Manned Spacecraft Design Principles

634 Pages·2016·46.755 MB·English

by  Pasquale M Sforza

Manned Spacecraft Design
Principles
Manned Spacecraft Design
Principles
Pasquale M. Sforza
University of Florida
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Preface
This book builds upon a handbook used to support a one-semester senior undergraduate or entry-
level graduate course intended to involve students in the preliminary design of a manned spacecraft
and associated launch vehicle. The course followed a one-semester design course for aerospace
engineering students devoted to design of a commercial jet transport. Commercial aircraft design is
a relatively mature field and sufficient reference material is available to provide a secure mooring
for student research and study. The manned spacecraft design course demands more from the
student because the subject lacks a broad well-documented database and covers topics that rarely
receive substantial attention in current curricula. An industrial approach is taken in order to help
instill the spirit of the design process, which is that of making informed choices from an array of
competing options and developing the confidence to do so. In the classroom setting, this design
effort culminates in the preparation of a professional quality design report and an oral presentation
describing the design process leading to the proposed space access vehicle. This report and presen-
tation requires students to develop technical, time-management, and communication skills for a
successfulcareer.
The material is arranged in a manner that facilitates a team effort, the usual course of action,
and also provides sufficient guidance to permit individual students to carry out a
creditable design as part of independent study. Emphasis is placed on the use of standard, empir-
ical, and classical methods in support of the design process in order to enhance understanding of
basic concepts and to gain some familiarity with employing such approaches which are often
encountered in practice. No particular computational approaches are specifically used, although
student teams may choose to use available codes, and have done so, with varying degrees of
success. CAD courses are generally required in engineering programs and their use is encour-
aged. My experience in teaching design over the years has led me to embrace the use of simple
basic analyses and empiricisms so that students have the opportunity to learn some of those
applied aerospace engineering skills that have been edged out of modern curricula by reductions
in total credit hours and the perceived need for broadening of skills in other areas. Spreadsheet
skills are quite sufficient to support the preliminary design process and such skills are
quite valuable to those setting out on industrial careers. Class meetings in a university setting
rarely provide more than 40 contact hours for explaining the design process and for conferring
with the instructor. Thus there must be a substantial amount of time spent outside class in
preparing the design.
This design handbook represents the cumulative efforts of the author over a number of
years of offering this course at the University of Florida, and before that, at the Polytechnic
Institute of Brooklyn, now New York University’s Polytechnic School of Engineering. Because
of the wide diversity of subject matter and techniques employed, errors are bound to appear.
The responsibility for such errors is mine and I would appreciate learning of any so they may be
corrected.
The author was just graduating from the Polytechnic Institute of Brooklyn when the first astro-
nauts were launched into space. The science of hypersonic flight and access to space has since
xiii
xiv Preface
occupied a large portion of my professional life. I acknowledge a debt to the inspired research of
many aerospace pioneers, especially Professor Antonio Ferri, champion of the scramjet, who lit the
path to the stars. Finally, I am delighted to once again thank my wife, Anne, for her loving encour-
agement andsupportfor myefforts inwriting thisbook.
Pasquale M.Sforza
Highland Beach, FL, USA
[email protected]
Introduction and Outline
of a Spacecraft Design Report
Thisbookhas itsorigininahandbookdeveloped tosupportaone-semestercourseinwhichstudent
teams were formed to carry out a preliminary design for a space transportation system capable of
carrying astronauts torendezvous with and dock at the International Space Station (ISS) for a given
period of time, and then to return the crew safely to Earth. This mission, though limited in scope,
forms a sound basis for considering the broader one of returning people to the moon and visiting
other planets and asteroids.
I.1 SUBJECTS COVERED
Chapter 1 begins with the space race precipitated by the convergence of reduced weight nuclear
weapons and increasedpayload capability of ballistic missiles. The geopolitical implicationsof put-
ting satellites into orbit were great and the next step of safely sending humans back and forth to
space bespoke a technical mastery that fired national pride and power. A brief description of the
development of manned spaceflight starting from the Vostok launch by the USSR in 1961 and the
Mercury capsule launched in reply by the USA in 1962 is presented. Over time, national
competition became planetary cooperation culminating in the operation of the ISS. The outlook for
the future of human spaceflight now ranges from interplanetary missions of discovery to space as a
theme park for tourism.
Earth’s atmosphere and the theoretical foundation for a model of the earth’s atmosphere, but
extendable to other planetary atmospheres, is the subject of Chapter 2. The 1976 US Standard
Atmosphere is used as the model of choice in the book and the equations necessary to develop the
appropriate data and procedures to define the atmospheric properties over the manned spacecraft
flight envelope are derived. For convenience, tables are generated from these equations and are
presented in SI units and also in English engineering units because their use is still quite pervasive,
especiallyinthebackgroundliterature.Standard atmospheric models areused toprovide acommon
basis for comparing investigations by different teams and several such models currently in use are
reviewed. Flight operations often encounter deviations in atmospheric properties from those
predictedby standard models and mustbeconsidered inthe design process.
The space environment in which a manned spacecraft must carry out part of its mission as it
leaves the atmosphere is described in Chapter 3. The major influences on human space travel are
shown to be the solar wind and the earth’s gravitational and magnetic fields. The nature of solar
radiation and the interaction of the solar wind of energetic protons and electrons with the earth’s
magnetic field are discussed. Gravitational constraints on achieving orbital motion and rarefied
atmospheric drag effects on maintaining an orbit are illustrated. The energetic particles in the Van
Allen radiation belts, the electron density in the ionosphere, and the increasing population of space
xv
xvi Introduction and Outline of a Spacecraft Design Report
debris are shown to pose dangers to astronaut health, space to ground communications, and
spacecraft integrity.
A discussion of the nature of high-speed flight through the atmosphere in order to gain
access to space is presented in Chapter 4. Various spaceplane projects aimed at human space-
flight that have been pursued in recent years are described. The nature of flight trajectories in
the sensible atmosphere is described and vehicles that have successfully operated in the human
flight design space are identified. The goal of reusable spaceplanes that operate like conven-
tional airplanes is placed in perspective by addressing the design issues associated with such
craft. The transatmospheric manned missions which are likely to develop in the near future are
discussed.
Chapter 5 presents the equations of orbital motion with particular reference to characteristics of
earth orbits and the manner of altering those orbits. The basic ideas of conservation of energy and
angular momentum for closed and open orbits are used to illustrate the maintenance of orbits and
theachievement ofescape fromorbitforinterplanetary missions. Theground trackoforbits,effects
of earth’s rotation and precession, determination of longitude, the spacecraft horizon and effects on
communication are analyzed. Interplanetary trajectories are discussed and the orbital transfer pro-
cess for atmospheric entry is presented.
The most stressful part of human spaceflight is atmospheric entry from space and this is the
subject of Chapter 6. The equations of motion for spacecraft entry into the atmosphere are derived
and the general characteristics of gliding trajectories discussed. The spacecraft ballistic coefficient
and earth’s atmospheric density profile are important considerations in limiting the effects of decel-
eration on human physiology. These factors are combined in defining an entry trajectory corridor
that lies within a restricted range of acceptable dynamic pressure levels. A similar corridor for
assuring safe heating levels for entering spacecraft is also defined. Detailed studies of entry dynam-
ics are divided into three categories: ballistic (zero-lift), low lift to drag ratio (L/D), and moderate
L/D.Thisdivisionmaybeillustratedbymeteorsandearlyspacecapsules(e.g.,Mercury),nextgen-
eration space capsules (e.g., Apollo and now Orion), and spaceplanes (e.g., the Space Shuttle
Orbiter), respectively. The low-speed return and recovery analysis is divided into parachute-type
systems like those used for capsule recovery and airplane-type systems like the Space Shuttle
Orbiter.
Only when one is convinced of the ability to return humans safely from space is it appropriate
to entertain the means for launching them into space. The general equations for launching space-
craft into orbit are developed and the influence of thrust, lift, and drag are assessed in Chapter 7.
Equations for the practical preliminary design case of constant thrust and negligible lift and drag
are solved and permit determination of boost trajectories, burn-out velocities, and postburn-out
booster trajectories. The selection of a launch system for a spacecraft of a given mass involves
evaluating the use of one, two, or three stages and each is subjected to detailed analysis. The
design choices are shown to be dependent upon the assumptions made concerning structure and
engine weights, even in a preliminary design process. Because launch systems are large structures
it is important to consider them at least as rigid bodies; the effects of elastic deformations are
generally deferred to advanced stages of design. Moments of inertia, force and moment estima-
tion procedures, and static longitudinal stability requirements are incorporated in developing the
Introduction and Outline of a Spacecraft Design Report xvii
configuration and size of launch systems and thrust vector control requirements are assessed.
Liquid and solid propellant rockets are discussed and the determination of tank size and weight
is evaluated.
The flight mechanics of manned spacecraft during hypersonic entry are developed in Chapter 8.
The application of Newtonian theory for normal stresses and the flat plate reference enthalpy
(FPRE) method for shear stresses forms a simple but sound basis for spacecraft design. Because
Newtonian theory depends on the local flow deflection, a unit problem for the local surface pres-
sure may be defined involving the elemental surface area and the impinging velocity vector. Thus a
relatively complex spacecraft design may be modeled as a collection of surface panels and simple
summations used to generate the pressure forces and the associated moments. The FPRE method is
also formulated as a unit problem so that frictional forces can be evaluated for both laminar and
turbulent flow. A simple criterion for boundary layer transition is also provided. Blunt body space
capsules and slender body spaceplanes are both treated in some detail. Because of the high tem-
peratures of hypersonic flight, a development of the thermodynamic and transport properties of air
relevant to atmospheric entry is given and useful approximations are illustrated. Both capsules and
spaceplanes are treated as rigid bodies and their longitudinal and lateral static stability characteris-
tics are evaluated. Some attention is also paid to the assessment of their dynamic stability charac-
teristics. Aerodynamic and reaction control systems appropriate to entering spacecraft are
described.
Thermal protection systems are crucial to safe and reliable human spaceflight and this topic is
the subject of Chapter 9. The primary determinant of thermal protection is stagnation point heat
transfer and attention is paid to the most useful correlations for design applications. The high tem-
peratures ensure dissociation and ionization of air molecules so approximations are developed for
the treatment of air chemistry. Heat transfer on a blunt hemispherical body and a spherically
capped cone is addressed to highlight the different mechanisms at work. The analyses developed
are extended to the design of heat shields for entry vehicles. Heat sink, melting ablator, and char-
ring ablator heat shields are analyzed, as are active systems involving surface injection of coolants.
The similarity parameters crucial toheat transfer effects are reviewed.
Chapter 10 covers spacecraft configuration design. The spacecraft environment and its effect on
design are discussed and crew volume allowance in spacecraft is contrasted with passenger volume
allowance on commercial, business, and military aircraft. The influence of mission duration on
cabin configuration is considered. Vehicle mass characteristics as evidenced by successful manned
spacecraft and the resultant ballistic coefficient are explored. Human factors in spacecraft design
are assessed as the major areas of thermal control and management of the habitable volume.
Environmental control and life support systems including heating, ventilating and air conditioning,
air and water purification, waste management, fire and emergency control systems, and communi-
cations are discussed. Aspects of basic structural design issues along with space propulsion and
power systemsare described.
The definitions of safety and reliability and the means of apportioning mission reliability are
discussed and the reliability function is introduced in Chapter 11. Failure rate models are used in
the development of reliability estimates and apportionment goals are evaluated. Propulsion system
reliability is used as an example of estimating mission success. An overview of probabilistic risk
xviii Introduction and Outline of a Spacecraft Design Report
assessment is presented and the question of functional failures is addressed using the Space
Shuttle as an example. The Weibull distribution and its role in risk and reliability studies are
described.
Economic aspects of manned spaceflight including the costs of previous manned spaceflight
programs like Apollo and the Space Shuttle are discussed in Chapter 12. An assessment of the gen-
eral costofspaceflightmeasuredintermsofpayload massinorbitiscarriedout.Thecostofspace-
flight is evaluated on a component basis including development, production, flight operations,
refurbishment,recovery, andinsurance. General characteristicsofthe cost ofvarious launch vehicle
components are described.
The technical foundation for hypersonic flight back and forth across the atmosphere as used and
discussed in the main text is presented in Appendix A including normal and oblique shocks, small
disturbance theory,Prandtl(cid:1)Meyer flow, Newtonian theory, and conical flow, among others.
Detailed configuration data on seven spaceplanes that have been flown or were the subject of
wind tunneltests is providedin tables and drawings inAppendix B. Flight characteristics ofseveral
of these vehicles are described based on the methods of calculation given in Chapter 8. This mate-
rial is notreadilyavailable inone collection elsewhere.
I.2 AN APPROACH FOR A DESIGN COURSE
A basic mission profile that has been used successfully in a one-semester course involved the fol-
lowing tasks:
1. Lift-off from Earth’s surface with aspecifiednumber of crew members
2. Climb/accelerate through the atmosphere toorbitat 400km
3. Remain onorbitfor two fullorbits
4. Dock with ISS for a specified time
5. Undock and deorbit at 400kmaltitude
6. Atmospheric entry at 100kmto descend anddecelerate
7. Approach andlandingon Earth’s surface.
A design team comprised of six people was found to be most practical. This would include a
program manager and five specialists, one in each of the following areas: aerodynamics, propul-
sion, trajectories and orbits, thermal protection, and configuration design. Each student submitted a
request for one of these positions, in order of preference. Based on these requests, the instructor
selected a specific role for each student and assigned them to a design team. Thus students about to
embark on an engineering career would experience being part of a team of people previously not
wellknowntothemaswouldlikelybethecaseintheirfirstjob.Exposuretotheneedforcooperat-
ing as part of a team was considered part of the educational process in design. Students in the
course were in their last semester so that all had or were concurrently taking analysis courses
in the areas listed. Therefore all had some exposure to the breadth of material to be covered and
Introduction and Outline of a Spacecraft Design Report xix
the design course was intended to bring much of it into better focus. The main product of the
design course was the design report although oral presentation of the design report in a symposium
setting with invited faculty and guests was an important adjunct.
I.2.1 PREPARATION OF THE DESIGN REPORT
One of the most important tasks facing every engineer is the preparation of a technical report. This
may be a document like a proposal, which seeks to engage the interest of a sponsor to financially
support the technical task proposed, or one describing the work that has been carried out in com-
pleting a technical task. Typically, engineers enjoy performing the technical work required to solve
the particular problem at hand but often dread the planning, writing, and preparation of the techni-
cal document thatdescribes the work.
A report is intended to present information clearly and in a manner that is both self-contained
and interesting. Conceptually, report preparation is rather simple, being in essence an edited log
of the work that has been, or is proposed to be, performed. Thus, it is convenient to keep a good
journal of the work done along with the relevant background and illustrative material used.
Though the technical work done may be well understood and appreciated by the engineer who
carried it out day by day, this is not necessarily the case for other people who also need to know
about that work. If the reader finds the report difficult to understand because the presentation is
poor, then the engineer has wasted all the technical work done because the information cannot
get beyond the person who actually did the work. Thus it is important to be sure that some basic
requirements are met by the design report, such as the following: the reader should not have to
search for important facts, the technical content should not be obscured by poor writing, and
ambiguity should be avoided.
There is always some concernabout the perspective of the report,that is, who is the reader? For
design reports, there are generally three classes of readers: business and sales executives, technical
managers, and technical staff engineers. To satisfy this broad group with one report, it is common
to include an executive summary, a main text, and detailed appendices. Executives generally read
the brief executive summary to clearly understand the general approach and results of the study.
Technical management personnel read the executive summary and the main text so as to be able to
guide the executive group as necessary. The technical staff needs all three sections since they may
be called upon to review detailed questions from the other two groups who are involved in making
major business decisions.
I.2.2 OUTLINE OF THE DESIGN REPORT
Aircraft and spacecraft companies generally have standard formats for reports used both within
and outside the company. Though the details may vary from company to company, there is a
general outline that tends to be followed. A layout of the chapters of a typical final report for a
one-semester course along with a brief description of the material that should be addressed in