Spacecraft Systems Engineering

Peter Fortescue, Graham Swinerd, John Stark, Peter Fortescue, Graham Swinerd, John Stark

• Publisher: Wiley
• Year: 2011
• ISBN:
  9781119978367
• Edition: 4
• Topic: Technologie et ingénierie
• Subtopic: Ingénierie de l'aéronautique et de l'astronautique

This fourth edition of the bestselling Spacecraft Systems Engineering title provides the reader with comprehensive coverage of the design of spacecraft and the implementation of space missions, across a wide spectrum of space applications and space science. The text has been thoroughly revised and updated, with each chapter authored by a recognized expert in the field. Three chapters – Ground Segment, Product Assurance and Spacecraft System Engineering – have been rewritten, and the topic of Assembly, Integration and Verification has been introduced as a new chapter, filling a gap in previous editions.

This edition addresses 'front-end system-level issues' such as environment, mission analysis and system engineering, but also progresses to a detailed examination of subsystem elements which represents the core of spacecraft design.This includes mechanical, electrical and thermal aspects, as well as propulsion and control. This quantitative treatment is supplemented by an emphasis on the interactions between elements, which deeply influences the process of spacecraft design.

Adopted on courses worldwide, Spacecraft Systems Engineering is already widely respected by students, researchers and practising engineers in the space engineering sector. It provides a valuable resource for practitioners in a wide spectrum of disciplines, including system and subsystem engineers, spacecraft equipment designers, spacecraft operators, space scientists and those involved in related sectors such as space insurance.

In summary, this is an outstanding resource for aerospace engineering students, and all those involved in the technical aspects of design and engineering in the space sector.

Chapter 1

Introduction

John P. W. Stark1, Graham G. Swinerd2 and Adrian R. L. Tatnall2

1School of Engineering and Material Science, Queen Mary, University of London

2Aeronautics and Astronautics, Faculty of Engineering and the Environment, University of Southampton

Man has only had the ability to operate spacecraft successfully since 1957, when the Russian satellite Sputnik I was launched into orbit. At the time of writing (2010) the Space Age is just over half a century old. In that time technology has made great strides, and the Apollo human expedition to the Moon and back is now a rather distant memory. In little more than five decades, unmanned explorer spacecraft have flown past all the major bodies of the Solar System, apart from the ‘dwarf planet’ Pluto—this exception will soon be remedied, however, by the ‘New Horizons’ spacecraft that is due to fly through the Pluto-Charon system in 2015. Space vehicles have landed on the Moon and Venus, and in recent years Mars has seen a veritable armada of orbiters, landers and rovers in preparation for a hoped-for future human expedition to the red planet. The Galileo Jupiter orbiter successfully deployed a probe in 1995, which ‘landed’ on the gaseous ‘surface’ of Jupiter. The Cassini/Huygens spacecraft has been a stunning success, entering orbit around Saturn in 2004, and executing a perfect landing on Titan of the European built Huygens probe in 2005. Minor bodies in the Solar System have also received the attention of mission planners. The first landing on such a body was executed by the Near Earth Asteroid Rendezvous (NEAR) Shoemaker spacecraft, when it touched down on the Eros asteroid in February 2001. This was succeeded in 2005 by the attempted sampling of material from the Itokawa asteroid by the Japanese Hayabusa spacecraft. Although the sampling operation was unsuccessful, the spacecraft is now on a return journey to Earth in the hope that some remnants of asteroid material may be found in its sealed sampling chamber. Similarly, a prime objective of the ambitious European Rosetta programme is to place a lander on a cometary body in 2014. There is also a growing awareness of the impact threat posed by near-Earth asteroids and comets, which is driving research into effective means of diverting such a body from a collision course with Earth.

Since our brief sojourn to the Moon in 1969–1972, human spaceflight has been confined to Earth orbit, with the current focus on construction and utilization of the International Space Station (ISS). The United States, Europe, Russia and Japan are all involved in this ambitious long-term programme. The ISS has been a major step for both the technology and politics of the space industry, and has been a useful exercise in learning to live and work in space—a necessary lesson for future human exploration of the Solar System. The ‘work horse’ of this activity has been the US Space Shuttle, which has been the United States' principal means of human access to orbit over almost three decades. However, 2011 sees the retirement of the Shuttle. This is a major event in NASA's space operations, and it has forced a radical rethink of the United States' human spaceflight programme. This led to the proposal of a less complex man-rated launch vehicle, Ares 1, which is part of the Constellation Programme. The objective of this programme is to produce a new human spaceflight infrastructure to allow a return of US astronauts to the Moon, and ultimately to Mars. However, the shuttle retirement coincides with a deep global financial recession, and the political commitment to the Constellation Programme appears to be very uncertain. This re-evaluation by the US will perhaps herald the reinvigoration of the drive towards the full commercialization of the space infrastructure.

There is no doubt, however, that the development of unmanned application spacecraft will continue unabated. Many countries now have the capability of putting spacecraft into orbit. Satellites have established a firm foothold as part of the infrastructure that underpins our technological society here on Earth. There is every expectation that they have much more to offer in the future.

Before the twentieth century, space travel was largely a flight of fantasy. Most authors during that time failed to understand the nature of a spacecraft's motion, and this resulted in the idea of ‘lighter-than-air’ travel for most would-be space-farers [1, 2]. At the turn of the twentieth century, however, a Russian teacher, K. E. Tsiolkovsky, laid the foundation stone for rocketry by providing insight into the nature of propulsive motion. In 1903, he published a paper in the Moscow Technical Review deriving what we now term the rocket equation, or Tsiolkovsky's equation (equation 3.20). Owing to the small circulation of this journal, the results of his work were largely unknown in the West prior to the work of Hermann Oberth, which was published in 1923.

These analyses provided an understanding of propulsive requirements, but they did not provide the technology. This eventually came, following work by R. H. Goddard in America and Wernher von Braun in Germany. The Germans demonstrated their achievements with the V-2 rocket, which they used towards the end of World War II. Their rockets were the first reliable propulsive systems, and while they were not capable of placing a vehicle into orbit, they could deliver a warhead of approximately 1000 kg over a range of 300 km. It was largely the work of these same German engineers that led to the first successful flight of Sputnik 1 on 4 October 1957, closely followed by the first American satellite, Explorer 1, on 31 January 1958.

Five decades have seen major advances in space technology. It has not always been smooth, as evidenced by the major impact that the Challenger (1986) and Columbia (2003) disasters had on the American space programme. Technological advances in many areas have, however, been achieved. Particularly notable are the developments in energy-conversion technologies, especially solar photovoltaics, fuel cells and batteries. Developments in heat-pipe technology have also occurred in the space arena, with ground-based application in the oil industry. Perhaps the most notable developments in this period, however, have been in electronic computers and software. Although these have not necessarily been driven by space technology, the new capabilities that they afford have been rapidly assimilated, and they have revolutionized the flexibility of spacecraft. In some cases they have even turned a potential mission failure into a grand success.

But the spacecraft has also presented a challenge to Man's ingenuity and understanding. Even something as fundamental as the unconstrained rotational motion of a body is now better understood as a consequence of placing a spacecraft's dynamics under close scrutiny. Man has been successful in devising designs for spacecraft that will withstand a hostile space environment, and he has found many solutions.

1.1 Payloads and Missions

Payloads and missions for spacecraft are many and varied. Some have reached the stage of being economically viable, such as satellites for communications, weather and navigation purposes. Others monitor Earth for its resources, the health of its crops and pollution. Determination of the extent and nature of global warming is only possible using the global perspective provided by satellites. Other satellites serve the scientific community of today and perhaps the layman of tomorrow by adding to Man's knowledge of the Earth's environment, the solar system and the universe.

Each of these peaceful applications is paralleled by inevitable military ones. By means of global observations, the old ‘superpowers’ acquired knowledge of military activities on the surface of the planet and the deployment of aircraft. Communication satellites serve the military user, as do weather satellites. The Global Positioning System (GPS) navigational satellite constellation is now able to provide an infantryman, sailor or fighter pilot with his location to an accuracy of about a metre. These ‘high ground’ space technologies have become an integral part of military activity in the most recent terrestrial conflicts.

Table 1.1 presents a list of payloads/missions with an attempt at placing them into categories based upon the types of trajectory they may follow. The satellites may be categorized in a number of ways such as by orbit altitude, eccentricity or inclination.

Table 1.1 Payload/mission types

Mission	Trajectory type
Communications	Geostationary for low latitudes, Molniya and Tundra for high latitudes (mainly Russian), Constellations of polar LEO satellites for global coverage
Earth resources	Polar LEO for global coverage
Weather	Polar LEO, or geostationary
Navigation	Inclined MEO for global coverage
Astronomy	LEO, HEO, GEO and ‘orbits’ around Lagrange points
Space environment	Various, including HEO
Military	Polar LEO for global coverage, but various
Space stations	LEO
Technology demonstration	Various

Note: GEO: Geostationary Earth orbit; HEO: Highly elliptical orbit; LEO: Low Earth Orbit; MEO: Medium height Earth Orbit.

It is important to note that the specific orbit adopted for a mission will have a strong impact on the design of the vehicle, as illustrated in the following paragraphs.

Consider geostationary (GEO) missions; these are characterized by the vehicle having a fixed position relative to the features of the Earth. The propulsive requirement to achieve such an orbit is large, and thus the ‘dry mass’ (exclusive of propellant) is a modest fraction of the all-up ‘wet mass’ of the vehicle. With the cost per kilogram-in-orbit being as high as it currently is—of the order of $30 000 per kilogram in geostationary orbit—it usually becomes necessary to optimize the design to achieve minimum mass, and this leads to a large number of vehicle designs, each suitable only for a narrow range of payloads and missions.

Considering the communication between the vehicle and the ground, it is evident that the large distance involved means that the received power is many orders of magnitude less than the transmitted power. The vehicle is continuously visible at its ground control station, and this enables its health to be monitored continuously and reduces the need for it to be autonomous or to have a complex data handling/storage system.

Low Earth orbit (LEO) missions are altogether different. Communication with such craft is more complex as a result of the intermittent nature of ground station passes. This resulted in the development, in the early 1980s, of a new type of spacecraft—the tracking and data relay satellite system (TDRSS)—operating in GEO to provide a link between craft in LEO and a ground centre. This development was particularly important because the Shuttle in LEO required a continuous link with the ground. More generally, the proximity of LEO satellites to the ground does make them an attractive solution for the provision of mobile communications. The power can be reduced and the time delay caused by the finite speed of electromagnetic radiation does not produce the latency problems encountered using a geostationary satellite.

The power subsystem is also notably different when comparing LEO and GEO satellites. A dominant feature is the relative period spent in sunlight and eclipse in these orbits. LEO is characterized by a high fraction of the orbit being spent in eclipse, and hence a need for substantial oversizing of the solar array to meet battery-charging requirements. In GEO, on the other hand, a long time (up to 72 min) spent in eclipse at certain times of the year leads to deep discharge requirements on the battery, although the eclipse itself is only a small fraction of the total orbit period. Additional differences in the power system are also partly due to the changing solar aspect angle to the orbit plane during the course of the year. This may be offset, however, in the case of the sun-synchronous orbit (see Section 5.4 of Chapter 5), which maintains a near-constant aspect angle—this is not normally done for the benefit of the spacecraft bus designer, but rather because it enables instruments viewing the ground to make measurements at the same local time each day.

It soon becomes clear that changes of mission parameters of almost any type have potentially large effects upon the specifications for the subsystems that comprise and supp...