterministic, real-time media access mechanisms that make efficient use of limited communications bandwidth over a wide range of spacecraft separation distances and network populations. The data link protocol is highly robust to module failure. The physical layer waveform provides robust communication, precision time transfer throughout the network, and continuous estimation of distance between spacecraft for use in navigation. The views expressed are those of the author and do not reflect the official policy or position of the Department of Defense or the U.S. Government. Distribution Statement “A”: Approved for Public Release, Distribution Unlimited.

Evolution of digital signal processing based spacecraft computing solutions

The ever-increasing information processing needs and data complexity of space exploration has motivated the constant development of higher speed DSP processor modules. These changes and the need to maximize the science data gathered and returned from satellite instruments has led to the development of a line of space qualified, DSP based spacecraft computers (DSP modules) at Southwest Research Institute. The DSP module family (SC-DSP) established at Southwest Research Institute (SwRI) forms an integral part of SwRIs SC-9, VME based, command and data handling systems. Included in the SC-DSP line are the space proven TMS320C30 based, SC-7 module, several module variants of the RTX2010 processor, and a radiation tolerant version of the Analog Devices 21020 in the newest SC-21020 DSP module. SwRIs newest module (SC-21020) was developed to provide superior data handling functionality, while maintaining support for critical spacecraft control functions. The SC-21020 spacecraft computer utilizes these features coupled with high performance radiation hardened memories and the space proven VME bus. All together, the SC-DSP spacecraft computers have been space proven and used on several NASA and other missions. This paper addresses the evolution of SwRIs family of DSP based spacecraft computers, including the next generation of modules. Emphasis is placed on the advantages, tradeoffs, and applicability of high performance DSP spacecraft computers for space exploration. The performance and roadmap of the entire SC-DSP line is discussed in detail.

Leveraging flight heritage to new compactPCI space systems: a fusion of architectures

The advent of NASA-JPLs X2000 architecture has brought compactPCI (cPCI) to the forefront as the system bus of choice for space data processing. This paper presents a hybrid architecture allowing the inclusion of new, high performance cPCI modules with heritage VME-based modules. The hybrid system yields a cost-effective, performance optimized processing solution for space.

Leveraging flight heritage to new CompactPCI space systems: a fusion of architectures

The advent of NASA-JPLs X2000 architecture has brought compactPCI (cPCI) to the forefront as the system bus of choice for space data processing. This paper presents a hybrid architecture allowing the inclusion of new, high performance cPCI modules with heritage VME-based modules. The hybrid system yields a cost-effective, performance optimized processing solution for space.The advent of NASA-JPLs X2000 architecture has brought CompactPCI (cPCI) to the forefront as the system bus of choice for space data processing. This paper presents a hybrid architecture allowing the inclusion of new, high performance cPCI modules with heritage VME based modules. The hybrid system yields a cost effective, performance optimized processing solution for space.

A practical application of a systems engineering process in space avionics design and development

The ongoing development of avionics to support the Spectral Imaging of the Coronal Environment (SPICE) Electronics Box (SEB) program as part of the European Space Agencys (ESA) Solar Orbiter program has presented numerous design and verification challenges. A unique challenge in the development of the SPICE electronics is the validation of the system due to its multi-national elements and their concurrent development timelines. The practical application of a systems engineering process has reduced and mitigated these risks through requirements flow-down to subsystems and a comprehensive verification program to ensure all specifications are met. This paper discusses the lessons learned from requirements development and verification and validation activities. These lessons have resulted in a substantial risk reduction as the program has moved forward with flight model design development and testing activities.