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2012 | Buch

Introduction Kapitel lesen Erstes Kapitel lesen

Onboard Computers, Onboard Software and Satellite Operations

An Introduction

verfasst von: Jens Eickhoff

Verlag: Springer Berlin Heidelberg

Buchreihe : Springer Aerospace Technology

Enthalten in: Springer Professional "Wirtschaft+Technik" , Springer Professional "Technik"

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SUCHEN

Über dieses Buch

This book is intended as a system engineer's compendium, explaining the dependencies and technical interactions between the onboard computer hardware, the onboard software and the spacecraft operations from ground. After a brief introduction on the subsequent development in all three fields over the spacecraft engineering phases each of the main topis is treated in depth in a separate part.

The features of today’s onboard computers are explained at hand of their historic evolution over the decades from the early days of spaceflight up to today. Latest system-on-chip processor architectures are treated as well as all onboard computer major components.

After the onboard computer hardware the corresponding software is treated in a separate part. Both the software static architecture as well as the dynamic architecture are covered, and development technologies as well as software verification approaches are included.

Following these two parts on the onboard architecture, the last part covers the concepts of spacecraft operations from ground. This includes the nominal operations concepts, the redundancy concept and the topic of failure detection, isolation and recovery.

The baseline examples in the book are taken from the domain of satellites and deep space probes. The principles and many cited standards on spacecraft commanding, hardware and software however also apply to other space applications like launchers. The book is equally applicable for students as well for system engineers in space industry.

Inhaltsverzeichnis

Frontmatter

Context

Frontmatter
Introduction
Abstract
Although the payloads of a satellite such as radar or optical instruments are the principle performance driver for a spacecraft, the platform control functionality plays a significant role in mission efficiency. Considering key characteristics like required payload data geolocation precision of today’s Earth observation missions, the requirements towards the satellite platform control functionality are even more continuously increasing. The same trend can be detected for specific missions like Earth gravity field measurements, for deep space missions and for latest concepts on Earth observation from geostationary orbit positions.
The platform control functionality is centrally driven by the functionality included in the onboard software, (OBSW), and the operational flexibility from ground – being based on onboard software functions and features. The performance of the onboard software itself is driven respectively limited by the performance of the available onboard computer, (OBC), hardware. Thus the chain of spacecraft operations from ground, complemented by the OBSW and controlling platform and payload equipment via the OBC hardware is the key system engineering challenge.
Jens Eickhoff
Mission / Spacecraft Analysis and Design
Phases and Tasks in Spacecraft Development
The following figure shows the phase breakdown of spacecraft development. Listed in addition are also the main tasks to be performed within each phase. Figure 2.2 depicts additionally the prescribed review milestones according to ECSS-E-M30A.
Jens Eickhoff

Onboard Computers

Frontmatter
Historic Introduction to Onboard Computers
Abstract
This chapter gives a brief overview of the historic development of onboard computers since the early days of the Space Age. It is not intended as a complete compilation of all missions and their computer equipment, but targets for understanding the major milestones on the way to today’s implementations concerning both OBC hardware and OBSW. Both human space missions as well as unmanned deep space probes including satellite missions are treated respectively.
Jens Eickhoff
Onboard Computer Main Elements
Abstract
Figure 1.2 and in more detail figure 4.3 show the embedding of an OBC into the overall spacecraft avionics system. The OBC is connected to the transponders for interfacing with the ground, has bus interfaces connecting it to intelligent spacecraft control units and to the “Remote Interface Unit”, (RIU) – in figure 4.3 called “I/O Board” – and finally the OBC has interfaces to dedicated payload computers or controllers. The RIU couples the OBC to all spacecraft equipment which does not provide a high level data bus interface. The following figures show examples of real OBCs to give an impression on state of the art machines (both ERC32 based). The CryoSat OBC in figure 4.1 – cabled in the test bench – is an engineering model.
Jens Eickhoff
OBC Mechanical Design
Abstract
The mechanical design of an OBC in the first place seems a rather simple task compared to the electronics. However it has to fulfill a number of non trivial requirements and may not be underestimated. Not only the interconnection between OBC PCBs and OBC housing but also the entire assembly of the OBC has to withstand
  • sine vibration and shock loads during launch and
  • permanent temperature cycles (and resulting mechanical implications) in orbit.
First of all the chips are mounted with according soldering connections onto the boards. The most common designs used are “Surface Mounted Devices”, (SMD), or chip implementation as “Ball Grid Array”, (BGA), assemblies respectively.
Jens Eickhoff
OBC Development
OBC Model Philosophy
OBC models differ from mission to mission. In the telecom satellite domain the highest level of standardization can be achieved since the platforms of such S/C are really series products concerning their platform, equipped with more or less transponders and positioned at different geostationary longitudes.
Jens Eickhoff
Special Onboard Computers
Abstract
Inside a satellite the central OBC is usually not the only computer. Besides computers in instruments there are typical AOCS equipment components which include considerable computational power. The most obvious components are navigation receivers for GPS, Galileo and / or GLONASS. Another class of equipment requiring significant CPU performance are star trackers. Modern star trackers are equipped with their own ERC32 or even LEON processor for fast star map identification and quaternion computation. These units however are very specific electronic equipment.
Jens Eickhoff

Onboard Software

Frontmatter
Onboard Software Static Architecture
Onboard Software Functions
Already in the introduction to chapter 7 it was explained that more S/C onboard units than just the central OBC are in fact computers. And obviously they contain and need onboard software for operation. Besides the computers cited in chapter 7 quite a significant number of microcontrollers are hidden in intelligent sensor and actuator units which including their own embedded software. Typical components providing functions achieved in software are
  • obviously the S/C platform central OBCs,
  • instrument / payload control computers and payload data processors (image compression units etc.),
  • the aforementioned Memory Management and Formatting Units,
  • Power Control and Distribution Units,
  • and complex AOCS sensors and actuators such as
    • the previously mentioned star trackers,
    • GPS / Galileo / GLONASS receivers,
    • other position sensors such as DORIS receivers,
    • as well as fiber-optic gyros and
    • as well as fiber-optic gyros and
    • intelligently controlled reaction wheels.
Jens Eickhoff
Onboard Software Dynamic Architecture
Abstract
For all those OBSW building blocks which were presented in the previous chapter the dynamic architecture has to be developed in a further design step. This comprises the detailed elaboration and design of
  • the internal scheduling of all RTOS threads which encapsulate the presented building blocks,
  • the channel acquisition scheduling,
  • FDIR handling,
  • processing of Onboard Control Procedures and the
  • Service Interface data supply.
These topics shall be addressed subsequently in the following sections.
Jens Eickhoff
Onboard Software Development
Abstract
Onboard Software development is a very complex task which by far is not only difficult due to code implementation challenges but it also implies a lot of spacecraft systems engineering effort beforehand. The entire OBSW development comprises the steps:
  • Software functional analysis
  • Software requirements definition
  • Software design
  • Software implementation and coding
  • Software verification and testing
Each of these topics is worth being addressed separately and is worth being treated in an individual chapter below.
Jens Eickhoff
OBSW Development Process and Standards
Software Engineering Standards – Overview
The goal of software development processes and software coding and development standards is to achieve a sophisticated software design quality with respect to maintainability and a high SW operational reliability under all nominal and system failure conditions. For satellite OBSW it has to be considered in addition that the satellite design typically is only single failure tolerant and that the satellite cannot be contacted again without running OBSW – except for the limited scope controllable via High Priority Commands.
Jens Eickhoff

Satellite Operations

Frontmatter
Mission Types and Operations Goals
Abstract
S/C Operations is the domain of controlling a S/C from ground “to perform its work” in orbit or for deep space probes during target approaches – under nominal and failure recovery conditions respectively. For enabling this – besides a suitable ground infrastructure – a suitable operations concept for has to be engineered and according functionality has to be designed and implemented on board.
Jens Eickhoff
The Spacecraft Operability Concept
Abstract
The spacecraft operability concept, which will be explained in this chapter, covers diverse engineering topics such as the S/C modes, system autonomy and the like. They have already to be considered during S/C system conceptualization and have to be refined subsequently over the development phases – as was already expressed. And obviously these topics have to be treated during OBSW requirements definition, OBSW design and testing. However since these topics become fully visible not before the start of S/C operations tests and since these topics are only partly covered by OBC hardware or OBSW, they are treated in this part IV of the book in a consolidated manner.
Jens Eickhoff
Mission Operations Infrastructure
The Flight Operations Infrastructure
The missions operations infrastructure shall be explained by redirecting the reader first to figure 13.8 of the S/C ground segment infrastructure which depicts the interconnections of FOC, PGS, ground communications system and the antenna ground stations. Key element in the FOC is the “Mission Control System”, (MCS), for the S/C platform. An Example of such a system – the ESA SCOS 2000 – already was presented in figures 13.10 and 13.11.
The PGS is targeted for download of payload data from the S/C and it hosts the infrastructure and team for mission product data processing over the diverse levels. The PGS – ‘̀PDGS” in ESOC terminology – furthermore is responsible for mission product archiving and mission product distribution to customers or into the public domain.
Jens Eickhoff
Bringing a Satellite into Operation
Mission Operations Preparation
For the mission operations team it is an essential task to familiarize oneself with the ground segment infrastructure, the Mission Control System, its control consoles, databases etc. The ground operations team must be in the position to exercise all nominal and contingency operations for LEOP phase, the commissioning phase and the routine operations phase. Satellites are usually operated in two shifts per day. The A or prime team is the one which has already participated in the System Validation Tests and in verification of the S/C Flight Procedures. This team handles the critical operations sequences. The B or secondary team is subsequently trained up. This can comprise less experienced operations engineers or operations experts from other missions.
Jens Eickhoff
Backmatter
Metadaten
Titel
Onboard Computers, Onboard Software and Satellite Operations
verfasst von
Jens Eickhoff
Copyright-Jahr
2012
Verlag
Springer Berlin Heidelberg
Electronic ISBN
978-3-642-25170-2
Print ISBN
978-3-642-25169-6
DOI
https://doi.org/10.1007/978-3-642-25170-2

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